Solar Radiation
Sun-Earth relationships
Array Orientation
Solar Radiation Data Sheets
US Energy Consumption
A false color image of
the sun enhances the
turbulent nature of the
sun’s photosphere,
including a roiling
surface, sunspots,
and giant flares.
Distance from Sun to Earth
Even over the vast distance, an
enormous amount of energy reaches
Earth from the sun.
Harnessing the Sun
Solar irradiance is
solar radiation power
per unit area.
Inverse Square Law
The inverse square law states that radiation energy
is reduced in proportion to the inverse square of
the distance from the source.
Solar Irradiation
Solar irradiation
equals to solar
irradiance over
time.
Electromagnetic Spectrum
The electromagnetic spectrum
is composed of
electromagnetic radiation with
varying with wavelengths.
Solar Spectrum
The wavelength distribution of the sun from UV to infrared
reaching earth.
Atmospheric Effects
Solar radiation
entering Earth’s
atmosphere
becomes direct,
diffuse, or albedo
radiation.
Air Mass
Air mass is a representation of the amount of
atmosphere radiation that must pass through to
reach Earth’s surface.
Peak Sun Hours
Peak sun hours is an
equivalent measure
of total solar
irradiation in a day.
Average Annual Isolation Map
Insolation maps rate locations by their average daily
peak sun hours.
Terrestrial Solar Spectrum
The atmosphere absorbs extraterrestrial radiation
at certain wavelengths, resulting in an altered
spectral distribution for terrestrial radiation.
Spectral PV Device Response
PV devices are designed to respond to the
wavelengths corresponding to the greatest amount
of solar energy.
Pyranometers
A pyranometer
measures total
solar irradiance
from the whole
sky.
Handheld Pyranometers
Handheld pyranometers use less
precise sensors than precision
pyranometers but are more
suitable for field measurements.
Some use separate sensors that
are connected to a meter, while
some have the sensor and meter
integrated in one unit.
Pyrheliometers
A pyrheliometer
measures the direct
component of solar
irradiance, which is
important when
installing
concentrating
collectors.
Reference Cells
Reference cells
output a certain
electrical current
for each unit of
solar irradiance
received.
Earth’s Orbit Around the Sun
The ecliptic plane is formed by Earth’s elliptical
orbit around the sun.
Solar Declination
The equatorial plane is tipped 23.5° from the ecliptic
plane. Over a year, this orientation produces a
varying solar declination.
Solstices
The summer solstice
occurs when the Northern
Hemisphere is tipped
towards the sun. The
winter solstice occurs
when the Northern
Hemisphere is tipped
away from the sun.
Equinoxes
The fall and spring
equinoxes occur
when the sun is
directly in line with
the equator.
Solar Azimuth and Altitude Angles
Solar azimuth and altitude angles are used to
describe the sun’s location in the sky.
Sun Paths
The sun’s path across the sky at
various times of the year can be
illustrated on a diagram. The
diagrams change for different
latitudes.
Solar Window
The solar window is the area of sky containing all
possible locations of the sun throughout the year
for a particular location.
Array Orientation
Array orientation can be described using azimuth
and tilt angles.
Optimum Array Tilt Angles
Energy production at certain times of the year can
be optimized by adjusting the array tilt angle.
Seasonal Declination
The average
seasonal
declinations
define the optimal
tilt angles for
those periods.
NREL Solar Radiation Data
The National
Renewable Energy
Laboratory (NREL)
provides solar
radiation data for
various locations,
times of the year, and
array orientations for
use in planning PV
installations.