An office park in Alhambra is about to start drawing a quarter of its electricity from the devices. It joins commercial properties in more than 40 cities statewide. Behind a chain-link fence next to a parking structure at an office park in the San Gabriel Valley sit five softly humming gray boxes that could change the way homes and offices are powered. On Tuesday, the boxes — each somewhat bigger than an SUV — will begin generating enough electricity to power about a quarter of the complex, saving the property owner about $500,000 a year in electricity bills. The Energy Servers use fuel-cell technology to create low-emission electricity. The product, developed by Bloom Energy, a Sunnyvale, Calif., start-up, has been hailed as an innovation that could change the power industry. "We were convinced that this was a technology that was extraordinarily good," said Wayne Ratkovich, chief executive of Ratkovich Co., which owns the Alhambra office park. "And we're not paying as high of an electric bill, so we'll save a lot of money."