research about solar energy

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Strengthen the connections

Achieving good electrical contact without damaging underlying layers is critical to the performance of photovoltaic modules. Research now reports a silver electrode embedded into a polymer matrix and a silver/chromium protection layer, enabling over 14%-efficient flexible organic photovoltaic modules with improved stability under illumination.

• Eul-Yong Shin
• Hae Jung Son

Ultralightweight perovskite solar cells for use in drones

Ultralightweight perovskite solar cells that achieve a specific power of up to 44 W g –1 and good stability are developed through engineering of the photoactive layer and substrate. These solar cells can be integrated into a drone to enable energy-autonomous flight.

Related Subjects

• Artificial photosynthesis
• Photovoltaics
• Solar fuels
• Solar thermal energy
• Thermophotovoltaics

Latest Research and Reviews

Sustainable thermal regulation improves stability and efficiency in all-perovskite tandem solar cells

Mixed Sn-Pb perovskites have emerged as promising photovoltaic materials for both single- and multi-junction solar cells. Here, authors reveal the thermal degradation mechanism and incorporate carboranes for thermal regulation, resulting in stable all-perovskite tandems with efficiency of over 27%.

• Shuchen Tan
• Chongwen Li
• Zhongmin Zhou

Sustainable coatings for green solar photovoltaic cells: performance and environmental impact of recyclable biomass digestate polymers

• Aiyeshah Alhodaib
• Zeinebou Yahya
• M. Javed Idrisi

Correlating activities and defects in (photo)electrocatalysts using in-situ multi-modal microscopic imaging

Physicochemical heterogeneity poses a significant constraint in photocatalyst advancement. Here the authors introduce a multimodal optical microscopy platform to assess activity and defects concurrently in photoelectrocatalysts, revealing that disorder can unexpectedly enhance local photoelectrocatalytic performance in certain instances.

• Camilo A. Mesa
• Michael Sachs

Free-standing ultrathin silicon wafers and solar cells through edges reinforcement

Lightweight and flexible thin crystalline silicon solar cells have huge market potential but remain relatively unexplored. Here, authors present a thin silicon structure with reinforced ring to prepare free-standing 4.7-μm 4-inch silicon wafers, achieving efficiency of 20.33% for 28-μm solar cells.

• Zhaolang Liu
• Wenzhong Shen

Control strategy for current limitation and maximum capacity utilization of grid connected PV inverter under unbalanced grid conditions

• Jyoti Joshi
• Vibhu Jately
• Brian Azzopardi

Novel risk index integrating practical operation limits enhances probabilistic contingency ranking for large-scale photovoltaic plant planning

• Rasha Elazab
• Mohamed K. El-Aser
• Adel A. El-samahy

News and Comment

Getting a charge out of perovskites.

• Giulia Tregnago

Breaking the reaction chain

Wide band gap perovskite solar cells suffer from halide segregation, which hampers their use in tandem solar cells. Now, researchers develop an additive with redox and defect passivating capabilities to suppress halide migration, enabling perovskite–organic tandems with over 25% efficiency.

• Aleksandra B. Djurišić

Delivery of CO

• James Gallagher

Tolerance testing

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The Future of Solar Energy

Read the report.

Executive summary (PDF) Full report (PDF)

The Future of Solar Energy considers only the two widely recognized classes of technologies for converting solar energy into electricity — photovoltaics (PV) and concentrated solar power (CSP), sometimes called solar thermal) — in their current and plausible future forms. Because energy supply facilities typically last several decades, technologies in these classes will dominate solar-powered generation between now and 2050, and we do not attempt to look beyond that date. In contrast to some earlier Future of studies, we also present no forecasts — for two reasons. First, expanding the solar industry dramatically from its relatively tiny current scale may produce changes we do not pretend to be able to foresee today. Second, we recognize that future solar deployment will depend heavily on uncertain future market conditions and public policies — including but not limited to policies aimed at mitigating global climate change.

As in other studies in this series, our primary aim is to inform decision-makers in the developed world, particularly the United States. We concentrate on the use of grid-connected solar-powered generators to replace conventional sources of electricity. For the more than one billion people in the developing world who lack access to a reliable electric grid, the cost of small-scale PV generation is often outweighed by the very high value of access to electricity for lighting and charging mobile telephone and radio batteries. In addition, in some developing nations it may be economic to use solar generation to reduce reliance on imported oil, particularly if that oil must be moved by truck to remote generator sites. A companion working paper discusses both these valuable roles for solar energy in the developing world.

Related publications

Shaping photovoltaic array output to align with changing wholesale electricity price profiles

December 2019

Spatial and temporal variation in the value of solar power across United States electricity markets

Solar heating for residential and industrial processes

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MIT Energy Initiative Director Robert Armstrong shares perspectives on past successes and ongoing and future energy projects at the Institute.

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Solar Research

For more than 40 years, NREL has led innovation in solar research, enabling the U.S. solar industry to grow rapidly as solar energy becomes more affordable and accessible than ever.

Research Challenges

We work toward finding solutions for today’s solar R&D challenges, which include:

• Integrating large amounts of solar energy into the power grid while maintaining security and reliability, and enhancing resilience
• Improving the efficiency, lifetimes, and manufacturability of photovoltaic materials
• Developing technologies for a third generation of concentrating solar power plants to further reduce costs and improve thermal storage capabilities
• Capturing surplus solar energy to provide heat and produce fuels and clean water
• Creating flexible, highly efficient solar cells that can make low-cost power available without wires anywhere the sun shines
• Making solar an even better investment through work on bankability, reliability, and recyclability.

Research Areas

Solar research at NREL is multifaceted, incorporating basic energy science, engineering, and energy analysis.

Photovoltaics

Our photovoltaic (PV) research spans across fundamental and applied research and development, including theory and modeling, materials deposition, device design, engineering, and measurements and characterization. It focuses on boosting solar cell conversion efficiencies, lowering the cost of PV technologies, and improving the reliability of PV components and systems.

Concentrating Solar Power

We play a critical role in the advancement of concentrating solar power (CSP) technologies through a wide range of scientific, engineering, and analytical expertise along with facilities and tools.  Our CSP research even goes beyond electricity generation, moving into emerging markets for long-duration thermal energy storage, process heat, solar fuels, and desalination.

Solar Market Research and Analysis

Through rigorous data collection, analysis, and stakeholder engagement, NREL's solar market research and analysis  efforts further solar technologies' role in supporting a more efficient and better performing U.S. electricity system. This crosscutting set of activities leverages NREL's unique analytical and deployment capabilities.

Solar Grid and Systems Integration

Energy-to-grid integration

Grid interconnection standards

PV reliability and system performance

Solar measurement and modeling .

Solar Tech to Market

We connect NREL’s leading research, staff expertise, and facilities with private companies to support investigation, validation, and commercialization of solar technologies. By enabling early-stage solar technology and supporting the development of a skilled workforce, NREL strengthens the market and prepares solar for greater investment and commercialization. Whether supporting individual companies or leveraging American innovation and competitive spirit through the American-Made Solar Prize challenges, we help move technology to market and increasing U.S. manufacturing and competitiveness.

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Article Contents

Introduction, 1 installed capacity and application of solar energy worldwide, 2 the role of solar energy in sustainable development, 3 the perspective of solar energy, 4 conclusions, conflict of interest statement.

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Solar energy technology and its roles in sustainable development

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Ali O M Maka, Jamal M Alabid, Solar energy technology and its roles in sustainable development, Clean Energy , Volume 6, Issue 3, June 2022, Pages 476–483, https://doi.org/10.1093/ce/zkac023

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Solar energy is environmentally friendly technology, a great energy supply and one of the most significant renewable and green energy sources. It plays a substantial role in achieving sustainable development energy solutions. Therefore, the massive amount of solar energy attainable daily makes it a very attractive resource for generating electricity. Both technologies, applications of concentrated solar power or solar photovoltaics, are always under continuous development to fulfil our energy needs. Hence, a large installed capacity of solar energy applications worldwide, in the same context, supports the energy sector and meets the employment market to gain sufficient development. This paper highlights solar energy applications and their role in sustainable development and considers renewable energy’s overall employment potential. Thus, it provides insights and analysis on solar energy sustainability, including environmental and economic development. Furthermore, it has identified the contributions of solar energy applications in sustainable development by providing energy needs, creating jobs opportunities and enhancing environmental protection. Finally, the perspective of solar energy technology is drawn up in the application of the energy sector and affords a vision of future development in this domain.

With reference to the recommendations of the UN, the Climate Change Conference, COP26, was held in Glasgow , UK, in 2021. They reached an agreement through the representatives of the 197 countries, where they concurred to move towards reducing dependency on coal and fossil-fuel sources. Furthermore, the conference stated ‘the various opportunities for governments to prioritize health and equity in the international climate movement and sustainable development agenda’. Also, one of the testaments is the necessity to ‘create energy systems that protect and improve climate and health’ [ 1 , 2 ].

The Paris Climate Accords is a worldwide agreement on climate change signed in 2015, which addressed the mitigation of climate change, adaptation and finance. Consequently, the representatives of 196 countries concurred to decrease their greenhouse gas emissions [ 3 ]. The Paris Agreement is essential for present and future generations to attain a more secure and stable environment. In essence, the Paris Agreement has been about safeguarding people from such an uncertain and progressively dangerous environment and ensuring everyone can have the right to live in a healthy, pollutant-free environment without the negative impacts of climate change [ 3 , 4 ].

In recent decades, there has been an increase in demand for cleaner energy resources. Based on that, decision-makers of all countries have drawn up plans that depend on renewable sources through a long-term strategy. Thus, such plans reduce the reliance of dependence on traditional energy sources and substitute traditional energy sources with alternative energy technology. As a result, the global community is starting to shift towards utilizing sustainable energy sources and reducing dependence on traditional fossil fuels as a source of energy [ 5 , 6 ].

In 2015, the UN adopted the sustainable development goals (SDGs) and recognized them as international legislation, which demands a global effort to end poverty, safeguard the environment and guarantee that by 2030, humanity lives in prosperity and peace. Consequently, progress needs to be balanced among economic, social and environmental sustainability models [ 7 ].

Many national and international regulations have been established to control the gas emissions and pollutants that impact the environment [ 8 ]. However, the negative effects of increased carbon in the atmosphere have grown in the last 10 years. Production and use of fossil fuels emit methane (CH 4 ), carbon dioxide (CO 2 ) and carbon monoxide (CO), which are the most significant contributors to environmental emissions on our planet. Additionally, coal and oil, including gasoline, coal, oil and methane, are commonly used in energy for transport or for generating electricity. Therefore, burning these fossil fuel s is deemed the largest emitter when used for electricity generation, transport, etc. However, these energy resources are considered depleted energy sources being consumed to an unsustainable degree [ 9–11 ].

Energy is an essential need for the existence and growth of human communities. Consequently, the need for energy has increased gradually as human civilization has progressed. Additionally, in the past few decades, the rapid rise of the world’s population and its reliance on technological developments have increased energy demands. Furthermore, green technology sources play an important role in sustainably providing energy supplies, especially in mitigating climate change [ 5 , 6 , 8 ].

Currently, fossil fuels remain dominant and will continue to be the primary source of large-scale energy for the foreseeable future; however, renewable energy should play a vital role in the future of global energy. The global energy system is undergoing a movement towards more sustainable sources of energy [ 12 , 13 ].

Power generation by fossil-fuel resources has peaked, whilst solar energy is predicted to be at the vanguard of energy generation in the near future. Moreover, it is predicted that by 2050, the generation of solar energy will have increased to 48% due to economic and industrial growth [ 13 , 14 ].

