On A late-winter's day, Bob Shea huddles before a small fire that crackles softly in one of his woodburning stoves. A telephone sits silently by his side on the floor. He hunches forward in a chair. Bob Shea alternately watches the fire and "The Mary Tyler Moore Show" on television. A little of this, a little of that. There's not much to do. Bob Shea is in the solar business.

Where many other solar businesses have failed, Shea, whose Energy Center Inc. is sandwiched into an industrial park on Tyco Road in Tysons Corner, has managed to keep his firm alive. Barely. In the last three years he has sold about 75 solar systems, 30 for heating swimming pools, the rest for domestic hot water. Despite all the ballyhoo about solar as a viable energy alternative, Shea concedes the idea is a little "slow in catching on."

Swimming pool heating is as good a place as any to begin a solar education. Although scientists and government officials sometimes regard swimming pools as a frivolous use of solar energy (swimming pools are not included in energy tax credit laws), more solar collectors are sold to heat pools than for any other reason.

A july 1978 study of manufacturing activity commisioned by the Solar Energy Industries Association, the industry trade group, showed that of approximately 5 million square feet of collectors sold in the first half of that year, 3 million were "low temperature," the industry euphemism for swimming pool collectors. Perhaps this is because low temperature collectors are the cheapest, the most efficient and the easiest to install.

Unlike solar hot water and space heating collectors, low temperature collectors require no "glazing," (glass covering) or insulation. Glazed collectors heat the air or water within them by trapping the sun's radiation between the glass and metal, the so-called greenhouse effect. While these collectors can raise temperatures to 140 degress or more, they also lose much of their heat in the process. Of course, glazed collectors are usually essential for winter use.

The National Solar Heating and Cooling Information Center, the information clearinghouse of the Department of Energy, estimates glazed collectors are only 30 to 50 percent efficient. Low temperature collectors, without glazing, however, raise water temperatures only to about 80 degrees. They lose very little heat to their surroundings, often operating at lower than "ambient" temperatures, or at 70 to 80 percent efficiency.

Although glazed copper collectors are used for pool heating, and some systems are designed to heat both pool and tap water, most experts consider glazing unnecessary for swimming pool collectors only used during spring summer and fall months. This allows low temperature manufacturers to sell solar collectors for considerably less.

Shea distributes swimming pool systems made by a California company called Fafco. In the 10 years it has been in operation, Fafco has produced more than 100,000 collectors and sold them all over the world. The Fafco collector, little more than 1/4-inch thick, is made of black plastic. Dozens of tiny holes perforate the honeycomb inside of the 4 by 10-foot sheet from top to bottom. As the plastic absorbs the sun's rays, it transfers its heat to water circulated by the pool's filter pump, through the collectors and back into the pool.

While collectors may not be needed to heat pool water during the hottest summer months, since the pool absorbs much of the sun's energy itself, a solar system can raise pool temperature up to 10 degrees above normal and extend the swimming season of an unprotected outdoor pool by two to four months, even more in some areas.

"We are swimming in that pool from the end of March, right up to December," said David Pinhey, an elementary school physical education instructor in Annandale, Va. Both Pinhey, 39, and his wife Wendy, 36, are avowed swimming addicts.

Previously the Pinheys needed three tanks - 275 gallons each - of oil to heat their 800-square-foot pool during the year. Although the solar panels, installed by Shea, have been in place less than a year, Pinhey says he already saved one tank of oil.

"I thought it was immoral to burn fossil fuels to heat a swimming pool," said Washington attorney Arthir Birney. Birney says his system, installed by Shea two years ago, "prolongs the season about a month on either side [of the summer]," without any back-up heating.

Robert Adams, a management director at the Department of Transportation, bought a system for his pool in Rockville a year ago. He turned it on again this year at the beginning of May when the water temperature was less than 60 degrees. A week ago, pool temperatures were climbing past 80.

The simplicity of the low temperature collector permits pool owners with basic plumbing and carpentry skill to install it themselves. Shea and his crew can finish the job in a day. A mechanically inclined owner, Shea says, can perform the same task in as little as three days and save about one third on the total cost.

"It was extremely simple," said Morley shamblen, who installed his own system for his 16 by 32-foot enclosed pool in La Plata, Md. Shamblen just happens to be a mechanical engineer at Naval Surface Weapons Center in Dahlgren, Va. Still, he says the job required little more than a drill, a screwdriver and "an understanding of a simple line diagram on plumbing."

Shamblen says the system "did better than I hoped it would do." Before the collectors were heating the pool, he used 250 gallons of oil in just two and a half weeks during the Christmas season. The next Christmas, in a period of more than a month, he used less than 100 gallons with the collectors. And he was heating the pool at temperatures of 80-82 degrees. When Samblen is not circulating the water on those winter days when the pool is not used, the collectors automatically drain water back into pool so they do not freeze and crack.

