By JOHN COLMEY   KUALA LUMPUR

EOH SIANG TEIK DIDN'T SET OUT TO DESIGN THE WORLD'S most powerful solar water heater. He just wanted to go trekking. As an architecture student in Scotland in 1979, the young Malaysian was looking for a way to prolong a visit to Nepal when a local businessman asked him to design a hotel in a rural area with no electricity. His energy-efficient solution won first prize from Scotland's Royal Incorporation of Architects. He returned with his architecture degree and designed 69 rural buildings for the Nepalese government, incorporating solar water heating. "My professors had told me to leave engineering to engineers and be an architect," Teoh recalls. "I was just looking for a way to save money on materials."

That quest resulted in a stunningly simple engineering breakthrough. At the time, there was essentially one way to build solar water heaters, using a 1976 Japanese patent that is still commonly applied today. In that basic design, an array of tubes in a flat glass panel is placed on a slope or roof and connected to a water tank. The water in the tubes is heated by the sun, rises slowly and enters a pipe running across the top of the panel, where it pushes forward and empties into the tank. The circle is completed when cold water is forced out of the bottom of the tank into a pipe running to the bottom of the panel. From there it begins the journey through the panel and back up to the tank again.

Standing on the roof of one his houses in Nepal, Teoh was watching the hot water rise and shoot into a black 55-gallon drum when he realized how much heat was being lost pushing the water through the system. Says Teoh: "The first rule of solar water heating was that the tank was separate from the panel" and connected by a single tube. "I knew there had to be a more efficient way."

There was. After pondering the problem for several years, Teoh designed a heater in which each tube in the panel pours hot water directly into the tank. That shortens the path the water has to travel by nearly a meter and thus slashes the energy loss in transport. Building on the notion of reducing resistance to hot water flow, Teoh's research over the next decade led to several more design improvements. For example, he added an additional lower panel with exposed tubes suspended over a mirror that allows the heater to receive additional sunlight and even work on a cloudy day.

Teoh's solar water heater, which was granted one of three international patents issued by the World Intellectual Property Organization (under the Patent Cooperation Treaty) in 1997, out-performs the competition. It guarantees a water temperature of 60-78 degrees - as opposed to the previous 50-60 degrees ceiling - more than enough for an entire family of five to take two hot showers a day. Unlike other solar water heaters, it doesn't need an electric-powered backup which, on cloudy days, can make operating costs sky-rocket. And Teoh's model can be built using materials available at a local hardware store.

Such simplicity allows the company Teoh has set up in his home, Microsolar Malaysia, to sell heaters for as little as $1,000. That's one-third the cost of a more technologically sophisticated solar model designed by the U.S. National Aeronautics and Space Administration. Teoh's design not only produces hot water without burning fossil fuels, but it operates more cheaply than other solar models. In the first 10 years, his heater costs a family of five $100 annually, compared with $200 for a conventional solar unit with an electric booster and just under that for an all-electric model. "It works," says one of Microsolar Malaysia's 1,000 customers, Affendy Th'ng, a Kuala Lumpur sales executive. Affendy went solar to help the environment and to avoid buying individual electric heaters for his three bathrooms. He now enjoys "a substantial savings on my monthly bill."

More importantly, Teoh's innovation could unlock many more, including solar air-conditioners. Until now, finding an efficient way to use the sun's energy to cool air has eluded engineers because the water temperature must be maintained at an average 75 deg. in order to run existing solar air-conditioning models. Currently, five to eight panels are required to reach that temperature, far too cumbersome and costly for a typical roof, where Microsolar could potentially do it with two to four panels. Many air-conditioners now use a volatile gas like freon, which is known to contribute to global warming. So a freon-free model could be a boon for the environment, as well as an important new industry for Malaysia, already a major manufacturer of air-conditioners.