The sun is the closest star to Earth. Even at a distance of 150 million kilometers (93 million miles), its gravitational pull holds the planet in orbit. It radiates light and heat, or solar energy, which makes it possible for life to exist on Earth.

Plants need sunlight to grow. Animals, including humans, need plants for food and the oxygen they produce. Without heat from the sun, Earth would freeze, and there would be no winds, ocean currents, or clouds, which are needed to transport water around the globe.

Solar energy has existed as long as the sun—about 4.6 billion years. While people have not been around that long, they have been using solar energy in a variety of ways for thousands of years.

Developed over 11,000 years ago, agriculture had a key role in the rise of cities. Since then, solar energy has played an essential role in agriculture, from producing crops to preserving food. Intentional planting of crops in vast, sunny areas increased yields, and drying food in the sun prevented it from spoiling. This helped create surpluses of food, which allowed for growing populations and structured societies.

Early urban societies around the world positioned buildings to face south to gather heat and light. They used windows and skylights for the same reason, as well as to allow for air circulation. These are elements of solar architecture. Other aspects include using selective shading and choosing building materials such as stone and concrete that have thermal mass, meaning they store heat. Today, computer programs make solar architectural applications easier and more precise.

The greenhouse is another early solar development. By converting sunlight to heat, greenhouses make it possible to grow plants out of season and in climates that may not be suited for them. One of the earliest greenhouses dates between 14 and 37 C.E., before glass was even invented. Constructed from translucent sheets of mica, or a similarly thin mineral, it was built for the Roman Emperor Tiberius, who wanted to be able to eat vegetables from a Cucumis plant all year. The general technique is the same today, although there have been many improvements in greenhouses to increase the variety and amount of crops grown inside them.

Once food is harvested, solar energy can be used to cook it. The first solar box cooker was built in 1767 by Horace de Saussure, a Swiss physicist. It reached a temperature of about 88 degrees Celsius (190 degrees Fahrenheit) and was used to cook fruit. Today, there are many different types of solar cookers and similar devices, such as solar dryers, being used for cooking, dehydrating and pasteurization, which slows the growth of microbes in food. These devices do not use fossil fuels and do not produce pollution or cause deforestation. There are millions of solar cookers in use around the world. India, for example, has the world’s largest solar cooking system, which can prepare food for nearly 50,000 people daily.

Solar cooking technology can also help healthcare providers in remote, rural areas without reliable electricity. In the 1970s, Iranian engineering professor Mehdi Bahadori reported his design for a solar autoclave that used mirrors to concentrate sunlight to heat water to sterilize medical instruments. Since then, engineers and scientists have tested similar, updated designs, though they are not in widespread use and mainly exist as prototypes. In Nicaragua, however, solar autoclaves are commonly used to sterilize medical equipment in rural clinics.

Solar water heaters are another innovation that harnesses the sun’s power. U.S. inventor Clarence Kemp developed the first commercial solar water heater in 1891, an improvement over stoves that burned wood or coal. These solar water heaters were cleaner and cost less to operate. However, in the early 1900s, when low-cost oil and natural gas became available, solar water systems were replaced. Today, they are not only popular again, they are becoming the norm in some countries, including China, Türkiye, Barbados, Greece and Cyprus. They are even required to be used in most new residential construction in some countries, including Kenya, China and Spain.

Besides heating water, solar energy can be used to make it potable, or suitable for drinking, through methods like solar disinfection (SODIS). India has used sunlight to disinfect water for millennia. Developed for modern use in the 1980s by Professor Aftim Acra and his colleagues at the American University of Beirut, SODIS involves filling transparent bottles with water and then exposing them to sunlight for several hours. This process kills the microbes, such as viruses, bacteria and protozoa, in water. More than five million people in low- and middle-income nations use this method daily for their drinking water.

Solar power—the conversion of sunlight into electricity—is yet another application of solar technology. This can be done in a number of ways. The two most common are photovoltaics (solar cells) and concentrating solar-thermal power.

Solar cells convert sunlight directly into electricity. The amount of power generated by each cell is very low. Therefore, large numbers of cells must be grouped together, like the panels mounted on the roof of a house, to generate enough power.

