Well the loans are contracts to pay back with interest backed by collateral (probably even including the house equity), so it's guaranteed profit for Google. Since the savings are placed so forward in time and are not guaranteed at all, by the time the problem becomes a concern the money will already have been made. Let's say a homeowner starts a blog showing that they are paying much more for power with their new system than from the grid and questions it. Google then points out that the savings will come in 2030 at the end of the loan. If a journalist looking into this is persistent and good they will get a commitment to show exact numbers, which can then be directly discussed as to likelihood. But more likely the graphs will continue to have unmarked y axes, and those doing an analysis of how much the systems cost and what it means to charge 11% interest for 20 years will be discounted as not having the right facts, but no details as to what facts are incorrect and what the correct facts are will be forthcoming. Then, in 2030 the articles will either say how forward thinking the purchasers were to have bought in before electricity skyrocketed, or there will be a retrospective on how they got ripped off. In both cases, Google will have made their money back on their investment in collateral backed AAA rated debt securities.