By David Kligman
SAN JOAQUIN COUNTY — In a clearing surrounded by walnut trees, an enormous rig drills deep into the earth.
The 120-foot-tall rig isn’t digging for oil. It’s testing the soil a mile deep for what could be a major energy breakthrough for PG&E.
The utility is overseeing a project to see whether compressed air could be stored underground in depleted natural gas reservoirs. Air would be pumped underground when demand for electricity is low. The air would be stored and then released through an industrial gas turbine to create electricity when demand is high.
According to the National Renewable Energy Lab, the technology needs less gas to produce power because it uses air that has already been compressed.
Energy used only by two other utilities
It’s a form of clean, renewable energy that only two other utilities in the world use — one in Alabama, the other in Germany. Mike Medeiros, PG&Es manager of renewable energy development, calls compressed air energy a “green enabler” because it would allow the utility to store wind and solar energy.
“We have a lot of wind and wind can blow quite a bit at night in California,” Medeiros said. “And obviously loads aren’t very high at nighttime. So what we would do is use that excess wind energy to run these compressors, store the air underground and then when the peak loads hit — afternoon, late evening when people start getting home — we would take that air that was generated from the excess wind energy and generate electricity for when it matches peak loads we have at that point in time.”
Over three weeks, a team of engineers and geologists is studying 30-foot sections of porous rock formations encased in a steel tube brought up from the ground.
What’s really driving this technology is California’s aggressive goal that a third of all energy provided by utilities must be renewable by 2020.
“Unfortunately, renewable energy sources are intermittent,” Medeiros said. “Solar only when the sun is shining. Wind only when the wind is generating. And then it’s not necessarily at the times of day when we need it most to meet our demands.”
Similar to PG&E’s Helms facility
The project would be similar to the Helms Pumped Storage facility in Fresno County, which pumps water during off-peak hours and generates energy during peak hours.
The first order for PG&E is doing all its research to prove the technology will work.
“I think the big questions will be cost,” Medeiros said. “What’s it going to cost? We think it can be competitive with other resources today that provide the same types of services. But you want to be able to answer all of those technical questions because there’s going to be somebody else that may develop this project and they’re going to say, ‘OK. I’m interested but have you answered the technical questions that are going to allow me to take the risk to develop this project and allow somebody to lend me the money to construct it.”
After drilling was completed at the site, samples were gathered at a new location a few miles away. The drilling was completed last week and the samples — tubes of the earth cut into pieces — were sent in a refrigerated truck to a lab in Kern County for more analysis.
While this new energy looks promising, it’s a project years in the making. The initial phase to analyze the feasibility of compressed air from three sites will be completed in 2015. And if the project does move forward, a 300 megawatt plant could be in operation in eight years.
Email David Kligman at David.Kligman@pge.com.