PG&E, one of the United States’ largest and greenest utilities, is working on technology that would allow plug-in hybrid cars to feed electricity to the power grid during peak demand, Green Wombat has learned. That would reduce greenhouse gas emissions by letting the utility to switch to Prius power when demand spikes rather than being forced to buy "dirty energy" from coal-fired power plants. In effect, a plug-in hybrid becomes a back-up generator. "Your car will be able to keep your home powered during a blackout," Roland Risser, PG&E’s director of customer energy efficiency, told Green Wombat last night at a dinner put on by the utility, Sun Microsystems and eBay to promote their environmental programs.
Risser says PG&E (PCGPRE) is in discussions with Toyota (TM)
about producing a plug-in version of its hybrid Prius like the one
above photographed by venture capitalist Steve Jurvetson. To create a
plug-in hybrid you swap out the car’s battery for a rechargeable
lithium ion version so the car relies less on its gas engine.
Environmentalists and companies like car dealer AutoNation have been pressing automakers to make a production version of plug-in hybrids being sold by companies like EDrive and Hymotion.
The technology PG&E is developing would allow the utility to
know whether you were charging your plug-in hybrid at home, work or
wherever. Let’s say it’s a scorching summer’s day in Silicon Valley and
all those air conditioned tech companies are threatening to overload
the power grid. At the Googleplex, Larry and Sergey’s new plug-in
Priuses, along with scores of other hybrids, are parked in docking
bays. The cars were charged up at home overnight when electricity
demand is low. Now with a brownout looming, a PG&E manager presses
a button and all the cars participating in the program begin
transferring electricity from their batteries into the power grid.
Obviously, it would take a lot of plug-in hybrids to have any
significant impact on the power grid, not to mention global warming.
But Risser says the key isn’t so much scale as the concentration of
cars. California greenie cities like Davis, Santa Cruz and Santa Monica
sport way more Priuses per capita than, say, Stockton, and could serve
as alt energy nodes. My block in the Berkeley hills, for instance,
tends to go black during fierce winter storms but there’s also a Prius
in every fifth garage. Interconnect the homes and cars and you can keep
the lights on when that tree takes out the power line.
Risser stresses there are many details and some technological
challenges to be worked out and a rollout date has not been set yet
(much will depend on whether carmakers begin production of plug-in
hybrids.) There’s also the trade-off that if your Prius is generating
electricity for the grid you’ll probably be using the gas engine more
and thus emitting more greenhouse gases. But the fact that a giant
utility like PG&E is pursuing such a program is yet another
indication of the sweeping changes headed our way.
Green Wombat 
We’ll need batteries with better deep-cycle discharge performance before this has much appeal.
Both NiMH and Lithium batteries have a limited number of charge cycles, and that number falls steeply if you allow them to deep discharge.
I sure wouldn’t want the electric company yanking power in and out of my plug-in hybrid, unless they offered to replace the batteries at their expense when they fail prematurely.
The reason that the Prius’s batteries can last as long as the rest of the car is that the system is careful to keep the charge between about 55% and 80%. Wander outside that range, and you shorten battery life. Li-Ion really isn’t much better than NiMH when it comes to charge cycles and deep discharge.
These battery technologies lend themselves to recovering and reusing relatively small amounts of energy (regenerative braking). Storing and releasing large quantities of energy is something else.
There are promising energy storage technologies for electric vehicles in the lab (e.g., Altairnano, Firefly Energy, and possibly EEStor) that claim to have greatly improved on the deep discharge and charge cycle limitations. If and when they hit the market, this idea could be a winner.