At what Brightness/Solar Radiation does the Tempest receive enough energy to function and then start adding charge to the battery? I live in a cloudy area in the winter and am interested when that line is crossed on a cloudy day or early morning.
not an easy question as the birghtness sensor is looking in a horizontal plane and the solar panels are mounted vertically. But it is save to say that they need direct sunlight to function.
To add to what @sunny said, it seems to typically need to be a little under 200W/m^2 for good charging to occur.
It appears with my current Tempest the highest solar radiation has been 160 and it was charging well so it must be some point below that.