THE SECRETS TO THE SOLAR SYSTEM The thermal-solar system (left) consists of an 800-gallon water storage tank, a maze of glass tubes, and copper bulbs and receptacles that transfer heat to water. The sophisticated tubing is what "transformed the industry,” says homeowner David Hall. “Previously, water had to pass into and out of each tube.” If a sequence of cloudy days causes the temperature in the shed to drop below 120 degrees, a small demand-style heater warms the water in the pipe as it returns to the house.