Glossary of Solar Radiation Resource Terms

Other relevant glossaries

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Saturated Air - air that has the maximum amount of water vapor; any increase in water vapor will cause condensation.

Scattered Radiation - radiation that has been reflected from particles, disrupting the original direction of the beam.

Click Shining On (Figure 3) to see solar components

Semiconductor - a material that has much lower resistance to the flow of electrical current in one direction than in another. Diodes, transistors, and many photovoltaic cells contain semiconductive materials.

SERI - the Solar Energy Research Institute, which became the National Renewable Energy Laboratory in 1991.

Shading Disk - a disk on a tracking arm which blocks the direct normal irradiance so as to allow a pyranometer to measure only the diffuse sky radiation. Below is a picture of a pyranometer shaded by a shading disk.


Shadow Band - a metal strip which blocks the direct normal radiation so as to allow a pyranometer to measure only the diffuse sky radiation. Below is a picture of a pyranometer shaded by a shadow band.


Shortwave Radiation - the principal portion of the solar spectrum that spans from approximately 300 nanometers (nm) to 4000 nm in the electromagnetic spectrum. Longwave radiation is infrared radiation (>4000 nm).

Silicon Sensor - a photovoltaic cell that is being used to measure solar irradiance. Because its spectral response is not as exact as that of thermopile instruments, it has a higher uncertainty.

Sky Chart -

Sky Dome - refers to the appearance of the entire sky, from horizon to zenith in all directions. Below is a picture of the sky dome at the Solar Radiation Research Laboratory taken by an all-sky camera.


Sky Radiation - synonymous with diffuse sky radiation, the radiation component that strikes a point from the sky, excluding circumsolar radiation. In the absence of atmosphere, there should be almost no sky radiation. High values are produced by an unclear atmosphere or reflections from clouds.

Click Shining On (Figure 3) to see solar components

Solar Absorber - a sheet of material, usually copper, aluminum, or steel that forms the surface of a solar collector. It collects and retains solar radiation, which is passed to a heat transfer medium.

Solar Almucantar -

Solar Cell - a photovoltaic cell that is used to convert solar energy into electricity.

Solar Collector - a device that receives solar energy and converts it to useful energy forms. The following figure from Shining On illustrates several types of solar collectors.

Solar Concentrator - a solar collector that enhances solar energy by focusing it onto a smaller area through mirrored surfaces or lenses.

Solar Constant - although not strictly constant, this number is the amount of solar power flux that passes through the mean Earth orbit. The currently accepted value is 1366 W/m2. Note that Earth-based instruments record lower values of solar power flux because of atmospheric attenuation. (See also

Solar Conversion Technologies - collective name for all methods for converting the sun's energy into usable energy.

Solar Detoxification - technology for using concentrated sunlight to break down and destroy hazardous waste.

Solar Electric - technology for converting sunlight directly into electricity.

Solar Energy Technology - method for harnessing, storing, and using the sun's energy.

Solar Fuel Technology - methods for converting biomass into fuels and by-products.

Solar Heat - technology to harness the sun's energy for heating buildings, air, and water for industrial and household uses.

Solar Irradiance - the amount of solar energy that arrives at a specific area of a surface during a specific time interval (radiant flux density). A typical unit is W/m2.

Solar Noon - the time at which the position of the sun is at its highest elevation in the sky. At this time, the Sun is either due South (typically in the Northern Hemisphere) or due North (typically in the Southern Hemisphere). This time can be quite different from noon according to local standard time.

Solar Radiation - the electromagnetic radiation emitted by the sun.

Solar Spectrum - the electromagnetic spectral distribution emitted by the sun or received by a collector or instrument on Earth. For example, Figure 2 from Shining On below shows the solar spectrum as measured in space and on the Earth's surface.

Solar Thermal Electric - technology for using the sun's energy to produce steam to run turbines that generate electricity.

SOLMET - the 26 measurement sites in the 1952-1975 SOLMET/ERSATZ solar & meteorological hourly network that measured global horizontal solar radiation. The SOLMET/ERSATZ network has been replaced by the 1961-1990 National Solar Radiation Data Base.

Spatial - pertaining to space, or pertaining to distance such as spatial variation (variation over distance).

Specific Humidity - the mass of water vapor per unit mass of air, including the water vapor (usually expressed as grams of water vapor per kilogram of air).

Spectral Distribution - the solar spectral distribution.

Spectral Irradiance - the amount of radiant energy flux expressed in terms of the solar spectrum. NREL's Solar Spectral Radiation Data Base contains thousands of irradiance spectra.

Spectroradiometer - an instrument designed to measure spectral irradiance. Spectroradiometers gathered the data in NREL's Solar Spectral Radiation Data Base.

SRRL - the Solar Radiation Research Laboratory at the National Renewable Energy Laboratory.

Stratosphere - the relatively isothermal (constant temperature) layer of the atmosphere above the troposphere and below the mesosphere.

Sunshine - used interchangeably with the more precise term bright sunshine, when the sun casts an obvious shadow or when a Campbell-Stokes sunshine recorder is recording, usually above 210 W/m2.

Sunshine Duration - the length of time for which the sun casts an obvious shadow or when a Campbell-Stokes sunshine recorder is recording. The lower limit for bright sunshine (based on a Campbell-Stokes recorder) is between 70 W/m2 (very dry air) and 280 W/m2 (very humid air).

Sun Position - the location of the sun in the sky, expressed in terms of azimuth angle and zenith angle.

Suns - a unit which multiplies the amount of energy the Earth can receive from the sun, typically used by the solar concentrator community; e.g., a concentrator might focus the energy of 40 suns onto a central receiver. Note that this unit is not precisely defined, and is usually less than the solar constant.

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