Anti-fossil fuel activists like 350.org’s Bill McKibben often pretend the United States can run on 100 percent renewable energy without the use of any traditional fuel sources. McKibben recently wrote in Rolling Stone that “the sundown problem is being solved fast, as batteries are able to store the energy from the morning sun and the wind from a gusty evening to keep the power running overnight.”

McKibben’s claims simply aren’t true though, and preparations for next week’s total solar eclipse illustrate this cold, hard fact.

Because storage technology to allow for solar power to stand alone — even during a brief loss of sunlight — doesn’t currently exist, the solar industry has been actively preparing for how to mitigate the issue in places like sunny California where that industry thrives. The solution? Natural gas.