Solar energy

• 1. The Sun's Hourly Abundance

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  Earth receives 174 petawatts of incoming solar radiation at the upper atmosphere. This massive flow of energy strikes our planet every single day. Approximately 30% reflects back into space while the rest absorbs into clouds, oceans and land masses. The total solar energy absorbed by Earth's atmosphere, oceans and land masses equals approximately 122 petawatt-years per year. That figure translates to 3,850 exajoules annually. In 2002, this amount represented more energy in just one hour than humanity consumed in an entire year. One hour and 25 minutes of sunlight hitting Earth contains enough power for global use over twelve months.

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• 2. Steam Engines And Early Pioneers

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  Augustin Mouchot demonstrated a working solar steam engine at the Universal Exposition in Paris during 1878. He could not continue development due to cheap coal availability. Frank Shuman built a small demonstration solar engine in 1897 that reflected solar energy onto square boxes filled with ether. Ether has a lower boiling point than water and powered his steam engine system. Shuman formed the Sun Power Company in 1908 to build larger solar power plants. His team developed an improved system using mirrors to reflect solar energy upon collector boxes. They increased heating capacity so water replaced ether as the working fluid. Shuman constructed the world's first solar thermal power station in Maadi, Egypt between 1912 and 1913. The plant used parabolic troughs to power a 50 horsepower engine pumping over 460 cubic meters of water per minute from the Nile River. Cheap oil discoveries in the 1930s discouraged further advancement despite Shuman's vision.

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• 3. Heating Water And Buildings

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  Solar hot water systems provide 60 to 70% of domestic hot water use in middle geographical latitudes. These systems reach water temperatures up to 60 degrees Celsius. Evacuated tube collectors account for 44% of global installations while glazed flat plate collectors make up 34%. China leads worldwide deployment with 309 gigawatts of installed capacity representing 71% of the market. Israel and Cyprus lead per capita usage with over 90% of homes utilizing these systems. MIT built Solar House #1 in 1939 using seasonal thermal energy storage for year-round heating. Thermal mass materials like stone, cement and water store heat from the Sun during daytime hours. These materials radiate stored heat to cooler atmospheres at night maintaining comfortable space temperatures. A solar chimney connects building interiors to exteriors creating an updraft that pulls air through structures. Deciduous trees planted on southern sides of buildings in northern hemispheres provide summer shade while bare limbs allow winter light penetration.

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• 4. Photovoltaics And Concentrated Power

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  Concentrating Solar Power systems use lenses or mirrors to focus large areas of sunlight into small beams. Parabolic troughs remain among the most developed concentrating technologies alongside solar tower collectors. The Solar Total Energy Project in Shenandoah, Georgia used 114 parabolic dishes providing 50% of process heating requirements for a clothing factory. This grid-connected cogeneration system delivered 400 kilowatts of electricity plus thermal energy forms including steam and chilled water. Molten salt technology stores collected thermal energy so plants generate electricity during bad weather or nighttime hours. The Solar Two project demonstrated this method between 1995 and 1999 achieving annual efficiency ratings near 99%. Cerro Dominador power plant in Chile generates around 110 megawatts using molten salts transferring heat to water generating superheated steam. Solana Generating Station in the United States features six hours of storage by molten salt enabling stable supply without interruptions if required.

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• 5. Solar Vehicles And Aircraft

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  The World Solar Challenge race spans 3,027 kilometers across central Australia from Darwin to Adelaide every two years. Teams compete over distances where average speeds improved from 60 kilometers per hour in 1987 to 90 kilometers per hour by 2007. Kenichi Horie made the first solar-powered crossing of the Pacific Ocean in 1996 while Sun21 catamaran crossed the Atlantic Ocean in winter 2006-2007. AstroFlight Sunrise became the first unmanned solar flight in 1974 followed by Solar Riser's controlled man-carrying flight reaching 1,500 meters altitude on the 29th of April 1979. Gossamer Penguin achieved the first piloted flights powered solely by photovoltaics in 1980. Solar Challenger crossed the English Channel in July 1981 marking another milestone. Eric Scott Raymond flew from California to North Carolina in 21 hops using solar power during 1990. Helios set an altitude record for non-rocket-propelled aircraft at 29,524 meters in 2001. Solar Impulse successfully circumnavigated the globe between March 2015 and July 2016 as a single-seat plane capable of remaining airborne for several days.

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• 6. Economics And Future Projections

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  The International Energy Agency stated that affordable clean solar energy technologies will have huge longer-term benefits globally. A 2011 report found these technologies could provide one-third of world energy by 2060 if politicians commit to limiting climate change. Carbon Tracker Initiative estimated land area needed to generate all global energy from solar alone equals 450,000 square kilometers. This area matches Sweden or Morocco or California representing just 0.3% of Earth's total land area. Lazard estimated levelized cost of new build unsubsidized utility scale solar electricity below 37 dollars per megawatt-hour in 2021. New solar costs less than existing coal-fired power exceeding that amount significantly. The 2021 report also noted new solar cheaper than new gas-fired power though not generally existing gas power. Annual growth rates averaged 20% since 1999 for solar water heating sector despite falling petroleum prices during 1980s.

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