Hah... you don't live where I am living. A bad year can be dull an dark, very thick clouds all through the summer, with very few clear days and temperatures not higher that 15-17C. A very good year, like two years ago, can be very clear and sunny almost every day for three months and temperatures around or even over 30C several times. While I know you don't need clear and sunny days for producing electricity, the clearer and the sunnier it is, the better it is also. So yes, there are some good years and some bad years, and during such short payback period, you don't need more than one or two bad years to ruin that calculation, since it is based on average weather and what statistically is expected, not the extremes. On the other hand, one or two extremely good years would of course balance that, or make it much better, especially if the bad years never come during that period.I can't understand that. A bad year isn't that much different to a good year.
Never the less, my point was that you never know, you make a long term investment based on the assumption that the weather will be a certain type, following statistical data. Reality may be different, so if that is critical to anyone, then solar panels may not be the best investments one can make in ones future economy planning.
I will have no problems using up almost all of my self produced electricity, at least 8-9 months of the year as it is. My house is pretty large, not using any fossil fuel, have electric heating, plus one EV and a PHEV today, which are charged every day so I am consuming quite some power most of the year. During high summer I will be producing most of it during the working hours, will not need heating and the cars are out. Coming home around 5 pm, and while normally during summer we have good sun a fair bit more and is not getting dark before 10-11pm, also getting light again around 2am, it will not be enough for charging two cars, so I have to buy at least part of the power. Some times (not unusual) we also need to heat the house during the night, especially during "bad" summers. If I would get a high capacity EV to replace my PHEV with, then I would need to use even more electricity from the grid.Increasing consumption would ensure that you have more chance of using your own power and help guarantee the return. I was lucky in getting the early FIT, so mine are already paid for and into profit.
Anyway, I hope I am wrong about this, but I think not, so for me it is more about "giving back" than making profit, but of course, if I can make profit in 8-10 years, and I am still alive then that's even better. Right now, I am a newbie, my solar panels being in operation only since the beginning of this year, but I am an engineer, so I am not totally lost in the subject, but also not overly optimistic. In this respect, regarding the financial investments, I think it is better to be a bit pessimistic than optimistic. It is a big investment for most people, so i my opinion, it is better to have a pragmatic approach, not to be overly optimistic when one decides for going solar.