Renewable Energy World Conference and Expo Interview Darren Kimura in Las Vegas

11 December 2008, 15:08
by Justin Moresco

Sopogy, the Honolulu company makes a “micro” version of concentrated solar power systems, which traditionally have been used on larger, utility-scale projects. Sopogy’s proprietary technology uses large metal troughs with mirrors that reflect sunlight onto a tube filled with fluid.

That solar energy is transferred to the fluid, an oil, and used to drive electrical turbines, adsorption air conditioning and steam creation. Sopogy’s software helps these troughs, or collectors, to rotate up to 270 degrees to follow the sun’s path.

The solar startup is trying to set itself apart from others by packaging this emerging solar technology in a smaller scale. The company sees a market niche for commercial and industrial customers, such as hospitals and hotels, that need between 1 and 20 megawatts of power and factories that need that power plus heat.

Initially focused on Hawaii and later California, Sopogy has turned its sights toward opportunities in Europe and Asia. The new financing, added to the $60 million in debt and equity already raised, will help the startup hire more staff and put more emphasis on those markets, where incentives like feed-in tariffs are especially attractive, Mr. Kimura said.

Hawaiian Electric, the island state’s largest utility, has ordered a 10 MW facility using Sopogy’s technology. Other projects, like one for the Natural Energy Laboratory of Hawaii, are in the 1 MW range.

Each Sopogy collector generates 500 watts and can be strung together for larger generation. Mr. Kimura said they have been designed to be installed by local contractors without specialty training and can be transported flat, which keeps costs lower.

But cost is still an issue. Mr. Kimura said his systems can produce electricity over their lifetime at about 17 cents per kilowatt-hour. While this is cheaper power than that from solar photovoltaic systems, which run higher than 25 cents/kwh, it’s still more expensive than conventional electricity generated from fossil fuel sources.

Still, companies have reason to look to clean energy systems. Their costs, free from fossil fuel volatility, are more predictable over the long run, and with the right government incentives are competitive with the electric grid.

The large scale concentrated solar power companies, such as Israel’s Solel and Palo Alto, Calif.-based Ausra, so far appear focused on massive projects. That’s good news for Sopogy. But Geortina Venezetti, an analyst with Frost & Sullivan, said waste-to-energy technology is still the most popular renewable energy source for commercial and industrial markets, and its costs are coming down.

Agricultural outfits, breweries, and paper and pulp factories, for example, can use their own waste as feedstock to run co-generation systems that produce electricity and heat. And unlike solar power, these systems run around the clock and on cloudy days.

Solar Process Heat

A transpired collector is installed at a FedEx facility in Denver.

Commercial and industrial buildings may use the same solar technologies—photovoltaics, passive heating, daylighting, and water heating—that are used for residential buildings. These nonresidential buildings can also use solar energy technologies that would be impractical for a home. These technologies include ventilation air preheating, solar process heating, and solar cooling.

Many large buildings need ventilated air to maintain indoor air quality. In cold climates, heating this air can use large amounts of energy. A solar ventilation system can preheat the air, saving both energy and money. This type of system typically uses a transpired collector, which consists of a thin, black metal panel mounted on a south-facing wall to absorb the sun’s heat. Air passes through the many small holes in the panel. A space behind the perforated wall allows the air streams from the holes to mix together. The heated air is then sucked out from the top of the space into the ventilation system.

Solar process heating systems are designed to provide large quantities of hot water or space heating for nonresidential buildings. A typical system includes solar collectors that work along with a pump, a heat exchanger, and/or one or more large storage tanks. The two main types of solar collectors used—an evacuated-tube collector and a parabolic-trough collector—can operate at high temperatures with high efficiency. An evacuated-tube collector is a shallow box full of many glass, double-walled tubes and reflectors to heat the fluid inside the tubes. A vacuum between the two walls insulates the inner tube, holding in the heat. Parabolic troughs are long, rectangular, curved (U-shaped) mirrors tilted to focus sunlight on a tube, which runs down the center of the trough. This heats the fluid within the tube.

The heat from a solar collector can also be used to cool a building. It may seem impossible to use heat to cool a building, but it makes more sense if you just think of the solar heat as an energy source. Your familiar home air conditioner uses an energy source, electricity, to create cool air. Solar absorption coolers use a similar approach, combined with some very complex chemistry tricks, to create cool air from solar energy. Solar energy can also be used with evaporative coolers (also called “swamp coolers”) to extend their usefulness to more humid climates, using another chemistry trick called desiccant cooling.

Find out about NREL solar technologies research for nonresidential buildings from its Advanced Desiccant Cooling & Dehumidification Program and High Performance Buildings Research Program.

The U.S. Department of Energy’s Consumer Guide has in-depth information on Active Solar Heating.

For more information, you might want to see Advanced Buildings Technologies and Practices.

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