Have a 3.92 KW system in Hawaii, which of course has great solar insolation and is producing a little over the rated 6,600 KwH annually. Until we started driving/charging (L2) at home the LEAF, we were net producers, utilizing about 5,000 KwH annually for household needs. After a couple months with the LEAF, seeing about 4.00 Wall to Wheels KwH efficiency, I'm estimating about 2,800 KwH annual consumption for charging - which will clearly require an upgrade of our net metered PV system to zero out.
Hawaii has the highest residential electrical costs in the nation, currently running about $ 0.36 per KwH for a typical user, with a 7% inflation curve over last 5 years....which makes using solar more critical to EV economics than maybe so in other places with more reasonable electricity rates. Our power company, HECO, uses a running cash credit reconciliation process, but at the end of a 12 month period, any cash credits go back to them and you are zeroed out for the next 12 months. Their feed in tariff program, wherein one can sell power to the grid at a long term fixed rate, is generally considered unfavorable to residential users because it locks in about $ .21 per KwH provided for a long period. HECO also has a TOU program specifically for EV users, but it is indexed so that you pay 0.06 less than the going rate for off-peak charging, and if you happen to charge during peak hours, you pay $ 0.02 more than the going rate. And the user has to pay for the separate meter dedicated to the EV charging circuit - so I'm not sure that is such a great deal.
As I have TED to monitor both the PV system generation and household consumption, with a 3rd independent monitor for the EV charging circuit, I should be able to nail down the EV consumption data pretty well with a few more months experience with the LEAF.
One question I have, that I will probably post in the battery/efficiency sub-forum, is whether I can expect the efficiency of the battery to degrade over the years of operation - or just the battery capacity. Since our short commute doesn't make the expected degradation in battery capacity (e.g. range on a single charge) a major issue, what about efficiency. Can I expect the wall-to-wheels efficiency to degrade with time, even at a lesser rate? Some say no, but it seems that as a battery's capacity to carry power gets reduced over time, it's ability to receive that power and to convert it to mechanical power would be less than when it is brand new. Another factor to consider when designing the solar system upgrade...including the 0.5% annual de-rate in PV production, electrical rate inflation, increase in household consumption with two growing kids...and the like.