If solar power activitsts are right, today's buyers and builders of solar homes are pioneers of an important way of life for the future.

Barry Commoner argues that the sun will eventually be the dominant source of power because it is the only energy alternative that is all of these: srenewable, environmentally benign and potentially economical.

To make solar power a major energy source, said Commoner, we need a market large enough to economize solar technology -- much of which is already available -- and a departure from traditional thinking on energy. That thinking, according to Commoner, is keeping the country from proceeding imaginatively and soon toward the inevitable solar future.

At first, it might seem a bit presumptuous to talk of solar power in the northern United States, where for months at a time the sun seems more like a reluctant guest than a reliable energy source. But, in fact, some solar experts think this area may be the very place where solar technology will flower because it can't survive without heat. The cost of fossil fuels in the northern region is rising at a rate that may soon create the kind of competitive market for solar power that Commoner says will stimulate its development.

In any case, solar power involves more than proximity to the equator. Miami, for example, gets only 2,800 hours of sunlight per year. Fargo, N.D., also gets 2,800 hours of sunlight. But homes in the Midwest, for example, need about seven times more heat than those in Miami. (Floridians, however, need considerable energy to keep cool, and that is another developing solar frontier.)

Some solar homes demonstrate that we can get all the home-heating energy we need from the sun, even in northern climes. For example, a home built by the Canadian government in Saskatchewan as a demonstration of solar potential is heated 100 percent by the sun.

Solar systems don't work when the sun doesn't shine, so some kind of storage is required to retain the heat. And at least until the technology is perfected, a conventional backup system is necessary to ensure adequate heat. Solar experts stress that the most important underpinning of an effective solar house is good, housewide insulation.

So far, it's not easy to find a true "solar house" in America. According to Home Data, a marketing research firm, few housing developers are now building solar homes.

One that does is the Chicago-based Hawkweed Group. The firm sells only solar homes, both the active and passive types.

Larry Dieckman, a Hawkweed partner, said the 1973 energy crisis made Hawkweed architects decide they could not in good conscience continue to build homes to be heated with fossil fuels -- homes that might become obsolete within a couple of decades.

The firm takes its name from the hawkweed, a relative of the sunflower that looks like the sun, and that "tracks" the sun in its daily route through the sky, always facing it.

One family said it wanted "something different", and they built an active solar home according to a Hawkweed design.

The family moved into their home last October, too late for the summer warmth to heat the rocks that eventually will work with the "active" solar panels to provide most of their winter heat.

However, they did notice that their new home is "very tight; very warm." In the long run, they said, "We will save considerable money in fuel bills. The house has better insulation and is simply warmer than a convential house would be."

The house's solar aspects took some getting used to, however, its occupants said. It is heated by the sun by day, but at least until the rock-stored heat is available (and use of the backup will probably have to continue in extremely cold weather), they had to turn the furnace on at night.

In addition to the heating system, there is a solar hot water system and a 10-by-14-foot greenhouse.