Is Google claiming that this is profitable overall? As in the lifetime costs for installing the solar panels on my house are less than the equivalent cost of electricity from the grid? If so, shouldn't someone be offering to pay me to install this on my house and then selling the electricity back to me directly?
Usually the deal is something called a PPA -- Power Purchase Agreement. It's usually set up that you agree to pay some fixed price-per-kWh, and that price escalates by some regular way over the life of the contract. That price could be higher, or lower, than the prevailing rates for electricity in that market, and that escalator could be higher or lower than rates at which energy prices increase -- but either way, they're locked in from the start.
I was following through some of Google's references and eventually found a graph without units perhaps explaining their reasoning behind this claim. It shows the cost of grid electricity undergoing massive exponential hockey stick growth from 2020 to 2030. So, if that happens, and you have a fixed percent 20 year mortgage on these panels, then sure, you might end up doing great compared to the suckers paying $100 a kilowatt hour (or whatever their exact number is since the y axis is not labelled) in 2030. On the other hand, an analysis that simply shows such apocalyptic increases in the cost of energy and considers no other factors is overly simplistic since in such an end times scenario mass-starvation, cannibalism, revolution, and the overthrow of the government would be likely accompanied by this situation and those homeowners with PV panels who did not have their own private armies and weapons stash would have long been dispatched and robbed of their valuable panels by those who do.