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Windpower's Warning

ERCOT’s February emergency suggests storage capacity is needed to support renewables.

Fortnightly Magazine - May 2008

the ability to buffer wind volatility. Meeting current wind-penetration targets, however, ultimately might require the development of an economically viable means of storing windpower.

Storage Pros & Cons

The advantages of implementing storage technology for windpower are huge. Storage virtually eliminates the need to curtail wind output, guaranteeing high utilization of potential wind energy. The stored power can be dispatched during peak periods, reducing the need to run older, expensive units that are often high polluting. Storage capacity reduces the need for investment to expand the transmission grid, avoids the cost of increasing operating reserves as a buffer for wind variability, and actually might reduce the cost of carrying reserves.

Using windpower as a firm peaking resource allows a much greater percentage of installed wind capacity to be credited toward system-reserve margins, reducing the need to build new peaking resources. Being able to store and dispatch windpower renders wind integration into a non-issue, and removes almost all operational obstacles confronting the wind industry.

So if energy storage makes so much sense, why isn’t it happening? The answer is clear: Up until now it just hasn’t made economic sense to install. When there is a relatively small amount of wind being produced, the regional power system can absorb it quite easily even at full utilization. And storing power is expensive. The primary means involve construction of pumped hydro or compressed air storage plants, or via use of battery-storage technology.

Pumped hydro has the advantage of being a fairly well-known technology, where cheap off-peak power is used to pump water to an elevated reservoir, then released to generate power during peak demand hours. There are currently 31 operating pumped-storage plants in the continental United States, supplying roughly 2.5 percent of total electrical demand. Pumped storage units, however, require a large up-front capital investment and have specific siting requirements than can be problematic. West Texas, for example, is notably short on water supplies, which is obviously a key requirement for locating a pumped-storage plant.

The same pros and cons hold for compressed-air storage, which requires well-defined natural geological structures, usually salt mines. This technology has been utilized heavily in Europe in concert with wind generation, but has much less natural application in the Great Plains region of the United States. So while these traditional, large-scale technologies may work well in certain areas, it is unlikely they can be utilized at the magnitude needed to effectively deal with the anticipated large-scale wind energy expansion in the Midwest.

Battery Power Arrays

These obstacles leave battery storage as the perhaps the most feasible option for storing wind generation for peak demand use in many regions. In fact, there have been two recent announcements of initial tests of megawatt-scale batteries being installed at wind farms in Minnesota and in Ireland. Battery arrays can be located at each individual wind tower and even utilize the electronics of the wind equipment to provide grid connectivity, thus lowering the storage cost. This also makes the battery-storage option extremely scalable, because power can be diverted from the grid into the battery as needed