Glossary of Solar Radiation Resource Terms

Other relevant glossaries


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Parabololic Collector Trough - a system that tracks the path of the sun by pivoting on one axis (typically East-West or North-South), using shiny parabolic troughs to heat the collector fluid that passes through a tube at the focus. Below is an illustration from the Solar Radiation Data Manual for Flat Plate and Concentrating Collectors .


Passive Solar - technology for using sunlight to light and heat buildings directly, with no circulating fluid or energy conversion system.


Peak Watt - the maximum amount of power produced or demanded in a time interval, measured in watts.


Percent Possible Sunshine - the ratio of measured bright sunshine to the total possible bright sunshine in a given time period such as an hour or a day, expressed as a percent.


Photoelectric - pertaining to the conversion of light (radiant energy) to electricity.


Photometer - an instrument that measures illuminance.


Photon - the fundamental particle or quantum of electromagnetic radiation (radiant energy).


Photovoltaic - technology for converting sunlight directly into electricity, usually with photovoltaic cells.


Photovoltaic Cell - a single semiconducting element of small size (for example, 1 cm2) that absorbs light or other bands of the electromagnetic spectrum and emits electricity.


Photovoltaic Module - a unit comprised of several photovoltaic cells that is the principal unit of photovoltaic array. A photovoltaic module's size is on the order of 1 m2, although its size is governed by convenience and application.


Photovoltaic Array - a photovoltaic module or set of modules used for converting solar radiation to energy.


PMOD/WRC - the Physikalisch-Meteorologisches Observatorium Davos / World Radiation Center, at Davos, Switzerland. PMOD/WRC determines and maintains world-wide standards for measurement of solar radiation, including the World Radiometric Reference (WRR), for the World Meteorological Organization.


Point-focusing Concentrator - a solar power generator which uses a series of tracking mirrors (heliostats), Fresnel lenses, or a paraboloid (3-dimensional parabola, or dish) of mirrors to focus solar energy onto a single central receiver such as a boiler, engine, or photovoltaic array.


Polarimeter - An instrument for determining the amount of polarization of light. Ordinary light from the sun or a lamp is composed of disorderly waves that vibrate in all directions perpendicular to the light beam. But polarized light consists of orderly waves that vibrate in only one direction.


Power - the amount of work or energy expended in a given amount of time. For example, the watt is a unit of power, which is defined as a joule per second.


Precipitable Water - the amount of water in a vertical column of atmosphere. The unit of measure is typically the depth to which the water would fill the vertical column if it were condensed to a liquid. For example, 6 centimeters of precipitable water (in the absence of clouds) indicates a very moist atmosphere. Precipitable water is often used as a synonym for water vapor.


PSP - precision spectral pyranometer, a pyranometer with an outer clear dome that can be replaced by colored domes that transmit specific bandwidths of the solar spectrum. The PSP is a specific instrument of Eppley Laboratory, Inc. Below is a picture of a PSP.

   


Pyranometer - an instrument with a hemispherical field of view, used for measuring total or global solar radiation, specifically global horizontal radiation; a pyranometer with a shadow band or shading disk blocking the direct beam measures the diffuse sky radiation, as is illustrated in the picture below. A picture of the Eppley PSP pyranometer is included in the PSP definition above.

   


Pyrheliometer - instrument with a narrow ( circumsolar) field of view which measures direct normal irradiance. Pyrheliometers are mounted on sun-following trackers so that the instrument is always aimed at the sun. Below is a picture of two (silver) pyrheliometers mounted on a (white) tracker.

   


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