Solar Basics
Solar Glossary D - E - F
- Declination
- The angular position of the sun at solar noon with respect to the plane of the equator.
- Differential Thermostat
- A type of automatic thermostat (used on solar heating systems) that responds to temperature differences (between collectors and the storage components) so as to regulate the functioning of appliances (to switch transfer fluid pumps on and off).
- Diffuse Solar Radiation
- Sunlight scattered by atmospheric particles and gases so that it arrives at the earth's surface from all directions and can not be focused.
- Direct Beam Radiation
- Solar radiation that arrives in a straight line from the sun.
- Direct Solar Water Heater
- These systems use water as the fluid that is circulated through the collector to the storage tank. Also known as "open-loop" systems.
- Donor
- In a solar photovoltaic device, an n-type dopant, such as phosphorus, that puts an additional electron into an energy level very near the conduction band; this electron is easily exited into the conduction band where it increases the electrical conductivity over than of an undoped semiconductor.
- Double Wall Heat Exchanger
- A heat exchanger in a solar water heating system that has two distinct walls between the heat transfer fluid and the domestic water, to ensure that there is no mixing of the two.
- Drainback (Solar) Systems
- A closed-loop solar heating system in which the heat transfer fluid in the collector loop drains into a tank or reservoir whenever the booster pump stops to protect the collector loop from freezing.
- Draindown (Solar) Systems
- An open-loop solar heating system in which the heat transfer fluid from the collector loop and the piping drain into a drain whenever freezing conditions occur.
- Edge-Defined Film-Fed Growth (EFG)
- A method for making sheets of polycrystalline silicon (for solar photovoltaic devices) in which molten silicon is drawn upward by capillary action through a mold.
- Epitaxial Growth
- In reference to solar photovoltaic devices, the growth of one crystal on the surface of another crystal. The growth of the deposited crystal is oriented by the lattice structure of the original crystal.
- Eutectic Salts
- Salt mixtures with potential applications as solar thermal energy storage materials.
- Evacuated-Tube Collector
- A collector is the mechanism in which fluid (water or diluted antifreeze, for example) is heated by the sun in a solar hot water system. Evacuated-tube collectors are made up of rows of parallel, transparent glass tubes. Each tube consists of a glass outer tube and an inner tube, or absorber. The absorber is covered with a selective coating that absorbs solar energy well but inhibits radiative heat loss. The air is withdrawn ("evacuated") from the space between the tubes to form a vacuum, which eliminates conductive and convective heat loss. Evacuated-tube collectors are used for active solar hot water systems.
- Expansion Tank
- A tank used in a closed-loop solar heating system that provides space for the expansion of the heat transfer fluid in the pressurized collector loop.
- Flat Plate Solar Thermal/Heating Collectors
- Large, flat boxes with glass covers and dark-colored metal plates inside that absorb and transfer solar energy to a heat transfer fluid. This is the most common type of collector used in solar hot water systems for homes or small businesses.
- Flat Plate Solar Photovoltaic Module
- An arrangement of photovoltaic cells or material mounted on a rigid flat surface with the cells exposed freely to incoming sunlight.
- Float-Zone Process
- In reference to solar photovoltaic cell manufacture, a method of growing a large-size, high-quality crystal whereby coils heat a polycrystalline ingot placed atop a single-crystal seed. As the coils are slowly raised the molten interface beneath the coils becomes a single crystal.
- Flow Condition
- In reference to solar thermal collectors, the condition where the heat transfer fluid is flowing through the collector loop under normal operating conditions.
About the list of terms on this page.
The U.S. Department of Energy Efficiency and Renewable Energy Home Page is a great starting point for learning about renewable energy methods and sources. To assist the educated consumer, the website provides calculators and guides of all kinds to assist the consumer in saving money, saving energy and making the most of the renewable energy sources available. The solar energy terms and definitions on our glossary pages were extracted from the extensive DOE EERE glossary of terms about all aspects and forms of energy.