Power plants don’t move.

That likely is one of the reasons stealthy startup LightSail Energy has shifted from trying to build a car that runs on compressed air to building a machine for energy storage.

The Oakland, Calif.-based company, backed by Khosla Ventures, has joined the ever-expanding race to develop inexpensive, reliable and ideally easy-to-deploy systems for storing energy at strategic spots on the grid or at wind and solar farms.

Like SustainX out of Dartmouth College, LightSail’s goal is to develop a mechanical unit that stores energy as compressed air, probably in above-ground tanks. Air compressors can accomplish this task today. Unfortunately, the energy required to compress the air and keep it sealed with conventional technologies outweighs the benefits.

SustainX says it has devised an electric piston, backed by a complex system of software controls, that keeps the air at a nearly constant temperature during compression and expansion, thereby improving the efficiency and reducing the cost. As air gets compressed, it heats up the air and in turn increases the power required to compress more. SustainX controls this by precisely timing the compression process, timing compression with colder and hotter ambient temperatures and bleeding off heat for other purposes. has raised around $25 million. (We will provide an overview of grid storage at Networked Grid 2011 on May 3 and 4 in San Francisco.)

LightSail is remaining relatively mum at the moment, but its LinkedIn page indicates it has honed in on the same issue:

“The thermodynamic inefficiency of conventional air compressors and motors has rendered them impractical for this application. Our technology directly addresses these thermal losses and, for the first time, enables large-scale storage systems with high round-trip efficiency and high power density, as well as low cost.”

Co-founder Danielle Fong has an interesting bio. She entered Dalhousie University in Nova Scotia at age 12 to study physics. (By contrast, I entered the Boy Scouts at this time to study fire.) She graduated at 17 and later studied nuclear fusion at Princeton. After that, she worked at an online gaming company; go figure.

LightSail has applied to erect a gas generator in Oakland, likely to test out a prototype.

Another one to check out: Isentropic Energy. It uses air pressure, hot and cold gravel, and a heat engine to store energy.

Another reason that LightSail may have shifted from cars to storage is that compressed air cars are viewed as a technology for crazy people. Storage will be a big business in which the answers and ultimate winners have yet to be determined. The proliferation of solar and wind have created a massive market for storage and microgrid technologies. State laws and federal regulations will also mandate investment in storage by utilities and power providers.

Geologic compressed air energy storage (CAES)  is the cheapest form of energy storage, according to, among others, the Electric Power Research Institute. Underground CAES runs about $1,500 per kilowatt to build and adding additional kilowatts in many regions is somewhat simple.

Limitations, however, exist with geological storage that portable air storage could ameliorate. You need a big cave and, preferably, one in an area where environmental and neighborhood groups won’t object. So far, only two CAES plants exist in the world. PG&E has won Department of Energy grants to build one in Kern County. PG&E has a great location: the underground cavern sits in an old oil and gas field and it will connect somewhat readily to the Tehachapi wind projects.

Still, it might take eight to ten years to complete the project, admits Hal LaFlash, the director of emerging clean technologies at PG&E.