How big a PV array do I need to run my all-electric car?

One hears reports that soon-to-be-coming (or already in existence Tesla Motors) electric cars get effectively 200 – 250 MPG using some method of fairly(?) converting the electricity use into “gallons of unleaded” (is that with or without the 10% ethanol like we have in MA! 🙂

Anyway, let’s use some math to see what that means in KWh per year and see how many solar PV panels we would need to charge
such a car.

250 miles/gallon * 1 gallon unleaded / 114,000 BTUs * 3413 BTUs / 1 KWh * 2000 KWh / PV array => 14,969 miles!

OK, so that is enough miles for one year of driving for me. And the array we are installed (30 panels * 200W/panel=>6KW) will hopefully output approximately 7200 KWh per year, so the 2000 KWh I plugged in above is just a fraction. So assuming we can charge the car solely when the sun shining, that means we will still have 5200 KWh (433/month on average) left for “household operations”. That should be fine since in Shutesbury we averaged close to 4200 KWh/year (350 KWh/month), but we will probably(?) have an electric stove and oven this time(?) so that will use a bit. Plus some air-source heat pump usage for heat and AC. Still thinking about a pellet stove for heat on occasion. And aiming for nearly 100% solar for hot-water, instead of the MA typical 60%. More on that in another post.

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