Solar Energy and Its Uses
Utility scale solar energy facilities generate electricity that is sent to energy consumers via electric transmission systems. On a smaller scale, solar energy facilities can be used to generate electricity or hot water for use in individual buildings.
What is Solar Energy?
Solar energy is the radiant (light and heat) energy produced by the sun. The solar energy that reaches the earth can be used to produce electricity or heat through the use of solar collectors. As an example, a closed car can be viewed as a solar collector—the light energy that passes through the window glass is absorbed by the car's interior and is converted into heat energy, which becomes trapped inside the vehicle. In optimal areas, the amount of solar energy falling on an area the size of a basketball field, in thermal energy terms, is equivalent to about 650 barrels of oil a year. Solar energy is a renewable resource whose use does not affect its future supply.
Conventional power plants use fossil fuels or nuclear energy as a heat source to boil water. The steam from the boiling water rotates a turbine, which activates a generator to produce electricity. Solar energy facilities use concentrating solar power (CSP) as the heat source to boil water, or they convert sunlight directly into electricity using solar cells, also known as photovoltaics (PV). The CSP technologies are also referred to as solar thermal or thermoelectric technologies, while PV technologies are also referred to as solar electric or photoelectric technologies.
The main types of CSP systems are linear (i.e., parabolic trough and compact linear Fresnel reflector), power tower, and dish engine. CSP plants consist of two parts: one that collects solar energy and converts it to heat, and another that converts the heat energy to electricity. More information about CSP technologies is available through the U.S. Department of Energy's (DOE's) Solar Energy Technology Web site CSP page.
The two types of PV technologies are flat plate and concentrating PV. Both PV technologies use solar cells that are made of semiconductor materials to absorb sunlight. The solar energy knocks electrons loose from their atoms, allowing electrons to flow through the material to produce electricity. A brief animation titled "Sunlight to Electricity" that shows how a solar cell works is available on the Animations page of the DOE Solar Energy Technologies Program Web site. More information about PV technologies is available through the DOE's Solar Energy Technology Web site PV page.
How can we use energy from the sun?
CSP systems can absorb sunlight and change it into heat that can be used to power a steam-driven generator to heat a building or water. PV systems change sunlight directly into electricity that can be used for heating purposes. Both systems can be used to generate utility-scale electricity in place of a conventional fossil- or nuclear-fueled power plant.
How is electricity from solar energy sent to users?
Electricity is sent to users through a transmission system consisting of electric transmission lines, towers, substations and other components (see Energy Transmission section to learn more). The integration of solar energy into a transmission system requires careful planning to balance the mix of solar energy with other sources of energy generation. One challenge for generating electricity from solar energy is that sunlight is intermittent (it occurs only during daylight hours and can be obscured by clouds, rain, fog, and other climatic conditions). The intermittency of sunlight creates concerns for the stability and reliability of utility-scale solar energy developments. This issue can be alleviated at solar energy facilities that have heat or electric storage capacity or that are part of a hybrid system (e.g., collocated with one or more conventional fossil-fueled generation technologies).