-- the world's first privately financed home which will get all of its electricity as well as all of its heat from the sun is being planned here.

Not that it doesn't owe a debt to government research. Building on the experience gained from the federally funded solar cell test system in Los Cruces, N.M., and a federally subsidized house recently completed in Carlisle, Mass., Rational Alternatives Inc. -- a Santa Fe Solar building company -- has decided to construct a similar house on speculation.

"We will build the house and see what happens. The minute it sells, we'll start another, perhaps two more," explained the company's vice president, Mark Conkling.

Nestled in the pine-covered foothills of the Sangre de Cristo Mountains near Santa Fe, the 2,250-square-foot house with a 350-square-foot array of solar cells perched inconspicuously on its roof will sell for $175,000 to $185,000. Construction on it will begin in two weeks and completion is expected by fall, it will join 32 passive solar homes (which cannot generate electricty) in a 214-unit solar community the company is developing.

All the rational alternative houses are built in the style of the area. They are single-story, abode-type houses with flat roofs supported by vigas, or peeled logs. Actually, the exterior walls are concrete blocks which are filled with concrete and coated with urethane insulation and concrete plaster. The floors also are concrete stamped in a square pattern which, when polished, looks like ceramic tile. Almost every room has south-racing windows and the interior walls are made of adobe which "absorbs and reradiates heat more slowly and gently than concrete," Conkling said.

According to the solar builder, the south-facing windows and the "thermal mass" of adobe and concrete which soaks up heat during the day and releases it during the evening reduced the electric heating costs of his standard homes to $24 last year. Also, the large expense of south-facing windows reduce the amount of electricty required for lighting.

"This, combined with the excellent solar climate here, has allowed us to put up a much smaller solar cell array than has been used on the federal demonstration homes," explained Steven J. Strong, president of Solar Design Associates of Lincoln, Mass., who designed the Carlisle house and is collaborating with Rational Alternatives on their photovoltaic house.

The solar cell array on the Santa Fe house is about one-third the size of that used on the house in Massachusetts. The amount of sunlight falling on the array will be increased by a flat reflector. This will increase the electric output of the solar cells by better than 20 to 25 percent, said Strong. The peak electrical output of the system will be 2.5 to 3 kilowatts. s

The small size of the array is the key to making the house practical. Solar cells, originally developed to power satellites, were exorbitantly expensive at first. Although their price has fallen 10,000 percent over the years, the cost -- $10 per watt -- still is five to 10 times more than conventional energy sources.

"Still, it's the only source of electricty that I can think of which is actually decreasing in cost," commented Strong.

This house will have no storage batteries. The electricty is immediately converted from direct to alternating current equivalent to that produced by the utility. When more electricty than is being used is produced by the solar cells, it will be sold to Public Service of New Mexico by feeding it into the grid -- in effect running the meter backward. When the house is drawing more power than its solar cells are producing, it will draw on the utility. Public Service is donating the extra meters required.

"We have been very lucky with this photovoltaic house," reported Conkling. "Things have fallen together much better than they did with our first solar homes."

Not only has the utility been cooperateive, but several bankers are backing the innovative house, as is the New Mexico Solar Industries Development Corp., which is trying to increase the number of solar-related jobs in the state, he said.