In recent years, it has become increasingly obvious that the globe must decrease greenhouse gas emissions by 2050, ideally towards net zero, if we are to fulfil the Paris Agreement’s goal to reduce global temperature increases [ 3 , 4 ]. The net-zero emissions complement the scenario of sustainable development assessment by 2050. According to the agreed scenario of sustainable development, many industrialized economies must achieve net-zero emissions by 2050. However, the net-zero emissions 2050 brought the first detailed International Energy Agency (IEA) modelling of what strategy will be required over the next 10 years to achieve net-zero carbon emissions worldwide by 2050 [ 15–17 ].

The global statistics of greenhouse gas emissions have been identified; in 2019, there was a 1% decrease in CO 2 emissions from the power industry; that figure dropped by 7% in 2020 due to the COVID-19 crisis, thus indicating a drop in coal-fired energy generation that is being squeezed by decreasing energy needs, growth of renewables and the shift away from fossil fuels. As a result, in 2020, the energy industry was expected to generate ~13 Gt CO 2 , representing ~40% of total world energy sector emissions related to CO 2 . The annual electricity generation stepped back to pre-crisis levels by 2021, although due to a changing ‘fuel mix’, the CO 2 emissions in the power sector will grow just a little before remaining roughly steady until 2030 [ 15 ].

Therefore, based on the information mentioned above, the advantages of solar energy technology are a renewable and clean energy source that is plentiful, cheaper costs, less maintenance and environmentally friendly, to name but a few. The significance of this paper is to highlight solar energy applications to ensure sustainable development; thus, it is vital to researchers, engineers and customers alike. The article’s primary aim is to raise public awareness and disseminate the culture of solar energy usage in daily life, since moving forward, it is the best. The scope of this paper is as follows. Section 1 represents a summary of the introduction. Section 2 represents a summary of installed capacity and the application of solar energy worldwide. Section 3 presents the role of solar energy in the sustainable development and employment of renewable energy. Section 4 represents the perspective of solar energy. Finally, Section 5 outlines the conclusions and recommendations for future work.

1.1 Installed capacity of solar energy

The history of solar energy can be traced back to the seventh century when mirrors with solar power were used. In 1893, the photovoltaic (PV) effect was discovered; after many decades, scientists developed this technology for electricity generation [ 18 ]. Based on that, after many years of research and development from scientists worldwide, solar energy technology is classified into two key applications: solar thermal and solar PV.

PV systems convert the Sun’s energy into electricity by utilizing solar panels. These PV devices have quickly become the cheapest option for new electricity generation in numerous world locations due to their ubiquitous deployment. For example, during the period from 2010 to 2018, the cost of generating electricity by solar PV plants decreased by 77%. However, solar PV installed capacity progress expanded 100-fold between 2005 and 2018. Consequently, solar PV has emerged as a key component in the low-carbon sustainable energy system required to provide access to affordable and dependable electricity, assisting in fulfilling the Paris climate agreement and in achieving the 2030 SDG targets [ 19 ].

The installed capacity of solar energy worldwide has been rapidly increased to meet energy demands. The installed capacity of PV technology from 2010 to 2020 increased from 40 334 to 709 674 MW, whereas the installed capacity of concentrated solar power (CSP) applications, which was 1266 MW in 2010, after 10 years had increased to 6479 MW. Therefore, solar PV technology has more deployed installations than CSP applications. So, the stand-alone solar PV and large-scale grid-connected PV plants are widely used worldwide and used in space applications. Fig. 1 represents the installation of solar energy worldwide.

Installation capacity of solar energy worldwide [ 20 ].

1.2 Application of solar energy

Energy can be obtained directly from the Sun—so-called solar energy. Globally, there has been growth in solar energy applications, as it can be used to generate electricity, desalinate water and generate heat, etc. The taxonomy of applications of solar energy is as follows: (i) PVs and (ii) CSP. Fig. 2 details the taxonomy of solar energy applications.

The taxonomy of solar energy applications.

Solar cells are devices that convert sunlight directly into electricity; typical semiconductor materials are utilized to form a PV solar cell device. These materials’ characteristics are based on atoms with four electrons in their outer orbit or shell. Semiconductor materials are from the periodic table’s group ‘IV’ or a mixture of groups ‘IV’ and ‘II’, the latter known as ‘II–VI’ semiconductors [ 21 ]. Additionally, a periodic table mixture of elements from groups ‘III’ and ‘V’ can create ‘III–V’ materials [ 22 ].

PV devices, sometimes called solar cells, are electronic devices that convert sunlight into electrical power. PVs are also one of the rapidly growing renewable-energy technologies of today. It is therefore anticipated to play a significant role in the long-term world electricity-generating mixture moving forward.

Solar PV systems can be incorporated to supply electricity on a commercial level or installed in smaller clusters for mini-grids or individual usage. Utilizing PV modules to power mini-grids is a great way to offer electricity to those who do not live close to power-transmission lines, especially in developing countries with abundant solar energy resources. In the most recent decade, the cost of producing PV modules has dropped drastically, giving them not only accessibility but sometimes making them the least expensive energy form. PV arrays have a 30-year lifetime and come in various shades based on the type of material utilized in their production.

The most typical method for solar PV desalination technology that is used for desalinating sea or salty water is electrodialysis (ED). Therefore, solar PV modules are directly connected to the desalination process. This technique employs the direct-current electricity to remove salt from the sea or salty water.

The technology of PV–thermal (PV–T) comprises conventional solar PV modules coupled with a thermal collector mounted on the rear side of the PV module to pre-heat domestic hot water. Accordingly, this enables a larger portion of the incident solar energy on the collector to be converted into beneficial electrical and thermal energy.

A zero-energy building is a building that is designed for zero net energy emissions and emits no carbon dioxide. Building-integrated PV (BIPV) technology is coupled with solar energy sources and devices in buildings that are utilized to supply energy needs. Thus, building-integrated PVs utilizing thermal energy (BIPV/T) incorporate creative technologies such as solar cooling [ 23 ].

A PV water-pumping system is typically used to pump water in rural, isolated and desert areas. The system consists of PV modules to power a water pump to the location of water need. The water-pumping rate depends on many factors such as pumping head, solar intensity, etc.

A PV-powered cathodic protection (CP) system is designed to supply a CP system to control the corrosion of a metal surface. This technique is based on the impressive current acquired from PV solar energy systems and is utilized for burying pipelines, tanks, concrete structures, etc.

Concentrated PV (CPV) technology uses either the refractive or the reflective concentrators to increase sunlight to PV cells [ 24 , 25 ]. High-efficiency solar cells are usually used, consisting of many layers of semiconductor materials that stack on top of each other. This technology has an efficiency of >47%. In addition, the devices produce electricity and the heat can be used for other purposes [ 26 , 27 ].

For CSP systems, the solar rays are concentrated using mirrors in this application. These rays will heat a fluid, resulting in steam used to power a turbine and generate electricity. Large-scale power stations employ CSP to generate electricity. A field of mirrors typically redirect rays to a tall thin tower in a CSP power station. Thus, numerous large flat heliostats (mirrors) are used to track the Sun and concentrate its light onto a receiver in power tower systems, sometimes known as central receivers. The hot fluid could be utilized right away to produce steam or stored for later usage. Another of the great benefits of a CSP power station is that it may be built with molten salts to store heat and generate electricity outside of daylight hours.

Mirrored dishes are used in dish engine systems to focus and concentrate sunlight onto a receiver. The dish assembly tracks the Sun’s movement to capture as much solar energy as possible. The engine includes thin tubes that work outside the four-piston cylinders and it opens into the cylinders containing hydrogen or helium gas. The pistons are driven by the expanding gas. Finally, the pistons drive an electric generator by turning a crankshaft.

A further water-treatment technique, using reverse osmosis, depends on the solar-thermal and using solar concentrated power through the parabolic trough technique. The desalination employs CSP technology that utilizes hybrid integration and thermal storage allows continuous operation and is a cost-effective solution. Solar thermal can be used for domestic purposes such as a dryer. In some countries or societies, the so-called food dehydration is traditionally used to preserve some food materials such as meats, fruits and vegetables.

Sustainable energy development is defined as the development of the energy sector in terms of energy generating, distributing and utilizing that are based on sustainability rules [ 28 ]. Energy systems will significantly impact the environment in both developed and developing countries. Consequently, the global sustainable energy system must optimize efficiency and reduce emissions [ 29 ].

The sustainable development scenario is built based on the economic perspective. It also examines what activities will be required to meet shared long-term climate benefits, clean air and energy access targets. The short-term details are based on the IEA’s sustainable recovery strategy, which aims to promote economies and employment through developing a cleaner and more reliable energy infrastructure [ 15 ]. In addition, sustainable development includes utilizing renewable-energy applications, smart-grid technologies, energy security, and energy pricing, and having a sound energy policy [ 29 ].

The demand-side response can help meet the flexibility requirements in electricity systems by moving demand over time. As a result, the integration of renewable technologies for helping facilitate the peak demand is reduced, system stability is maintained, and total costs and CO 2 emissions are reduced. The demand-side response is currently used mostly in Europe and North America, where it is primarily aimed at huge commercial and industrial electricity customers [ 15 ].

International standards are an essential component of high-quality infrastructure. Establishing legislative convergence, increasing competition and supporting innovation will allow participants to take part in a global world PV market [ 30 ]. Numerous additional countries might benefit from more actively engaging in developing global solar PV standards. The leading countries in solar PV manufacturing and deployment have embraced global standards for PV systems and highly contributed to clean-energy development. Additional assistance and capacity-building to enhance quality infrastructure in developing economies might also help support wider implementation and compliance with international solar PV standards. Thus, support can bring legal requirements and frameworks into consistency and give additional impetus for the trade of secure and high-quality solar PV products [ 19 ].

Continuous trade-led dissemination of solar PV and other renewable technologies will strengthen the national infrastructure. For instance, off-grid solar energy alternatives, such as stand-alone systems and mini-grids, could be easily deployed to assist healthcare facilities in improving their degree of services and powering portable testing sites and vaccination coolers. In addition to helping in the immediate medical crisis, trade-led solar PV adoption could aid in the improving economy from the COVID-19 outbreak, not least by providing jobs in the renewable-energy sector, which are estimated to reach >40 million by 2050 [ 19 ].

The framework for energy sustainability development, by the application of solar energy, is one way to achieve that goal. With the large availability of solar energy resources for PV and CSP energy applications, we can move towards energy sustainability. Fig. 3 illustrates plans for solar energy sustainability.

Framework for solar energy applications in energy sustainability.

The environmental consideration of such applications, including an aspect of the environmental conditions, operating conditions, etc., have been assessed. It is clean, friendly to the environment and also energy-saving. Moreover, this technology has no removable parts, low maintenance procedures and longevity.

Economic and social development are considered by offering job opportunities to the community and providing cheaper energy options. It can also improve people’s income; in turn, living standards will be enhanced. Therefore, energy is paramount, considered to be the most vital element of human life, society’s progress and economic development.

As efforts are made to increase the energy transition towards sustainable energy systems, it is anticipated that the next decade will see a continued booming of solar energy and all clean-energy technology. Scholars worldwide consider research and innovation to be substantial drivers to enhance the potency of such solar application technology.

2.1 Employment from renewable energy

The employment market has also boomed with the deployment of renewable-energy technology. Renewable-energy technology applications have created >12 million jobs worldwide. The solar PV application came as the pioneer, which created >3 million jobs. At the same time, while the solar thermal applications (solar heating and cooling) created >819 000 jobs, the CSP attained >31 000 jobs [ 20 ].

