Will it work? Don’t bet on it, says Jeremy Michalek, a professor of mechanical engineering at Carnegie Mellon University and director of its Vehicle Electrification Group.

Quartz asked Michalek to estimate how far the best solar panels could propel a typical electric car on the market. He broke down the math for us.

Michalek says about 1 kilowatt (kW) of solar energy falls on a square meter of the Earth’s surface on a clear day. That’s all the solar energy available to collect. For a company like Sono, which says it can convert about a quarter of that energy into electricity (although that’s very optimistic), a full site of panels might generate roughly 8 kilowatt hours of energy per day (a best-case scenario with four square meters of solar panels).

Michalek says that’s enough to drive a car like the comparable Nissan Leaf about 25 miles.
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