A powerful winter storm swept across northeastern Ohio in early January, knocking out power for nearly 60,000 customers. But in an isolated one-story building, tucked among the trees and fields of Cuyahoga Valley National Park, the lights stayed on. So did the computers. The power source: two fuel cells, each about the size of a refrigerator. It worked seamlessly," said Tom Toledo, maintenance operations supervisor at the park. "We didn't even realize there was a power outage." The performance of these fuel cells, a demonstration project for fuel cell maker Acumentrics Corp. of Westwood, is an example of a technology whose time may be approaching. Unlike traditional technologies, which burn fuels like oil, coal, and natural gas to make power, fuel cells rely on chemical reactions to produce electricity and heat. Fuel cells are most frequently imagined as an advanced engine for automobiles. But as Acumentrics' success in Ohio demonstrates, on-site generation represents another application, one that specialists say will make it to market long before fuel cells replace the internal combustion engine. Acumentrics, in fact, is moving toward commercial production of a compact fuel cell system to power and heat homes. Working with the Italian heating products company Merloni TermoSanitari, Acumentrics hopes to get these household units, small enough to hang on a wall, into European markets by 2010. Estimated price: $5,200. "This is a new way of making electricity," said Gary Simon, Acumentrics chief executive. "It's like going from vacuum tubes to microchips." Acumentrics is one of about 40 Massachusetts firms developing fuel cell technology that someday may power everything from military outposts to cellphones.