According to the reports, although top markets such as the USA, the EU and China had the highest investment in renewables jobs, other Asian countries have emerged as players in the solar PV panel manufacturers’ industry [ 31 ].

Solar energy employment has offered more employment than other renewable sources. For example, in the developing countries, there was a growth in employment chances in solar applications that powered ‘micro-enterprises’. Hence, it has been significant in eliminating poverty, which is considered the key goal of sustainable energy development. Therefore, solar energy plays a critical part in fulfilling the sustainability targets for a better plant and environment [ 31 , 32 ]. Fig. 4 illustrates distributions of world renewable-energy employment.

World renewable-energy employment [ 20 ].

The world distribution of PV jobs is disseminated across the continents as follows. There was 70% employment in PV applications available in Asia, while 10% is available in North America, 10% available in South America and 10% availability in Europe. Table 1 details the top 10 countries that have relevant jobs in Asia, North America, South America and Europe.

List of the top 10 countries that created jobs in solar PV applications [ 19 , 33 ]

Solar energy investments can meet energy targets and environmental protection by reducing carbon emissions while having no detrimental influence on the country’s development [ 32 , 34 ]. In countries located in the ‘Sunbelt’, there is huge potential for solar energy, where there is a year-round abundance of solar global horizontal irradiation. Consequently, these countries, including the Middle East, Australia, North Africa, China, the USA and Southern Africa, to name a few, have a lot of potential for solar energy technology. The average yearly solar intensity is >2800 kWh/m 2 and the average daily solar intensity is >7.5 kWh/m 2 . Fig. 5 illustrates the optimum areas for global solar irradiation.

World global solar irradiation map [ 35 ].

The distribution of solar radiation and its intensity are two important factors that influence the efficiency of solar PV technology and these two parameters vary among different countries. Therefore, it is essential to realize that some solar energy is wasted since it is not utilized. On the other hand, solar radiation is abundant in several countries, especially in developing ones, which makes it invaluable [ 36 , 37 ].

Worldwide, the PV industry has benefited recently from globalization, which has allowed huge improvements in economies of scale, while vertical integration has created strong value chains: as manufacturers source materials from an increasing number of suppliers, prices have dropped while quality has been maintained. Furthermore, the worldwide incorporated PV solar device market is growing fast, creating opportunities enabling solar energy firms to benefit from significant government help with underwriting, subsides, beneficial trading licences and training of a competent workforce, while the increased rivalry has reinforced the motivation to continue investing in research and development, both public and private [ 19 , 33 ].

The global outbreak of COVID-19 has impacted ‘cross-border supply chains’ and those investors working in the renewable-energy sector. As a result, more diversity of solar PV supply-chain processes may be required in the future to enhance long-term flexibility versus exogenous shocks [ 19 , 33 ].

It is vital to establish a well-functioning quality infrastructure to expand the distribution of solar PV technologies beyond borders and make it easier for new enterprises to enter solar PV value chains. In addition, a strong quality infrastructure system is a significant instrument for assisting local firms in meeting the demands of trade markets. Furthermore, high-quality infrastructure can help reduce associated risks with the worldwide PV project value chain, such as underperforming, inefficient and failing goods, limiting the development, improvement and export of these technologies. Governments worldwide are, at various levels, creating quality infrastructure, including the usage of metrology i.e. the science of measurement and its application, regulations, testing procedures, accreditation, certification and market monitoring [ 33 , 38 ].

The perspective is based on a continuous process of technological advancement and learning. Its speed is determined by its deployment, which varies depending on the scenario [ 39 , 40 ]. The expense trends support policy preferences for low-carbon energy sources, particularly in increased energy-alteration scenarios. Emerging technologies are introduced and implemented as quickly as they ever have been before in energy history [ 15 , 33 ].

The CSP stations have been in use since the early 1980s and are currently found all over the world. The CSP power stations in the USA currently produce >800 MW of electricity yearly, which is sufficient to power ~500 000 houses. New CSP heat-transfer fluids being developed can function at ~1288 o C, which is greater than existing fluids, to improve the efficiency of CSP systems and, as a result, to lower the cost of energy generated using this technology. Thus, as a result, CSP is considered to have a bright future, with the ability to offer large-scale renewable energy that can supplement and soon replace traditional electricity-production technologies [ 41 ]. The DESERTEC project has drawn out the possibility of CSP in the Sahara Desert regions. When completed, this investment project will have the world’s biggest energy-generation capacity through the CSP plant, which aims to transport energy from North Africa to Europe [ 42 , 43 ].

The costs of manufacturing materials for PV devices have recently decreased, which is predicted to compensate for the requirements and increase the globe’s electricity demand [ 44 ]. Solar energy is a renewable, clean and environmentally friendly source of energy. Therefore, solar PV application techniques should be widely utilized. Although PV technology has always been under development for a variety of purposes, the fact that PV solar cells convert the radiant energy from the Sun directly into electrical power means it can be applied in space and in terrestrial applications [ 38 , 45 ].

In one way or another, the whole renewable-energy sector has a benefit over other energy industries. A long-term energy development plan needs an energy source that is inexhaustible, virtually accessible and simple to gather. The Sun rises over the horizon every day around the globe and leaves behind ~108–1018 kWh of energy; consequently, it is more than humanity will ever require to fulfil its desire for electricity [ 46 ].

The technology that converts solar radiation into electricity is well known and utilizes PV cells, which are already in use worldwide. In addition, various solar PV technologies are available today, including hybrid solar cells, inorganic solar cells and organic solar cells. So far, solar PV devices made from silicon have led the solar market; however, these PVs have certain drawbacks, such as expenditure of material, time-consuming production, etc. It is important to mention here the operational challenges of solar energy in that it does not work at night, has less output in cloudy weather and does not work in sandstorm conditions. PV battery storage is widely used to reduce the challenges to gain high reliability. Therefore, attempts have been made to find alternative materials to address these constraints. Currently, this domination is challenged by the evolution of the emerging generation of solar PV devices based on perovskite, organic and organic/inorganic hybrid materials.

This paper highlights the significance of sustainable energy development. Solar energy would help steady energy prices and give numerous social, environmental and economic benefits. This has been indicated by solar energy’s contribution to achieving sustainable development through meeting energy demands, creating jobs and protecting the environment. Hence, a paramount critical component of long-term sustainability should be investigated. Based on the current condition of fossil-fuel resources, which are deemed to be depleting energy sources, finding an innovative technique to deploy clean-energy technology is both essential and expected. Notwithstanding, solar energy has yet to reach maturity in development, especially CSP technology. Also, with growing developments in PV systems, there has been a huge rise in demand for PV technology applications all over the globe. Further work needs to be undertaken to develop energy sustainably and consider other clean energy resources. Moreover, a comprehensive experimental and validation process for such applications is required to develop cleaner energy sources to decarbonize our planet.

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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Researchers find benefits of solar photovoltaics outweigh costs

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Over the past decade, the cost of solar photovoltaic (PV) arrays has fallen rapidly. But at the same time, the value of PV power has declined in areas that have installed significant PV generating capacity. Operators of utility-scale PV systems have seen electricity prices drop as more PV generators come online. Over the same time period, many coal-fired power plants were required to install emissions-control systems, resulting in declines in air pollution nationally and regionally. The result has been improved public health — but also a decrease in the potential health benefits from offsetting coal generation with PV generation.

Given those competing trends, do the benefits of PV generation outweigh the costs? Answering that question requires balancing the up-front capital costs against the lifetime benefits of a PV system. Determining the former is fairly straightforward. But assessing the latter is challenging because the benefits differ across time and place. “The differences aren’t just due to variation in the amount of sunlight a given location receives throughout the year,” says  Patrick R. Brown PhD ’16, a postdoc at the MIT Energy Initiative. “They’re also due to variability in electricity prices and pollutant emissions.”

The drop in the price paid for utility-scale PV power stems in part from how electricity is bought and sold on wholesale electricity markets. On the “day-ahead” market, generators and customers submit bids specifying how much they’ll sell or buy at various price levels at a given hour on the following day. The lowest-cost generators are chosen first. Since the variable operating cost of PV systems is near zero, they’re almost always chosen, taking the place of the most expensive generator then in the lineup. The price paid to every selected generator is set by the highest-cost operator on the system, so as more PV power comes on, more high-cost generators come off, and the price drops for everyone. As a result, in the middle of the day, when solar is generating the most, prices paid to electricity generators are at their lowest.

Brown notes that some generators may even bid negative prices. “They’re effectively paying consumers to take their power to ensure that they are dispatched,” he explains. For example, inflexible coal and nuclear plants may bid negative prices to avoid frequent shutdown and startup events that would result in extra fuel and maintenance costs. Renewable generators may also bid negative prices to obtain larger subsidies that are rewarded based on production. 

Health benefits also differ over time and place. The health effects of deploying PV power are greater in a heavily populated area that relies on coal power than in a less-populated region that has access to plenty of clean hydropower or wind. And the local health benefits of PV power can be higher when there’s congestion on transmission lines that leaves a region stuck with whatever high-polluting sources are available nearby. The social costs of air pollution are largely “externalized,” that is, they are mostly unaccounted for in electricity markets. But they can be quantified using statistical methods, so health benefits resulting from reduced emissions can be incorporated when assessing the cost-competitiveness of PV generation.

The contribution of fossil-fueled generators to climate change is another externality not accounted for by most electricity markets. Some U.S. markets, particularly in California and the Northeast, have implemented cap-and-trade programs, but the carbon dioxide (CO 2 ) prices in those markets are much lower than estimates of the social cost of CO 2 , and other markets don’t price carbon at all. A full accounting of the benefits of PV power thus requires determining the CO 2  emissions displaced by PV generation and then multiplying that value by a uniform carbon price representing the damage that those emissions would have caused.

Calculating PV costs and benefits

To examine the changing value of solar power, Brown and his colleague Francis M. O’Sullivan, the senior vice president of strategy at Ørsted Onshore North America and a senior lecturer at the MIT Sloan School of Management, developed a methodology to assess the costs and benefits of PV power across the U.S. power grid annually from 2010 to 2017. 

The researchers focused on six “independent system operators” (ISOs) in California, Texas, the Midwest, the Mid-Atlantic, New York, and New England. Each ISO sets electricity prices at hundreds of “pricing nodes” along the transmission network in their region. The researchers performed analyses at more than 10,000 of those pricing nodes.

For each node, they simulated the operation of a utility-scale PV array that tilts to follow the sun throughout the day. They calculated how much electricity it would generate and the benefits that each kilowatt would provide, factoring in energy and “capacity” revenues as well as avoided health and climate change costs associated with the displacement of fossil fuel emissions. (Capacity revenues are paid to generators for being available to deliver electricity at times of peak demand.) They focused on emissions of CO 2 , which contributes to climate change, and of nitrogen oxides (NO x ), sulfur dioxide (SO 2 ), and particulate matter called PM 2.5 — fine particles that can cause serious health problems and can be emitted or formed in the atmosphere from NO x  and SO 2 .

The results of the analysis showed that the wholesale energy value of PV generation varied significantly from place to place, even within the region of a given ISO. For example, in New York City and Long Island, where population density is high and adding transmission lines is difficult, the market value of solar was at times 50 percent higher than across the state as a whole. 

The public health benefits associated with SO 2 , NO x , and PM 2.5  emissions reductions declined over the study period but were still substantial in 2017. Monetizing the health benefits of PV generation in 2017 would add almost 75 percent to energy revenues in the Midwest and New York and fully 100 percent in the Mid-Atlantic, thanks to the large amount of coal generation in the Midwest and Mid-Atlantic and the high population density on the Eastern Seaboard. 

