Thanks to Felix Kramer of the California Cars Initiative for tipping off Green Wombat to an enlightening exchange between a Toyota executive and a U.S. energy commissioner on the automaker's blog. The topic: plugging a plug-in hybrid electric (PHEV) version of the Prius into the power grid to supply electricity when demand peaks.

In a lengthy reply posted less than a day later - warp speed for a multinational corporation dealing with a hot-button topic - Miller said Toyota's priority is to produce production-ready PHEVs rather than build mini power plants. "Our expertise is in building motor vehicles. It’s not in power generation," wrote Miller. "That’s something that we would prefer to leave to those best equipped to do it." Nevertheless, he went on to discuss the challenges of V2G (vehicle-to-grid capability). Among them:

* Battery performance.
* Coordinating thousands of PHEVs to supply power to the grid.
* Building and financing the V2G infrastructure.
* Consumer's willingness to accept lower fuel efficiency by giving up battery power to the grid.

(One hurdle not mentioned but something that Tesla Motors CEO Martin Eberhard has raised with Green Wombat is the impact of V2G on PHEV or electric car battery life.)

"The automobile business is changing and will, we feel sure, require strategies, partnerships and alliances we might not even have thought of yet. We don’t even know, for sure, if PHEVs will come to market in the way in which we think they will," concluded Miller. "So while the potential for V2G is another intriguing aspect of hybrid technology, we must not become sidetracked so that we lose sight of the immediate goal. That goal is to produce an affordable, reliable PHEV that can be sold in large quantities, that can be serviced at any dealership, and that will meet the needs of the American motorist."

For CalCars's Kramer, whose organization promotes plug-in hybrids, Toyota's willingness to even publicly discuss vehicle-to-grid was more important than Miller's laundry list of obstacles to V2G. "The company's reservations are less significant than the fact that it is paying very serious attention to the subject," Kramer told Green Wombat in an email. If you live in the San Francisco Bay Area you might spot the PHEV enthusiast tooling around in his converted 100-miles-to-the-gallon plug-in Prius, as Green Wombat did just the other weekend out at Point Reyes National Seashore.

Green Wombat is also fascinated by how a high-level U.S. government energy official and a corporate executive are having a direct, and apparently minimally mediated, open discussion via blog on a matter of public policy. Toyota's willingness to talk no doubt owes in part to the pressure exerted by groups like CalCars and the interest of utilities like PG&E (PCG) and Southern California Edison (EIX) in V2G. Google (GOOG) also has focused attention on the issue by installing a vehicle-to-grid charging stations at its corporate headquarters in Mountain View. Now the question is, will Honda (HMC), General Motors (GM) and Ford (F) join the discussion?