The cost of equipment to generate electricity with solar energy will be cut in half by a new installation to be built this summer by Solarex Corp. of Rockville.

The 250-kilowatt solar electrical generator will be part of the largest solar power project ever, a community college complex in Mississippi County, Ark.

In bidding on the Department of Energy demonstration project, Solarex said it could supply concentrating solar cells that would cost less than $6 for every watt of electricity they produce.

Previous solar electricity generating gear has cost at least twice that much, although Solarex's $6-a-watt cost is still several times the cost of conventional power plants, which cost around a dollar a watt to build.

But Solarex officials say the technical innovations that allowed them to cut costs in half in one jump are other milestone en route to the Energy Department's goal of bringing the cost of solar electricity down to $2 a watt by 1982 and to 50 cents by 1986.

Solar cells cost $500 a watt when Solarex was founded in 1973 by Dr. Joseph Lindmayer and Dr. Peter Varadi, who are still its top executives.

"All the government studies said it would be impossible to bring costs down to 1/1000th," admits Lindmayer.

He and Varadi worked on solar cells for Comsat, which uses them to power its communications satellites. Because Comsat's charter prohibits down-to-earth projects, the two scientists started their own firm to pursue photovoltaic research and development.

Barely five years later, Solarex is the biggest manufacturer in the tiny solar electricity business. In a plant off I-270, its 150 workers produced $3 million worth of solar cells last year, out of an industry output estimated at $10 million.

Besides making the biggest solar generating unit ever, Solarex also makes some of the smallest - the solar cells that power watches, calculators and flashlights.

"The thing that makes us unique is that we make competitively-priced cells and are very good at research and development," said Anthony Clifford, assistant to the president.

Soar cells are thin wafers of silicon crystals that emit a tiny electrical current when the sun shines on them.

Although the phenomenon - called the photo-voltaic effect - has been known for a century, it was not until 1955 that Bell Laboratories demonstrated workable solar cells and not until the space program that solar cells found a use.

With sky's-the-limit budgets, space scientists powered their mechanical moons with solar rays that cost $500 a watt - generating emough power to light a 100-watt bulb required a $50,000 investment.

Research has brought the cost down and raised the efficiency of solar cells so they now can turn about 14 or 15 per cent of the solar energy they receive into electricity.

Solarx's state of the art system is the first full scale use of concentrating solar cells. Since the silicon cells are the most costly part of solar electricity generating gear, Solarex reduced the number of cells needed by concentrating the sunlight on the cell surface.

It's done with mirrors, curved reflectors with a mechanical system that tracks the sun across the sky, focusing bright rays on the cells. The reflectors and tracking gear - built by Honeywell, Inc.- will amount to about half the cost of the system.

With concentrators the cells receive up to 40 times normal sunlight - "40 suns" as solar scientists put it.

Solarex began making concentrator cells 2 1/2 years ago getting a head start on competitors which enabled it to win DOE's contract for the $1.1 million solar generating project at the Arkansas community college.

The college will be completely solar powered, using various kinds of solar collectors to make electricity, heat buildings and water and run air conditioners. It will also test new batteries for storing solar-generated power and computerized control's for the solar systems.

"Nobody has ever merged all these elements," explained Lindmayr, who said there is a blacklog of technology that has never been fully utilized. "Now we will learn how to put the pieces together."

Solarex will start producing the cells this spring for the system, which will use 300 concentrator units, each 16 feet long. The federal contract calls for an output of 250 kilowatts, but Clifford said the Solarex system will put out about 360 kilowatts on clear days.

Lindmayer said dconcentrating cells appear to be the best method of producing immediate reductions in solar generating costs and opening up the market.

When costs get into the $2 range "all sorts of markets appear," he said. Now solar cells are used only in situations where no cheaper source of power is available.

They power navigation lights on buoys - ending the need for replacing batteries and run remote weather stations on mountain tops - saving the cost of stringing cables for miles.

Lindmayer forsees highway lights powered by solar cells, irrigation pumps run by the sun, and extensive use of solar electricity in developing countries which lack interconnected electrical systems.

Solarex, he noted, has doubled in size every year since it was started and probably can maintain that pace as the industry expands with encouragement from federal subsidies.

Owned by about two dozen local investors, the company ideally ought to go public someday, but that isn't possible in the current stock market, the founder said.

Solarex is working on more advanced concentrator systems under a $287.000 contract with the Department of Energy's Sandia Laboratories. Contract research brings in about $1 million of its current annual sales.

The Sandia contract includes developing a high technology manufacturing process capable of turning out large quantities of solar cells.

Even though it is the biggest manufacturer in the business, Solarex's production basically is a hand assembly operation.

Solar cell technology is changing too fast for automation, Lindmayer explained. By the time engineers could design and build an automated assembly line, the product it would produce be obsolete.