Based on the calculated energy and capacity revenues and health and climate benefits for 2017, the researchers asked: Given that combination of private and public benefits, what upfront PV system cost would be needed to make the PV installation “break even” over its lifetime, assuming that grid conditions in that year persist for the life of the installation? In other words, says Brown, “At what capital cost would an investment in a PV system be paid back in benefits over the lifetime of the array?” 

Assuming 2017 values for energy and capacity market revenues alone, an unsubsidized PV investment at 2017 costs doesn’t break even. Add in the health benefit, and PV breaks even at 30 percent of the pricing nodes modeled. Assuming a carbon price of $50 per ton, the investment breaks even at about 70 percent of the nodes, and with a carbon price of $100 per ton (which is still less than the price estimated to be needed to limit global temperature rise to under 2 degrees Celsius), PV breaks even at all of the modeled nodes. 

That wasn’t the case just two years earlier: At 2015 PV costs, PV would only have broken even in 2017 at about 65 percent of the nodes counting market revenues, health benefits, and a $100 per ton carbon price. “Since 2010, solar has gone from one of the most expensive sources of electricity to one of the cheapest, and it now breaks even across the majority of the U.S. when considering the full slate of values that it provides,” says Brown. 

Based on their findings, the researchers conclude that the decline in PV costs over the studied period outpaced the decline in value, such that in 2017 the market, health, and climate benefits outweighed the cost of PV systems at the majority of locations modeled. “So the amount of solar that’s competitive is still increasing year by year,” says Brown. 

The findings underscore the importance of considering health and climate benefits as well as market revenues. “If you’re going to add another megawatt of PV power, it’s best to put it where it’ll make the most difference, not only in terms of revenues but also health and CO 2 ,” says Brown. 

Unfortunately, today’s policies don’t reward that behavior. Some states do provide renewable energy subsidies for solar investments, but they reward generation equally everywhere. Yet in states such as New York, the public health benefits would have been far higher at some nodes than at others. State-level or regional reward mechanisms could be tailored to reflect such variation in node-to-node benefits of PV generation, providing incentives for installing PV systems where they’ll be most valuable. Providing time-varying price signals (including the cost of emissions) not only to utility-scale generators, but also to residential and commercial electricity generators and customers, would similarly guide PV investment to areas where it provides the most benefit. 

Time-shifting PV output to maximize revenues 

The analysis provides some guidance that might help would-be PV installers maximize their revenues. For example, it identifies certain “hot spots” where PV generation is especially valuable. At some high-electricity-demand nodes along the East Coast, for instance, persistent grid congestion has meant that the projected revenue of a PV generator has been high for more than a decade. The analysis also shows that the sunniest site may not always be the most profitable choice. A PV system in Texas would generate about 20 percent more power than one in the Northeast, yet energy revenues were greater at nodes in the Northeast than in Texas in some of the years analyzed. 

To help potential PV owners maximize their future revenues, Brown and O’Sullivan performed a follow-on study focusing on ways to shift the output of PV arrays to align with times of higher prices on the wholesale market. For this analysis, they considered the value of solar on the day-ahead market and also on the “real-time market,” which dispatches generators to correct for discrepancies between supply and demand. They explored three options for shaping the output of PV generators, with a focus on the California real-time market in 2017, when high PV penetration led to a large reduction in midday prices compared to morning and evening prices.

• Curtailing output when prices are negative: During negative-price hours, a PV operator can simply turn off generation. In California in 2017, curtailment would have increased revenues by 9 percent on the real-time market compared to “must-run” operation.
• Changing the orientation of “fixed-tilt” (stationary) solar panels: The general rule of thumb in the Northern Hemisphere is to orient solar panels toward the south, maximizing production over the year. But peak production then occurs at about noon, when electricity prices in markets with high solar penetration are at their lowest. Pointing panels toward the west moves generation further into the afternoon. On the California real-time market in 2017, optimizing the orientation would have increased revenues by 13 percent, or 20 percent in conjunction with curtailment.
• Using 1-axis tracking: For larger utility-scale installations, solar panels are frequently installed on automatic solar trackers, rotating throughout the day from east in the morning to west in the evening. Using such 1-axis tracking on the California system in 2017 would have increased revenues by 32 percent over a fixed-tilt installation, and using tracking plus curtailment would have increased revenues by 42 percent.

The researchers were surprised to see how much the optimal orientation changed in California over the period of their study. “In 2010, the best orientation for a fixed array was about 10 degrees west of south,” says Brown. “In 2017, it’s about 55 degrees west of south.” That adjustment is due to changes in market prices that accompany significant growth in PV generation — changes that will occur in other regions as they start to ramp up their solar generation.

The researchers stress that conditions are constantly changing on power grids and electricity markets. With that in mind, they made their database and computer code openly available so that others can readily use them to calculate updated estimates of the net benefits of PV power and other distributed energy resources.

They also emphasize the importance of getting time-varying prices to all market participants and of adapting installation and dispatch strategies to changing power system conditions. A law set to take effect in California in 2020 will require all new homes to have solar panels. Installing the usual south-facing panels with uncurtailable output could further saturate the electricity market at times when other PV installations are already generating.

“If new rooftop arrays instead use west-facing panels that can be switched off during negative price times, it’s better for the whole system,” says Brown. “Rather than just adding more solar at times when the price is already low and the electricity mix is already clean, the new PV installations would displace expensive and dirty gas generators in the evening. Enabling that outcome is a win all around.”

Patrick Brown and this research were supported by a U.S. Department of Energy Office of Energy Efficiency and Renewable Energy (EERE) Postdoctoral Research Award through the EERE Solar Energy Technologies Office. The computer code and data repositories are available here and here .

This article appears in the  Spring 2020  issue of  Energy Futures, the magazine of the MIT Energy Initiative. 

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• Paper: “Shaping photovoltaic array output to align with changing wholesale electricity price profiles.”
• Paper: “Spatial and temporal variation in the value of solar power across United States electricity markets.”
• Report: “The Future of Solar Energy”
• Patrick Brown
• MIT Energy Initiative
• Energy Futures magazine

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Solar Energy

Solar energy is created by nuclear fusion that takes place in the sun. It is necessary for life on Earth, and can be harvested for human uses such as electricity.

Earth Science, Engineering, Physics

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Solar energy is any type of energy generated by the sun . Solar energy is created by nuclear fusion that takes place in the sun. Fusion occurs when protons of hydrogen atoms violently collide in the sun’s core and fuse to create a helium atom. This process, known as a PP (proton-proton) chain reaction, emits an enormous amount of energy. In its core, the sun fuses about 620 million metric tons of hydrogen every second. The PP chain reaction occurs in other stars that are about the size of our sun, and provides them with continuous energy and heat. The temperature for these stars is around 4 million degrees on the Kelvin scale (about 4 million degrees Celsius, 7 million degrees Fahrenheit). In stars that are about 1.3 times bigger than the sun, the CNO cycle drives the creation of energy. The CNO cycle also converts hydrogen to helium, but relies on carbon, nitrogen, and oxygen (C, N, and O) to do so. Currently , less than two percent of the sun’s energy is created by the CNO cycle. Nuclear fusion by the PP chain reaction or CNO cycle releases tremendous amounts of energy in the form of waves and particles. Solar energy is constantly flowing away from the sun and throughout the solar system . Solar energy warms Earth, causes wind and weather , and sustains plant and animal life. The energy, heat, and light from the sun flow away in the form of electromagnetic radiation (EMR). The electromagnetic spectrum exists as waves of different frequencies and wavelengths. The frequency of a wave represents how many times the wave repeats itself in a certain unit of time. Waves with very short wavelengths repeat themselves several times in a given unit of time, so they are high-frequency. In contrast, low-frequency waves have much longer wavelengths. The vast majority of electromagnetic waves are invisible to us. The most high-frequency waves emitted by the sun are gamma rays, X-rays, and ultraviolet radiation (UV rays). The most harmful UV rays are almost completely absorbed by Earth’s atmosphere . Less potent UV rays travel through the atmosphere, and can cause sunburn. The sun also emits infrared radiation , whose waves are much lower-frequency. Most heat from the sun arrives as infrared energy. Sandwiched between infrared and UV is the visible spectrum, which contains all the colors we see on Earth. The color red has the longest wavelengths (closest to infrared), and violet (closest to UV) the shortest. Natural Solar Energy Greenhouse Effect The infrared, visible, and UV waves that reach Earth take part in a process of warming the planet and making life possible—the so-called “greenhouse effect.” About 30 percent of the solar energy that reaches Earth is reflected back into space. The rest is absorbed into Earth’s atmosphere. The radiation warms Earth’s surface, and the surface radiates some of the energy back out in the form of infrared waves. As they rise through the atmosphere, they are intercepted by greenhouse gases , such as water vapor and carbon dioxide.

Greenhouse gases trap the heat that reflects back up into the atmosphere. In this way, they act like the glass walls of a greenhouse. This greenhouse effect keeps Earth warm enough to sustain life. Photosynthesis Almost all life on Earth relies on solar energy for food, either directly or indirectly. Producers rely directly on solar energy. They absorb sunlight and convert it into nutrients through a process called photosynthesis. Producers, also called autotrophs , include plants, algae, bacteria, and fungi. Autotrophs are the foundation of the food web . Consumers rely on producers for nutrients. Herbivores, carnivores, omnivores, and detritivores rely on solar energy indirectly. Herbivores eat plants and other producers. Carnivores and omnivores eat both producers and herbivores. Detritivores decompose plant and animal matter by consuming it. Fossil Fuels Photosynthesis is also responsible for all of the fossil fuels on Earth. Scientists estimate that about three billion years ago, the first autotrophs evolved in aquatic settings. Sunlight allowed plant life to thrive and evolve. After the autotrophs died, they decomposed and shifted deeper into the Earth, sometimes thousands of meters. This process continued for millions of years. Under intense pressure and high temperatures, these remains became what we know as fossil fuels. Microorganisms became petroleum, natural gas, and coal. People have developed processes for extracting these fossil fuels and using them for energy. However, fossil fuels are a nonrenewable resource . They take millions of years to form. Harnessing Solar Energy Solar energy is a renewable resource , and many technologies can harvest it directly for use in homes, businesses, schools, and hospitals. Some solar energy technologies include photovoltaic cells and panels, concentrated solar energy , and solar architecture . There are different ways of capturing solar radiation and converting it into usable energy. The methods use either active solar energy or passive solar energy . Active solar technologies use electrical or mechanical devices to actively convert solar energy into another form of energy, most often heat or electricity. Passive solar technologies do not use any external devices. Instead, they take advantage of the local climate to heat structures during the winter, and reflect heat during the summer. Photovoltaics Photovoltaics is a form of active solar technology that was discovered in 1839 by 19-year-old French physicist Alexandre-Edmond Becquerel. Becquerel discovered that when he placed silver-chloride in an acidic solution and exposed it to sunlight, the platinum electrodes attached to it generated an electric current. This process of generating electricity directly from solar radiation is called the photovoltaic effect, or photovoltaics.

