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Solar Water Heating

Posted on Nov 11 2008 by Alex Wilson

Brattleboro, Vermont is fortunate to have a long history with solar water heating. When I moved to the area in 1980, the company Solar Applications had been installing solar hot water systems for five years, and a spin-off company, Solar Alternatives, was manufacturing quality flat-plate solar collectors—many of which are still in use in the area. While Solar Alternatives closed down in the 1980s with falling energy prices and the end of solar tax credits, Solar Applications, has continued to install and service solar water heating systems for more than thirty years.

Frenchman Alain Ratteau, who founded Solar Applications in 1975, sold his company this year to Andy Cay, and it has been renamed Integrated Solar Applications. When interest in solar waned in the mid-80s, my friend Alain shifted most of his focus to oil or gas space heating (specializing in the more sophisticated systems), but I was always impressed that he maintained the company name Solar Applications and maintained a deep commitment to renewables. Alain works with the new company and is helping to establish it as a premier provider of not just solar water heating systems, but also solar space-heating, solar-electric, micro-hydro, wind, and biomass. Visit the company on Spring Tree Road (past the Marina Restaurant).

Most solar water heating systems consist of one or more flat-plate collectors mounted on a roof or separate rack through which potable water or another heat-transfer fluid is pumped. This fluid circulates to a storage tank where the solar-heated fluid passes through a heat exchanger to heat water in the tank. With “closed-loop” systems, the heat-transfer fluid—usually a mix of water and nontoxic propylene glycol antifreeze—remains in the collector all the time. In other systems, referred to as “drainback systems,” plain water is used in the collector, and when the collector gets too cold, the water drains back into a small tank in the house.

Other systems operate passively by “thermosiphoning” (the principle that heated water rises naturally). With this approach, more common in warmer climates, potable water in the collector naturally circulates into a storage tank located above the collector.

A fairly recent option with some solar water heaters is a solar-electric (photovoltaic) panel to power the circulation pump. In this case, the PV panel serves as both the pump’s energy source and the controller. When the sun is shining and the PV panel is generating electricity, the pump operates and water is heated; when there isn’t enough sunlight to power the circulator pump, the solar water heater shuts down—it’s a simple control system.

No matter what type of solar water heating system is used, in our climate it is generally used as a “preheater” for a conventional water heater—which can be either a storage-type water heater or an on-demand (tankless) water heater. The standard water heater, which could be electric or gas-fired, boosts the water temperature as needed.

Don’t expect a solar water heater to provide all your hot water. A well-designed and properly sized system in our climate may provide all of the summertime hot water, but it is likely to provide less than half of what you need during the winter months. Some homeowners combine solar water heating with a heat exchanger in a wood stove—so that they’re heating their water primarily with renewable energy sources year-round.

To maximize the percent of hot water your family can obtain from the sun, it’s important to conserve hot water use: install low-flow showerheads and faucet aerators; insulate your hot-water pipes; buy a top-efficiency dishwasher and only wash full loads; and consider washing clothes in cold water.

Installers of solar hot water systems in the area include Integrated Solar Applications in Brattleboro (257-7493), Gary MacArthur in Marlboro (257-7026), John Kondos of Home-Efficiency Resources in Spofford (603-363-4505), Green Energy Options in Keene (603-358-3444), and the Greenfield Solar Store (413-772-3122). Somewhat farther afield are groSolar in White River Junction (802-374-4494, www.grosolar.com) and Solar Works, Inc. in Montpelier (800-339-7804, www.solarworksinc.com).



Image Credits:

  1. SCHÜCO, LP

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