✔ 最佳答案
That average insolation value is low enough that it's probably averaged over a 24-hour period already.
So I would do
3600 seconds / hour * 24 hours / day * 365 days / year * 8 years * 230 W/m^2 * 8.1% efficiency = a certain number of W-seconds/m^2.
1 watt-second = 1 J (Joule)