Solar water heaters were cool in 1980s. They could be again.
In the early 198os, my dad installed a solar thermal panel on our roof in Florida. For a 5-year-old, the big black square looked like a portal into the future. The device, essentially a glass box with metal water pipes running through it, converted sunlight into hot water. By trapping solar energy like a greenhouse, it heated the water to a scorching 180 degrees Fahrenheit. Solar Pv Panel Ground Mounting Brackets Structure
It furnished much of the hot water for a family of four. “We had no trouble with it,” my dad tells me. “It was still working when we sold the house 10 years later.”
But today, hardly anyone is using these solar water heaters even as photovoltaic (PV) panels have popped up on the roofs of nearly 4 million American homes.
Unlike photovoltaic panels, which can power your home, solar thermal panels are mainly used to heat water. But they’re smaller and more efficient. The technology converts 60 to 70 percent of the sun’s energy into heat. Even the best photovoltaics, which generate electricity, only achieve 24 percent efficiency.
Now, a new generation of solar water heater manufacturers is hoping subsidies under the Inflation Reduction Act, and growing interest in net-zero emissions, will reignite their growth.
Theoretically, solar thermal offers a big opportunity to slash emissions. Nearly 20 percent of an average home’s energy is used to heat water, and nearly 50 percent globally, according to MIT. By adopting solar water heaters, the average household can keep 2 tons of carbon dioxide out of the atmosphere, the equivalent of not driving your car for four months, estimates the Environmental Protection Agency.
Solar water heaters can also save money, cutting the average utility bill by $400 to $600 per year, the Energy Department estimates.
Is solar thermal right for you? Here’s what you need to know.
In 1909, the first solar thermal water heater was commercialized in the United States. The “Day and Night Solar Heater” featured a coil of copper pipe in an insulated box under a pane of glass. As water in the pipes was heated by the sun, it flowed into a storage tank supplying the house.
The basic principles haven’t changed much in the intervening century. Solar water heaters, perhaps the simplest way of turning the sun’s energy into heat, are made from little more than copper, aluminum and glass. Water in these solar collectors routinely reaches temperatures around 180 degrees Fahrenheit and can soar as high 400, before being mixed and stored in a standard water heater tank. A backup gas or electric heating element provides supplemental heat.
Back in the 1980s and 1990s, solar water heaters were poised to be a major player in America’s energy mix. Taking advantage of generous federal incentives, Americans had installed nearly 1 million solar thermal systems by 1990, reports the University of Minnesota’s Institute on the Environment. Photovoltaic solar panels, meanwhile, were still prohibitively expensive and relatively rare.
Over the next few decades, the popularity of photovoltaics exploded as prices fell and the government poured millions into incentives for homeowners. But several factors doomed solar thermal’s national expansion: unskilled installers and shoddy designs, plunging natural gas and solar photovoltaic prices, and, crucially, the end of tax incentives in 1986 under the Reagan administration. By 1990, the industry had nearly collapsed.
Only about 370,000 solar thermal systems were operating in the United States by the end of 2021, according to the International Energy Agency, many of them on larger commercial buildings.
Wherever the sun comes out, solar thermal collectors work well. Since they can cut fuel consumption to heat water by 50 percent to 70 percent, other countries are embracing the technology: Almost all new residential buildings in Israel must include solar thermal, while in countries as far north as Canada and Denmark, solar thermal energy warms millions of homes with district heating systems.
Yet these systems represent a tiny fraction of the potential, supplying 0.4 percent of today’s global energy demand for domestic hot water.
“It’s always been about money,” says Adam Chrisman, president of SunEarth, a California-based solar thermal manufacturer. “Where the cost of heat energy is high, there is a solar thermal market. Where it’s not high, there isn’t.”
Take Hawaii. The tropical archipelago must import all its fossil fuels to burn for electricity. With electricity retail prices nearly triple the U.S. average, and constant sunshine, the state’s utility estimates one in four single-family homes in Hawaii now heat their water with the sun.
But elsewhere in the United States, energy prices remain relatively low, making it hard for solar thermal to compete, even with Inflation Reduction Act incentives and other discounts and tax credits (a searchable database of incentives lets you search by state), that can cut the price of a solar thermal system by about half.
For Martin Morehouse of Sun Light & Power, a developer with more than 3,000 solar projects of all kinds across California, that’s darkened home solar thermal’s prospects in the United States.
“When I was getting started around 2007, most of our [solar thermal] customers were residential,” he says. “But the market has changed, now it’s commercial.” Larger buildings can take advantage of economies of scale.
The main reason is economic. Over the last two decades, the price of solar photovoltaic panels, natural gas and heat pumps have all fallen dramatically. The prices for solar thermal materials such as copper pipes have risen. In most cases, the economics now favor photovoltaics for single-family homes.
“Our recommendation for residential customers interested in looking at solar thermal is adding more solar PV, and a heat pump water heater,” says Morehouse. The big exception is pool heating. Thanks to modest temperature requirements, low-cost plastic pipes and high demand during warm summer months, “they’re still a fantastic opportunity,” he says.
Are you likely to see solar thermal back on America’s roofs?
Maybe, but it is likely going to require more than a dollars-and-cents calculation. The United States enjoys an abundant supply of cheap and reliable gas, unlike many places in Europe and Asia. But the cost of solar thermal could look like a bargain if we consider increasingly unreliable electric grids and the cost to the climate from burning fossil fuels.
“You’re buying energy security for the future,” argues SunEarth’s Chrisman.
And for many homeowners, like my dad, the idea of getting nearly all their energy from the sun holds enormous appeal. He already wants solar power back on his roof. The home he bought about a decade ago came without it. So when he replaces the roof, he plans to add a couple of solar photovoltaic panels and batteries.
He is even giving solar thermal a second look.
Where does it work best? Sunny climates, even if it’s cold. The panels for solar water heating systems are angled to capture the most energy from Alaska to Arizona. To avoid freezing in subzero temperatures, many systems use glycol, an antifreeze fluid, to transfer heat to water inside a tank.
Chrisman at SunEarth has a rule of thumb: Solar water heaters can be effective anywhere below the 55th parallel (just north of the Canadian border) with high energy prices. But finding a skilled contractor can be difficult if you’re not in one of the handful of states with a history of solar thermal.
At the moment, he estimates, home solar water heating for single-family homes can theoretically pencil out in places along the West Coast and Northeast if energy prices are at least 20 cents per kilowatt hour or $1.50 per therm for natural gas, slightly above national averages. While the technology works elsewhere, the payback period — not counting emissions and its cost to the climate — may not materialize quickly or at all.
How much will I save? It depends. A typical single-family residential system costs $4,000 to $10,000. But that can nearly be cut in half with a 30 percent federal tax credit and other incentives.
Studies have found the payback period can range from five to 15 years (or even two years in Hawaii). Systems last 20 years with modest maintenance, and have been known to operate for more than 30 years.
The economics can be especially attractive, says the Energy Department, if you’re financing them as part of a 30-year mortgage. That effectively adds a monthly cost of $8 to $17. If monthly savings are greater, a solar investment is immediately profitable. The DOE has a more technical calculator here.
What type of system should I buy? Solar water heating systems are either active, with circulating pumps and controls, or passive, with hot water naturally flowing into the plumbing system. Systems that heat air directly also exist. You can explore the different types here.
12 Volt Solar Panel Price To search for products and rebates by Zip code, the EPA has a simple tool. Since the results aren’t easy for first-time buyers to parse, hiring a contractor to get a quote is crucial. Searching for “solar thermal water heating contractors” will usually turn up experienced contractors.