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Old 12-20-2009, 01:34 PM
AemJeff AemJeff is offline
 
Join Date: Feb 2007
Posts: 7,750
Default Re: The Next Rare Earth Crisis

Quote:
Originally Posted by osmium View Post
yeah, that's the general idea. You're always going to get less energy out than you put in, but the considerations are efficiencies and costs (both $$ and environmental, which in a perfectly operating market would be equivalent). Batteries can be 90% efficient, fuel cells can be 60% (reversible cycle with hydrogen), and turbines with fossil will be something less than 40%. But fossil fuel stuff is cheapest due to 100 years of optimization and the relative ease that you just take it out of the ground.

For pumped hydro storage (I am not an expert, but this is my impression), it won't scale down very far in size. I think you need a lot of gravity behind water to get that kind of power back out of it, so you essentially need a mountain. (But if you happen to own a mountain already, I bet it's pretty cheap.) Batteries, fuel cells, and turbines can all probably work on a scale small enough to distribute them fairly evenly through a city, and if one breaks, then the others can bring up the slack, much like the internet.

I don't know the numbers either, Whatfur, but those ones you give in your last sentence capture the idea.
I haven't totally given up the idea that smaller scales might be workable. The 75% efficiency achieved at Dinorwig surprised me. I have no idea how to quantify the amount of power that could be generated by a water tower size pair of tanks - but, if you powered the pumps with combination of solar and wind, e.g., the cost of storage seems pretty reasonable. If it's possible to generate useful power on that scale, then there might be the germ of a workable idea here. That said, I hear what you're saying.
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Last edited by AemJeff; 12-20-2009 at 01:43 PM..
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