Tony Wildish's Simple Idea: Read His Electricity Meter. Then Record What it Tells Him.

By Tony Wildish*

A year ago, I started hearing a lot about the TED Energy Detective products. I thought at the time that they sounded like a great idea. Like a calorie-counter for dieters, being able to see the numbers whenever you need to is a great way to make you aware of your consumption.

The only problem for me is that I live in France, and TED was not available for our 230 volt/50 Hz supply at that time. So what could I do to begin to understand my electricity consumption? I decided to make a weekly reading of my electricity meter, and see if that would tell me anything useful over time. Reading the meter once a week is a far cry from having real-time results like the TED would give me, but I figured I might still learn something useful. Here's what I found out:

Plotting my energy use

The graph shows the result, with the day of the year along the x-axis and the number of kWh per day on the y-axis, calculated as the daily average between two successive weekly readings. Our total electricity use for the year is about 13,000 kWh, or 36 kWh per day, averaged over the year.

If my math is correct, the average in France works out to 41 kWh per person per day, so we're about 14 percent below average for a 2-person home. About two-thirds of homes in France are heated primarily by electricity, ours among them. So we're probably doing a bit better than that number alone suggests, because the average is including people who heat their homes with gas and oil. That's nice to know, since we had already taken steps to reduce our consumption.

We don't use heating in summer, of course, and we don't have air-conditioning, either. So the flat summer use of about 17 kWh per day is also instructive. That represents electricity used for our hot water, cooking, washing machine, fridges, computers, TV, lighting and other constant factors of life.

Clearly we use more electricity for lighting in winter than we do in summer because of the shorter days. We doubtless use more for heating water, too, because the water that comes into the apartment is colder to start. I can't quantify how much more that would be because I don't have detailed measurements, so I'll just ignore that effect for now. I'll assume that my 17 kWh per day baseline in summer is the same in winter, which means that anything above that constant load can only be the electric heating.

Given that 17 kWh per day is almost half my total, that leaves the remaining 19 kWh per day for heating. Heating is the biggest single system for which I use electricity. If I want to save 1 percent on my total electricity use, I can do it by saving 2 percent on my winter heating. That's good to know; it's nice to have a number for the amount it represents.

That 19 kWh per day is an average throughout the year, but that doesn't tell me much about daily use. The graph peaks at about 62 kWh per day, so heating was accounting for 45 kWh per day at those times. The first 60-80 days of the year show considerable fluctuation from one week to the next. There are two high-consumption weeks around day 50 which stand out from the rest, and indeed we did have a very cold spell here at the beginning of February. But that two-week period only adds about 6 or 7 kWh per day over the weeks around it. So I can see that my heating demands vary with the weather, and now I have some idea of how much.

Hot water as electricity hog

There's another very instructive feature in that plot: It's not one I had planned on, nor do I care to repeat it. At the beginning of September, on about day 240, our water heater broke down. The plumbers took about four weeks to fix it completely, and we had two weeks without any hot water at all. During that two weeks, our baseline dropped to about 7 kWh per day. So I learned that heating water takes about 10 kWh per day in summer; the other 7 kWh per day power all the other things we use all the time.

Thanks to this experiment, I discovered that our cooking, lighting, computers, fridges, and washing machine use about 7 kWh per day. Providing us with hot water takes 10 kWh per day, and heating in winter takes up to 45 kWh per day, depending on how cold it gets. I also learned that heating accounts for a bit more than half of our electricity use, averaged over the year (19 kWh per day).

That's nowhere near as much detail as I could get from a real-time energy monitor, but I think that's an impressive amount to deduce from a simple weekly reading of my electricity meter.

*Tony is a programmer living and working in France, in the Geneva valley. A lifelong interest in science and nature has fueled his concern about the environment and the ways we are affecting it. When he's not surfing the Web, he enjoys photography, gardening, and walking through the Jura foothills.