It's not quite that bad. Solar panels that point directly at the sun during the summer solstice will still receive 91% the density of light during the winter solstice. ( cos(24deg) ~= 0.91 ) Where I live (about 40deg north), the winter solstice is 63% as long (9.5 hours) as the summer solstice (15 hours). Even a thick blanket of snow, or 100% cloud cover, will only reduce power by about 50%.

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Under the worst possible conditions (not considering temperature), on the shortest day of the year, with 100% clouds and a thick layer of snow, PV panels would produce 14% as much power per day as on the longest day of the year with 0 cloud cover.

Not at all, except if you mean arctic winter (when it's technically night all the day).

Also, electric offers you the plethora of choices in methods to produce your energy. If it's not photovoltaic, you still have many solutions. Could as well be eolian, or a dam, or hundred of people riding generator-bikes (half-kidding), or etc.

>hundred of people riding generator-bikes (half-kidding)

I've wondered if it makes sense for gyms to be paying for electricity.

It's funny to think about, but if you do the math even dozens of humans riding bikes contribute so little energy compared to what a building requires it is totally negligible and would never be worth the cost beyond a gimmick.

Also, what about energy-producing gym equipment in airliners?

Free energy (but maybe only an epsilon), and no more deep vein thrombosis!!

Easy to fix with overpaneling unless you’re over 60ish latitude or live in a valley or something.