How sunshine turns into hot water in St. Paul


It’s a well-known experience. Dip your toes in Spring Lake and you’ll see that the shallow water of the lake is usually warmer than the deep water. This is nature’s way of solar water heating. But sunlight is not only useful for heating the Minnesotan lakes. In basically the same way, it may heat domestic hot water.

“It’s phenomenal,” says Greg Schmidt about the solar hot water system (solar thermal) that he installed at his house a few years ago. Schmidt is one of the pioneers using solar energy in the Twin Cities. Starting with solar electric panels on his garage in 2000, he began generating electricity. After he caught the solar bug, he continued to add renewable energy. Today, his solar hot water system consists of four evacuated solar collecting tube arrays on the south roof of his house. As part of the Solar Energy Tour, organised by the Minnesota Renewable Energy Society, Greg Schmidt opened his house October 6 to visitors interested in solar energy.

A simple water heating system pumps cold water to the collector and the heated water flows back to a collection tank. The tubes carrying the water to be heated are attached to an absorber plate which is painted black to absorb the heat. As heat builds up in the collector, it heats the water passing through the tubes. Finally, the heated water is transferred to a storage tank. Besides these direct-circulation systems, other systems pump heat transfer fluids through the collectors. Heat exchangers transfer the heat from these fluids to the potable water. Besides the supply of domestic hot water, solar panels also supply water to a hot-water central heating system, using in-floor radiant heat and radiators.

Depending on the sunshine, Greg Schmidt’s 355 gallon storage tank in the basement supplies hot water for washing and bathing of about 25 degree Celsius (77 degrees Fahrenheit) each day. Sunny days give the best performance, but the water will heat up even on cloudy days. Solar heated water is boosted to a higher temperature by a gas heater. Although some gas heat is used, the solar heat reduces the amount of gas needed.

“I’m very interested and I’m slowly adapting to the idea of using solar thermal for my house,” says James Madland, one of the Solar Tour visitors. As energy prices go up, saving money is one incentive to use solar hot water, “but the bigger drive is environmental reasons,” says James.

As a matter of fact, it seems difficult to estimate the final economic profitability of solar hot water systems. “It’s hard to do the math, since every day, every month and every house is different,” says Greg Schmidt. Justin Eibenholzl, the environmental coordinator for the Southeast Como Improvement Association, indicates: “Right now, it’s for people wanting to do the right thing for environment. But as energy prices increase, the payback will be earlier and the system much more affordable.”

A federal tax credit applies to solar hot water systems, which rebates 30% of the system up to $2000 for residential installations. But the rebate programs are usually temporary, and this one may expire next year. “I’m always in the pool when the water is out,” says Greg, who missed out on the rebates.

He thinks that the local government should be more supportive. Unfortunately, there are no local or state incentives for solar hot water systems yet, except that you don’t have to pay any state tax on the equipment.

Although the solar upgrade of the Schmidt residence is done, but there is still work left. As a further step to improve his energy bills, Greg Schmidt wants to replace all the “energy pigs” of the household. Since old refrigerators, fridges and washing machines require much current, buying new energy-saving machines will be a profitable investment.

Having examined how sunshine is turned into hot water, the participants of the Solar Energy Tour are impressed. “I’m getting excited,” says Madland. Maybe he will be the next solar energy user in the Twin Cities. But for sure, in the future, when taking a hot shower in the morning, he will be thinking of yesterday’s sunshine.

Julia Degen is a student at Hamline University and an intern with the TC Daily Planet.