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Energy savings actually save energy August 16, 2012

Posted by Maury Markowitz in power grid.
Tags: , ,

For the last couple of years, with increasing frequency, I’ve been hearing about something called “the rebound effect“.

The rebound is, supposedly, something that happens when people do a good thing… then they do more “bad” things that offset all the good. So if you take up jogging, you feel good about your health, so you eat an extra donut. Or when you put in energy-saving appliances, you feel good about that, so you leave the TV turned on longer and end up using more electricity.

I’ve always been suspicious of these claims, they sound too simple to be true. Most joggers I know are in better shape than I am! But I never had a smoking gun, nor the time to look into it too much. Well that’s over. I was listening to The Agenda in the Summer and I heard someone repeat a whole list of these stories, which included a new one…

Buy a hybrid car and you drive longer distances.

*sigh* Game on…

Math challenges

Before I get into this too much, let’s look at why I was so skeptical. One of the examples I heard about was that if you changed out all your old-skool incandescent light bulbs with CFLs, you ended up leaving the lights on longer and burning more power in the end.

Uhhh, did anyone making this claim bother to check this on a calculator? I have a light in the dining room that’s on for maybe 3 hours a day. A CFL requires 1/9th the amount of power. So how long would I have to burn it each day to use more power? 3 x 9 = 27. That’s right, 27 hours a day.

This is obviously bogus, but in spite of that the claim just keeps getting repeated.

Ahhh, but some go on to claim that you have more money because you didn’t buy that power, so you go and spend that on something that uses more power.

Really? You’re claiming that the dollar I saved somehow translates into a higher energy value product? What if I leave it in the bank? Or give it as a tip at the bar? Come on, you’re claiming to have measured the downstream energy use of ever dollar saved on electricity bills?


Driving up daisy

But what was it about the hybrid car issue that triggered all of this?

Well go back to the original claim – if you buy a hybrid you drive more miles. This implies that someone studied the average milage that people drove before and after getting a hybrid. I find this extremely difficult to believe. I believe the only number they have, if they even have one at all, is the number of miles driven per type of car. So they noticed hybrids have more miles, and ascribe this to the rebound.

Here’s another theory… maybe those people bought a hybrid because they drive more miles? Gas is expensive and going up all the time. Hybrids save you 25% on gas. For people doing short distances, the savings in gas don’t make sense, the extra cost of the car wipes it out. But if you’re commuting long distances every day, that equation changes, and the hybrid makes more and more sense.

So which do you think is more likely? That people buy hybrids because they have some sort of subconscious post-feel-good factor that magically makes them start going on long trips they didn’t used to? Or that people buy hybrids to save money on long trips?

So, here comes an antidotal example – me. I drive a Honda Civic Hybrid because my work is about 100 km one-way from the house. The meter tells me I get an average of 54.1 mpg (64.9 mpg Imperial, 4.4 l/100km). So that means I burn 8.8 litres of gas a trip, which at current prices is about $11.50 a day in gas.

If I was in my old clunker I’d be getting maybe 35 to 40, so around 6 l/100 km. That would cost me $15.60 a day. So $4 a day, times 250 days a year, times, say, 4 years  = $4,000. I got my HCH for $14k, when normal Civic SE’s with similar miles were around $12,000. So I win, $2,000 in my pocket. And I get to feel good.

Don’t argue, measure!

I’m an empiricist. You can give me all the theory you want, and I won’t believe a word of it. Go and measure it.

So I was rather happy when someone did that, and went out and actually measured this rebound effect. As I suspected, it’s BS. Actually it’s not complete BS, there is a measurable effect. But that effect is much smaller than the original savings.

The paper measured about a 20% rebound in power use. That is, if you did something that saved you 10 kilowatt hours a year, you’ll rebound, on average, 2 kWh. So the total savings are 8 kWh a year. The common definition of the rebound is that you use more power. So I stick with my original definition: it’s BS.

So keep on buying hybrids, CFLs and new fridges. You are doing good, no matter how bad you try to be.


1. The Abundance Effect « Donal - November 1, 2012

[…] so the answer there is always less regulations. But the Rebound Effect is a well-known meme. In Energy savings actually save energy, Energy Matters disagrees with common perceptions of the Rebound Effect, and resorts to using […]

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