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
Open-loop systemPros: Heats more efficiently than a closed-loop system; good freeze protection when installed correctly; uses water rather than antifreeze (which costs money and can break down over time)
Cons: Requires more energy to push working fluid into heat collectors; piping layout is critical; requires drainback tank
Flat plate collectorPros: Simple; technology has not changed in 30 to 40 years; doesn’t break easily
Cons: Loses heat in high winds; heavier than evacuated tube collectors
Evacuated tube collectorPros: Doesn’t break easily; most efficient in certain environments; transfers and collects more heat; retains heat even in high winds
Cons: Complex system with 20 to 30 tubes; if one part breaks, system must be replaced; generally used only with closed-loop systems
Need More Incentive?
The cost of solar hot water systems varies dramatically by region but often can be offset by incentives and tax breaks. In Oregon, for example, incentives and tax credits can cover up to 70 percent of the cost.
Every state differs, but it’s easy to research your state incentives using the Database of State Incentives for Renewables and Efficiency.
"All kinds of different things are out there, depending where you live," says Steve Kalland, director of North Carolina State University’s Solar Center. "We’ve seen everything from tax credits to property tax exemptions to sales tax exemptions."
Some utilities also offer renewable energy credits, Kalland says. "In essence, they’re paying you the equivalent of what you’re saving in kilowatt-hours by using solar."
DON’T forget to check the Database of State Incentives for Renewables and Efficiency website to learn which tax credits and rebates are available in your state.
DO consider a solar-thermal system before a solar-electric system. They’re cheaper and generally offset more electric generation.
Lori Tobias lives on the Oregon Coast with her husband and two dogs. She’s a staff writer for The Oregonian and has written for Natural Home for nearly a decade.