The first solar cell was constructed in the 1880s. One of the earliest major applications was on the U.S. satellite Vanguard I, the first satellite to use solar power, launched in 1958. The satellite was able to operate for about six years; other satellites using conventional batteries lasted only days. Since then, solar cells have been the power source for satellites, including those used in the telecommunications industry.

On Earth, solar cells are used for everything from calculators and watches to homes and commercial buildings. Individuals and countries are increasingly turning to solar power. This growth is due in part to the dramatic decrease in the cost of solar panels in the first couple decades of the 21st century. Another reason for the push for more solar power is human-caused climate change. The burning of fossil fuels accounts for about 80% of the global energy supply and is a major driver of the climate crisis. As the effects of climate change grow in frequency and intensity, the world must transition to renewable energy sources. As of 2023, China led the world in electricity generation from solar power, and the International Energy Agency predicts that by 2029, solar cell power will be the largest source of renewable energy.

While governments can be a driving force in countries adopting renewable forms of energy such as solar, sometimes change comes from local community sources. The falling costs of solar panels has made solar an attractive energy alternative to more people. For example, in the mid-2020s, Pakistan was one of the world’s largest new adopters of solar energy, a change brought about by Pakistani people looking for alternatives to high electricity prices for their homes. They found a solution in China’s cheaper solar panels. "The scale of solar being deployed in such a short period of time has not been seen, I think, anywhere ever before,” Jan Rosenow, leader of the energy program at the Environmental Change Institute at the University of Oxford, told U.S.-based National Public Radio.

Unlike solar cells in panels, which use sunlight to generate electricity, concentrating solar-thermal power technology uses the sun’s heat. Lenses or mirrors focus sunlight into a small beam that can be used to operate a boiler. The boiler then produces steam that turns turbines, generating electricity. This method is used at the Solana Generating Station, near Phoenix, Arizona, in the United States. It sells its electricity to the Arizona Public Service utility company. At full capacity, it can serve up to 70,000 homes at once, but it often does not meet its potential output.

There are some challenges with solar power. First, it is intermittent, or not continuous. When there is no sun—at night or on cloudy days—power cannot be generated. In order to provide continuous power, energy must either be stored or obtained from other sources, such as wind power. Second, while both photovoltaic and concentrating solar-thermal power can be used virtually anywhere, the equipment used takes up a lot of space. Installation can have a negative impact on the ecosystem by displacing plants and wildlife, and it can disrupt communities living near sites of solar utility projects. For instance, the qualities that make land attractive for agriculture also make it attractive for large-scale solar power facilities, and solar development has taken place on former farmland.

Another concern is the harm that can arise from producing the materials needed for solar panels. Making solar panels requires the mining of quartzite, which is then made into polysilicon, an essential material of the sun-catching cells. In China’s Xinjiang province, where the government has forced relocations, family separations and re-education of ethnic minorities, primarily the Uyghur, Kazakh and Kyrgyz people, they have also forced these people into labor programs to produce polysilicon. Some governments have introduced regulations to try to eliminate products that come from supply chains that use forced labor. Community-based efforts around the world are working to push governments into taking stronger actions.

Although solar power is a renewable energy source, some solar power efforts can also pollute the environment. For example, the Solana Generating Station is responsible for air quality violations. The plant’s mirrors focus sunlight on tubes of oil, called heat transfer fluid, which heats water to generate steam. But the plant regularly has issues with this fluid leaking into the environment, and the fumes are dangerous to inhale. Maricopa County fined the company $1.5 million in 2016, and though it committed to making repairs, a county official told the Phoenix New Times that he expected the pollution would continue for the time being. Another environmental concern is how to dispose of solar panels when they can no longer be used. Some countries have implemented regulations for solar panel recycling, but recycling solar panels can release harmful pollutants, depending on the method used.

Fossil fuels, such as coal, oil and natural gas, currently produce most of our electric and engine power. They also produce almost all of our pollution. Plus, they are nonrenewable resources, meaning there is a limited supply.

On the other hand, the sun offers an abundance of free and clean energy when governments and communities work to lessen the drawbacks of solar power. People have been relying on the sun’s energy since the first humans. Relying on the power of the sun and other renewable energy forms is not only possible, but critical for addressing climate change.