HolidayBuyer's Guide

Utility energy storage no longer just giant batteries

The latest smart-grid programs give alternative storage technologies--including compressed air, flow batteries, and flywheels--a shot at proving themselves at utility scale.

If you need more evidence that energy storage is much more than lithium ion batteries, take a look at the latest smart-grid utility storage projects.

The Department of Energy on Tuesday announced that $620 million in stimulus funding is going to 32 smart-grid programs, which will be coupled with another $1 billion in private money. A total of $770 million from government and industry sources in the next few years will go to energy storage, giving a number of storage technologies a dose of real-world experience. (See this PDF for details.)

Photo by PG&E

Notable in the list is the prominence of compressed-air energy storage and flow batteries, two technologies rarely discussed just a few years ago. Also in the mix are flywheels and using batteries for distributed energy storage in communities.

It's unlikely that all the DOE-aided projects will immediately prove to be commercially viable. But storage has clearly emerged as a key component in the vision of the smart grid. A number of start-ups are developing technologies they hope can address a specific storage application or undercut pumped hydro, considered the cheapest form of utility storage, on price. With pumped hydro, water is pumped uphill and released at peak times to run a generator. But its use is limited by geography.

Many of the 16 Energy Department power storage grants were focused on storing wind power, which is a variable source of energy. In California, for example, utility Pacific Gas & Electric plans to store the power generated by wind turbines at night, when turbines are most productive in underground caverns. During the day, when grid demand is higher, the air is released and passed through a turbine to make electricity.

The advantage of underground compressed air storage is that it can be cheaper than batteries and can store many hours worth of energy. PG&E forecasts that its Kern County, Calif., project can deliver 300 megawatts of power for 10 hours, enough to supply tens of thousands of homes.

Another novel technique is using metal tanks to store compressed air, a technology being developed by a Dartmouth College spin-off SustainX. The compressed air is released to run a hydraulic motor that drives a generator to make electricity.

Flow batteries, meanwhile, use tanks of liquid electrolyte solutions. When the two liquids interact, there is a chemical reaction that creates a flow of electricity.

An advantage of this approach is that store large amounts of energy and discharge relatively quickly, according to the Electricity Storage Association. One project will use technology from Premium Power, which makes tractor trailer-size zinc flow batteries to maintain a steady frequency on the grid and supply power during times of peak demand.

Different strokes
The variety of technologies points to the range of energy storage applications. Flywheels from award winner Beacon Power, for example, can absorb and discharge megawatts' worth of power to the grid but only in 15-minute bursts. Still, flywheels are getting more attention because they are a nonpolluting replacement to the natural-gas plants now used to smooth out short-term fluctuations in grid frequency, according to the company.

Click on the image for a slide show of different energy storage technologies.Photo by AEP

Large batteries, too, will be further tested for grid storage. Duke Energy plans to use multiple battery types for 20 megawatts' worth of power delivery at the Notrees Windpower project in Texas. The "hybrid" battery system is being designed for two tasks: to smooth out short-term grid fluctuations and to supply hours' worth of power during the day, according to a Duke Energy representative.

Utility Portland General Electric in the next two years plans to install five batteries from auto battery supplier Ener1 to supply enough juice to power 400 homes for about an hour. Alternative chemistries, including lead carbon batteries from East Penn Manufacturing, will also be used.

One project will test the viability of used car batteries for grid storage. Lithium ion plug-in car batteries from A123 Systems will be used to supply 25 kilowatts for two hours in 20 community energy storage projects. The performance of lithium ion batteries degrades after many years in a car, but there is still sufficient storage and power for grid applications, utility executives say.