On any morning, when the sun has risen high enough to steam through the windows of the Cambridge Altnernative Power Co. here, the music begins. The tune is "Edelweiss," which issues forth from a small acrylic-covered music box set in motion by the arrival of the light.

In Florida, not far from the Kennedy Space Center at Cape Canaveral, a pot starts to perk within minutes of the morning sun's striking the southfacing roof.

What powers both the music box and the pot is sun-generated electricity. A single solar cell, or photovoltaic cell, to give it its more technical name, generates the power for the music box while 5,880 cells power the pot, refrigerator, stove, air conditioner and every other electrical appliance in the house on the grounds of the Florida Solar Energy Center.

Solar cells are solid-state devices that generate electricity when struck by light. The brighter the day, the more electricity is produced, even in the wintertime. So, even on a bitterly cold but clear winter day, the solar cell remains an effective power-generating device.

While the music box is an interesting conversation piece and a valid example of yet another way in which the sun's energy might be tapped, the three-bedroom, two-bath Florida provides a full-scale example of a system that should become economically feasible late in this decade and commonplace in the 1990s.

Already, with funds from the Department of Energy, some residential buildings (as distinct from institutional experiments, such as the Florida Solar Energy Center house) are being fitted with solar cells that will generate the bulk of the household's electrical energy needs. They will be used to monitor photovoltaics under normal, everyday, lived-in circumstances.

One of the first, in Carlisle, Mass., has 1,850 square feet of living space (dining room, living room, kitchen, den, three bedrooms and 2 1/2 baths) and currently is up for sale on the open market. A 1,000-square-foot array of photovoltaic cells, mounted onto racks and set on the roof, will provide some 86 percent of the electricity -- or 9,500 kilowatt hours a year -- needed to power this large home.

In a sense, then, the space-age technology of generating electricity directly from sunlight finally has come down to earth. As yet, the problem blocking mass consumer use is the initial installation cost -- about $100,000 for the powerful system on the Carlisle home. But, because of the progress made since solar cells first were developed to power spacecraft and the promise of continuing progress, many forecasters believe photovoltaics will compete with conventional power generation before this decade is out.

A $100,000 installation such as this could price out at perhaps $7,000, they suggest.

Some optimistic DOE forecasts suggest this might come about as early as 1984. Speaking to public utility executives in California last year, Paul Maycock, branch chief for photovoltaics in the Department of Energy, publicly predicted that photovoltaics will be cost-effective (when subsidies and tax credits are considered) by 1984, and by 1986 purely on the basis of comparative costs.

Others consider this a too-optimistic view, but there is general confidence within the industry that the target will be met by the decade's close.

Even now, in remote areas far from power lines, photovoltaics is considered competitive with home diesel generation. Sandra Dickson, on Monhegan Island off the cost of Maine, has proved that. With no utility-supplied power, the island's residents, for the most part, rely on diesel-powered generators to meet their needs. But not Dickson. She draws all the power she needs for house lights, the TV and stereo from a small system that cost $2,400 (before tax credits) to install.

These are some of the advantages photovoltaics can off the nation:

Solar cells promise vast energy savings. Individual homes will generate the bulk of their electrical power needs. On a large scale such home-power generation could save up to 10 percent of the nation's energy bill and may well eliminate a need for additional nuclear power plants.

Solar cells are energy efficient. Little, if any, of the electricity generated on the roof of your house will be lost before it is used to power your vacuum cleaner, washing machine, blender or range. In contrast, only 29 percent of the energy in fossil fuel used to generate electricty reaches your home as usable energy. Some 71 percent, a quite unacceptable level of waste, is lost in conversion, transmission and distribution.

They are pollution free. The widespread use of photovoltaics would dramatically lower the nation's pollution load, reducing burned-fuel emission from coal- or oil-burning plants and radioactive-waste accumulation from atomic power plants.

They have a proven track record both in space and in as yet isolated applications on the earth's surface.

They are durable. In calculating the cost-effectiveness of solar power generation, the photovoltaic system is given a life expectancy of 20 years.

In other words, the initial cost of an installation, when divided by 20 years, should come out to equal or less per month than a standard utility bill. But, barring violent hail storms or other inflicted damage, there is every reason to believe they will last for much longer than that -- a lifetime, in fact -- as there are no moving parts to wear out and the materials will not degrade in the atmosphere.

The Carlisle home is designed to produce about 7.3 peak kilowatts of electricity (when the sun is most advantageously placed in the sky) for a total of between 20 and 30 kilowatt hours during an average New England day. A similar system in the dryer Southwest would produce some 10 kilowatt-hours more a day. This means that while the New England home would produce more than it would need over a year.