Solar Panels Completely Power High-Efficiency House–Including A/C

Ed Hunter (352) 392-1773 x 278

Wendell Porter (352) 392-3122

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GAINESVILLE — Tired of paying a power bill? Go ahead and pull the plug, but make sure your solar power system is installed first.

To show that it can be done, University of Florida researchers have built a house that runs completely on solar power, including an air conditioner — with a heat pump to keep things warm in the winter — as well as lights and several computers.

“The house is extremely well-insulated, and because of this it’s very inexpensive to operate,” said Wendell Porter, an energy extension specialist with UF’s Institute of Food and Agricultural Sciences. “We have taken that a step further and powered the house completely from the sun.”

While the UF house doesn’t include a kitchen, Porter said the solar panels could easily handle one, including a refrigerator, provided the stove used natural gas. Another major power-guzzling electrical applicance in a home — the clothes dryer — also would have to use natural gas, he said.

The goal of the project was to show that it is technically feasible today to run a house primarily on solar energy using off-the-shelf hardware. The 900-square-foot house was built using a new method that combines plastic foam and concrete, giving walls an R-40 insulation rating and ceilings that are rated R-50. In a typical modern house with traditional construction, R-values for walls run from R-11 to R-13 and for ceilings up to R-30.

The solar power system consists of 24 solar panels mounted in three passive solar trackers that use the sun’s own heat to track it throughout the daylight hours. The direct current from the panels is routed to a commercially purchased power panel that contains several electronic components — inverters that convert the direct current into alternating current to power the house and chargers that keep a bank of 32 high-capacity batteries charged up to power the house during the night and when weather conditions block the sun.

Porter said the Florida Energy Office and the U.S. Department of Energy built the house to show how far solar energy has come and what can be done with existing technologies.

“The equipment used here is factory built, installed by qualified people and can be done at any house or any business in the country. This shows where the industry is today,” he said.

But while running a house completely on solar power makes for an interesting demonstration, Porter said a more practical application of solar power would be as a backup or supplement to utility-provided power, especially when the weather can cause service interruptions.

“People up north might use a system like this to provide backup lighting and refrigeration and then use a wood stove to heat the house,” Porter said. “You could put in a smaller, and less expensive, system than you would use to run an entire house to provide for critical needs.”

And even if electricity is flowing, Porter said, a solar power system could run high-energy appliances such as an air conditioner to reduce the need for purchased electricity.

“A homeowner could install a system without the battery backup and route the electricity directly into a circuit panel through an inverter,” Porter said. “During the hottest times of the year, most of the energy to power the air conditioner comes from the sun. It decreases the demand on local power companies and allows them a little more flexibility in buying and producing electricity.”

A local power company utility analyst said recent developments might make it possible in the near future for consumers to actually generate at least some of their own electricity.

“Utility companies are vitally interested in renewable resources,” said Mark Spiller, with Gainesville Regional Utilities. “The difficulty to this point in time has been the interconnection issues and the safety of line workers.”

Spiller said if the power goes out, a house equipped with solar cells could continue to generate electricity that would flow into the power grid, creating a shock hazard for workers attempting to restore service. To protect workers, the Institute of Electrical and Electronic Engineering in January approved Standard 929-2000, which requires that solar power systems shut off in the event the utility-provided power fails.

“This assumes the strategy is to supplement the electrical needs of the house rather than replace the power grid,” Spiller said. “In order to safely provide emergency power, a homeowner would have to add an automatic transfer switch, at substantial cost, to automatically disconnect the home from the utility grid.”

Porter said with rapidly falling prices, solar energy is approaching the break-even point.

“Just a few years ago, a solar cell was something you put on a satellite and cost $40,000 a watt; now you can buy them wholesale for less than $4 a watt,” Porter said. “This is an example of things to come, and how at some point in the future power will be able to be produced by the consumer in an application that is both good for the environment and good for their pocketbook.”