Calculating my home’s energy inputs and outputs.

I’ve been wondering what the inputs and outputs are of my home energy usage. For some months now, I’ve used a CurrentCost Envi to track my house’s energy usage, so I know the numbers in kilowatt hours: 8,166 kWh in the past 12 months, an average of 680 kWh/month, with a low of 454 kWh (September 2010) and a high of 1,180 kWh (January 2010). But what does that mean?

My power comes from approximately an equal mix of coal and nuclear, according to Dominion, my power company. Let’s start with coal.

Although not all coal is created equal, it basically takes one kilogram of coal to generate two kilowatt hours of electricity. Coal itself contains rather more power, but a lot is wasted as heat in the generation process, and still more is lost in the distribution process. Of my 8,166 kWh, about 4,093 kWh came from coal. That means that 4,511 pounds of coal were burned to power my home in the past year. The pollution side of coal is rather worse. Each unit of coal results in the emission of 2.93 times as much CO2 by weight (assuming 80% carbon coal), a result of carbon emissions bonding with oxygen. The coal burned to power my home, therefore, resulted in 13,217 pounds—six and a half tons—of CO2 to be emitted.

Nuclear is rather different, at least by weight. Uranium produces 360,000 kWh per kilogram, meaning that the 4,093 kWh of nuclear power for my home required 1.2 grams of uranium, which is approximately half of the weight of a penny, and slightly more than a paperclip. The amount of waste is similarly minute, in quantity. Uranium generates 3 milligrams of waste per kilowatt hour, or the size of a standard-issue snowflake. For my home’s usage in a year, that’s 12 grams of nuclear waste, the weight of two quarters. Of course, a straight comparison of uranium to coal by weight isn’t particularly meaningful.

None of this considers the mining or transport of that coal or uranium, the storage of the waste, etc. But I find it useful to know that powering my house for the last year required a over two tons of coal, a single gram of uranium, and produced north of six tons of CO2 and twelve grams of nuclear waste.

For the record, I participate in Dominion’s Green Power program, meaning that I pay 1.5¢ extra per kWh to offset 100% of my power use via renewable sources. But those very electrons don’t travel to my home—they just get mixed into the regional grid. So while I can feel good that I have prevented all of the enumerated energy sources and pollution from being used and emitted on my behalf, I’m not kidding myself—it’s 98% coal and nuclear power that’s coming into my home.

(Previously: “Rethinking Virginia’s energy infrastructure” and “Degree days and energy usage.”)

16 thoughts on “Calculating my home’s energy inputs and outputs.”

  1. ” it basically takes one kilogram of coal to generate two kilowatt hours of electricity”

    think about this.

    suppose you had a local house coal generator. You’d really put power your house on one lb of coal per hour?

    12 lbs per day x 30 = 360 lbs per month….

    oops… that’s not working.. cuz you said a ton (2000 lbs) for the year…

    so could you actually power your house with coal if you were so inclined to?

  2. You said that it takes about 2Kg of coal to make one Kw of power. Shouldn’t that then mean that you use 2,046.5 Kg (not pounds) of coal annually? That would then be about 4,511 pounds.

  3. 8,166 kWh / 2.2 lbs = 3711 lbs

    back of envelope dooding…….

    8166 kwh / 365 days = 22 kwh per day

    22 kwh / 2.2 lbs coal = 10 lbs coal

    Waldo frets about environmental damage and should.

    besides mountain top removal, mercury contamination, etc.

    but also keep in mind that Nukes are subsidized and if ratepayers had to pay the actual (unsubsidized) cost of nuke power it likely would be far more expensive:

    http://www.stanford.edu/group/siepr/cgi-bin/siepr/?q=system/files/shared/pubs/papers/briefs/policybrief_jan02.pdf

  4. You said that it takes about 2Kg of coal to make one Kw of power. Shouldn’t that then mean that you use 2,046.5 Kg (not pounds) of coal annually? That would then be about 4,511 pounds.

    I should retitle this blog entry “On not doing math in public.” Because, Sean, you are absolutely right. :) I thought I was being so cautious in my metric->imperial conversions, figuring that American relate to imperial far better than metric, but clearly I did the opposite. :) I have corrected the series of mistakes that cascaded from that kilogram/pound error.

    NASA has my sympathies now. ;)

    so could you actually power your house with coal if you were so inclined to?

    Larry, I once read about somebody who had created a wood-fired pickup (the entire bed had been given over to a steam engine), so I don’t see any reason why somebody couldn’t use a small turbine to create what’s basically a steam-operated house. Just like running your house on wind, though instead it’d be steam turning the axle. But I imagine that the coal dust pollution would put a real damper on the endeavor. Also, with a generator of that size, I bet that it’d be a lot less efficient, requiring a great deal more coal to get the job done.

  5. Waldo – the concept of residential energy is fascinating to me.

    For instance, the are net zero homes these days that run on a combination of solar/wind with natural gas backup generators. One could live “mostly” off grid (using the grid for backup power) ….. for a price.

  6. yes….exactly….

    but as long as coal-powered plants deliver “cheap” – even if the attendant environmental impacts – we’ll continue to use it.

    and I absolutely LOVE the “Clean Coal” commercials on TV these days.

    I’m thinking… how clean would that coal be if you used it at your house to generate power – even using advanced boilers….

  7. Waldo, I’d second Brian’s train of thought and heartily endorse a blog post reviewing the CurrentCost Envi, talking a bit about the pros and cons, your experiences with it, how it works, how installation went, what metrics you found the most useful, whether you were able to make energy gains, what new insights you gained into the impact of energy use decisions, etc, etc. Even an evil coal-burning conservative like myself is all into reducing energy use because it saves money. :-D

  8. I’ll add an Envi blog entry to my to-do list, Hans. :)

    Brian, if I properly recall the book on magnetism that I read last month, the Envi works by measuring the strength of the magnetic field in the power line that comes into the house. The more electricity that is being drawn, the stronger the electromagnetic field. That can be measured quite precisely, allowing the measurement of the power usage within a few watts. Which might just be a long way of saying “magic.” ;)

  9. The pickup looks like an AC clamp meter used to measure amperage. Watts = Voltage * Amperage. While it may be an iron vane type (as you describe), I suspect it is a current transformer type which acts like a transformer – taking a higher current past a secondary coil, the resulting secondary output provides a converted reading for the conductor being measured – your house electrical supply.

  10. Without knowing the size of your house, that seems pretty impressive if you are all electric.

    I have wondered about that Dominion program. Is it a regulated activity? It would seem on the surface to have a lot of complexity. So, I wonder how Dominion actually proves the effectiveness of the program and that they have acted as good stewards of customer contributions.

  11. Without knowing the size of your house, that seems pretty impressive if you are all electric.

    It should be—we had our house designed to be as energy-efficient as possible. :) We sited it cautiously and used copious used blown cellulose insulation. We’ve got a conditioned crawlspace, and the whole thing is passive solar, which significant reduces our need for heat and air conditioning. Instead of a traditional water heater, we’ve got a hot-water-on-demand system. Part of the process of having a (relatively) energy-sipping house was having a (relatively) small house—it’s about 1,400 square feet.

    There are a few non-electric elements: the range, the water heater, and the clothes dryer. Everything else is electric.

    I have wondered about that Dominion program. Is it a regulated activity?

    I used to know this, but I must admit that it has all left my head. :) I seem to recall that it was part of Dominion’s re-regulation a few years ago, after they discovered that the world of deregulation was big and scary, and came back to the state fairly begging to be regulated.

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