On a recent visit to Yunnan Province in southwest China, I was pleasantly surprised to see solar water heaters on countless home and building rooftops, even in remote rural villages. These installations, featuring an array of tubes and a storage tank, use the sun’s rays to produce hot water.
Today, China is the world leader in solar water heater (SWH) production and installation, but SWH is now catching on in the U.S., too.
The California Public Utilities Commission in January launched the California Solar Initiative Thermal (CSI-Thermal), a $350 million incentive program for solar water heaters. The goal of CSI-Thermal, which begins in May and runs through 2017, is to install 300,000 additional solar water heater systems by 2018. It is expected to eliminate 100,000 tons of greenhouse gas emissions each year.
U.S. Sen. Bernie Sanders (I-Vt.) followed California’s lead in February by introducing the . Modeled after CSI-Thermal, the bill would provide rebates to cover up to half the cost of 10 million new solar power systems and 200,000 solar water heater systems.
With water heating the third largest energy expense in most homes, solar water heating is a green and cost effective way to produce hot water and can cut annual hot water bills in half.
How SWH Systems Work
Solar water heater systems have solar collectors and a storage system; active systems have circulating pumps and controls, while passive systems depend on convection to move the water from the collectors to the storage tank as it heats up.
For residences, there are three types: Flat-plate collectors, which are insulated boxes with a dark absorber plate made of metal or polymer under glass; integral collector-storage systems (ICS) or batch systems, which consist of one or more black tanks or tubes in an insulated, glazed box; and evacuated-tube solar collectors (the type I saw in China) feature rows of glass tubes with metal absorber tubes attached to a fin whose coating absorbs solar energy.
Active solar water systems can be either direct circulation systems, which use a pump to push water through the collectors then into the home, or indirect circulation systems, which use pumps to circulate a nonfreezing heat transfer fluid through the collectors and heat exchangers, which heats the water. The latter is better for areas where freezing temperatures occur.
Passive systems are simpler, less expensive and may last longer, but are not as efficient. There are two types: ICS and thermosyphon systems that position the solar collectors below the storage tank, allowing warmed water to rise into the tank. Solar water heaters are used with a conventional storage water heater, usually natural gas or electric powered, as a backup for cloudy days or in case of increased demand.
The U.S. Department of Energy estimates that installing a solar water heater can reduce a home’s water heating bills between 50 and 80 percent, while reducing CO2 emissions by 4,000 pounds each year.
The payoff can be significant.
Monique Hanis, a spokesperson for the Solar Energy Industries Association (SEIA), estimates that the SWH system she installed at her Arlington, Va., home handles 25 percent of her water use and saves her $400 a year. “And even though my kids are now teenagers and are taking more and longer showers, my bills have gone down,” Hanis said.
With the variety of federal, state, city and utility incentives now available, and the savings on water heating bills, solar water heater systems can pay back their investment fairly quickly.
The American Recovery and Reinvestment Act (ARRA) offers a 30 percent tax credit for residences on the cost and installation of solar water heaters. The , available through 2016, does not apply to swimming pools or hot tubs, and requires that the system be certified by the Solar Rating and Certification Corporation.