Here in Sydney, Australia until recently the state government had a very generous solar scheme. You paid for the panels, then received a 60c/kW feed-in tariff for 7 years. Generally, your system would be paid off within 5-6 years, after which you are generating pure state subsidised profit, before dropping back to a much lower rate, and continuing to profit for the life of the panels.
I'm all for solar, but I disliked the scheme because it disadvantaged the poor who simply couldn't afford the capital outlay to purchase the system. But it got even worse because the government massively underestimated the take up rate for the scheme, and it blew out by a couple of billion dollars. As a result, electricity prices as a whole have to rise to cover the discrepancy, further punishing the poor.
Implementation is the downfall of many a good idea.