## 02 October 2010

### Four light bulbs = 15,000 miles in the Mini E

There has been an interesting analogy mentioned on a few blogs lately, and I have confirmed the calculation.

The claim is that driving 15,000 miles per year in a Mini E or a similar electric car uses about as much electricity as four 100 watt light bulbs burning all year. You can read Tom's explanation here, near the end of the fifth paragraph. So much for those who say large numbers of electric cars cannot be supported by the present electric grid. Nonsense!

To go further, I am curious how many of those 4 light bulbs I can offset by efficiency measures. So I just counted up all the light bulbs in my house, found out how much electricity this house used last year and got average percentages of residential electricity usage consumed by lighting from a Wikipedia article.

Here is how it works out: I have over one hundred light bulbs in my home, but according to the statistics they are probably only on for an average of 2.3% of the time. My math says this is equivalent to two light bulbs being on all year, one of them at 60 watts and the other at 75 watts. That's roughly 1.2 megawatt hours per year for lighting, or 12% of the total 10 mWh this house used last year.

Even so, since about 93 of my lights are now high efficiency fluorescent bulbs, I am saving about the equivalent of one of those 100 watt incandescent bulbs burning all year. One down, three to go to offset the electricity used by an electric car.

We have only been in our new house for several months, but our electricity usage is trending 10% below last year, even though this summer was much hotter. This is because we keep the thermostat at 78 degrees F in summer and open windows at night if is cool outside. So I figure that saves the equivalent of about another two light bulbs burning all year at 100 watts each. Now I am three down, one to go.

Many other electric car drivers have mentioned that they have installed solar power on their homes, which easily offsets more than all the energy used by their electric car. We have looked into solar power, but here in North Carolina we see a better return from installing a ground source heat pump to replace the upstairs zone of our air conditioning and furnace. So we are doing that now.
I have not run the numbers yet, but I feel confident that we have already offset more than enough electricity to power an electric car. We don't have the Mini E anymore, since they would not let us bring it to North Carolina. But we will probably get another electric car in the near future.

Plus, we will probably add solar power in the coming years. We are holding off for several reasons: While the federal and state tax incentives in North Carolina cover two thirds of solar power installation cost, the market for the production credits has dried up here. I understand that in New Jersey, the Solar Renewable Energy Credits (SRECs) can be worth about 60 cents per kilowatt hour generated. But at the moment there is almost no market for SRECs in NC. Plus, electricity in NC costs about half of what it costs in NJ. So payback times for solar power are longer in NC. In addition we are in an urban setting and have a lot of trees, not to mention a hip roof, all of which is less than ideal for solar power. Still, we believe we can design a good system to generate 3 kilowatts of solar power in the coming years. Maybe more over time if micro inverters that support battery backup systems become available. And of course prices of solar panels should continue to drop.

So in summary the argument that electric cars just move pollution from the tail pipe to the smoke stack is ridiculous. It is easy to offset the electricity used by an electric car.