Thursday, August 13, 2015

Solar Thermal, the Other Solar

Thursday, March 21, 2013 9:34 AM
Solar thermal can be used to heat hot water and even heat homes. But the technology is most commonly used to provide cheaper hot water than can oil or conventional electric. For Ben Mailloux of Belfast, the payback has been considerable. After having his three-panel system installed in 2011, Mailloux says he cut his oil use by two-thirds in the first year, saving about $1,200.

"I'm surprised that we don't have at least some requirement to put solar hot-water systems in every house in Maine," said Mailloux. "For the amount of money that it's saved us in one year, it's well worth it."

There are different types of solar hot-water systems. Direct-circulation systems circulate water to solar collectors on the roof, where it is heated by the sun and then sent back to a tank or used directly. These are more commonly used in temperate climates, due to the risk of freezing. Closed-loop systems use a type of antifreeze solution that transfers heat from the roof solar collectors through a heat exchanger to the water storage tank. Passive-solar hot-water systems move water to the tank through the natural convection process, while forced-circulation systems use electric pumps. In closed-loop pump systems, an electronic sensor automatically turns on the pump when the collectors on the roof are hot enough to heat the water. The antifreeze solution is then pumped down to the storage tank, where it runs through a heat-exchange coil, transferring the heat to the water. Solar hot-water systems usually have some kind of boiler or electric backup for when sun power isn't coming in, particularly in the winter months.

Economic Benefits?

Solar hot-water systems are generally recommended for households of over three people consuming the amount of water produced in a typical 80-gallon tank. According to Efficiency Maine, for a family of three, with a solar thermal hot-water system providing 70 percent annually, the cost is about $164 a year. Comparatively, a standard oil boiler with an indirect tank is about $675, and natural gas with a direct-fired tank is around $378 a year. Those in the industry estimate that the payback time for solar hot water is about six to eight years, but it depends how much the household's water usage is. Unlike solar electric systems which can store energy credits, solar hot water has to be used within a certain number of days or the heat is lost. In the summer months that means there can often be a surplus. For an average family, the cost of solar hot water installation is around $4,700 to $5,500 after state and federal incentives. The warranty on the systems runs about 10 years, but they are expected to last at least 20 years.

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