After almost 18 months of operation, our solar panels appear to be generating a net surplus of ~5200 kWh per year, measured as a running annual average. That's net surplus on top of what our household actually uses (about another 5000 kWh/year).
We just
bought a Nissan Leaf all-electric car. If it drives 1000 miles/month at 3.9 kWh/mile, it will use 256 kWh of electricity at a cost of 7.41 cents per kWh. That works out to 1.9 cents per mile, or $19/mo. In a year of driving, the Leaf should use about 3000 kWh and cost us $230 in electricity.
So if our solar panels are already generating 5200 kWh of surplus energy, and the car is going to consume about 3000 kWh of that, then on an annual basis our panels should still generate more power than our house and car together will use. We're approaching net zero.
Before the Leaf, our panels were generating about $400 in free power that we used in our home, and then $400/year in surplus (~10,000 kWh at 8.75 cents/kWh).
After the Leaf, our panels should generate the same $370 in free power that we use at home, $230 in power for the Leaf, and then about $160/year in surplus energy (2128 kWh at 7.41 cents/kWh), in part because our power rates went down.
Separate from these cost savings are the $5,000/year production incentive, which we get for generating at least 9260 kWh gross power, before household usage, at 54 cents/kWh.
Also separate is the cost of gasoline we're not burning by driving the Leaf. At $2/gallon the SUV costs us 11.7 cents/mile in gas (as compared to 1.9 cents/mile for the Leaf). So driving 1000 miles/mo in the Leaf instead of the SUV would save us $98/mo in net fuel cost after accounting for electricity costs. So that's ~$1400 in avoided gasoline costs and $230 in new power costs, for a net savings of $1170/year. So from a financial perspective, our electricity is much more efficiently spent driving our car (if it displaces gasoline) than being sold back to the grid.
If I've done the math right, our household budget should be improved by $5k+$1170+$370+$160 = $7000 per year by having solar panels and an electric car. That's $7k more I can put into the stock market. Our total out of pocket costs for these items was about $30,000 (32k solar panels - 30% tax rebate +$7700 car), so one convoluted way to look at this math is that we're "earning" $7000 on $30k, or 23.3% guaranteed return per year. That only lasts until 2020, at which point the production incentives expire, and our return drops to a more meager $2000/$30k or 6.66% per year. Good for the environment AND my bottom line!
That math is more than a little bogus because it's figured on initial purchase price, not compound growth, because those profits are not re-invested into more income-producing assets like they would be if they were stock earnings. I'm not complaining.