If now temperature solar collectors represent some of the industry's brightest hopes, they also illustrate some of solar energy's thorniest problems. Few have been on the market long enough to demonstrate durability and warranty claims. Standards for testing have yet to be finished. There is little agreement on which materials are best, or which products represent the most favorable design concepts and how many collectors are enough in different areas of the country.

"Copper is going to be more durable in the long haul," said an engineer at one of the country's largest outdoor testing operations. "But there's a real trade-off. If a manufacturer makes a plastic collector that's cost effective compared to the copper, then you have your druthers. And that happens to be the case.

"There are plastic swimming pool collectors that are satisfactorily durable," he said. "There are some manufacturers who have put out plastic collectors that didn't have sufficient water flow, on one hand, and weren't sufficiently durable. There are some around that will survive for a completely satisfactory length of time, based on the price." But, "You can't really go wrong with a well constructed copper swimming pool conductor. It will just cost more."

"There have been a number of very poor porducts on the marker", says Ken Kauffman, a senior staff scientist at the Franklin Research Corp. in Philadelphia. "One particular problem was that plastic, on exposure to ultraviolet light, tended to fall apart."

When Shamblen bought his first plastic Fafco collectors, in 1973, "it started splitting. I called up to get the repair kit and had so many patches I was patching the patches." Fafco later replaced his panels.

Whether solar will ever fly may well depend on how materials hold up to the elements. Some do not, conceded Fafco president Freeman Ford. The orginal Fafco model, Ford said, used a plastic material from a suncontractor that "turned out to be inadequate . . . We went to our engineering department and asked for a product we could produce ourselves."

The makers of plastic collectors claim copper is subject to corrosion and leaches chemicals into pool water. "That," says W. Stuart Lyman, teachnical manager for the Copper Development Association, the industry's trade group, "is a redherring that's been drawn across our trail all across the country." Although some cases of "green staining" have been reported, Lyman says a survey of 807 installations revealed only 1 percent with staining problems.

Swimming pools with copper solar systems must be carefully maintained. Deviations from recommeded pH levels, and harsh, untreated water, will attack copper parts.

While testing standards for low temperature collectors are being written by such professional organizations as ASHRAE (American Society of Heating, Refrigerating and Airconditioning Engineers) and the National bureau of Standards is currently testing the thermal performance and durability of collectors at its laboratories in Gaithersburg, consumers have no assurance that the collector they buy isn't a dud.

Standards, says Kauffman, "don't say you can't have a shoddy product. They just tell you how to test your shoddy product."

Solar collectors are expensive and how many you need to heat a swimming pool depends on who you talk to. Fafco collectors, 40-foot-square, sell for $170 to $200 apiece. The Pinheys spent about $2,500 for their system, installed. To heat their pool with glazed copper collectors, they would have spent around $4,000, although the copper industry distributes do-it-yourself plains for pool systems to cut costs considerably. They figure collectors for an average size pool at $1,000.

One of Washington's preeminent pool builders, William J. Moeller, recently installed a pool heating system at a Northwest Washignton home. He used five 32-square-foot copper collectors - eight square feet smaller than the Fafco collectors - built by the Revere company, one of the larger solar manufacturers. Revere collectors range in price from around $250- $350, depending on size and amount of glazing. The Grumman company manufactures an unglazed, low temperature collector. They system costs about $3,800 for a 600-square-foot pool, installed.

The sheer volume of water in a swimming pool demands a large area of collector panels to heat it. Conventional wisdom says the area of collectors should be 50 to 75 percent the area of the pool. Some scientists say 100 percent coverage is necessary. This depends largely on northerly latitude, daily amount of sun and exposure to wind. Ideally the collectors face south and are tilted at an angle equal to the latitude minus 10-15 degrees (or about 30 degrees in the Washington area).

Most authorities agree that the cheapest way to save heat in a swimming pool by far is to use a cover. One type of clear double-wall plastic cover remains over the pool during the day to help the water beneath it absorb the sun's rays. It's folded back for swimming. Another type is spread out at night to contain heat the pool absorbs during the day but would otherwise lose through evaporation in the evening. While some covers may not last more than a few seasons, those who have used them say they usually pay for themselves in fuel savings - around $300 to $400 for an average pool.

Other systems roll up the cover automatically and cost considerably more. Moeller estimates he has installed 300 automatic pool covers of reinforced viny1 in the Washington area in thelast 12 years, at an average cost of $3,000. CAPTION: Picture, Mindy Adams' pool is heated by solar collectors on roof of house. by Tom Allen - The Washington Post.