Does your example include a FIT (feed in tariff) provided by government at a much higher rate than grid power, or are you doing a calculations at grid power? A

Does your example include a FIT (feed in tariff) provided by government at a much higher rate than grid power, or are you doing a calculations at grid power? A lot of places have a high FIT value currently, but this is subject to political whims and any incoming government might find it easy to gain votes by trimming the FIT, as has already happened in many places around the world. Another huge problem with these calculations is the very small fraction of people who stay in one house for more than 10 years. Essentially you have to stay in the house for the entire payback period or you've lost out. Personally I think the solar price will have to drop to the point where it is much lower than grid (with no subsidies), rather than just about equal. At that point, takeup will be much higher.