Renewable Energy Glossary
“The amount of electricity a generator can produce when it’s running at full blast. This maximum amount of power is typically measured in megawatts (MW) or kilowatts and helps utilities project just how big of an electricity load a generator can handle.” (US Department of Energy, March 2018)
Capacity does not reflect the same level as actual electricity generated, because plants do not run all the time.
Capacity factor is a measure of how much energy is produced by a plant compared with its maximum output. It is measured as a percentage, generally by dividing the total energy produced during some period of time by the amount of energy the plant would have produced if it ran at full output during that time. “(NREL Sept 2013)
“Capacity factors allow energy buffs to examine the reliability of various power plants. It basically measures how often a plant is running at maximum power. A plant with a capacity factor of 100% means it’s producing power all of the time.” (US Department of Energy, March 2018)
Describes power generation that releases net zero carbon dioxide (CO2) emissions into the atmosphere. (Fast Company, 2018)
Power generation considered carbon neutral would include (Nature.org, May 2013):
- Synthetic fuels
- Wave energy
Biofuels are not included in a zero carbon category (Study.com) because producing biofuels contributes more carbon dioxide to the atmosphere than it displaces in energy generation.
Concentrating Solar Power
Definition below an extract from the SEIA.org Site
Concentrating Solar Power (“CSP”) plants use mirrors to concentrate the sun’s energy to drive traditional steam turbines or engines that create electricity. The thermal energy concentrated in a CSP plant can be stored and used to produce electricity when it is needed, day or night. Today, roughly 1,815 megawatts (MWac) of CSP plants are in operation in the United States.
Components of a Concentrating Solar Power System:
- Parabolic Trough Systems
- Compact Linear Fresnel Reflector
- Power Tower
1. Parabolic Trough Systems
Parabolic trough systems use curved mirrors to focus the sun’s energy onto a receiver tube that runs down the center of a trough. In the receiver tube, a high-temperature heat transfer fluid (such as a synthetic oil) absorbs the sun’s energy, reaching temperatures of 750°F or higher, and passes through a heat exchanger to heat water and produce steam. The steam drives a conventional steam turbine power system to generate electricity. A typical solar collector field contains hundreds of parallel rows of troughs connected as a series of loops, which are placed on a north-south axis so the troughs can track the sun from east to west. Individual collector modules are typically 15-20 feet tall and 300-450 feet long.
2. Compact Linear Fresnel Reflector
CLFR uses the principles of curved-mirror trough systems, but with long parallel rows of lower-cost flat mirrors. These modular reflectors focus the sun’s energy onto elevated receivers, which consist of a system of tubes through which water flows. The concentrated sunlight boils the water, generating high-pressure steam for direct use in power generation and industrial steam applications.
3. Power Tower
Power tower systems use a central receiver system, which allows for higher operating temperatures and thus greater efficiencies. Computer-controlled mirrors (called heliostats) track the sun along two axes and focus solar energy on a receiver at the top of a high tower. The focused energy is used to heat a transfer fluid (over 1,000° F) to produce steam and run a central power generator. Energy storage can be easily and efficiently incorporated into these projects, allowing for 24 hour power generation.
Mirrors are distributed over a parabolic dish surface to concentrate sunlight on a receiver fixed at the focal point. In contrast to other CSP technologies that employ steam to create electricity via a turbine, a dish-engine system uses a working fluid such as hydrogen that is heated up to 1,200° F in the receiver to drive an engine. Each dish rotates along two axes to track the sun.
Key Requirements for Concentrating Solar Power Plants
Financing – The primary challenge for any utility-scale energy generating facility, including CSP, is project financing.
Areas of high solar radiation – In order to concentrate the sun’s energy, it must not be too diffuse. This is measured by the direct normal intensity (DNI) of the sun’s energy. Production potential in the U.S. Southwest stands apart from the rest of the U.S., as the map from the National Renewable Energy Laboratory below demonstrates.
An abbreviation for “Concentrating Solar Power.”
Please see Concentrating Solar Power.