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Alternative Energy (Solar/Wind) - Economics of Charging car batteries through renewable energy sources
Expert: Marshall Scott - 8/28/2008
Question
Dear Marshall
I have a query regarding a paper that I’m writing on renewable energy charging solutions for electric car batteries. I read online that the Tesla Roaster for example uses a Lithium-ion battery that stores 53 Kilowatt hours (Kwh) of energy on a single charge. Is it correct to assume that if for example the costs of generating wind power is say 5 cents per KWH then fully charging the Tesla battery (53 kwh) from wind power would cost 53 x 5= 265 cents or USD 2.65 for a full charge? I’m not familiar with the technical aspects of battery charging (for instance how much energy is lost in charging) so wasn’t not sure about the economics either.
Would be glad for your feedback!
Thanks!
Mahesh
Answer
Hello Mahesh,
I asked a friend of mine who supposed to be getting his Tesla somethime in 2010, to look at your inquiry. I figured he would have a good idea about cost and charge loss associated. He sent me a quote from a Tesla representative.
September 24, 2007
„The Recharge Energy of 31kWh/100mi is the electricity you pay for from
the grid to recharge your Roadster. It works out to ~75kWh of alternating
current (AC) for a full recharge. Our ESS (battery) produces direct
current (DC) and holds ~53kWh. The difference between these two numbers
is due to charging inefficiencies, including the use of air-conditioning
to thermally-manage the battery during charging‰.
-Andrew Simpson
Tesla Vehicle Systems Engineer
Now the 31kWh/100mi is the EPA test cycle, which is under ideal lab conditions and so the ratio will vary based on actual driving conditions. The test cycle is the standard for all the milage ratings you see on the stickers for cars at the lot. I have yet to achieve 29 MPG on my 2004 Saturn wagon, and wouldn't expect to with the family weighing it down. For the Tesla I would guess (with extremes conditions nulled), 130 to 200 mile range per charge based on how and where it was driven.
As far as the cost per kWh for wind generation, I would imagine that, the 5 cents per kWh is (the cost of the system + the life time maintenance) divided (by the average profit per kWh produced x the life of the system). My knowledge of wind is very limited so I can't confirm your 5 cents per kWh.
Now if you were to look at a solar system on a residential site, the typical break-even is about 10-20 years depending on the site electrical consumption. As the warranty for the panels is 25 years, the life of the system can be double that, with a replacement of the inverter about every 15 years. So unlike wind, its cost per kWh is a negative figure.
Example: 10 kW solar that produces 1650kWh per month. Cost about $85,000 and lets say it was designed with the Tesla load anticipated. We call it a 15 year payback with a 30 year life for the solar system. That means that in 30 years the system would have made another $85,000, without extrapolating for the energy cost increase over time (otherwise it would be more).
I hope this helps
Marshall
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