Less than a decade ago, renewable energy in the US meant hydropower; everything else was just a rounding error. Times have definitely changed. Yesterday, the US Energy Information Agency announced that non-hydro renewable had gone eight months where it outproduced hydroelectric dams. And that's without counting residential or distributed solar power.

The EIA defines non-hydro renewables as a mix of solar, wind, geothermal, biomass, landfill gas, and municipal solid waste; currently, the largest contributors there are solar and wind. But the EIA doesn't track projects below one megawatt of capacity, which would include all residential solar installations, as well as distributed projects like the ones New Jersey is placing on utility poles. As a result, the numbers for non-hydro renewables should be considered a lower bound on the true output. (The EIA estimates distributed solar's 2013 output as 10 billion kilowatt hours.)

Despite that caveat, the growth has been impressive. The non-hydro output had never been more than half the renewable total before late 2012, but it had already started its eight-month run just a year later. The high variability of hydro output (which has seasonal and other water availability limitations) caused it to bounce back above half in May, but the EIA expects that, on the whole, it will be below half of the annual generation for the year. And given current trends, it's unlikely to ever dominate renewable generation again.

In fact, because of the distinctive properties of wind, solar, and hydro, it's unlikely we'll ever see a single source dominate the way hydropower has. There's a very real chance, however, that wind power will eventually become the largest single renewable source, as it now accounts for over 30 percent of the annual generation and has grown 10-fold over the last decade.