Interest in Solar Water Heating Spreads Globally

SAN FRANCISCO — To produce milk and cheese for the world, dairies need cows and grass. But they also go through enormous amounts of hot water each day to flush out milk lines and clean other equipment. And so farmers on King Island, part of the Australian state of Tasmania, were delighted when workers began installing solar arrays on their dairies’ rooftops to capture the energy of the harsh Australian sun and use it to heat water.

“They actually look quite attractive, believe it or not,” said Troy Smith, who heads a farmers’ group on the island. He estimates that the solar hot water gear, set up earlier this year, will lower power costs 10 to 15 percent. The Tasmanian government financed the equipment with a $188,000 grant, and the dairy farmers paid for related expenses like roofing and electrical upgrades.

Interest in solar water heating has spread quietly around the world. Though the technique has been around for more than a century, the concept of using the sun to heat water gets far less attention than its better-known cousin, solar electricity produced from photovoltaic panels.

The technologies are different. The hot-water application uses plates or tubes — often called solar collectors — to capture the energy from the sun’s rays and use it to heat water that is circulating nearby. The King Island’s farms are using glass-encased tubes made by the Australian company Apricus to heat liquid to transfer the energy of the sun’s heat to water. Photovoltaic panels, by contrast, use semiconducting materials, typically silicon, to stimulate electrons and generate electricity. Both are seen as a solution by governments and individuals eager to move away from fossil fuels, which can be expensive in isolated places like King Island.

The decision to install solar water heating is “very cost-dependent,” said Carl Zichella, a San Francisco-based director at the Natural Resources Defense Council who works on renewable energy development. In the United States, where low natural gas prices undercut solar hot water, installations are relatively sparse, he said. Americans tend to use solar collectors to heat swimming pools, though elsewhere in the world they are mostly used to heat water for homes.

The market for solar collectors grew nearly 10 percent from 2011 to 2012, according to a report this year from the International Energy Agency. (Those figures, which are the agency’s latest, include a small percentage of collectors that heat air instead of water.)