Sun's energy in Whitehorse
Insolation (Incoming Solar Radiation) is the amount of solar radiation incident on any surface.. The amount of insolation received at the surface of the Earth is controlled by the angle of the sun, the state of the atmosphere, altitude, and geographic location. The graph to the left shows average solar insolation at different latitudes. The Whitehorse graph, in red, shows energy above 300 watts per square meter occours between mid-April to early September. Lags in the earth cooling creates a growing season the lasts beyond September 1.
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Sunlight passes through the atmosphere and is spread out across a horizontal land. As the angle of the sun (solar angle) get smaller, less energy from the sun strikes the surface at a given place. The chart to the right show how much of the sun's energy is decreased as the angle from the horizon decreases. This means that in the early morning on April 21, about 1/4 of the suns energy strikes the surface. The amount absorbed depends on the type of surface the sun's rays strike.
If the rays hit snow, most of the energy is reflected back into space. Putting soot on the snow in front of your greenhouse will increase the the energy and decrease the albido. (energy reflected back out into space.) |
Because the Earth is a sphere, only areas near the equator at midday come close to being perpendicular to the path of incoming light. Everywhere else, the light comes in at an angle. The progressive decrease in the angle of solar illumination with increasing latitude reduces the average solar irradiance by an additional one-half.
The solar radiation received at Earth’s surface varies by time and latitude. This graph illustrates the relationship between latitude, time, and solar energy during the equinoxes. The illustrations show how the time of day (A-E) affects the angle of incoming sunlight (revealed by the length of the shadow) and the light’s intensity. |