Over the past year we've reported on several so-called V2G schemes, in which plug-in hybrid owners could charge their vehicles during off-peak hours and sell power from their vehicles back to the public grid at high-demand times, possibly providing more stability to the grid if the system were designed smartly.

Now Google's involved. The company recently had six hybrids - four Toyota Prius and two Ford Escape hybrid models - retrofit as plug-in hybrids. With a number of changes to their electrical componentry and software, so that they can run farther and faster on electric power before starting their gasoline engines, the hybrids post substantial fuel economy gains. The Prius can cover up to 75 miles per gallon as reconfigured. Google is tracking data on these versus stock hybrids and hopes to eventually expand its demonstration fleet to over 100 plug-ins.

The vehicles are using the Hymotion conversion already available from A123 Systems, a Massachusetts battery-tech company that is already working with General Motors to establish next-generation lithium-ion battery packs, which would allow a much longer range and more power with packaging and weight benefits.

One of the vehicles, a Prius, has been configured for two-way power flow and can transmit data on its power systems. With this, Pacific Gas & Electric, a northern California public utility, will study grid stability effects by storing and releasing small amounts of power at various times, which it could use to model, or optimize, the effects of hundreds of thousands of such vehicles.

Google Monday also unveiled a system of solar panels, effectively covering nearly all the roof space at its offices in Mountain View, California . The panel system is claimed to be the largest solar installation on a corporate campus in the U.S.   Google also announced that $10 million has been set aside for related projects, through the company's philanthropic foundation, Google.org.

Regularly updated information about the plug-in hybrid fleet can be seen at www.RechargeIT.org.

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