The chart below shows monthly installation statistics for rooftop solar under the California Solar Initiative, a state program to subsidize the installation of 1,940 megawatts of rooftop solar.

That only solar power plants came online in October speaks to some inherent advantages solar holds over fossil fuels – beyond not roasting the planet. One is that photovoltaic power stations can be built relatively quickly given that they essentially involve deploying thousands of solar panels over hundreds or thousands of acres of land. Photovoltaic power plants are modular, meaning that you can build them small near cities to avoid the huge costs of new transmission lines, or build them big to take advantage of economies of scale. More than half of the new solar power plants that came online in October were photovoltaic.

The rest were solar thermal projects that use thousands of mirrors called heliostats to focus the sun on a liquid-filled boiler to create steam that drives an electricity-generating turbine. Such projects more resemble a natural gas-fired power plant in their complexity and the years it takes to construct them.

But they also have an advantage over photovoltaic power plants – the heat solar thermal power plants produce can be stored to run the turbine at night and other times when the sun isn’t shining. The 250-megawatt Solana Generating Station that came online in Arizona in October, for example, is the first in the U.S. with an energy storage system that allows it to keep electricity flowing to the grid six hours after the sun sets.

And if a report issued yesterday is accurate, October will not be an aberration. The number of planned photovoltaic installations in the pipeline has grown 7% to 43,000 megawatts over the past year as developers rush to get projects online before a key federal tax credit for renewable energy falls from 30 percent to 10 percent at the end of 2016. If all were built, that’s enough electricity to power six million American homes.

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