Plugging into the sun for electricity

Another small step toward plugging American homes into the sun is about to take place in an affluent neighborhood here.

One of only a few homes that use the sun to produce electric current for household appliances, heating and cooling, will be sold.

Instead of the usual utility room downstairs, the new owners will find a computer that will automatically switch between rooftop-gathered electric power and the normal electric power line coming in from the street.

Most solar homes in the United States use rooftop panels for water or space heating. But a few - including the one here - use rooftop photovoltaic panels that actually convert the sun's rays to electricity.

On sunny days the house is expected to run entirely on sun power. At other times it will use purchased power like most homes.

Cheaper utility bills are expected. But in this experimental home, the cost of the solar cells and installation is about $45,000, a cost that far outweighs expected savings. Altogether some $100,000 of solar features have been built into the home.

That's why it is considered experimental. The new owners will pay the going market price for a comparable non-solar home, about $200,000 to $250,000, with the Georgia Power Company, the sponsors, picking up the rest of the tab in the name of research.

Along with some $100,000 worth of monitoring devices and analysis time, the total cost of the home is closer to $450,000, according to Georgia Power engineer Gary Birdwell.

Why all the monitoring? To see how well the solar features work, says Mr. Birdwell.

Georgia Power officials claim this will be the most extensively monitored, privately funded photovoltaic solar home yet.

Next to the computer will be a series of measuring devices attached to some 70 sensors throughout the house to help Georgia Power monitor temperature, humidity, and use of power to some major appliances.

The development of solar cells at affordable costs is still, however, a number of years off, according to most assessments.

Photovoltaic-powered homes will likely become affordable ''sometime in the next decade,'' says Barry Graves, director of the federally funded Southern Solar Energy Center. Used with passive solar features (such as south-facing windows for maximum exposure to sunlight), homes with photovoltaic systems could eventually provide 50 to 75 percent of the family's power needs, he says.

Such systems, as used in Georgia Power Company's home here, require expensive equipment, including safety devices, to allow excess power from the home to flow backward into power company lines, Mr. Graves points out. One option being studied in other projects, he says, is using excess power from rooftop panels to chill water for use in cooling the home. Solar cooling costs are still prohibitively expensive, he says.

Future I, as Georgia Power has dubbed its home here, is a ''useful and bold step,'' says Graves.

It is also an investment. Power company officials face multiple pressures. In this steadily growing region, they must expand capacity to produce power, even as conservative state utility boards try to hold down rates. Construction costs for new power plants have risen sharply in recent years.

Summer is the peak power demand time for this region, as homeowners switch on their air conditioners. It is also the sunniest time. Getting homeowners to make greater use of the sun can reduce some of the plant-contruction needs.

Future I provides the company with a live-in testing laboratory. It will also provide the new homeowners with a lot of conversation pieces.

''We put just about everything we could put into it,'' says Richard Sibly of the architectural firm for this expensive home, Sibly & Seedorf. (By contrast, his partner, Richard Seedorf, built a passive solar home for himself in Atlanta at a cost of about $65,000 recently.)

There are long black plastic pipes in the living room, discreetly hidden by cloth but open to the sun rays entering the wall to wall widows on the south side. The pipes contain eutectic salts to absorb heat from the winter sun (summer sun is blocked by an overhang) and release it in the evening as it cools. Mr. Sibly questions whether the round pipes will trap enough heat, however, suggesting flat ones might be better.

The lower level of the two-floor, 3,100-square-foot home (four bedrooms and three and a half bathrooms), has another surprise: large double-paned windows that open onto - a thick wall.

Known as a trombe wall, the unit is heated by the sun's rays in the winter and the warm air flows into the rooms through vents. Summer sun is blocked from hitting the wall by an overhang.

Under the yard are tanks where 1,500 gallons of water are stored, at the cooler underground temperatures, then pumped into the family's air conditioning system to cut power demand for cooling.