In general, how efficient is the act of charging a battery? For example, the battery for the Leaf is supposed to hold 23kW-h. How much, in kW-h going through your electric meter is it likely to take to get a kW-h into the battery? Put another way, if I want to zero out usage for an electric car using solar panels, will an AC kW-h coming from the panels (or the grid) be nominally equivalent to a usable kW-h in the car, or will I have to generate a lot more than the car will “use”?