Underground 'Wind Mines' Could Keep Datacenters Powered 109
Nerval's Lobster writes "Major IT vendors have been including custom-built wind- and solar-power farms in their datacenter construction plans. But while wind and solar power may be clean, they're often unreliable, especially by the standards of datacenters that need a way to keep operating through any unexpected surges or drops in power. How about saving the wind that generates the power? That might work, according to researchers at the federal Bonneville Power Administration (BPA), and U.S. Department of Energy's Pacific Northwest National Laboratory. A study published in February (PDF) outlined the potential benefit of pumping pressurized air into caverns deep underground as a way to store wind energy, then letting it out whenever demand spikes, or the wind drops, and the above-ground facilities need help spinning enough turbines to keep power levels steady. The technique, called Compressed Air Energy Storage (CAES) isn't new: existing CAES plants in Alabama and Huntorf, Germany (built in 1991 and 1978, respectively) store compressed air in underground salt caverns hollowed out by solution mining (pumping salt-saturated water out of concentrations of salt buried far underground and replacing it with fresh water). But implementing such a technique for datacenters might take a little work. The BPA and the Pacific Northwest National Laboratory have already identified, and are evaluating, sites in the Pacific Northwest that would be suitable for CAES underground reservoirs; the first, which could be located in Washington's Columbia Hills could—via existing CAES technology—store enough compressed air to generate a steady 207MW for 40 days of continuous usage, ultimately delivering 400 additional hours without adding any compressed air."
If you use an air-water mixture (Score:4, Interesting)
Complex problem, many answers (Score:5, Interesting)
Using compressed air as a storage medium has a number of problems:
1) Low energy density. Air is very compressible. While that's what makes it usable as power storage in the first place, the amount of energy that can be saved in a gallon-sized container as compressed air pales next to a gallon of gasoline.
2) Power loss through thermal contraction.. When you compress air, it heats up. As that heat energy escapes, it effectively takes away a good chunk of the energy you consumed compressing it in the first place. Once the compressed air has cooled, the effective pressure drops. The more air you compress into the same space (See Energy Density above) the worse this effect is.
3) Power loss through leakage Even when available, caves are terrible places to store compressed air. Even if you seal the cave somehow, you then have to deal with seismic shifting, creating leaks and causing your beautiful, N-redundant power source to leak into an underwater stream bed. Lastly, even when sealed properly, air will *still* leak out. Ever wonder why your bike/car tires need to be aired up every so often even when they *aren't leaking?
Air molecules are wily little critters
4) turbine inefficiency The higher the pressure of compressed air, the more the above problems manifest themselves. However, the lower the pressure of compressed air, the less efficient it is to convert the compressed air back to electricity!
Good solutions address the multiple facets of the problem. For example, much of the cost of running a data center is spent on cooling. It might be preferable to store "coolth" in a stone or liquid cooling chamber under the facility than to try to store compressed air. Compressed air can be turned into electricity, which is more flexible, but is also more lossy for the reasons listed above. A combination of technologies will be needed to provide the best answer for redundancy and efficiency.