@digitaltim: right, it serves as a capacity resource but, so far, retail loads aren't able to provide ancillary services because PJM (nor any other grid operator) can measure and verify their performance. @rolosrevenge is thinking that the Model S's ability to report out and adjust its rate of charging directly over the air would allow cars to offer regulation while charging. The open question is whether PJM would accept that automated response as equivalent to a "revenue quality" meter. I'll ask Mike Kormos next time I see him, or one of you should if you get to him first. I've been looking for an excuse to drive my Model S down to King of Prussia, but I haven't needed to go to any of the stakeholder meetings lately.