There is a lot of alternative energy hype these days, but you have to be careful with solar installation sales people. Often, they make claims that you will have the unit, installation and equipment all paid off within 5-10-years with all the money you save on energy, the ROI or return on your investment. If the company's salesman takes an overly optimistic approach to such promises to get you to buy, you may find yourself underwhelmed with the results and later determine that you didn't save any money after all.
Not long ago this exact issue occurred and the homeowner being a lawyer asked for the ROI in writing. He lived in a very sunny city with only 6-9 rain days a year on average, so he accepted the salesman on his word, but got it in writing just in case, because he'd heard of problems that other consumers had encountered. Turns out that in 2.5 years of the 10 year so-called ROI, he had not saved more than 10% on his energy bill. Worried that the company wouldn't be around in 7 and a half years, he took them to court for the entire cost of the unit.
He offered to allow them to remove it or leave it there, but wanted his money back, as he had been lied too. The solar company had all sorts of excuses such as cloudy weather, house facing the wrong direction, and even energy cost increases of 3%. The judge was hearing none of this nonsense and awarded the gentleman full re-imbursement. The solar company could take the unit away or sell the unit for 15% of the original cost and walk away.
The homeowner had agreed that 15% was fair because a home buyer might like a solar system on the house and figured that he could raise the price of the house that small amount and recover that cost at a later date, which is more than fair considering he was lied to, and whether they meant to or not is irrelevant, the point is beware of these ROI claims during the initial purchase of your solar alternative energy system.