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Friday, December 10, 2010

On the Grid

Our charging station was installed yesterday. As I mentioned in an earlier post, we're buying a Nissan LEAF™. Delivery of the vehicle should be in a few weeks, so we're getting our infrastructure in place. Until there's a network of public charging stations, our LEAF will mostly be recharged at home.

So what is the impact of a LEAF, on the grid, and the atmosphere? The charging station is on a 240V/40A circuit, slightly larger than what an electric clothes dryer plugs into. But we won't use all of the circuit's capacity. The battery charger is actually inside the LEAF, and is limited to 3.3 kilowatts (KW), slightly less than the clothes dryer or an electric oven, and slightly more than a dishwasher. It's also about half of what a typical central air conditioner uses. So not really a big deal.

What if everyone in my neighborhood gets an electric vehicle, and we all start recharging at midnight? Do we have a problem? Look at it this way. Already, pretty much every oven and plasma-screen TV in the neighborhood is going Thanksgiving Day, all day long. No brownouts so far. And all the turkeys get cooked.

Now, what about carbon footprint? If all we've done is move the CO2 emissions from the tailpipe to the power plant, have we really accomplished anything? The answer is: it depends. There are a number of ways to generate electricity: coal, natural gas, nuclear, wind, solar, and hydroelectric. The amount of CO2 produced depends on the source:

Source

Pounds of CO2 per kilowatt-hour (KWh)

Coal

2.25

Natural gas

1.4

Solar

0.24

Wind

0.05

Nuclear

0.01

Hydro

0.01

One KWh of electricity will propel the LEAF approximately 4 miles. We can calculate a "miles per gallon equivalent" (mpge) for the LEAF by taking the amount of CO2 produced by the source and comparing it to the CO2 produced by a gasoline-powered vehicle. Burning a gallon of gasoline produces approximately 19 lbs of CO2. Using this information and the table above:

Source

mpge

Coal

35.4

Natural gas

57.2

Solar

338

Wind

1690

Nuclear

5640

Hydro

5640

Fortunately, no utility is 100% coal-powered. Typically, a mix of sources is used. Our local utility, Puget Sound Energy, is balanced among coal (32%), natural gas (30%), and hydro (36%). Plugging in at home will give us 70 mpge. Across the lake, Seattle City Light is almost all hydro (91%), with a little nuclear (4%). If we recharged downtown, our mpge would jump to almost 1600. American Electric Power, the largest power supplier in the Southeast, uses primarily coal (66%) and natural gas (22%), yielding an mpge of 44.4

So, a LEAF recharging in Georgia is roughly equivalent to a Prius. That same LEAF recharging in Seattle has a carbon footprint 40 times smaller. I'm not keen on moving across the lake, so it looks like my next move is to install a nuclear power plant in the backyard.

1 comment:

Chad Schwitters said...

Hi,

That's a good start on the numbers, but if you're looking upstream for electricity, don't forget to look upstream for gas too. There are emissions involved in finding, extracting, refining and transporting gas; that adds somewhere in the range of 20-25% to their figures.

For a good overview of about 40 studies on the subject, see www.sherryboschert.com/Downloads/Emissions.pdf.

A mini nuke would be kind of cool, but you could also put solar panels on your roof--almost 40% of EV owners have done that. Or sign up for PSE's Clean Energy program, where an independent non-profit verifies that PSE adds enough wind power to cover your use. That costs about an extra 10%.