Solar power still has one pitfall: No sun, no power.

For decades, solar power pioneers have produced no reliable way to store the energy for use at night or on a cloudy day. Until now.

Bell Independent Power Corp. of Rochester, N.Y. is primed to demonstrate on a commercial scale its thermal storage technology for concentrated solar power. In partnership with Tucson Electric Power and The University of Arizona Science and Technology Park, Bell plans to start construction this summer on a 5-megawatt solar plant at the Tech Park with intentions to generate – and store – solar power by May 2011.

“It’s a game changer in solar power generation,” Bell Independent Power President Joseph Bell Jr. said. “Nobody is at this stage. In the U.S., we’re the only ones with a project under development.”

Bell Independent is the flagship for the Tech Park’s newly decreed 200-acre Solar Zone which will address all aspects of solar power, including research and development, manufacturing solar instruments and generating solar power, said Bruce Wright, UA’s associate vice president for research parks.   

The $32 million Bell project will occupy 60 acres with a traditional concentrated solar power plant, where 22,000 parabolic mirrors will heat oil to 750 degrees, which will create steam to turn power-generating turbines.

Where the Bell plant differs is at night, on cloudy days or during thunderstorms, the hot oil will detour to a tank of molten salt what can store the energy for two hours.

“The industry will dictate what makes sense of how much to extend that,” said Gerard Walter, Bell’s chief financial officer. “If you build a big enough storage tank and solar field, you could store power for 24 hours.”

Walter doesn’t foresee that happening for the same reason that thermal storage hasn’t happened so far: Traditional power sources are still far cheaper, but with a renewed interest in solar power, Bell Independent believes there’s a market for storing solar power for at least a few hours.

Bell responded to a TEP request for proposals for renewable energy sources to help the local power company comply with Arizona Corporation Commission mandate that 15 percent of TEP’s power come from renewable resources by 2025. TEP agreed to purchase Bell’s solar power for 20 years.

“Our ambition is to be a leader in solar energy,” said Paul Bonavia, chief executive at TEP and its parent company, UniSource Energy. “We want to make Tucson a national and even global leader in solar energy.”

The Bell plant at the Tech Park is a demonstration project, able to produce about one-third of the park’s energy needs or enough energy to power more than 1,500 typical Tucson homes while offsetting more than 16,000 tons of carbon dioxide (CO2).

Bell Independent is a small company with 15 employees, established in 2004. Developing this thermal storage technology has been a focus ever since. The company also develops wood-based (biomass) power technology and was involved in scheduling and commissioning Nevada Solar One, the largest concentrated solar power plant that went online in June 2007 near Boulder City.