Our sun is a star made mostly of hydrogen and helium. It produces energy inside its core through a process called nuclear fusion, where hydrogen fuses together to make a lighter atom of helium. The energy that’s lost in this process radiates into space as energy. A small amount of this energy reaches the Earth. Every day, the solar energy that reaches the U.S. alone is enough to meet a year and a half of our energy needs.
Currently, the U.S has a solar power capacity of around 97.2 gigawatts. Only about 3% of the electricity generated in the U.S. comes from solar energy. The rest comes overwhelmingly from conventional fossil fuels like coal and natural gas. The Department of Energy predicts that by 2030, one in seven homes in the U.S. will have rooftop solar panels thanks to government incentives and cost reductions through more efficient technology. Solar technology can take sunlight and change it into energy using photovoltaic (PV) solar panels or by concentrating the solar radiation using special mirrors. Individual particles of light are called photons. These are tiny packets of electromagnetic radiation that have different amounts of energy depending on how quickly they move. Photons are released by the sun during the process of nuclear fusion when hydrogen is converted to helium. If photons have enough energy, they can be harnessed to generate electricity. PV panels are made from individual PV cells. These cells contain materials called semiconductors which allow electrons to flow through them. The most common type of semiconductor used in PV cells is crystalline silicon. It is relatively inexpensive, abundant, and lasts a long time. Out of all of the semiconductor materials, silicon is also one of the most efficient conductors of electricity. When photons with a lot of energy come in contact with semiconductors, they can knock electrons loose. These electrons produce an electrical current that can be used for power or stored in a battery. Most energy produced by solar panels is sent into the electrical grid to be distributed to places that need electricity. Even private rooftop solar panels send extra electricity back into the power grid. Battery storage tends to be expensive and selling excess electricity back to electric companies is the most cost-effective way to produce solar electricity at the moment. 

Solar thermal energy (STE) technology captures solar energy and uses it for heat. There are three different categories of STE collectors: low, medium, and high temperature.3

Low-temperature collectors use either air or water to transfer heat energy collected by the sun to the location that needs to be heated. They may come in the form of glazed solar collectors that heat air to be transferred through a building, metal walls, or roof-mounted water bladders that are warmed by sunlight. They are most commonly used for small spaces or to heat swimming pools.

Medium-temperature collectors work by moving a non-freezing chemical through a series of pipes that collect sunlight to heat water and air in residential and commercial buildings.

High-temperature collectors use a series of parabolic mirrors to efficiently convert solar energy into high-temperature heat that can then generate electricity. The mirrors capture the sunlight and focus it into what’s called the receiver. This system then heats contained fluids and circulates them to produce steam. Much like conventional electrical generation, the steam then turns a turbine, which creates power for a generator to produce the desired electricity.

The mirrors that collect the sunlight must be able to follow the path of the sun throughout the day in order to maximize efficiency. These large systems are mostly used by utilities to create electricity to send through the power grid. 

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