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Other utilities are planning or considering the technology. In Long Island, N.Y., a group of utilities plans this summer to install an NaS battery at a bus depot. The battery is charged at night, when power prices are low, and discharged during the day to pump natural gas into tanks to provide fuel for the buses, says Mike Saltzman of the New York Power Authority. That cuts electric costs for the bus company and eases stresses on the grid. Pacific Gas & Electric is leaning toward installing a much larger, 5-megawatt battery by 2009, enough to power about 4,000 homes, says PG&E's Jon Tremayne.

The biggest drawback is price. The battery costs about $2,500 per kilowatt, about 10% more than a new coal-fired plant. That discourages independent wind farm developers from embracing the battery on fears it will drive the wholesale electricity prices they charge utilities above competing rates, says Christine Real de Azua, spokeswoman for the American Wind Energy Association.

Mass production, however, is expected to drive prices down, Mears says. He predicts NaS batteries will start to become widespread within a decade.

Meanwhile, other storage devices are gaining traction, too. A group of Iowa municipal utilities plans to use wind turbines to compress air during off-peak hours that will be stored in an underground cavern. The air would be released at peak periods to run turbines and generate power for about 200,000 homes. Another technology, the flywheel, has a massive cylinder that can spin for days after being started by a generator. The cylinder can then activate a turbine to supply electricity for a few seconds or minutes when it's needed, for instance, to head off an interruption to a computer center from a lightning strike.

"We'd like to see storage ubiquitous," says Imre Gyuk, head of energy storage for the Department of Energy, which helped fund the AEP project. "Stick it any place you can stick it."

An NaS battery, by contrast, uses a far more durable porcelain-like material to bridge the electrodes, giving it a life span of about 15 years, Mears says. It also takes up about a fifth of the space. Ford Motor pioneered the battery in the 1960s to power early-model electric cars; NGK and Tokyo Electric refined it for the power grid.

Since the 1990s, Japanese businesses have installed enough NaS batteries to light the equivalent of about 155,000 homes, says Brad Roberts, head of the Electricity Storage Association. In the USA, AEP is using the 30-foot-wide by 15-foot-igh battery to supply 10% of the electricity needs of 2,600 customers in north Charleston, says Ali Nourai, AEP manager of distributed energy. The battery, which cost about $2.5 million, is charged by generators from the grid at night, when demand and prices are low, and discharged during the day when power usage peaks.

The best metric is energy per unit weight, about 120-150 w-hr/kg for current commercial Li-ion rechargeable batteries. We expect that 500-700 whr/kg can be accomplished in the near term, rising to 1200-1500 whr/kg in the longer term (for the engine and its fuel supply).

Table 1. Turbogenerator Pricing





Machine Size


Cost per kW

1-2 MW


$600-$650

5 MW


$400-$450

50 MW


$275-$300

150 MW


$180-$190

250 MW


$175-$185

260-340 MW


$175-$180

news in CHPs is that they're becoming ultra-decentralized. That is, you can put one under your sink and heat and power your house with it. In Japan, over 30,000 household's already have micro-CHPs, and Europe boasts more than 80,000. Where's yours you ask? It's coming, just hold on a little bit. A few dozen units have been installed across America, but their spread is being held back by cheap energy prices and lack of the incentives that have driven the market in Japan and Europe. But two businesses are poised to begin marketing CHPs to environmentally conscious Americans.

But be ready to pay, even the cheapest model, producing enough heat for a three bedroom house and 1 kilowatt of electricity, will set you back $13,000. Even then, it's only likely to save you $800 a year, meaning that it will probably never completely pay for itself (unless you subtract the cost of a new high-efficiency furnace, then it will pay for itself in five to seven years.) But, if natural gas companies are smart, they will start offering incentives to buyers, since they will be guaranteeing themselves customers for the next twenty years at least.

lab director Alan Epstein, a prototype silicon microturbine produced using semiconductor-type microfabrication methods may be operating by the turn of the century.

"We are excited to use our MCHP technology for this partnership with Climate Energy," said Wade Terry, vice president of Honda Power Equipment, the Honda division responsible for overseeing the company's involvement in the project. "In the last 2 years, we have placed over 15,000 similar units in homes in Japan and the results have shown that the technology works and works now."

Micro-CHP