E&E postdoc puts solar technology to work at home

September 16, 1994

By Lynn Yarris, [email protected]

Not all scientists get a chance to put their theories into practice. Enjoying such a challenge is Chris Marnay, a post-doctoral fellow in the Energy and Environment Division.

During the week, Marnay models the effects of new energy technologies, policies, and regulations on utility costs. On weekends, he puts many of those technologies to work in his own solar-powered residence.

Marnay works for E&E's Appliance Standards Group. He creates computer models that project the impact of proposed DOE energy-efficiency standards for appliances on natural gas and electric utility companies.

The impact of DOE regulations not only varies widely from utility to utility, but from location to location, and even, in some cases, from residence to residence. In the case of Marnay and his wife, Nyla, their house is located outside of Comptche, in unincorporated Mendocino County. The cost of extending an electrical power line to such an out-of-the-way location would have been nearly $75,000.

"We live in a black hole in the PG&E galaxy," says Marnay. "But we're not alone. There are maybe tens of thousands of homes and vacation homes in California that are in a similar situation."

Marnay's case was unique in that he was able to design his own solar-based electrical power system, using off-the-shelf technology. He then employed some of the energy-efficient technology developed at LBL and now available on the market to help make it work. The system starts with eight photo-voltaic cells that can collect up to 600 watts of incoming solar energy--enough to provide an average of two to three kilowatt hours of electricity a day.

A typical Bay Area household uses about 10-15 kilowatt hours of electricity a day. However, Marnay says, "With energy efficient appliances such as the compact fluorescent lamps developed at LBL's Lighting Lab, we produce enough power to run our house." Marnay keeps on hand a small (3.5 kilowatt) generator as a backup, but so far has not had to use it.

The electricity generated by the photovoltaic cells is stored in a bank of 12 batteries with a total storage capacity of 12 to 24 kilowatt hours. Since this electricity is direct current (dc), it must be converted to alternating current (ac) in order to run household appliances. To make this conversion, Marnay uses a standard inverter with a peak capacity of 2.6 kilowatts.

"Everything downstream from the inverter is conventional, including the wiring of the house," he says. "The only evidence inside the house that we are not on PG&E power is an energy monitor that tells us important information, such as how much power is in the storage batteries."

Marnay's solar-based system cost about $11,500 to build and install. It would have been cheaper to build a diesel or propane-fueled generator installation, but that would have entailed environmental and other problems, including noise.

"You don't move to the country in order to spend your days living with a noisy, smoky generator," Marnay says. "For our house, the solar option is economically competitive with a generator without the negative environmental impact, and far cheaper than an ugly PG&E line extension."

Among the drawbacks to any solar-based power system, Marnay has learned, is that it must be custom-designed to fit the specific requirements of each site. Furthermore, solar-based systems are still a long way from being economically competitive with power from a utility company. For example, it costs Marnay about $1 to produce a kilowatt hour of electricity, compared to the typical PG&E residential rate of 12 cents per kilowatt hour.

"However, that gap is closing," he says, "and in some special circumstances that incur high utility costs, such as remote locations like ours, photo-voltaic systems may be competitive."

Furthermore, Marnay believes that expanded use of energy-efficient appliances together with tighter government restrictions on thermal power plants will increase the attractiveness of solar-based and other renewable energy systems at non-remote sites as well. Perhaps a good omen for him is the recent funding by DOE of his proposal to improve the representation of renewable energy systems in utility computer models.

"Future models are going to give renewable energy technologies a more prominent role," he says. "The objective is to bring renewable energy technologies into the forefront of utility planning for the future production of electricity."