Solar energy

Solar energy is the light and heat from the Sun that we can catch with different technologies. We can use solar energy to make electricity, heat water, or build homes that use the Sun's energy better. There are two main ways to use solar energy: passive and active. Passive solar means designing buildings to let in natural light and using materials that keep heat. Active solar uses special systems like photovoltaic panels or mirrors to change sunlight into power.

Solar energy is a key kind of renewable energy because it comes from the Sun, which will keep shining. In 2011, the International Energy Agency said that using solar energy has many good effects. It can make countries feel safer about their power because they do not need to get energy from other places. It also helps the environment by cutting down pollution and helping stop global warming. These good changes are felt everywhere.

Potential

Further information: Solar radiation

The Sun gives Earth a lot of energy. If we use it well, this energy can power the whole world.

The Earth gets about 174 petawatts of energy from the Sun. Some of this energy goes back into space, but most of it is taken in by clouds, oceans, and land. This energy keeps Earth warm and helps create weather like wind and rain. Plants use sunlight to grow, which is important for all living things.

We can use solar energy in two main ways: active and passive. Active ways use special panels and machines to turn sunlight into electricity or heat. Passive ways are simpler, like building designs that use natural light and warmth from the Sun. Both help us use clean energy from the Sun.

Yearly solar fluxes & human consumption¹
¹ Energy given in Exajoule (EJ) = 10¹⁸ J = 278 TWh ² Consumption as of year 2019
Solar	3,850,000
Wind	2,250
Biomass potential	~200
Primary energy use²	633
Electricity²	~86

Annual solar energy potential by region (Exajoules)
Region	North America	Latin America and Caribbean	Western Europe	Central and Eastern Europe	Former Soviet Union	Middle East and North Africa	Sub-Saharan Africa	Pacific Asia	South Asia	Centrally planned Asia	Pacific OECD
Minimum	181.1	112.6	25.1	4.5	199.3	412.4	371.9	41.0	38.8	115.5	72.6
Maximum	7,410	3,385	914	154	8,655	11,060	9,528	994	1,339	4,135	2,263
Notes: Total global annual solar energy potential amounts to 1,575 EJ (minimum) to 49,837 EJ (maximum) Data reflects assumptions of annual clear sky irradiance, annual average sky clearance, and available land area. All figures given in Exajoules. Quantitative relation of global solar potential vs. the world's primary energy consumption: Ratio of potential vs. current consumption (402 EJ) as of year: 3.9 (minimum) to 124 (maximum) Ratio of potential vs. projected consumption by 2050 (590–1,050 EJ): 1.5–2.7 (minimum) to 47–84 (maximum) Ratio of potential vs. projected consumption by 2100 (880–1,900 EJ): 0.8–1.8 (minimum) to 26–57 (maximum) Source: United Nations Development Programme – World Energy Assessment (2000)

Thermal energy

Main article: Solar thermal energy

Solar thermal technologies help heat water, warm buildings, cool spaces, and provide heat for factories.

Early commercial adaptation

In 1878, Augustin Mouchot showed a solar steam engine in Paris. But he could not keep developing it because coal was cheap.

In 1897, Frank Shuman, a US inventor, built a small solar engine. It used mirrors to focus sunlight onto boxes filled with a special liquid, powering a steam engine. By 1912, he had built the world’s first solar power station in Maadi, Egypt. It used mirrors to power an engine that pumped water from the Nile River. People became interested in solar energy again in the 1970s.

Water heating

Main articles: Solar hot water and Solar combisystem

Solar hot water systems heat water using sunlight. In places between 40 degrees north and south, they can provide most of a home’s hot water. Common types include special tube collectors and flat plate collectors for homes, and plastic collectors for swimming pools.

Heating, cooling and ventilation

Main articles: Solar heating, Thermal mass, Solar chimney, and Solar air conditioning

Solar energy can help heat and cool buildings. It can be used with or without special tools that follow the sun’s path. Materials like stone and water can store heat from the sun to keep buildings warm or cool.

Cooking

Main article: Solar cooker

Solar cookers use sunlight to cook food, dry things, and clean water. There are different kinds, like box cookers and reflector cookers. Box cookers are simple. Reflector cookers can get hotter but need direct sunlight.

Process heat

Main articles: Solar pond, Salt evaporation pond, and Solar furnace

Special mirrors can focus sunlight to provide heat for factories. Evaporation ponds use the sun to concentrate salts from seawater. Clothes can dry using just the sun and wind, saving energy.

Water treatment

Main articles: Solar still, Solar water disinfection, Solar desalination, and Solar Powered Desalination Unit

Solar energy can clean salty or dirty water. One old method used sunlight in special containers to make water safe to drink. Today, people in many countries use sunlight to clean water in bottles left in the sun for hours. Solar energy can also help treat wastewater.

Molten salt technology

Molten salt can store heat from solar power plants so they can make electricity even when the sun isn’t shining. This was tested in a project from 1995 to 1999. The salt stays liquid and can keep heat for days. When electricity is needed, the hot salt makes steam to run a turbine. Some plants in Spain and Chile use this method to provide steady power.

