Building a Better Battery (WSJ)

[jpak]

http://online.wsj.com/article/SB122661019700825653.html?mod=googlenews_wsj

The alternative-energy industry thinks it can make wind and solar power a lot more useful -- by building a better battery.

One of the big problems with wind and solar is that they're often not generated when they're needed. Winds are usually strongest at night, for instance, when demand for power is at its lowest. That makes it tough for utilities to effectively integrate alternative power sources into their energy mix.

Now companies across the globe are working on a potential solution: batteries that can store wind and solar power and release it onto the grid at times of heavy demand. Developers are investing millions -- and in some cases billions -- of dollars into a slew of promising technologies.

The battery industry "is going through a major growth phase," says Craig Irwin, vice president of equity research at New York-based financial-services firm Merriman Curhan Ford Group Inc.

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[safeinOhio]

1. I thought that they could just

pump water up during windy and sunny times and then use the power of it falling later on.

[phantom power]

2. Sure, if you are near a reservoir.

[jpak]

3. A group has proposed a 1000 MW pump storage system here in Maine that uses underground reservoirs

and a 2000 foot hydraulic head.

No need for a conventional dam...

[phantom power]

4. True, you can build them too.

Seems prohibitively expensive to me. But digging them out underground is an interesting solution to the footprint problem.

[jpak]

5. The key is the 2000 foot head

It doesn't take a whole lot of water falling that distance to generate power.

They plan to build five 200 MW turbines 2000 feet down.

The price tag was ~$2 billion - not bad for a 1G plant.

http://wiscassetnewspaper.maine.com/2008-09-25/energy_plant_proposed.html

[phantom power]

6. Good power. I can't find the storage capacity. How many GW-hours?

[wtmusic]

7. Not to mention, there is a conspicuous absence of any discussion

of efficiency.

[phantom power]

8. storage efficiency figures I've seen for pumped-hydro are 0.75 - 0.8

Respectable.

[wtmusic]

9. According to this source that's one-way

So round trip efficiency is 64%.

(figures from a site with animated GIF images taken with a grain of salt) :D

"Energy recovery depends on total volume of water and its height above the turbine

* need at least 100-meters this is a stringent limit on locations
* artificial lower reserviors can made via excavation can achieve higher energy density due to large vertical distance (up to 1000 feet!)
* facility does not impact free flowing stream
* sediment build-up at dam base is minimized
* Hydropower is 80% efficient (uphill or downhill). So to pump uphill and the get energy downhill, efficiency is 0.8x0.8 = 64%"

http://zebu.uoregon.edu/2001/ph162/l8.html