Intercontinental Hotels has run a trial with a 15-kilowatt Stem storage system for the past year, and though Hobbs would not discuss dollar 
savings he says he’s seen between a 17 percent and 30 percent improvement in his ability to manage demand. The hotel has 17 Stem systems on order and plans to install two 54-kilowatt battery packs at the Mark Hopkins in San Francisco, which would supply 20 percent of the hotel’s demand.
If a hotel’s energy consumption spikes—say on a hot day when guests all turn on their room air conditioners at once—the utility ratchets up the electricity rate they pay. To avoid these so-called demand charges—which can account for half of a monthly power bill—businesses can participate in programs that cut their bills if they allow their local utility take control of their air conditioners or lighting to reduce electricity use when the grid is overloaded.
Letting hotel guests who pay $300 a night sweat, however, is not an option. So Hobbs has pulled the plug on his utility by storing electricity in lithium-ion battery packs when rates are low for use when demand and prices rise. The battery and sophisticated software was built by a Silicon Valley startup called Stem and is another example of how technological innovation is upending utilities’ century-old stranglehold on power.
Patel says a 54-kilowatt system costs about $100,000, though California state incentives cover about 60 percent of that price. But thanks to a $5 million fund financed by Clean Feet Investors, Stem will offer customers no-money-down installation of battery storage in exchange for monthly fee paid out of the savings on utility bills. Such lease deals unleashed an explosion in residential solar systems and Patel expects to see a similar result in battery storage. Stem has orders for 6 megawatts’ worth of systems and Patel expects that to jump to 15 megawatts over the next year.