Electricity production

Solar energy can be used to make electricity. This is done by using special panels called solar panels. These panels have cells that change sunlight into power. This power can be used to light homes, run machines, and more.

Concentrated solar power

Main article: Concentrated solar power

Concentrated solar power systems use mirrors or lenses to focus sunlight into a small, bright beam. This makes a lot of heat, which can be used to make electricity, just like in regular power plants. There are different types of these systems, such as curved mirrors called parabolic troughs, tower collectors, flat mirrors called Fresnel reflectors, and special dishes called Stirling dishes. These systems move to follow the sun, keeping the light focused. The heat is used to warm a special liquid, which helps make or store electricity. Builders need to protect these systems from bad weather, like dust storms or hail, which could break the glass mirrors. Metal grills can let sunlight in while keeping most of the mirrors safe.

Architecture and urban planning

Main articles: Passive solar building design and Urban heat island

Sunlight has changed how buildings are made for a long time. Ancient Greeks and Chinese people built buildings to face south for natural light and warmth.

Passive solar architecture uses simple ideas like facing the sun, shaping buildings right, adding shade, and using materials that keep temperatures steady. When done right, these buildings stay bright and comfortable. One old example is Socrates' Megaron House. Today, computers help design buildings that work well with sunlight for lighting, heating, and air flow. Active solar tools like pumps and special windows can also help.

Big cities can get hotter than the areas around them because of dark roads and buildings that soak up heat. Painting buildings and roads lighter colors and planting more trees can help cool cities down. These ideas could help lower temperatures in places like Los Angeles.

Agriculture and horticulture

Agriculture and horticulture help plants grow by using sunlight. Farmers plant at the right time and arrange rows in special ways to help plants. Even when there is little sunlight, like during the Little Ice Age, people found ways to keep plants warm. For example, French and English farmers built walls to trap the Sun’s heat, helping fruits grow faster. Some even moved walls to follow the Sun.

Greenhouses are special buildings that trap the Sun’s heat, letting plants grow all year, even in cold weather. The Romans used early greenhouses to grow cucumbers for their leaders. Later, people in Europe built better greenhouses to grow rare plants from faraway places. Today, greenhouses and other covers like polytunnels and row covers are still useful for growing special plants.

Transport

Main articles: Solar vehicle, Solar-charged vehicle, Electric boat, Solar balloon, and Solar aircraft

People have been making cars run on sunlight since the 1980s. One big race for solar cars is the World Solar Challenge. Teams race across Australia from Darwin to Adelaide. These cars use sunlight to move.

Solar power is also used in boats and airplanes. Some boats have solar panels to help keep things cool. There have been many flights using only sunlight, including a plane that flew around the whole world.

A solar balloon is a special balloon that gets heated by the sun, making it rise like a hot air balloon.

Squad Solar vehicle

The Squad Solar is a small electric vehicle with a solar roof. It can also be plugged into a normal outlet to charge.

Fuel production

Main articles: Solar chemical, Solar fuel, and Artificial photosynthesis

Solar chemical processes use energy from the Sun to create chemical reactions. These reactions can change sunlight into fuels that can be stored and moved easily. One important fuel that scientists are working on is hydrogen, which can be made by splitting water using heat or light from the Sun. These fuels can help us use less energy from fossil fuels and can be a clean way to power our world in the future.

Energy storage methods

Main articles: Energy storage, Seasonal thermal energy storage, Phase change material, Grid energy storage, and Vehicle-to-grid

Thermal mass systems store solar energy as heat. They use materials like water, earth, and stone, which can hold a lot of heat. Good designs can save energy for later use.

Phase change materials, such as paraffin wax and Glauber's salt, also store heat. These materials are cheap and easy to find. They can reach temperatures useful for homes. One of the first homes to use this was built in Dover, Massachusetts, in 1948. Solar energy can be stored at very high temperatures using molten salts. These salts are good for storage because they are cheap and hold a lot of heat.

Off-grid solar systems often use rechargeable batteries to store extra electricity. When connected to the grid, extra electricity can be sent back to it. Net metering programs give homes credit for sending electricity back to the grid. Some systems use two meters, but this is less common.

Pumped-storage hydroelectricity stores energy by moving water to a higher place when energy is available. When energy is needed, the water is released, and the pump becomes a generator.

Development, deployment and economics

Further information: Deployment of solar power to energy grids

Solar energy use started in the 1860s because people worried coal might run out. But then coal and petroleum became cheaper and easier, so solar energy growth slowed.

Big energy problems in 1973 and 1979 made many countries focus on solar energy again. They created special programs and research places in the US, Japan, and Germany.

Solar water heaters were used in the United States a long time ago but were replaced by cheaper fuels. After the energy problems in the 1970s, people looked at solar water heating again. It has been growing since the 1990s.

The International Energy Agency says solar energy can help solve big world problems. It can make energy safer, cleaner, and cheaper. In 2011, they said solar could provide a third of the world's energy by 2060 if leaders work to change to renewable energy.