Dip Into Solar Water Heaters

Solar water heaters are the most efficient way to harness the sun's power to reduce your home's carbon emissions.


| January/February 2010


More than 100 years ago, William J. Bailey patented the first solar water heater, the Day and Night. Relatively affordable and reliable, the heaters were a lot more efficient than cooking a big pot of water on the woodstove. In the United States, solar water heaters were eventually eclipsed by gas and electric water heaters, but in other countries solar water heating technology, also called solar thermal, thrived. Now seeing a U.S. resurgence, solar thermal is one of the simplest and most-efficient means of saving energy, says John Perlin, co-author of A Golden Thread: 2,500 Years of Solar Architecture and Technology (Cheshire Books, 1980).

System specifics for solar water heaters

Solar water heaters can use either a closed-loop or an open-loop system. In a closed-loop system, rooftop solar collectors heat a nontoxic antifreeze mixture. Once heated, the mixture is pumped to a heat exchanger—or solar tank—through copper tubing, where it heats cold water for use. An open-loop system works similarly but uses water instead of the antifreeze mixture.

Closed-loop systems use less energy and are better suited for houses in which the building configuration requires pipes to be laid flat. It’s crucial that a closed-loop system be appropriately sized for the household—a too-large system results in unused fluid that can damage the system’s mechanics. Open-loop systems heat efficiently and don’t need to be sized as specifically as closed-loop systems, but they require a drainback tank and use more energy moving fluid.

Types of solar water heaters

There are essentially two types of heaters: a flat plate collector and an evacuated tube. “The evacuated tube is generally more expensive,” says Ryan Mayfield, president of Renewable Energy Associates in Corvallis, Oregon, “but depending on where you live, it can really have benefits. Evacuated tubes perform really well in cold, clear climates, like the Rocky Mountain region.”

Evacuated tube systems are complex, Mayfield says. If one of its 20 to 30 tubes breaks, the system must be replaced. “It’s not something you can fix,” he says.

Flat plate collectors are very simple and very robust. However, they lose heat more readily than the evacuated tubes.

Installing a solar thermal system requires plumbing skills and the ability to work with copper. Professional installation takes about two to three days and costs approximately $6,000 to $9,000 for an average residential system, depending on your region and available rebates or tax credits.

Which Solar Hot Water System is Right for You?

Closed-loop systemPros: Good freeze protection; requires less energy to move fluid; pipes can be laid horizontally (if you’re working with rafters)
Cons: Sizing is critical; unused fluid gets stuck in the collector and changes chemically, which can damage the mechanics





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