This point was driven home for me when I was at Google. Googlers being flush with money, we had a local solar installer stop by a few times. I attended one of the presentations. This was in WA, by the way, which turns into Mordor for 6 months in any given year. So the guy keeps going on about how it'll pay for itself and so on, and presenting all kinds of stats like the ones you responded to. Then someone asked him how much our typical lack of sunlight affects this thing. He was like, "not much, let me show you", and he brought up a management UI for a solar installation in some school that they've recently completed. That was a mistake on his part. It was mid day, although a cloudy day IIRC, and the page showed like 10% of the possible output was being produced. Audience chuckled and some people started heading for the exit.