You could drive by the place dozens of times without recognizing it. There's a sign, but it doesn't even face the road.
The small building, sitting amid the old barns and houses on River Road in Norwich, Vt., is the home of the Enertech Corporation, one of the nation's leading windmill manufacturers.
At Enertech, 70 people design and manufacture windmills, primarily for residential use. The company has already sold more than 700 machines, each able to produce between two and four kilowatts of electricity.
In a strong, steady wind, the windmills, which look like airplane propellers, can generate one-third to one-half the electricity needed for an average household.
One of some 40 windmill companies in the United States, Enertech opened its doors in 1975, just after the Arab oil embargo. To the company's founders, wind power holds great promise, but Enertech, like its competitors, must face serious challenges in the years ahead.
First, it must offer a competitively priced product. Right now, except in isolated rural areas, windmills generally cannot compete with local utility companies. An Enertech machine costs about $15,000 installed. Federal tax credits lower that price by about $4,000.
Depending on the price of local power and on wind speeds, this investment could take as little as five years or as many as 30 or 40 years to pay for itself in energy savings.
Enertech hopes design improvements will shorten the payback period and lower costs.
''We've already saved 50 percent using induction generators,'' says Ned Coffin, the company chairman. These devices allow customers to feed excess electricity into the local utility lines, thus eliminating the need for expensive and inefficient battery storage.
''Now we're working on the tower, foundation, and installation,'' he adds. ''They can cost $7,500, as much as the windmill itself.''
While Enertech tries to bring costs down, electricity rates are going up. New England is seen as a prime market for wind power, because its power plants depend heavily on foreign oil and charge very high electric rates.
Prices increased 11 percent a year between 1970 and 1980. At that rate of increase, eletricity could cost a predicted 12 cents a kilowatt hour by 1986 - high enough, wind manufacturers say, to make their machines more competitive.
No one knows, though, how quickly electric rates will rise. Oil prices may take off again, but many New England power plants are converting to coal-fired generators.
If electricity prices don't rise steadily, and if wind manufacturers cannot lower their costs enough, the companies may be in trouble. Federal tax credits expire in 1985.
Customers investing in windmills are, in a sense, paying their utility bills in advance on the assumption that electricity prices will continue to go up. They are also assuming that wind companies can meet their second serious challenge: producing reliable, dependable machines.
Enertech officials think of windmills as appliances. But unlike most home appliances, today's windmills do not have years of running time and proven reliability.
''We test the machines in the storms on Mt. Washington,'' Mr. Coffin says, ''and we start and stop them every two minutes until they've started up as often as they would in 20 years, their estimated life. But that's clearly not the same as running them for 20 years on Nantucket.''
Nor is fixing a windmill quite as easy as fixing a washing machine or a refrigerator.
But technical knowledge in this industry is increasing constantly, even if designers don't always know everything. Mr. Coffin recalls the time a few years ago when he got a call from Alaska after a windmill failed to shut off in a high wind and lost its blades. The company asked 180 people around the country who owned similar machines to turn them off while engineers redesigned and replaced the braking system.
It was an expensive lesson for a young company, but Coffin says he feels it can meet the design challenges ahead.
''Our goal,'' he says, ''is to make machines which will run for five years with just an annual inspection.''
Enertech is a privately held company, but investors seem to share Mr. Coffin's optimism. Last year the Bendix Corporation acquired 30 percent of its stock. Coffin says this provided much-needed capital and expertise in mass production.
In the 1930s some 6 million windmills were operating in the US, but with the widespread introduction of inexpensive fossil fuels, people abandoned these machines.
Enertech is looking to the day, not too far in the future, when windmills will once again dot the nation's landscape - and people will plug them in as confidently as they do their refrigerators today.