Overlooked but not forgotten, solar thermal deserves a second look

Wall-mounted evacuated tube solar thermal system

When Kevin Virkler’s daughter Megan takes a shower—the kind of long, hot shower that only an adolescent can take—he doesn’t worry anymore about how much warming up all that hot water is going to cost.

The reason? Solar hot water heating.

Solar hot water and heating, sometimes called solar thermal or, also, solar heating and cooling (because some cooling technologies are activated by heat), is a technology that’s more than 100 years old, invented first in Baltimore in the 1890s. Passed over in many of our attentions by its sexier cousin - solar photovoltaics, solar thermal has much to offer. In fact, a recent report by the Solar Energy Industries Association estimates that solar heating and cooling (SHC) in the U.S. could, by 2050:

  • Generate almost 8 percent of the nation’s heating and cooling.
  • Create more than 50,000 good paying jobs.
  • Save $61 billion annually on energy.
  • Cut carbon dioxide emissions by 226 million tons every year(the equivalent of taking 64 coal-fired power plants offline for good).
How it works

Solar hot water heating, and SHC in general, are based on a simple principle, one we know well from parking our cars in the hot sun. “Something left out in the sun is going to get hot. And if you put glazing over it, that’s going to trap the sun’s heat,” explains Tim Merrigan, a solar thermal expert from the National Renewable Energy Laboratory.

Residential solar thermal collectors, the most common type of solar thermal technology in use today, are pretty simple devices, usually just 4’ x 8’ black, metal boxes with glass covers that are mounted on roofs. Water or another liquid is piped through the box, to pick up the trapped heat. The hot water can be stored in a water tank; other liquids can be used to transfer that heat, or can power radiant heating systems or heat air to heat buildings or use as process heating in industry.

An overlooked American invention gets a second look

In the late 1800s and the early-to-mid 1900s, solar hot water collectors were so popular in California and Florida that by 1897, one-third of all Pasadena homes had solar hot water; in Miami, shortly after World War II, half the homes did. Cheap natural gas put an end to that era. Natural gas is cheap, though, because its market price doesn’t include the full social and environmental costs of drilling, transporting and burning the fossil fuel.

Today, natural gas' low price remains an impediment to wider-scale adoption of solar thermal in the U.S., and solar hot water in particular. But opportunities for cost savings on residential hot water and other thermal uses abound. In particular, more than 48 percent of American homes heat their hot water with something other than gas — usually expensive fuel oil, propane or electricity. And, in those cases, the cost savings with solar hot water can be tremendous. Solar thermal can provide hot water and heat at an energy rate equivalent of 6 cents per kilowatt hour, while oil and electricity cost 9 cents and 15 cents, respectively. (Delivered natural gas today costs only 4 cents.)

Helping further lower the cost of solar thermal are the federal 30 percent solar tax credit, which covers both residential and commercial/industrial systems, and a number of state and local incentives and rebates. In Hawaii, which already requires solar hot water heaters on almost all new housing, and whose primary energy resource comes from expensive oil imports, a 2014 on-bill financing program will allow renters, homeowners and small businesses to install solar thermal on existing homes and businesses with no upfront costs; they’ll pay for it through the energy savings on their utility bills while helping the state reduce its economic vulnerability to expensive oil imports. Lakeland Electric, a central Florida municipal utility, installs solar hot water systems in area homes, charging customers only a fixed monthly fee. (The equipment belongs to and is installed and maintained by a local vendor.)

Brian Abels of Energy Optimizers USA standing next to a company installation of evacuated tubes in Ohio
Businesses, schools, homeowners and more all stand to benefit

Solar thermal scales nicely, too, and is ideal for large users of hot water—schools, hospitals, hotels, car washes, indoor and outdoor pools — think: your local YMCA. “For our clients, solar thermal’s the most cost-effective way to move forward with financial and environmental stewardship,” explains Brian Abels, director of engineering at Energy Optimizers, USA, a Tipp City, Ohio energy efficiency company. The company has installed solar hot water systems at four or five Ohio schools and prisons in the last year. Abels notes that hot water often accounts for about 20 percent of an average school’s energy costs and the savings can be huge. (For the average American home, hot water accounts for 14-18 percent of energy use, costing between $400-600 a year.)

The US military is using solar thermal on military bases to cut costs as well as greenhouse gas emissions. And a Frito-Lay factory in Modesto, California famously uses solar thermal to heat the oil used to cook its SunChips.

Solar thermal evacuated tubes on numerous homes in Shanghai, China
Establishing new policies to scale solar thermal deployment

The U.S., however, sits low in the international rankings for solar thermal per capita—36th in the world—even though the technology was pioneered here and many systems and components are manufactured in the U.S. World leaders include Cyprus and Israel, Austria and Greece. But policy changes, including financial incentives aimed at displacing more polluting oil-based heating or more expensive electric water heating with solar thermal are a good start. States and localities can also help get the solar thermal market to scale by streamlining permitting processes and establishing binding long-term solar thermal deployment goals to build customer and investor demand.  

Such programs in New York state, along with the federal tax credit, helped cut the cost of the solar hot water system on Kevin Virkler’s home significantly. It should last for 25 years but will likely pay for itself in three, despite its location just an hour south of the Canadian border, in the Adirondack Mountains. After that, his hot water will likely be free. That’s a good thing, explains Virkler. Including his daughter, “there are three of us in this household, and we take a lot of hot showers.”