Solar energy has been used for centuries. Every day, energy from the sun is absorbed by plants, the land, and the oceans. Thirty percent of the sun’s energy is used to evaporate water that produces rain after being lifted into the atmosphere. Although humans have used solar power for centuries, it wasn’t until the early 1900’s that people started using solar energy for everyday needs, albeit on a small scale. The idea of using solar energy on a grand scale started in the 1920’s, although the public and the scientists employed by the world’s governments remained indifferent to the possibilities of using this plentiful alternative energy until the oil shortages of the early 1970’s.

Utilizing solar energy involves the direct use of the sun’s radiated heat and efficiently converting it into electricity. This can be difficult since the solar energy that reaches the earth is spread over such a large area, and how much the area receives depends on the time of day, the season, the latitude of the area, sky conditions, and other factors. Currently, solar collectors (or solar panels) use solar energy as space heaters and water heaters in residential and commercial buildings.

A closed car on a sunny day is like a solar collector. The sunlight passes through the windows and is absorbed by the interior, which changes into heat. The glass windows let light in but don’t let out the heat out, which is why greenhouses are effective and work year-round. Homes that use solar energy for space heating have passive and active heating systems. Passive systems store heat the same way a closed car does, while active systems use mechanical equipment and an outside energy source when solar energy is not enough.

A solar water heater also uses a solar collector mounted on the roof, which collects sunlight and converts it into heat that uses fairly simple technology similar to a hot water heater. Besides heating homes and water, solar energy can be used to produce electricity. Two ways to generate electricity from solar power are photovoltaics, or PVs, and solar thermal systems.

PV cells can create a moving electric charge that produces a direct electric current; solar thermal systems include heat-driven mechanisms, such as converting water to steam to power a steam engine that generates electricity. Scientists are researching ways for these methods to be used on a greater scale so as to compete, and eventually be a substitute, for fossil fuels.