One of the problems that has prevented wider adoption of solar panels is the drag on the grid. When the sun goes behind a cloud, there is a surge of power draw as a huge swath of panels is no longer able to provide electricity and they turn to the grid, all in unison. Not a problem today, because there just aren’t enough solar panels to be more than a drop in the power usage bucket.

The obvious solution to this problem is battery backup, but battery tech is expensive. Elon Musk, founder of SpaceX and Tesla, has created a rapidly growing company, SolarCity, to take on that problem by leveraging Tesla battery production.

SolarCity has an interesting business model. For years, they’ve provided the solar panels for free and charged you for the power you use. Since they charge less for the solar power than you’d pay the power company, it’s a good deal for you.

Now SolarCity is adding free batteries to the mix. More win for the consumer, since they can get cheaper power even when the sun isn’t shining. And more win for the power grid, since the power usage surge is eliminated as solar grows in popularity.

That Musk guy is one smart cookie.