They went about it in an interesting way.
First they looked up how much solar energy strikes the earth, in terms of energy per square meter. Then they adjusted this for average hours of direct sun (assuming the panels to be installed weren’t on a tracking system). Then they chose an average efficiency for solar panels of 10% and arrived at an amount of power available per square meter of solar panels on your roof.
Their base calculations relied on an average of 1kW of power used in the house, with peaks of up to 3kW. In the end they came up with a figure of 80 square meters of panels required.
To me the entire calculation seemed backwards, and much more complicated than it needs to be.
Solar panels are sold in standard sizes with specific Watt ratings. I.e., you can buy a 100 Watt panel, or a 160 Watt panel, or even a 200 Watt panel. (This is nominal output, of course. There’s some inefficiency in the wiring and other electronics, and they won’t work that well if they’re dirty.)
Why bother to go through the whole calculation of how much solar energy falls on the earth? What we want to know is how much can we generate with commonly available panels. We’re practical, not theoretical.