Today, photovoltaics is probably the most familiar way to harness solar energy. Photovoltaic arrays usually involve solar panels , a collection of dozens or even hundreds of solar cells. Each solar cell contains a semiconductor , usually made of silicon. When the semiconductor absorbs sunlight, it knocks electrons loose. An electrical field directs these loose electrons into an electric current, flowing in one direction. Metal contacts at the top and bottom of a solar cell direct that current to an external object. The external object can be as small as a solar-powered calculator or as large as a power station. Photovoltaics was first widely used on spacecraft. Many satellites , including the International Space Station (ISS), feature wide, reflective “wings” of solar panels. The ISS has two solar array wings (SAWs), each using about 33,000 solar cells. These photovoltaic cells supply all electricity to the ISS, allowing astronauts to operate the station, safely live in space for months at a time, and conduct scientific and engineering experiments. Photovoltaic power stations have been built all over the world. The largest stations are in the United States, India, and China. These power stations emit hundreds of megawatts of electricity, used to supply homes, businesses, schools, and hospitals. Photovoltaic technology can also be installed on a smaller scale. Solar panels and cells can be fixed to the roofs or exterior walls of buildings, supplying electricity for the structure. They can be placed along roads to light highways. Solar cells are small enough to power even smaller devices, such as calculators, parking meters, trash compactors, and water pumps. Concentrated Solar Energy Another type of active solar technology is concentrated solar energy or concentrated solar power (CSP). CSP technology uses lenses and mirrors to focus (concentrate) sunlight from a large area into a much smaller area. This intense area of radiation heats a fluid, which in turn generates electricity or fuels another process. Solar furnaces are an example of concentrated solar power. There are many different types of solar furnaces, including solar power towers , parabolic troughs, and Fresnel reflectors. They use the same general method to capture and convert energy. Solar power towers use heliostats , flat mirrors that turn to follow the sun’s arc through the sky. The mirrors are arranged around a central “collector tower,” and reflect sunlight into a concentrated ray of light that shines on a focal point on the tower. In previous designs of solar power towers, the concentrated sunlight heated a container of water, which produced steam that powered a turbine . More recently, some solar power towers use liquid sodium, which has a higher heat capacity and retains heat for a longer period of time. This means that the fluid not only reaches temperatures of 773 to 1,273K (500° to 1,000° C or 932° to 1,832° F), but it can continue to boil water and generate power even when the sun is not shining. Parabolic troughs and Fresnel reflectors also use CSP, but their mirrors are shaped differently. Parabolic mirrors are curved, with a shape similar to a saddle. Fresnel reflectors use flat, thin strips of mirror to capture sunlight and direct it onto a tube of liquid. Fresnel reflectors have more surface area than parabolic troughs and can concentrate the sun’s energy to about 30 times its normal intensity. Concentrated solar power plants were first developed in the 1980s. The largest facility in the world is a series of plants in Mojave Desert in the U.S. state of California. This Solar Energy Generating System (SEGS) generates more than 650 gigawatt-hours of electricity every year. Other large and effective plants have been developed in Spain and India.

Concentrated solar power can also be used on a smaller scale. It can generate heat for solar cookers , for instance. People in villages all over the world use solar cookers to boil water for sanitation and to cook food. Solar cookers provide many advantages over wood-burning stoves: They are not a fire hazard, do not produce smoke, do not require fuel, and reduce habitat loss in forests where trees would be harvested for fuel. Solar cookers also allow villagers to pursue time for education, business, health, or family during time that was previously used for gathering firewood. Solar cookers are used in areas as diverse as Chad, Israel, India, and Peru. Solar Architecture Throughout the course of a day, solar energy is part of the process of thermal convection , or the movement of heat from a warmer space to a cooler one. When the sun rises, it begins to warm objects and material on Earth. Throughout the day, these materials absorb heat from solar radiation. At night, when the sun sets and the atmosphere has cooled, the materials release their heat back into the atmosphere. Passive solar energy techniques take advantage of this natural heating and cooling process. Homes and other buildings use passive solar energy to distribute heat efficiently and inexpensively. Calculating a building’s “ thermal mass ” is an example of this. A building’s thermal mass is the bulk of material heated throughout the day. Examples of a building’s thermal mass are wood, metal, concrete, clay, stone, or mud. At night, the thermal mass releases its heat back into the room. Effective ventilation systems—hallways, windows, and air ducts—distribute the warmed air and maintain a moderate, consistent indoor temperature. Passive solar technology is often involved in the design of a building. For example, in the planning stage of construction, the engineer or architect may align the building with the sun’s daily path to receive desirable amounts of sunlight. This method takes into account the latitude , altitude , and typical cloud cover of a specific area. In addition, buildings can be constructed or retrofitted to have thermal insulation, thermal mass, or extra shading. Other examples of passive solar architecture are cool roofs, radiant barriers , and green roofs . Cool roofs are painted white, and reflect the sun’s radiation instead of absorbing it. The white surface reduces the amount of heat that reaches the interior of the building, which in turn reduces the amount of energy that is needed to cool the building. Radiant barriers work similarly to cool roofs. They provide insulation with highly reflective materials, such as aluminum foil. The foil reflects, instead of absorbs, heat, and can reduce cooling costs up to 10 percent. In addition to roofs and attics, radiant barriers may also be installed beneath floors. Green roofs are roofs that are completely covered with vegetation . They require soil and irrigation to support the plants, and a waterproof layer beneath. Green roofs not only reduce the amount of heat that is absorbed or lost, but also provide vegetation. Through photosynthesis, the plants on green roofs absorb carbon dioxide and emit oxygen. They filter pollutants out of rainwater and air, and offset some of the effects of energy use in that space. Green roofs have been a tradition in Scandinavia for centuries, and have recently become popular in Australia, Western Europe, Canada, and the United States. For example, the Ford Motor Company covered 42,000 square meters (450,000 square feet) of its assembly plant roofs in Dearborn, Michigan, with vegetation. In addition to reducing greenhouse gas emissions, the roofs reduce stormwater runoff by absorbing several centimeters of rainfall.

Green roofs and cool roofs can also counteract the “ urban heat island ” effect. In busy cities, the temperature can be consistently higher than the surrounding areas. Many factors contribute to this: Cities are constructed of materials such as asphalt and concrete that absorb heat; tall buildings block wind and its cooling effects; and high amounts of waste heat is generated by industry, traffic, and high populations. Using the available space on the roof to plant trees, or reflecting heat with white roofs, can partially alleviate local temperature increases in urban areas. Solar Energy and People Since sunlight only shines for about half of the day in most parts of the world, solar energy technologies have to include methods of storing the energy during dark hours. Thermal mass systems use paraffin wax or various forms of salt to store the energy in the form of heat. Photovoltaic systems can send excess electricity to the local power grid , or store the energy in rechargeable batteries. There are many pros and cons to using solar energy. Advantages A major advantage to using solar energy is that it is a renewable resource. We will have a steady, limitless supply of sunlight for another five billion years. In one hour, Earth’s atmosphere receives enough sunlight to power the electricity needs of every human being on Earth for a year. Solar energy is clean. After the solar technology equipment is constructed and put in place, solar energy does not need fuel to work. It also does not emit greenhouse gases or toxic materials. Using solar energy can drastically reduce the impact we have on the environment. There are locations where solar energy is practical . Homes and buildings in areas with high amounts of sunlight and low cloud cover have the opportunity to harness the sun’s abundant energy. Solar cookers provide an excellent alternative to cooking with wood-fired stoves—on which two billion people still rely. Solar cookers provide a cleaner and safer way to sanitize water and cook food. Solar energy complements other renewable sources of energy, such as wind or hydroelectric energy . Homes or businesses that install successful solar panels can actually produce excess electricity. These homeowners or businessowners can sell energy back to the electric provider, reducing or even eliminating power bills. Disadvantages The main deterrent to using solar energy is the required equipment. Solar technology equipment is expensive. Purchasing and installing the equipment can cost tens of thousands of dollars for individual homes. Although the government often offers reduced taxes to people and businesses using solar energy, and the technology can eliminate electricity bills, the initial cost is too steep for many to consider. Solar energy equipment is also heavy. In order to retrofit or install solar panels on the roof of a building, the roof must be strong, large, and oriented toward the sun’s path. Both active and passive solar technology depend on factors that are out of our control, such as climate and cloud cover. Local areas must be studied to determine whether or not solar power would be effective in that area. Sunlight must be abundant and consistent for solar energy to be an efficient choice. In most places on Earth, sunlight’s variability makes it difficult to implement as the only source of energy.

Agua Caliente The Agua Caliente Solar Project, in Yuma, Arizona, United States, is the world's largest array of photovoltaic panels. Agua Caliente has more than five million photovoltaic modules, and generates more than 600 gigawatt-hours of electricity.

Green Chicago Millennium Park in Chicago, Illinois, United States, has one of the most expansive green roofs in the world almost 100,000 square meters (more than a million square feet). Vegetation at ground level covers 24.5 acres of an underground parking garage, and includes gardens, picnic areas, and an outdoor concert facility.

Solar Decathlon The Solar Decathlon is a biannual international event presented by the U.S. Department of Energy. Teams compete to design, build, and operate the most attractive, effective, and energy-efficient solar-powered house.

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Solar Energy

Though costly to implement, solar energy offers a clean, renewable source of power.

Solar energy is the technology used to harness the sun's energy and make it useable. As of 2011 , the technology produced less than one tenth of one percent of global energy demand.

Many are familiar with so-called photovoltaic cells, or solar panels, found on things like spacecraft, rooftops, and handheld calculators. The cells are made of semiconductor materials like those found in computer chips. When sunlight hits the cells, it knocks electrons loose from their atoms. As the electrons flow through the cell, they generate electricity.

On a much larger scale, solar-thermal power plants employ various techniques to concentrate the sun's energy as a heat source. The heat is then used to boil water to drive a steam turbine that generates electricity in much the same fashion as coal and nuclear power plants, supplying electricity for thousands of people.

The sun has produced energy for billions of years. Every hour the sun beams more energy onto Earth than it needs to satisfy global energy needs for an entire year.

How to Harness Solar Power

In one technique, long troughs of U-shaped mirrors focus sunlight on a pipe of oil that runs through the middle. The hot oil then boils water for electricity generation. Another technique uses moveable mirrors to focus the sun's rays on a collector tower, where a receiver sits. Molten salt flowing through the receiver is heated to run a generator.

Other solar technologies are passive. For example, big windows placed on the sunny side of a building allow sunlight to heat-absorbent materials on the floor and walls. These surfaces then release the heat at night to keep the building warm. Similarly, absorbent plates on a roof can heat liquid in tubes that supply a house with hot water.

Solar energy is lauded as an inexhaustible fuel source that is pollution- and often noise-free. The technology is also versatile. For example, solar cells generate energy for far-out places like satellites in Earth orbit and cabins deep in the Rocky Mountains as easily as they can power downtown buildings and futuristic cars.

Solar energy doesn't work at night without a storage device such as a battery, and cloudy weather can make the technology unreliable during the day. Solar technologies are also very expensive and require a lot of land area to collect the sun's energy at rates useful to lots of people.

Despite the drawbacks, solar energy use has surged at about 20 percent a year over the past 15 years, thanks to rapidly falling prices and gains in efficiency. Japan, Germany, and the United States are major markets for solar cells. With tax incentives, and efficient coordination with energy companies , solar electricity can often pay for itself in five to ten years.

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Super-efficient solar cells: 10 Breakthrough Technologies 2024

Solar cells that combine traditional silicon with cutting-edge perovskites could push the efficiency of solar panels to new heights.

• Emma Foehringer Merchant archive page

Beyond Silicon, Caelux, First Solar, Hanwha Q Cells, Oxford PV, Swift Solar, Tandem PV

3 to 5 years

In November 2023, a buzzy solar technology broke yet another world record for efficiency. The previous record had existed for only about five months—and it likely won’t be long before it too is obsolete. This astonishing acceleration in efficiency gains comes from a special breed of next-­generation solar technology: perovskite tandem solar cells. These cells layer the traditional silicon with materials that share a unique crystal structure.

