Cogenra Solar Delivers Hot Water Along with Power

The solar power system Facebook Inc. plans for its new Menlo Park headquarters won't just supply electricity. It'll heat water for the showers, too. And maybe help clean dishes in the cafe.


The system will be designed and installed by Cogenra Solar, a Mountain View startup that uses the sun's energy to produce electricity and hot water at the same time. The collection of solar cells, mirrors and pipes will sit atop Facebook's 10,000-square-foot fitness center, powering the exercise equipment and churning out steaming water for the locker rooms.

The technology's dual use makes it far more cost-effective than conventional solar systems that provide electricity alone, said Cogenra CEO Gilad Almogy. And while neither company will say how much the array will cost Facebook, Almogy said the social networking giant will recoup its investment in less than five years.

"It'll be a shorter payback than any other form of renewable energy," Almogy said.

Planting solar panels on the office or warehouse roof has become de rigueur for many Bay Area companies. By those standards, Facebook's solar array will be small, generating just 10 kilowatts of electricity. A typical home solar system produces about 3 kilowatts.

The array will cover only one roof on the nine-building campus, which used to house Sun Microsystems. But Facebook could expand the system if it performs as advertised, possibly using the hot water in the existing cafe and another planned for the campus. John Tenanes, Facebook's director of global facilities, said his company is taking the same approach to solar that it takes to its Web service - checking out a promising new idea to assess its potential.

"We try stuff and see if it works," he said. "And that's what this is. Cogenra is really our initial investment (in solar power), and we're going to see how well it works."

Cogenra's technology is designed to use energy that other solar set-ups waste.

Photovoltaic panels absorb a small fraction of the energy the sun throws at them, typically 15 to 20 percent. The rest is wasted as heat.

Cogenra arrays, however, run fluid-filled tubes behind the solar cells, with the fluid absorbing some of the heat cast off by the cells. The fluid - a chemical compound kept in a sealed loop - then transfers the heat to water. Curved troughs of mirrors concentrate sunlight on the cells, while motors keep the troughs pointed at the sun as it arcs across the sky.

Cogenra has already installed a 272-kilowatt system at a Sonoma winery, which uses the hot water to clean barrels. The Sonoma Wine Co. array, however, is mounted on the ground. The Facebook array will rest on the rooftop and will weigh far less. The company also plans to install a rooftop version of its technology on a University of Arizona dormitory.

"Not all customers who need significant amounts of hot water have nearby land to use," Almogy said.

Backed by Khosla Ventures, Cogenra also tries to keep costs down by using solar cells, inverters, mirrors and tracking equipment made by other companies. The company's ability to take off-the-shelf gear and turn it into something new impressed Facebook.

"They mashed together all these different things, and it seems to work well together," Tenanes said.

Source: http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2011/11/02/BUA41LP7D0.DTL&type=tech