Eternal Vigilance is the Price of Efficiency, part 1 – electricity

Eternal Vigilance is the Price of Efficiency — power is ever stealing [into your home]. — Me, with apologies to Wendell Phillips, Thomas Jefferson, or whoever said it first.

Those who know me know that I’m a little obsessed with energy, specifically renewables, and conservation/efficiency (it all goes hand in hand; with more conservation & efficiency, renewables can be that much closer to powering our world).

To that end, I’ve done a lot of efficiency work on our house, and have tried to make some behavioral changes as well, to conserve. Some of this work has been chronicled in an answer at Quora.

But how do I know if it’s really paying off? Not from a financial payback sense, but from a “am I actually using less energy than before” sense?  We measure, of course… and we graph.

Let’s start with Electricity. It’s easy to measure from monthly bills, and since by and large we don’t use AC, our electricity use isn’t terribly seasonal (modulo more lighting in the winter, and a couple hot weeks in the summer). I’ve found two types of graphs to be informative. The first and most obvious is to graph usage over time. Because the number of days in a given utility bill can vary, I plot the usage from each month’s bill, normalized to kWh per day for that period:

The pure month-to-month is pretty noisy; a rolling 6 month average gets things reasonably smoothed out, and there I can see a trend that I like. It’s plateaued a bit, though; we seem to have reached an ongoing average of around 12 kWh/day, or around 365kWh/month. While that is less than half of the Minnesota state average, I do know of a family of four who can come in under 200kWh/month – so there is room for improvement (somewhere… finally getting this server down to 18W will help to the tune of about 10kWh/month).

(Note, above is actual household usage, independent of any solar production, which is another variable.  I have, however, plotted the ongoing percentage of our use covered by solar on the green line.)

But there is indeed some seasonal variability; for that, it’s neat to plot each month against the same month from previous years, a trick I learned from the soon-to-be-defunct Microsoft Hohm:

Apparently, around September 2009 is when I started paying attention. A few months after that, it got even better. Early on, it was obvious things like getting rid of the insane power-hogging Pentium 4 Mythbox that ran 24/7, and not leaving the electric heater running in the basement.  Many other improvements followed – incremental lighting efficiency improvements, diligent use of the clothesline, making sure all computers slept/suspended appropriately, etc.  What amazes me is that we’ve cut it almost in half since those early days.  Maybe I was just an unabashed power-pig before?

It looks like we’re hanging in there at 12kWh/day – I’m sticking to my diet. Yay!  I’ll talk about graphs for water and gas in subsequent posts.  I’ve slipped a bit on one of them.  Stay tuned…

See also:

6 thoughts on “Eternal Vigilance is the Price of Efficiency, part 1 – electricity

  1. Pingback: Eternal Vigilance is the Price of Efficiency, part 2 – water | Eric's Blog

  2. Eric, a couple of questions (I looked at some of the archives but didn’t see this mentioned). Have you done anything for energy storage? I’m interested in what the possibilities might be if the grid were unavailable. We actually have pretty frequent power failures and brown outs though they have never (since 1986 when I moved here anyway) lasted longer than a week. Frankly the week is long enough for me to be interested but especially if there for any reason were longer times without the grid some method of storage would become important to get through the times where the sun doesn’t shine. Second, do you have any data yet regarding the longevity of the solar panels? They must fall off in efficiency over time but I’m wondering whether you see anything on that yet. Thanks.

    • I haven’t looked into storage – for starters, my microinverters aren’t really designed to work with a battery system – usually one uses a central inverter for a setup like that. And without a setup like that, we actually go dark when the grid goes out just like anyone else – it’s an “anti-islanding” requirement so that your panels don’t energize the grid and zap a line worker.

      As for a week’s outage – I think that storing a week’s worth is pretty unlikely… for that, you probably just need a generator.

      The panels do degrade over time – at the time I bought mine, they had a staggered warranty of ?? ??90% rated output at 10 years and 80% of rated output at 25 years. These days I think manufacturers are going to something more gradual, like losses less than 1% per year or so. I don’t think I have enough data to know for sure how mine fare, yet – it hasn’t even been 2 years.

      • Actually let me revise what I said, I got up at 6am this morning and I’m not making sense yet. ;)

        An combination grid-tied/off-grid+battery-backup system would work just fine indefinitely as long as you have sunshine. In the winter, we produce a small-ish fraction of our total household use, because snow & cloud cover impacts production a fair bit. Our yearly average is about 70%, but it’s the winter months pulling it down.

        So a limited set of circuits on battery backup could make a lot of sense, to run the fridge, lighting, and other crucial things.

  3. Keep up the good work! Have to say we’re hogging electricity lately — but it’s temporary. We have a German exchange student living in our furnished basement, and she’s pretty much running our 450-watt e-heat wall heater 20 hours per day. Won’t be seeing 200 kWh months until she’s gone in March. Of course, she won’t be able to make much of a dent in our 7,000 kWh of banked home solar produced electricity, which, as you know, we’d be hoping to use for an EV that we won’t be able to buy for at least another year or two. Actually, we’re going to need two EVs some day to cut into that banked solar-produced electricity, either that, or invite other EV drivers over to tank up on our solar electricity.

  4. Pingback: Two Years of Solar | Eric's Blog

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