In the decade that scientists have been toying with perovskite solar technology , it has continued to best its own efficiency records, which measure how much of the sunlight that hits the cell is converted into electricity. Perovskites absorb different wavelengths of light from those absorbed by silicon cells, which account for 95% of the solar market today. When silicon and perovskites work together in tandem solar cells, they can utilize more of the solar spectrum, producing more electricity per cell. 

Technical efficiency levels for silicon-­based cells top out below 30%, while perovskite-only cells have reached experimental efficiencies of around 26%. But perovskite tandem cells have already exceeded 33% efficiency in the lab. That is the technology’s tantalizing promise: if deployed on a significant scale, perovskite tandem cells could produce more electricity than the legacy solar cells at a lower cost. 

But perovskites have stumbled when it comes to actual deployment. Silicon solar cells can last for decades. Few perovskite tandem panels have even been tested outside. 

The electrochemical makeup of perovskites means they’re sensitive to sucking up water and degrading in heat, though researchers have been working to create better barriers around panels and shifting to more stable perovskite compounds. 

In May, UK-based Oxford PV said it had reached an efficiency of 28.6% for a commercial-size perovskite tandem cell, which is significantly larger than those used to test the materials in the lab, and it plans to deliver its first panels and ramp up manufacturing in 2024. Other companies could unveil products later this decade. 

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Bright Future for Renewables: Solar Drives Energy Growth in 2024

After a record-breaking year for solar additions to the grid, the EIA predicts solar will continue to be the fastest growing renewable over the next two years.

Last year, solar panels were responsible for over 50% of the annual additions to America's energy generation. There's a sunny forecast for solar this year, too.

Energy generation in the US will grow by 3% in 2024 -- and solar power will be the main source of that expansion.

That's according to the latest report from the Energy Information Administration . The report indicates that, while  solar adoption throughout the United States has been steadily increasing in recent years, 2024 could see us approaching a landmark moment for the solar industry .

"In 2025, we expect generation from solar to exceed the contribution from hydroelectricity for the first time in history," said Joe DeCarolis, administrator of the EIA, in the report's press release .

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Renewable energy has been a focus of federal policy, with assurances being made that solar, wind and hydropower will be made more accessible to all American communities . 

With government support and lower and lower costs, solar and renewables will keep growing over the next two years.

The big picture projection

Renewable energy sources are expected to make up 22% of America's total energy generation capacity by the end of 2024, further increasing to 24% by the end of 2025, according to the EIA. That projection accounts for solar, wind and hydropower.

Those three renewable sources only accounted for 21% of US grid capacity in 2023.

Considering Solar Panels?

Solar energy is the most rapidly growing renewable energy source by far. The EIA projects that solar generation will increase by up to 41%, building on record setting growth in 2023. 

Energy generation from wind will grow 5% and energy generation from hydropower will grow 6% in 2024.

Building on last year's breakneck solar expansion

There was more solar power added to America's grid in 2023 than ever before , thanks in large part to federal incentives for solar installations included within the Inflation Reduction Act .

In 2023, over half of the new energy generating capacity in the US came from solar panels -- marking the first time in history solar eclipsed 50% of yearly additions to the grid.

The solar industry also had to reckon with some big challenges last year.

High interest rates have made financing solar panels untenable for some people, and some of the largest solar markets in America took a big hit last year -- California's solar installation rate suffered from a massive contraction after the state's net metering policy was revised to be much more restrictive.

While the federal government has passed favorable legislation, election results may affect how many solar panels are actually installed in the coming years.

Regardless, experts remain cautiously optimistic about the future of solar.

"If we stay the course with our federal clean energy policies, total solar deployment will quadruple over the next 10 years," said Abigail Ross Hopper , president and CEO of the Solar Energy Industries Association, in the US Solar Market Insight 2023 Year in Review .

How to get rooftop solar for your home

First and foremost, you need to find out if solar is available to you in your living situation.

If you're a renter, you can't install your own solar panel system, but expanding community solar programs across the country are being built to support your needs. Homeowners will need to do a little research to make sure that no HOA rules or historical preservation laws will prevent them from setting up their own solar panels.

Homeowners also need to ensure their roof is sound and a good fit for solar .

Reaching out to multiple solar installers is important; make sure to reach out to at least four or five companies to ensure the cost of your solar system is fair. Check reviews from the Better Business Bureau, Google, Yelp and speak to your neighbors who've installed solar panel systems.

Finally, make sure you're taking advantage of every available federal- and state-level solar incentive to make the most of your investment. The Inflation Reduction Act's 30% residential clean energy credit will stack with any potential state tax credits .

Claiming the federal tax credit is a fairly simple process . The year after your solar installation is completed, fill out and submit IRS Form 5695, Residential Energy Credits when you're filing your taxes. Your credit reduces the amount of taxes you owe.

The Inflation Reduction Act's residential clean energy credit applies to solar battery installation as well, and the energy efficient home improvement credit applies to certain furnaces , heat pumps , insulation and more.

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Article updated on May 13, 2024 at 3:14 AM PDT

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Scientists generate heat over 1,000 degrees Celsius with solar power instead of fossil fuel

Instead of burning fossil fuels to smelt steel and cook cement, researchers in Switzerland want to use heat from the sun. The proof-of-concept study, published May 15 in the journal Device , uses synthetic quartz to trap solar energy at temperatures over 1,000°C (1,832°F), demonstrating the method's potential role in providing clean energy for carbon-intensive industries.

"To tackle climate change, we need to decarbonize energy in general," says corresponding author Emiliano Casati of ETH Zurich, Switzerland. "People tend to only think about electricity as energy, but in fact, about half of the energy is used in the form of heat."

Glass, steel, cement, and ceramics are at the very heart of modern civilization, essential for building everything from car engines to skyscrapers. However, manufacturing these materials demands temperatures over 1,000°C and relies heavily on burning fossil fuels for heat. These industries account for about 25% of global energy consumption. Researchers have explored a clean-energy alternative using solar receivers, which concentrate and build heat with thousands of sun-tracking mirrors. However, this technology has difficulties transferring solar energy efficiently above 1,000°C.

To boost the efficiency of solar receivers, Casati turned to semitransparent materials such as quartz, which can trap sunlight -- a phenomenon called the thermal-trap effect. The team crafted a thermal-trapping device by attaching a synthetic quartz rod to an opaque silicon disk as an energy absorber. When they exposed the device to an energy flux equivalent to the light coming from 136 suns, the absorber plate reached 1,050°C (1,922°F), whereas the other end of the quartz rod remained at 600°C (1,112°F).

"Previous research has only managed to demonstrate the thermal-trap effect up to 170°C (338°F)," says Casati. "Our research showed that solar thermal trapping works not just at low temperatures, but well above 1,000°C. This is crucial to show its potential for real-world industrial applications."

Using a heat transfer model, the team also simulated the quartz's thermal-trapping efficiency under different conditions. The model showed that thermal trapping achieves the target temperature at lower concentrations with the same performance, or at higher thermal efficiency for equal concentration. For example, a state-of-the-art (unshielded) receiver has an efficiency of 40% at 1,200°C, with a concentration of 500 suns. The receiver shielded with 300 mm of quartz achieves 70% efficiency at the same temperature and concentration. The unshielded receiver requires at least 1,000 suns of concentration for comparable performance.

Casati and his colleagues are now optimizing the thermal-trapping effect and investigating new applications for the method. So far, their research has been promising. By exploring other materials, such as different fluids and gases, they were able to reach even higher temperatures. The team also noted that these semitransparent materials' ability to absorb light or radiation is not limited to solar radiation.

"Energy issue is a cornerstone to the survival of our society," says Casati. "Solar energy is readily available, and the technology is already here. To really motivate industry adoption, we need to demonstrate the economic viability and advantages of this technology at scale."

• Thermodynamics
• Solar Energy
• Energy and Resources
• Energy Technology
• Energy and the Environment
• Renewable Energy
• Environmental Science
• Sustainability
• Renewable energy
• Fossil fuel
• Potential energy
• Alcohol fuel
• Pyroelectricity
• Solar panel

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Journal Reference :

• Emiliano Casati, Leo Allgoewer, Aldo Steinfeld. Solar thermal trapping at 1,000°C and above . Device , 2024; 100399 DOI: 10.1016/j.device.2024.100399

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The accelerating buildout of solar farms on Earth is already hitting speed bumps, including public pushback against the large tracts of land required and a ballooning backlog of requests for new transmission lines and grid connections. Energy experts have been warning that electricity is likely to get more expensive and less reliable unless renewable power that waxes and wanes under inconstant sunlight and wind is backed up by generators that can run whenever needed. To space enthusiasts, that raises an obvious question: Why not stick solar power plants where the sun always shines?

Space-based solar power is an idea so beautiful, so tantalizing that some argue it is a wish worth fulfilling. A constellation of gigantic satellites in geosynchronous orbit (GEO) nearly 36,000 kilometers above the equator could collect sunlight unfiltered by atmosphere and uninterrupted by night (except for up to 70 minutes a day around the spring and fall equinoxes). Each megasat could then convert gigawatts of power into a microwave beam aimed precisely at a big field of receiving antennas on Earth. These rectennas would then convert the signal to usable DC electricity.

The thousands of rocket launches needed to loft and maintain these space power stations would dump lots of soot, carbon dioxide, and other pollutants into the stratosphere, with uncertain climate impacts. But that might be mitigated, in theory, if space solar displaced fossil fuels and helped the world transition to clean electricity.

The glamorous vision has inspired numerous futuristic proposals. Japan’s space agency has presented a road map to deployment. Space authorities in China aim to put a small test satellite in low Earth orbit (LEO) later this decade. Ideas to put megawatt-scale systems in GEO sometime in the 2030s have been floated but not yet funded.

The U.S. Naval Research Laboratory has already beamed more than a kilowatt of power between two ground antennas about a kilometer apart. It also launched in 2023 a satellite that used a laser to transmit about 1.5 watts, although the beam traveled less than 2 meters and the system had just 11 percent efficiency. A team at Caltech earlier this year wrapped up a mission that used a small satellite in LEO to test thin-film solar cells, flexible microwave-power circuitry, and a small collapsible deployment mechanism. The energy sent Earthward by the craft was too meager to power a lightbulb, but it was progress nonetheless.

The European Space Agency (ESA) debuted in 2022 its space-based solar-power program, called Solaris, with an inspiring (but entirely fantastical) video animation . The program’s director, Sanjay Vijendran , told IEEE Spectrum that the goal of the effort is not to develop a power station for space. Instead, the program aims to spend three years and €60 million (US $65 million) to figure out whether solar cells, DC-to-RF converters, assembly robots, beam-steering antennas, and other must-have technologies will improve drastically enough over the next 10 to 20 years to make orbital solar power feasible and competitive. Low-cost, low-mass, and space-hardy versions of these technologies would be required, but engineers trying to draw up detailed plans for such satellites today find no parts that meet the tough requirements.

With the flurry of renewed attention, you might wonder: Has extraterrestrial solar power finally found its moment? As the recently retired head of space power systems at ESA—with more than 30 years of experience working on power generation, energy storage, and electrical systems design for dozens of missions, including evaluation of a power-beaming experiment proposed for the International Space Station—I think the answer is almost certainly no.

Despite mounting buzz around the concept, I and many of my former colleagues at ESA are deeply skeptical that these large and complex power systems could be deployed quickly enough and widely enough to make a meaningful contribution to the global energy transition. Among the many challenges on the long and formidable list of technical and societal obstacles: antennas so big that we cannot even simulate their behavior.

