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Using solar energy to keep homes cool

SolCool's air conditioner can be run directly from solar panels, existing wiring or even, in a pinch, batteries. Photo: Keeping cool from the sun

SolCool One has developed what many people would expect to already be commonplace: An air conditioner that runs off the sun.

Later this week, the California-based company will launch the SolCool Millennia version 4, which it calls a hybrid solar air conditioner.

The air conditioning unit--sized to cool the space of a large room--can be run on solar panels, from a wall socket or, in a pinch, batteries.

Regardless of the power source, the system will lower electricity costs substantially, according to company executives. Potentially, if these units get used in a widespread manner, they could also reduce the odds of summer power outages, often caused because homes and buildings crank up their air conditioners. The unit operates at a maximum of 500 watts, far less than half what typical air conditioning units eat up.

"Air conditioning takes the biggest load on the power grid. We're trying to use small PV (photovoltaic solar) cells and equip them with 18,000 BTUs (a unit of energy) of air conditioning," said Roger Pruitt, the president of SolCool and GPM, the research and development and manufacturing arm of the company.

The system includes batteries that can run the unit for either 12 or 24 hours depending on the battery size.

"So if there's a blackout or if there's no sun, you can run it off of the batteries," Pruitt said.

The latest version can also heat a room and has attachments for purifying water and running other DC (direct current) appliances, like lights and ceiling fans.

The SolCool system, which has been under development for about four years, is one of a growing number of energy-efficient products gaining favor among consumers and businesses. With high energy prices and concerns over pollution, manufacturers are making energy efficiency a priority in product design.

Air conditioners in general consume a lot of power and are particularly taxing to electricity grids. Because the need for cooling is highest during the day, utilities often have to turn on auxiliary power generators during very hot days to meet demand.

These peaks in power demand, when not met, cause blackouts or brownouts. Consumers also pay the highest rate for electricity during this time of the day.

SolCool's unit can be thought of as going solar incrementally. Putting solar panels on a roof can cost $20,000 to $40,000 before subsidies, according to installers, a price tag that makes some consumers balk. But, by adopting solar power for smaller applications, sticker shock is eased.

Some companies are betting that solar water heaters, which cost about $7,000, will gain popularity in this manner.

The latest SolCool unit has an energy efficiency rating (EER) of 30, according to SolCool. (That ratio is calculated by dividing the cooling output by watt hours). Room air conditioners of similar cooling output with an EER of 9.7 meet the federal Energy Star rating standard by the U.S. Department of Energy.

Sam Little, the president of renewable energy installer EcoVantage Energy in Weatherford, Texas, has tested the previous versions of the SolCool air conditioner. He said that at 18,000 BTUs, the devices are not large enough to cool a very large house, but work well for a couple of rooms or to supplement another system. He estimated the previous version used one-fourth the electricity of other air conditioning units.

Needing 500 watts, SolCool's unit could run on five or six midsize panels, which would cost a fraction of a solar system sized for a full building.

SolCool has optimized the air conditioner to run on the direct current generated by the solar panels or batteries, rather than the alternating current that comes from electrical plugs. Building the product for direct current has allowed the company to build a very energy-efficient product which can run off-grid as well, Pruitt said. (In standard solar installations, the panels produce direct current, but then a device called an inverter switches it to AC before you use it in your home.)

The SolCool includes a sealed, two-gallon water tank that stores cooled water, which the air conditioner draws cooling from during a power outage.

Little said he regularly gets requests for solar air conditioners.

Another low-power option for cooling that Little uses is an evaporative cooler, which is a water basin and fan that blows evaporated water vapor. These systems, which have been installed in the Middle East, generally work well in lower humidity areas, but the SolCool system could work "just about anywhere," he said.

Other companies and some researchers also tout a system in which ice is created at night and stored in an underground tank. The vapor then wafts off in the daytime to cool a building.

The company is looking to sign on distributors who are either experts in air conditioning or are renewable energy installers looking to distribute new products.

The back-up power feature is compelling for off-grid applications or when people need to keep cool in their home during a power outage for health reasons, Little said.

"You don't (worry about) a return on investment, if you have to have oxygen," he said.

The price of the units will be between $2,600 and $3,000 before installation, which could run another $500, Pruitt estimated.

That's substantially more than a standard air conditioner, but Pruitt said the energy savings can help pay for the unit, particularly in areas like California with high heat and steep electricity fees. The product is also eligible for state-run rebate programs that promote energy-efficient products, he added.

"This is our fifth year doing it. When we started, it was hard because nobody wanted to be the first to try it," Pruitt said. "But in the last year, I think consumers are coming around to it."