Energy Per Square Metre
On average 1000 Watts of solar energy is projected over every square meter of space at or near sea level when the air mass index is at 1.5. Use this to calculate how much energy you can harvest from the sun from equipment that uses the STC (Standard Test Condition) rating.
Air Mass Index
Air mass index of 1.5 is derived from the position of the sun where we measure the collection of solar energy to be on average of the 1000 W/for every square meter. Which happens when the sun is at the zenith angle of 48.2 degrees. The zenith angle is from looking straight up. So it means that we can say that the earth is experiencing on average on a good solar day, 1000 Watts for every square meter of surface area. If you have a 1 meter by 1 meter patch of surface, when the sun was 48 degrees from over head in both directions, there would be 1000 Watts of energy hitting that surface.