There is a concept when dealing with solar that many people may not take into account when looking at a solar system design — insolation. So what is insolation? Well, that’s exactly what I’m about to tell you.
In scientific terms: The yearly average density of the Sun’s irradiance at the top of Earth’s atmosphere on an imaginary surface perpendicular to the sunlight rays is approximately 1366 watts per square meter. This value is known as the solar constant. After some of the light is reflected back to space and absorbed by the atmosphere, only around 15 watts per square foot hit the earth’s surface. Of course, this incoming energy is not distributed evenly. There is more sunlight available closer to the equator throughout the year.
But, even 15 watts per square foot is peak power. During a day, the sun’s radiation varies from a maximum value to zero as the sun moves across the sky. So, in order to calculate the average amount of energy a collector can generate, you need to know the concept of insolation (INcoming SOLar radiATION). Insolation levels represent daily average solar energy and are usually expressed in kilowatt-hours per square meter per day. NASA maintains an extensive database on insolation for most locations in the world.
To help give you some idea of what an insolation level would be, take a look at the high insolation level found in Phoenix, Arizona. In Phoenix, the insolation level comes in at a yearly average of 5.89. In contrast, the insolation level in Anchorage, Alaska, comes in at a yearly average of 2.87.
Do you have any questions about the scientific concept of insolation? Leave your questions in the comment section!