This home will plug into the sun -- not an electric utility

No electric bills! That's what solar-energy designer Frank Arenas promises for the house he has just begun to construct in one of Tampa's leading suburban neighborhoods.

The 2,400-square-foot home will not be connected to the local electric company, but instead will run almost entirely on solar power, with propane gas used only for drying clothes and cooking.

Everything else - lights, air conditioning, heating, and even the Jacuzzi - will run on energy from the sun.

Water will be heated in a solar water heater, and electricity will be generated by photovoltaic (PV) cells - pure silicon discs that can produce electric power directly from solar energy.

It will be among the largest suburban homes not to be connected to an electric grid system. Mr. Arenas, president of Solar Design Consultants, says it will demonstrate that solar energy is practical even for urban areas.

''The future is to build these solar-energy systems so we don't have to build new power plants,'' the builder says. ''Power plants cost too much to build, and they produce too much pollution.''

The builder says he is convinced that the price of solar energy is now cheaper than utility-provided electricity so long as the building and appliances in which solar energy is used are specifically designed for energy efficiency.

Further, the price of solar energy, especially photovoltaics, will be dropping while the price of utility-provided electricity is going up, according to solar-energy researchers.

''The price of PV cells dropped 20 percent last year, and I expect it will drop 20 percent again this year,'' says Dr. Paul Maycock, former head of the Department of Energy's photovoltaic-development division.''The more PV cells that are purchased, the lower the price will fall.''

Interest in photovoltaics is increasing nationwide although it is still a fledging industry:

* Simpler Solar Systems, a solar-energy company in Tallahassee, Fla., is close to finishing a medical clinic that will be powered entirely by solar energy. Al Simpler, president, says his company will build a home in Sarasota that will cost an estimated $70,000 and will be powered solely by the sun.

* Bob Laws, a Florida salesman for Solarex, one of the nation's largest producers of photovoltaics, says his sales, while still small, have tripled so far this year, compared to the same period of last year.

* Oil companies have become some of the largest investors in PV cells, because they see that solar energy may be the power supply for the future, says Mark Ethridge, a solar-energy expert for the American Petroleum Institute.

* Many people, especially in California, are looking at photovoltaics as a way to build homes on cheap land that does not have a nearby electric supply, according to Mr. Maycock, who adds that he's seen ''an incredible turnaround'' in interest in solar-generated electricity recently, probably fueled by federal tax credits and higher electricity hookup fees.

Even with the cost of PV cells dropping, however, they still cannot compete with utility companies in providing electricity to standard homes.

Mr. Arenas says the answer is to build unconventional, energy-efficient homes and equip them with the latest in power-stingy appliances.

''We started by surveying the homes in the neighborhood in which we planned to build this home,'' he says. ''We found that the average electric bill was more than $175 a month. So we had to find a system that would add less than that to the monthly mortgage payments of the home.''

The home will cost about $200,000 to build, he estimates. About $20,000 of that figure will pay for the solar-energy system and will add about $200 a month to the mortgage. After subtracting federal income-tax mortgage deductions, however, the monthly cost will be about $140.

On top of all that, Mr. Arenas says, the federal government will give a $4, 000 tax credit for installing this kind of solar-energy system. If the homeowner used that money to reduce his mortgage, the monthly payments would be even lower.

The advantage of putting all the energy costs into the mortgage, according to Mr. Arenas, is that the monthly amount remains constant for 30 years, regardless of what happens to the price of electricity.

To cut energy use by 70 percent, the Arenas home will generate much of its heat in winter with solar energy concentrated in a greenhouse built on one side of the house. Cooling in the summer will be aided by earthen berms insulating two sides of the home and by awnings that will shade the windows from the sun's rays.

The house could be cooled with a very small air conditioner, Mr. Arenas says, and the latest appliances can run on one-tenth of the power of older units. If electric consumption can be reduced by that much, why bother to buy expensive photovoltaic cells to produce electricity?

''We are looking at using an energy source that will not increase in cost - period,'' Mr. Arenas says. ''The system would not tie into the electric-power grid, and therefore would not contribute to the peak energy demands that force utilities to build more expensive power plants. It's a combination of self-interest and community interest.''

What happens when the sun doesn't shine?

The house will have 60 six-volt batteries in the garage attic that would provide enough electricty for the house even if the skies are overcast for five days, Mr. Arenas says.

The builder is also installing a small propane-gas generator as a backup, but he predicts it will never be needed.