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Renewable energy prices have plunged to the point where, for much of the planet, wind and solar power is now cheaper than fossil fuel-generated electricity. But the variability of these power sources can make managing them on an electric grid challenging—a challenge that can exact costs beyond their apparent price. The exact cost, however, has been heavily debated, with estimates ranging from “minimal” up to “build an entire natural gas plant to match every megawatt of wind power.”

Philip Heptonstall and Robert Gross of Imperial College London decided to try to figure out what the costs actually were. After wading through hundreds of studies, the answer they came up with is somewhere between “It’s complicated” and “It depends.” But the key conclusion is that, even at the high end of the estimates, the added costs of renewables still leave them fairly competitive with carbon-emitting sources.

Counting costs

Heptonstall and Gross start by breaking the potential for added costs down into three categories. The first is covering for the somewhat erratic nature of renewable power, which may incur expenses if their output doesn’t match their forecasted output. The second is the ability of renewables to meet the predictable daily peaks in demand—late afternoon in hotter climates, overnight in colder ones. Finally, there’s the costs of integrating renewables into an existing grid, as the best sites for generation may not match up with the existing transmission capacity.