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The challenge with putting solar on your roof is that even if it saves you money over the long run, you're essentially pre-paying your utility bill for the next ten to 20 years — and who has that kind of scratch?

That's why SolarCity exists: to pay for and install those solar panels, and then lease them to you or sell you the power they produce, for less than your current utility bill. Google just dropped $280 million on the company because they think this is such a fantastic and, in their words, "safe" investment.

The Goog’s investment is enough to put solar panels on up to 9,000 homes, which could ultimately mean that one in every 10 rooftop solar installations in the U.S. is Google-sponsored. (That means they won’t have ads, but they also will only support knockoff versions of Instagram.)

SolarCity says the biggest barrier to putting more solar panels on roofs isn't finding homeowners who want to do it — who would turn down lowering their utility bills for little or no up-front investment? — it's finding banks and other sources of capital to pay the up-front cost. Hopefully, having a flagship financier like Google means SolarCity, the biggest solar company of its kind, will have no trouble finding more sources of investment in the future.