SunDrum combines solar PV and solar thermal with a technology that comes from PCs. Could it make all-in-one solar cheaper?
Itboosts the power output of photovoltaic panels. It heats water. AndSunDrum’s solar collector is similar to one of the parts in a high-endPC or server.
Hudson, Mass-based SunDrumis raising funds now to go into further prototyping and manufacturing.The firm has devised a liquid-filled heat sink that effectively absorbsthe heat that builds up on photovoltaic panels and shuttles it to awater heater in a basement or utility room. The heat sink sits on theunderside of a solar panel and is roughly the same size.
Heat sinks – effectively hunks of metal shaped to carry heat fromone place to another – are standard equipment in PCs and LED lights. Tocool extremely powerful processors, some manufacturers have createdfluid-filled sinks that can remove even more heat than standard parts.Last year, IBM cameup with a heat sink for a high-end server that passed chilled water (incopper tubes) over chips. Hobbyists meanwhile, sometimes surroundcomponents with water or mineral oil to keep components cool.
In solar, a heat sink becomes a two-fer, explains CEO Ron Smith, who ran various divisions at Intel before SunDrum. (The chipmaker has in recent years become a finishing school for several greentech execs).Excess heat hurts the efficiency of solar panels and the heat builds asthe day goes on. The surface of a standard solar panel in the middayArizona sun can reach 130 degrees Fahrenheit or more. By cooling themby 20 degrees to 30 degrees Fahrenheit, the panels can perform closerto their rated power. The photo reflects a test conducted by thecompany.
"We can increase the power output by 6 to 7 percent consistently," he said.
At the same time, the panels generate enough heat to provide asubstantial amount of hot water to a building. The additional cost runsabout $2.50 per watt for a home installation or $1.50 for a commercialinstallation.
A host of startups have sprung up recently with the goal ofharnessing more of the power of the sun than standard PV panels can.The best solar panels only harvest 23 percent of the sun’s energy. Byharnessing heat as well, these devices can capture 75 percent of theenergy or more beaming toward earth.
Chromasun, founded by former AusraCEO Peter Le Lievre, makes a device that combines solar cells (forelectricity) along with a solar thermal collector that is used to powera chiller-style air conditioner. BrightPhase Energy, meanwhile, has a solar PV/thermal device that also lets in light through a skylight (see Can You Go Cheaper Than First Solar?). Other companies in the combo market include Entech SolarCool Energy. and
These devices, however, are complete solar systems in their ownright. By contrast, SunDrum just makes the device that conducts heat(along with the plastic tubes and services to connect the rooftopsystem to water tanks in the basement.). The one-fourth-inch thickcollector attaches to the back of a conventional PV panel. The plan isto get solar manufacturers and/or their dealer networks to carry it asa complimentary option. SunDrum, thus, won’t ideally have to competeagainst Suntech or other established PV makers to get into the market.
Smith also argues that the way it attaches to the back of the panelalso makes it easier in many instances for commercial buildings orapartment complexes to adopt both PV and solar thermal. Rooftops onlyhave so much spare room for solar devices. If there are three or fourstories in an apartment building, that may force a choice betweenputting up a solar thermal absorber or a PV system. Because SunDrum’sabsorber sits beneath PV panels, it doesn’t add to the amount of realestate used.
The collector consists of two sheets of aluminum with input/outputports for the fluid, which is a mixture of distilled water andpropylene glycol. The secret sauce lay in the design of the channelsinside the heat sink. The fluid does not travel in tubes — that wouldreduce the area of contact between the fluid and the aluminum. Instead,it flows through a maze of canals and the fluid touches the aluminumdirectly. The fluid additionally moves relatively slowly. As it oozesunder two or more PV panels, the fluid gathers heat.
The heated fluid then goes to a tank in basement where the heat canbe transferred to the water tank. Compared to some combination solardevices, SunDrum’s collector can only tolerate low temperature. Thefluid can’t go past 180 degrees Fahrenheit because the fluid travelsfrom the panel to the basement tanks in plastic tube rather than copperto economize on equipment. But that’s warm enough to provide hot waterfor a home or an apartment building, depending on the number ofcollectors.
So far, the company has certified compatibility with a variety of solar panels from Evergreen Solar, Sanyo, Sharp, and SunPower, but it will probably work with more. Solar panel frames aren’t standard across the industry, but they are somewhat close.
While it seems most appropriate for warm regions, it works in avariety of geographies. SunDrum rigged up a house in Massachusetts withit.
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