Here I offer a road map of the potential chasms and dead ends that could doom a premature space solar project to failure. Such a misadventure would undermine the credibility of the responsible space agency and waste capital that could be better spent improving less risky ways to shore up renewable energy, such as batteries, hydrogen, and grid improvements. Champions of space solar power could look at this road map as a wish list that must be fulfilled before orbital solar power can become truly appealing to electrical utilities.

Space Solar Power at Peak Hype—Again

For decades, enthusiasm for the possibility of drawing limitless, mostly clean power from the one fusion reactor we know works reliably—the sun—has run hot and cold. A 1974 study that NASA commissioned from the consultancy Arthur D. Little bullishly recommended a 20-year federal R&D program, expected to lead to a commercial station launching in the mid-1990s. After five years of work, the agency delivered a reference architecture for up to 60 orbiting power stations, each delivering 5 to 10 gigawatts of baseload power to major cities. But officials gave up on the idea when they realized that it would cost over $1 trillion (adjusted for inflation) and require hundreds of astronauts working in space for decades, all before the first kilowatt could be sold.

NASA did not seriously reconsider space solar until 1995, when it ordered a “fresh look” at the possibility. That two-year study generated enough interest that the U.S. Congress funded a small R&D program, which published plans to put up a megawatt-scale orbiter in the early 2010s and a full-size power plant in the early 2020s. Funding was cut off a few years later, with no satellites developed.

Then, a decade ago, private-sector startups generated another flurry of media attention. One, Solaren, even signed a power-purchase agreement to deliver 200 megawatts to utility customers in California by 2016 and made bold predictions that space solar plants would enter mass production in the 2020s. But the contract and promises went unfulfilled.

The repeated hype cycles have ended the same way each time, with investors and governments balking at the huge investments that must be risked to build a system that cannot be guaranteed to work. Indeed, in what could presage the end of the current hype cycle, Solaris managers have had trouble drumming up interest among ESA’s 22 member states. So far only the United Kingdom has participated, and just 5 percent of the funds available have been committed to actual research work.

Even space-solar advocates have recognized that success clearly hinges on something that cannot be engineered: sustained political will to invest, and keep investing, in a multidecade R&D program that ultimately could yield machines that can’t put electricity on the grid. In that respect, beamed power from space is like nuclear fusion, except at least 25 years behind.

In the 1990s, the fusion community succeeded in tapping into national defense budgets and cobbled together the 35-nation, $25 billion megaproject ITER, which launched in 2006. The effort set records for delays and cost overruns, and yet a prototype is still years from completion. Nevertheless, dozens of startups are now testing new fusion-reactor concepts . Massive investments in space solar would likely proceed in the same way. Of course, if fusion succeeds, it would eclipse the rationale for solar-energy satellites.

Space Industry Experts Run the Numbers

The U.S. and European space agencies have recently released detailed technical analyses of several space-based solar-power proposals. [See diagrams.] These reports make for sobering reading.

SPS-ALPHA Mark-III

Chris Philpot

Proposed by: John C. Mankins, former NASA physicist

Features: Thin-film reflectors (conical array) track the sun and concentrate sunlight onto an Earth-facing energy-conversion array that has photovoltaic (PV) panels on one side, microwave antennas on the other, and power distribution and control electronics in the middle. Peripheral modules adjust the station’s orbit and orientation.

Proposed by : China Academy of Space Technology

Features : Fifty PV solar arrays, each 200 meters wide and 600 meters long, track the sun and send power through rotating high-power joints and perpendicular trusses to a central microwave-conversion and transmission array that points 128,000 antenna modules at the receiving station on Earth.

Proposed by: Ian Cash, chief architect, Space Solar Group Holdings

Features: Circular thin-film reflectors track the sun and bounce light onto a helical array that includes myriad small PV cells covered by Fresnel-lens concentrators, power-conversion electronics, and microwave dipole antennas. The omnidirectional antennas must operate in sync to steer the beam as the station rotates relative to the Earth.

SPS (Solar power satellite)

Proposed by: Thales Alenia Space

Features: Nearly 8,000 flexible solar arrays, each 10 meters wide and 80 meters long, are unfurled from roll-out modules and linked together to form two wings. The solar array remains pointed at the sun, so the central transmitter must rotate and also operate with great precision as a phased-array antenna to continually steer the beam onto the ground station.

Electricity made this way, NASA reckoned in its 2024 report , would initially cost 12 to 80 times as much as power generated on the ground, and the first power station would require at least $275 billion in capital investment. Ten of the 13 crucial subsystems required to build such a satellite—including gigawatt-scale microwave beam transmission and robotic construction of kilometers-long, high-stiffness structures in space—rank as “high” or “very high” technical difficulty, according to a 2022 report to ESA by Frazer-Nash , a U.K. consultancy. Plus, there is no known way to safely dispose of such enormous structures, which would share an increasingly crowded GEO with crucial defense, navigation, and communications satellites, notes a 2023 ESA study by the French-Italian satellite maker Thales Alenia Space.

An alternative to microwave transmission would be to beam the energy down to Earth as reflected sunlight. Engineers at Arthur D. Little described the concept in a 2023 ESA study in which they proposed encircling the Earth with about 4,000 aimable mirrors in LEO. As each satellite zips overhead, it would shine an 8-km-wide spotlight onto participating solar farms, allowing the farms to operate a few extra hours each day (if skies are clear). In addition to the problems of clouds and light pollution, the report noted the thorny issue of orbital debris, estimating that each reflector would be penetrated about 75 billion times during its 10-year operating life.

My own assessment, presented at the 2023 European Space Power Conference and published by IEEE , pointed out dubious assumptions and inconsistencies in four space-solar designs that have received serious attention from government agencies. Indeed, the concepts detailed so far all seem to stand on shaky technical ground.

Massive Transmitters and Receiving Stations

The high costs and hard engineering problems that prevent us from building orbital solar-power systems today arise mainly from the enormity of these satellites and their distance from Earth, both of which are unavoidable consequences of the physics of this kind of energy transmission. Only in GEO can a satellite stay (almost) continuously connected to a single receiving station on the ground. The systems must beam down their energy at a frequency that passes relatively unimpeded through all kinds of weather and doesn’t interfere with critical radio systems on Earth. Most designs call for 2.45 or 5.8 gigahertz, within the range used for Wi-Fi. Diffraction will cause the beam to spread as it travels, by an amount that depends on the frequency.

Thales Alenia Space estimated that a transmitter in GEO must be at least 750 meters in diameter to train the bright center of a 5.8-GHz microwave beam onto a ground station of reasonable area over that tremendous distance—65 times the altitude of LEO satellites like Starlink. Even using a 750-meter transmitter, a receiver station in France or the northern United States would fill an elliptical field covering more than 34 square kilometers. That’s more than two-thirds the size of Bordeaux, France, where I live.

“Success hinges on something that cannot be engineered: sustained political will to keep investing in a multidecade R&D program that ultimately could yield machines that can’t put electricity on the grid.”

Huge components come with huge masses, which lead to exorbitant launch costs. Thales Alenia Space estimated that the transmitter alone would weigh at least 250 tonnes and cost well over a billion dollars to build, launch, and ferry to GEO. That estimate, based on ideas from the Caltech group that have yet to be tested in space, seems wildly optimistic; previous detailed transmitter designs are about 30 times heavier.

Because the transmitter has to be big and expensive, any orbiting solar project will maximize the power it sends through the beam, within acceptable safety limits. That’s why the systems evaluated by NASA, ESA, China, and Japan are all scaled to deliver 1–2 GW, the maximum output that utilities and grid operators now say they are willing to handle. It would take two or three of these giant satellites to replace one large retiring coal or nuclear power station.

Energy is lost at each step in the conversion from sunlight to DC electricity, then to microwaves, then back to DC electricity and finally to a grid-compatible AC current. It will be hard to improve much on the 11 percent end-to-end efficiency seen in recent field trials. So the solar arrays and electrical gear must be big enough to collect, convert, and distribute around 9 GW of power in space just to deliver 1 GW to the grid. No electronic switches, relays, and transformers have been designed or demonstrated for spacecraft that can handle voltages and currents anywhere near the required magnitude.

Some space solar designs, such as SPS-ALPHA and CASSIOPeiA , would suspend huge reflectors on kilometers-long booms to concentrate sunlight onto high-efficiency solar cells on the back side of the transmitter or intermingled with antennas. Other concepts, such as China’s MR-SPS and the design proposed by Thales Alenia Space, would send the currents through heavy, motorized rotating joints that allow the large solar arrays to face the sun while the transmitter pivots to stay fixed on the receiving station on Earth.

The net result, regardless of approach, is an orbiting power station that spans several kilometers, totals many thousands of tonnes, sends gigawatts of continuous power through onboard electronics, and comprises up to a million modules that must be assembled in space—by robots. That is a gigantic leap from the largest satellite and solar array ever constructed in orbit: the 420-tonne, 109-meter International Space Station (ISS), whose 164 solar panels produce less than 100 kilowatts to power its 43 modules.

The ISS has been built and maintained by astronauts, drawing on 30 years of prior experience with the Salyut, Skylab, and Mir space stations. But there is no comparable incremental path to a robot-assembled power satellite in GEO. Successfully beaming down a few megawatts from LEO would be an impressive achievement, but it wouldn’t prove that a full-scale system is feasible, nor would the intermittent power be particularly interesting to commercial utilities.

T Minus...Decades?

NASA’s 2024 report used sensitivity analysis to look for advances, however implausible, that would enable orbital solar power to be commercially competitive with nuclear fission and other low-emissions power. To start, the price of sending a tonne of cargo to LEO on a large reusable rocket, which has fallen 36 percent over the past 10 years, would have to drop by another two-thirds, to $500,000. This assumes that all the pieces of the station could be dropped off in low orbit and then raised to GEO over a period of months by space tugs propelled by electrical ion thrusters rather than conventional rockets. The approach would slow the pace of construction and add to the overall mass and cost. New tugs would have to be developed that could tow up to 100 times as much cargo as the biggest electric tugs do today. And by my calculations, the world’s annual production of xenon—the go-to propellant for ion engines—is insufficient to carry even a single solar-power satellite to GEO.

Thales Alenia Space looked at a slightly more realistic option: using a fleet of conventional rockets as big as SpaceX’s new Starship—the largest rocket ever built—to ferry loads from LEO to GEO, and then back to LEO for refueling from an orbiting fuel depot. Even if launch prices plummeted to $200,000 a tonne, they calculated, electricity from their system would be six times as expensive as NASA’s projected cost for a terrestrial solar farm outfitted with battery storage—one obvious alternative.

What else would have to go spectacularly right? In NASA’s cost-competitive scenario, the price of new, specialized spaceships that could maintain the satellite for 30 years—and then disassemble and dispose of it—would have to come down by 90 percent. The efficiency of commercially produced, space-qualified solar cells would have to soar from 32 percent today to 40 percent, while falling in cost. Yet over the past 30 years, big gains in the efficiency of research cells have not translated well to the commercial cells available at low cost [see chart, “Not So Fast”].

Is it possible for all these things to go right simultaneously? Perhaps. But wait—there’s more that can go wrong.

The Toll of Operating a Solar Plant in Space

Let’s start with temperature. Gigawatts of power coursing through the system will make heat removal essential because solar cells lose efficiency and microcircuits fry when they get too hot. A couple of dozen times a year, the satellite will pass suddenly into the utter darkness of Earth’s shadow, causing temperatures to swing by around 300 °C, well beyond the usual operating range of electronics. Thermal expansion and contraction may cause large structures on the station to warp or vibrate.

