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I don't think energy storage is that big of a deal. Assuming you need only need to store one night's worth of energy, the weight requirements would be about 85 grams/watt for lead-acid batteries, or 25 grams/watt for lithium-ion. For comparison, commodity solar panels are already about 70 g/W.

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I think you mean 25 grams/Watt-hour and keep in mind that you need ~12 hours of energy storage.

No, I meant grams/watt, but I glossed over how I derived those numbers.

My back-of-the-envelope assumption was that you get 4 effective hours of daylight per 24 hours. Which means that for every 1W of power generation at peak, you get 1/6W of average power consumption, which translates to 3.33Wh of storage to keep things running overnight. (For a land-based installation you would probably want a multiple-day power reserve to handle cloudy days, but I'm assuming that's not an issue for a stratospheric balloon.)

So you mean 25 grams of battery per watt of solar panels?

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