Angle of incidence
The angle at which light strikes a surface relative to the normal. It forms the complementary angle of the sun angle.
The surface included within a set of lines; specifically: the number of unit squares equal in measure to the surface.
Clear sky
Technical term for skies with less than a 10% cloud cover throughout an entire day.
Clear sky insolation clearness index
Fraction of insolation at the top of the atmosphere which reaches the surface of the earth during clear sky days. Units: dimensionless.
The use of computers to create mathematical models of real world events.
Daylight
cloud amount
Percent of cloud amount during daylight
within a region. Units: percent. Note: 0% = clear skies; 100% = overcast skies.
The length of a straight line (chord) through the center of an object (such as a circle).
Mathematical relationship between two variables that can be expressed by an equation in which one variable is equal to a constant times the other, often in the form y = kx when k is the constant of variation.
Insolation
Amount of the sun’s energy incident at some location in space or a planet’s
surface. Units: kWh/m2/day.
The rate at which energy is transferred per unit area. Units: typically, W/m2.
The brightness of a light, the amount of light shining on a surface. Units: typically, W/m2.
The lessening of brightness.
An attempt to create a reasonable model for a set of real world data by the use of a mathematical equation.
The normal is an imaginary line perpendicular to a surface at which point an incident light ray strikes.
An adjective referring to an event that occurs in regular cycles.
Finding a line (or curve) through actual data points so that the difference between the actual data points and the points on the line are as small as possible.
The angle of the sun above the horizon.
The time of day at which the solar angle is greatest.
Surface albedo
Fraction of insolation reflected by the surface of the earth. Units:
dimensionless.
Top-of-atmosphere insolation
Amount of electromagnetic energy (solar radiation) incident at the top of
the atmosphere. Units: typically, kWh/m2/day.
Trendline
Line of best fit or least squares line formed by a best average distance from the data points often used to display trends in data graphically and to analyze problems of prediction (such analysis is also called regression analysis).