idea: low cost, high capacity, lossy storage for solar/wind generation using hydrogen
I was brainstorming with a friend about what to do with excess power from renewable generating systems. It's becoming less desirable to shove it onto the grid now that incentives are expiring. I was trying to figure out ways to store more energy than you could with batteries, more cheaply, even if it was less efficient than using batteries.
Well, if you have excess electricity, it's fairly easy if inefficient to turn it into hydrogen. You can compress hydrogen, but it won't liquefy at higher than cryogenic temperatures so you'd need high pressures to store a lot in a small space. But what if you had more space to work with?
I calculated that a cylindrical balloon 15 feet in diameter and 20 feet tall would store less than 6 lbs of hydrogen gas at standard temperature and pressure, but that would produce 100 KWH of power (at 100% efficiency). You obviously wouldn't get 100% efficiency, and you'd constantly have hydrogen escaping through the skin of the balloon, and it'd be a potential fire hazard (though less so than you might think)... But I think it'd be workable with the right engineering. You'd put the balloon in a cage to keep it in place, but not fully enclose it to keep hydrogen gas from mixing with oxygen and building up. You'd want a fuel cell to convert the hydrogen back into electricity. A rough guesstimate says the cost of such a system would range between a third and a half that of the equivalent in storage using lead-acid batteries, and a whole lot less than lithium-ion.
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