The peak demand challenge -- Utility thinking includes wind

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The economic imperative for storing wind power is largely non existent, but that has not stopped a few major US utilities from also looking at dedicated storage for wind when looking at ideas for energy management. One of America's traditional power giants, AEP, is currently exploring the potential for 2 MW of on-site battery storage for what will perhaps amount to a 75-100 MW wind plant.

This wind plan is in addition to a scheme for 2 MW of non-wind battery storage planned at two locations, in Milton, West Virginia, and in Finley, Ohio, for traditional power. Both regions have experienced rapid growth in demand so AEP says the battery systems negate the need to rush into pricey substation planning and construction to enable power to be fed into the system to meet peak load. Power can be released from the battery instead.

AEP is motivated partly because of the possibility of a national green energy mandate. Although the company strongly opposes national legislation, preferring that states decide their own mandates, it wants to be prepared, says the utility's Pat Hemlepp. Battery storage is one way of coping with wind, he believes. "Once more wind generation gets put in place, perhaps it would be nice to be able to dispatch it," he explains.

Hemlepp does not necessarily disagree with other utilities, who are willing to accept wind penetrations of upwards of 20% before considering the economics of increasing their generation reserves. But, he says, "You can't wait until you start approaching that before you start looking for solutions."

The sodium sulphur batteries chosen by AEP are provided by NGK Insulators of Japan and Tokyo Electric Power. Each battery has a capacity of 1 MW, so two are being allocated for the three projects for a total project cost of $27 million for the 6 MW of storage. Each battery is the size of a double decker bus and can provide enough power for 1600 American homes for roughly seven hours, says AEP. They are expected to last 15 years or more.

Pacific Gas & Electric (PG&E), one of California's largest utilities, is also looking at managing wind energy using batteries. But instead of locating them at a wind project, PG&E is exploring the use of vehicle to grid (V2G) technologies. This is typically defined as the use of the electricity grid to charge on-board batteries in all electric or Plug-in Hybrid Electric (PHEV) vehicles that discharge their batteries by driving during the day. The next step is to feed that power back into the grid if the cars are parked.

Driving storage

The cars needed for a V2G system exist in many prototype or retrofit forms but are not yet commercialized. PG&E has one Toyota Prius that has been modified with a larger battery pack to become a PHEV and demonstrate the V2G approach. The latest development in this research is a new partnership announced last month between the utility and Tesla Motors, an electric car company. PG&E will work with Tesla on grid-to-car communication and "intelligent" charging. This would include looking at how power stored in parked fleets of charged PHEVs could send power back to the grid, providing stability during moments of peak demand.

It is a concept that has been modelled by another California utility, the Sacramento Municipal Utility District (SMUD). It found that if half of the homes in its service territory had PHEVs, these cars could power nearly half of SMUD's peak load (1425 MW), with no other generation, and hold it for over an hour, negating the need to fire up costly and polluting "peaker" gas plants.

An economic bonus

PG&E's Keely Wachs says it is less about wind "needing" storage but rather a desire to use it during times of peak energy demand. PG&E does not own any wind generation but it buys 910 MW of wind -- roughly 3% of its portfolio -- and Wachs says these projects deliver most of their power at night when grid demand is low. Storage offers the prospect that those wind contracts could become more valuable to the utility.

"The reason that storage is an important part of the wind and V2G equation is because we need to find ways to bring renewables on during peak load demand, when utilities typically use the more carbon intensive energy sources," says Wachs. He adds that throttling back traditional power at night to accommodate more wind would occur when demand is relatively low and PG&E is using less carbon intensive sources.

"So if you look at the carbon trade-off of doing so during the night versus the peak demand during the day, it makes storage an attractive option," he claims.

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