What will make rooftop solar a common home feature? Costs as low as or lower than electricity from the grid. When is that much-discussed “grid parity” going to happen? Soon — very, very soon.

Let’s start with where electricity costs are now. Check out this map of retail electricity prices around the country, from the U.S. Chamber of Commerce:


It’s from 2013, but the situation hasn’t changed much — other than for prices to go up in some areas. You can easily see here that some of the top solar states, like California, Hawaii, and Massachusetts, also have some of the highest power rates.

This is clear when you compare the map above to the current installed solar capacity around the country, from the Open PV Project (lightest color indicates most solar):


You can definitely see a correlation between electricity price and amount of solar installed, though there are exceptions. Kansas, for example, has fairly high grid prices but little solar — a testament to the fact that good policy is also a key ingredient in promoting solar. And Alaska is not exactly highly populated. For the most part, though, solar is flourishing in states with high electricity rates.

In some states like California, already one of the most expensive places for electricity in the country, residential rates will soon be going up further. Customers in the PG&E service area are looking at a 3.8% increase in electricity bills. Overall, electricity prices in the U.S. have been rising rapidly. According to the Energy Information Administration, in the first half of 2014, U.S. retail residential electricity prices went up 3.2% from the same period last year — the highest year-over-year growth since 2009.

Preliminary data from U.S. Energy Information Administration, August 2014 Electric Power Monthly

Meanwhile, the cost of solar just keeps going down. The Union of Concerned Scientists (USC) recently highlighted this in a great image that shows at a glance how affordable solar is becoming — and how quickly prices are dropping:


The fact is, solar and other renewables just keep getting cheaper. We’ve noticed a number of stories debating this recently, many in reaction to an Economist article on how expensive wind and solar really are. But as Amory Lovins points out, the reality is that renewables are getting cheaper all the time, regardless of anyone’s arguments.

What does this mean? It means that grid parity is coming sooner than you might think — as shown in yet another graphic from UCS:


As USC notes, solar is on a roll. Solar PV installations in the U.S. increased an impressive 485% from 2010 to 2013, and by early 2014, there were more than 480,000 systems in the country. That’s 13,400 MW, enough to power about 2.4 million typical American homes.

What’s needed to keep this number growing? UCS emphasizes the importance of strong, stable solar policies, as well as resources for R&D. With those, and grid parity in more states every year, we agree with USC that there’s a revolution happening. And it’s going to happen whatever the economists say.