Then there’s the physical toll of operating in space. Vibrations and torques exerted by altitude-control thrusters, plus the pressure of solar radiation on the massive sail-like arrays, will continually bend and twist the station this way and that. The sprawling arrays will suffer unavoidable strikes from man-made debris and micrometeorites, perhaps even a malfunctioning construction robot. As the number of space power stations increases, we could see a rapid rise in the threat of Kessler syndrome , a runaway cascade of collisions that is every space operator’s nightmare.

Probably the toughest technical obstacle blocking space solar power is a basic one: shaping and aiming the beam. The transmitter is not a dish, like a radio telescope in reverse. It’s a phased array, a collection of millions of little antennas that must work in near-perfect synchrony, each contributing its piece to a collective waveform aimed at the ground station.

Like people in a stadium crowd raising their arms on cue to do “the wave,” coordination of a phased array is essential. It will work properly only if every element on the emitter syncs the phase of its transmission to align precisely with the transmission of its neighbors and with an incoming beacon signal sent from the ground station. Phase errors measured in picoseconds can cause the microwave beam to blur or drift off its target. How can the system synchronize elements separated by as much as a kilometer with such incredible accuracy? If you have the answer, please patent and publish it, because this problem currently has engineers stumped.

There is no denying the beauty of the idea of turning to deep space for inexhaustible electricity. But nature gets a vote. As Lao Tzu observed long ago in the Tao Te Ching , “The truth is not always beautiful, nor beautiful words the truth.”

• Caltech’s SSPD-1 Is a New Idea for Space-Based Solar ›
• Solar Power from Space? Caltech’s $100 Million Gambit ›
• Caltech Tests Space-Based Solar Power ›
• New Study Updates NASA on Space-Based Solar Power - NASA ›

Henri Barde joined the European Space Agency in 2007 and served as head of the power systems, electromagnetic compatibility, and space environment division until his retirement in 2017. He remains active as an expert consultant to ESA and the European Commission. Prior to ESA, Barde worked in various engineering roles in the space industry for 27 years at MATRA Espace, which became EADS Astrium and is now Airbus Defence and Space. 

Not a mention in the article about safety. What about the aiming of the satellite going bad and whole towns being fried like our dinner! Personally, I don't want a GW of energy over my house.

Henri Barde has mostly focused on the difficulty of building out the space station collector and transmitter. But I see also a huge risk for the earth based end of the system. We would absolutely depend on the accuracy and integrity of the collector/transmitter to beam the power accurately to the collector array on earth. But what if any number of failure mechanisms (including micrometeorite damage or sabotage) caused the beam to veer off-target. Would not that immense power of incoming microwaves be capable of causing direct harm to civilian infrastructure, or even possibly harm living things?

I strongly support the authors critical view (in all aspects) on the this idea beaming a lot of microwave power from space to the earth. The near earth space is already very crowed and full of space junk. In addition one has to bring thos e gigantic structure not only up to some some high orbit but also down .

Video Friday: Robots With Knives

Credentialing adds value to training programs, hydrogen storage could slash renewables’ costs.

Climate Change Is Making Rooftop Solar More Valuable, Research Shows

Last year was the hottest year on record . This year could beat it .

Thanks to the past and ongoing fossil fuel use that drives climate change, more people are going to need more energy to keep cool, comfortable and safe. When it comes to the increased electricity demand for household cooling, rooftop solar panels  can fill some of that void and save homeowners even more money down the road than it does today.

That's according to new research published in the journal Nature Climate Change , which models the value of a rooftop solar system in a changing climate. For nearly all the 17 cities the researchers analyzed, rooftop solar got more valuable in 2050 and 2100 than it is today.

"Across all but one of our cities, households see an increase in the value of their rooftop solar by midcentury and by end of century," said Michael Craig , a professor in energy systems at the University of Michigan and one of the researchers involved in the study.

How climate change makes solar more valuable

Solar is valuable to homeowners in two ways: by helping them avoid buying energy from their utility and by earning them more savings for sending energy back to the grid. Recent regulation has made returning electricity to the grid less valuable in some places. 

"In general, it's better to consume the electricity you produce than it is to sell it off onto the distribution grid," said Craig. "You basically get paid a better premium for it if you consume it yourself."

That's why solar batteries , which let you avoid even more grid electricity by saving solar energy for later, can be a money-saving investment for some people. (The impact of battery storage is one thing the study doesn't fully consider, Craig said.)

In a changing climate, solar panels can be more valuable because they'll produce more energy in places where it gets sunnier and offset more energy with an increase in demand for air conditioning.

Air conditioning uses 6% of all the electricity generated in the US, according to the Department of Energy, and makes up a significant portion of a home's electricity bill . Besides keeping people comfortable, it can also keep them safe as  dangerously hot weather is expected to increase .

Miami, the city with the largest jump in rooftop solar's value, sees a 14% increase by the end of the century because cooling demand will go up while the city gets less cloudy. 

The only city that saw the value of solar decrease, Minneapolis, is likely to see solar panels produce less energy because it will be cloudier in the future. Other cities will also get cloudier, but the increased demand for cooling still makes solar panels more valuable.

Rooftop solar systems, which can last for decades , are often sized to match a house's past demand. Considering future conditions could help unlock even more value from rooftop solar.

"When you put a rooftop solar system in place, that's gonna be operating for 10, 20, maybe 30 years," Craig said. "If you put a panel on your roof today, that's gonna be operating in a midcentury context."

It can cost thousands of dollars to install solar panels on your home , but they can recoup that cost and more. Some sources put the payback period on rooftop solar panels at eight to nine years , though that timeline varies depending on factors like a state or utility's solar feed-in tariff . 

Energy Advances

Thermally deposited copper(i) thiocyanate thin film: an efficient and sustainable approach for hole transport layer in perovskite solar cells.

Solution-processable deposition of copper(I) thiocyanate (CuSCN) thin films have been widely used as hole transport layer (HTL) in optoelectronic applications, namely perovskite and organic solar cells. Herein, we report thermally deposited CuSCN thin film as an efficient, eco-friendly and scalable HTL in inverted perovskite solar cells as an alternative and solvent free approach to the conventional solution-processed methods. The structural, electrochemical, optical, and morphological properties of the CuSCN films were characterized. The long-term electrochemical and optical stability of thermally deposited CuSCN films were examined. The effect of CuSCN film thicknesses (20, 30, 40, 60, and 100 nm) and annealing temperatures (RT, 50, 100, 150, and 200 °C) of CuSCN films on the photovoltaic performance were investigated. The optimized device configuration ITO/CuSCN/MAPbI3/PC61BM/BCP/Ag with 30 nm thick CuSCN film annealed at 100 °C for 10 min exhibits the maximum power conversion efficiency (PCE) of 15.71% with Voc = 1.01 V, Jsc = 20.2 mA/cm2, and FF = 0.77. For reference, perovskite solar cells without HTL have been also fabricated simultaneously. Importantly, the thermally deposited CuSCN based devices show excellent reproducibility and stability up to 240 h with ⁓89% retention of the initial PCE. This study demonstrates a new methodology for obtaining better CuSCN film by thermal deposition technique for efficient, sustainable and scalable electronic device applications.

• This article is part of the themed collection: Research advancing UN SDG 7: Affordable and clean energy

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Northern Lights Set to Return During Extreme Solar Storm’s 2nd Night

Electrical utilities said they weathered earlier conditions as persistent geomagnetic storms were expected to cause another light show in evening skies.

By Katrina Miller ,  Ivan Penn and Emmett Lindner

Night skies in many parts of the Northern Hemisphere are expected to bloom again on Saturday night with the vivid colors of the northern lights , or aurora borealis, as a powerful geomagnetic storm caused by a hyperactive sun persists through the weekend.

The National Oceanic and Atmospheric Administration , which monitors space weather, said in an update on Saturday that it continued to observe solar activity that could lead to periods of “severe-extreme” geomagnetic storms . The federal agency first issued a warning on Friday as bursts of material from the sun’s surface traveled into Earth’s atmosphere, causing irregularities in power, navigation and communication systems.

Major power utilities had largely prepared their electrical grids for the solar storm, and their customers were unaffected.

For most people, the solar storm was a gift: It caused ribbons of pink, purple and green light across night skies of much of the United States, Canada and Europe . Where evening skies are clear on Saturday, the lights can be expected again.

Known as aurora, the light is caused by particles from the sun interacting with gases in Earth’s atmosphere, and is usually only observed at latitudes closer to the North or South Pole. But on Friday night, residents of lower latitudes, including those in North Carolina and Arizona, saw the dancing lights.

Jane Wong, 30, of San Francisco, drove to the Presidio overlooking the Golden Gate Bridge where conditions started out foggy. But at midnight, her wait paid off as the sky started to clear.

“It’s right here, which is really magnificent,” she said.

Benjamin Williamson, 41, of Bath, Maine, drove to the Portland Head Light, a lighthouse in the state. An aurora enthusiast, he’d seen the northern lights during another major solar event in 2003, and in Iceland in 2017. None of those events, nor the April 8 solar eclipse, prepared him for what he saw on Friday.

“The solar eclipse last month, I thought that was the coolest thing I’d ever seen,” he said. “This might have beat it.”

Solar storms are caused by violent expulsions of charged particles from the sun’s surface. When directed toward Earth the material can interact with our planet’s magnetic field, resulting in a geomagnetic storm.

NOAA categorizes geomagnetic storms on a “G” scale of 1, or “minor,” to 5, “extreme.” On Thursday, the agency issued its first watch in 19 years for a G4, or “severe,” storm, which escalated into a warning on Friday afternoon.

Activity has exceeded the agency’s prediction, and some of it is now classified as G5, making it the strongest storm to reach Earth since October 2003.

The storm is caused by a giant cluster of sunspots, or dark, cool regions on the solar surface with strong magnetic fields. (If you still have your eclipse glasses handy, you may be able to see the sunspots during the day.) According to NOAA, the cluster will continue to flare and explode, with effects on Earth through at least the weekend. In 1989, a geomagnetic disturbance disrupted power systems in Canada and the United States. Energy providers have been on guard ever since.

“The utilities have been preparing for a large storm with the required vulnerability assessments,” said Bob Arritt, a technical executive at the Electric Power Research Institute, an independent research and development organization.

Some utilities saw high temperature alarms triggered overnight on parts of the electric grid, Mr. Arritt said, but added that it was too early to know if the alarms were related to the solar storm. He said he could not disclose the locations of the alerts as of Saturday.

But while the power system faced some additional stress from the storm, he added, “We have no reason to feel that there is any imminent threat to damaging equipment.”

The solar storm prompted managers of a number of electric grids to take extra precautions to keep electricity flowing, and to issue warnings to customers about potential disruptions.

PJM, the manager of the nation’s largest grid network across 13 states from the East Coast to the Midwest, said its geomagnetic disturbance warning would continue through the end of Saturday. ISO New England, which manages the electric grid for six states in the Northeast, issued a precautionary alert, which notified participants in wholesale energy markets and owners of electrical generation equipment that abnormal conditions are present on the power system.

Katrina Miller is a science reporting fellow for The Times. She recently earned her Ph.D. in particle physics from the University of Chicago. More about Katrina Miller

Ivan Penn is a reporter based in Los Angeles and covers the energy industry. His work has included reporting on clean energy, failures in the electric grid and the economics of utility services. More about Ivan Penn

Emmett Lindner writes about breaking and trending news. He has written about international protests, climate change and social media influencers. More about Emmett Lindner

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