Personal energy consumption benchmark 2007

As of the start of 2007, I am living in Cambridge, Massachusetts, and commuting 16 miles round trip by car at 35 mpg to GreenMountain Engineering in Waltham 250 days/year. That's about 125 gallons of diesel per year, and I drive an additional 20% for other reasons. That's around 150 gallons * 155 MJ/gallon = 25000 MJ/year = 25 GJ/year. Increase that by about a third to include the amortization of the energy used to build the car and transport the fuel before sale, according to the Institute for Lifecycle Environmental Assessment (summary of study by Maclean and Lave of Carnegie Mellon, 1988). That's 33 GJ/year.

Additionally, I live in a house that consumes an average of 100 therms of natural gas and 400 kWh of electricity per month year-round. The total for the house is (100 therms * 105 MJ/therm) + (400 kWh * 3.6 MJ/kWh) = 10500 + 1440 MJ = 11940 MJ/year. I share the house with my girlfriend, so count this as 6 GJ/year. My office is similar in size to our house, but we have 4 employees, so add another 3 GJ/year. The total is now 42 GJ/year.

I eat about 2500 kilocalories of food per day, and that reflects 7500 kilocalories of energy used, once farming and transportation energy costs are included. I probably do slightly better than that buying local produce and eating mostly vegetarian. (The 3:1 ratio is from a 2002 paper by Leo Horrigan, et al., of the Johns Hopkins Bloomberg School of Public Health.) That's the same as 7500 kilocalories * ~4 kJ/kcal = 30000 kJ = 30 MJ/day, which corresponds to 11 GJ/year. The total is 53 GJ/year. Virtually all of it comes from non-renewable resources (diesel, natural gas, and electricity from mostly coal).

This omits the amortized manufacture and transportation energy for the physical goods I buy--computers, books, furniture, clothes.

For reference, I've read of typical consumption rates for North America in the range of 200-300 GJ/year.

Incandescent vs. compact fluorescent vs. LEDs vs. halogen

In 1996, I worked at an environmental foundation on the coast of Maine that was an early adopter of compact fluorescent bulbs. At the time, they were expensive, and they flickered when you turned them on. After a long winter of getting flickered at every time I turned on the light, I started avoiding compact fluorescent bulbs.

Last week, one of my energy-zealot friends gave me a 1200 lumen compact fluorescent bulb after I commented on how quickly her CF lamp turned on.

I now have the 1200 lumen CF bulb in one of the overhead lights in my house. There is an identical lamp on the same circuit that still has an incandescent bulb rated at 1280 lumens. Both lamps have glass enclosures around them, so this is not the strongest argument, but neither my friend Aaron nor I can tell the difference between the two lamps-- same brightness, same color, no flickering, and no buzzing. The CF does seem slightly dimmer for the first 30 seconds after a cold start, and I have been able to hear buzzing when the CF bulb is in an open socket less than six inches from my ear. These are the most minor of objections-- overall, my previous opposition to CF bulbs is now gone.

Now that I work at a renewable energy engineering company, I've been looking at the options more closely. Below the costs compared for the bulbs I have in my house. Compact fluorescent is the clear winner. In my calculations below, I assume electricity costs of $0.20/kWh, which is what I pay in Massachusetts, but CF's now beat incandescent even with free electricity.

Incandescent (GE Reveal 100, #48690) Cost for bulb: 1280 lumens, $1.25 ea. in qty. 4, 750 hours, 100 W: $0.014/lumen-year Cost for power: (0.100 kW * 24 hours * 365.25 days * $0.20/kWh / 1280 lumens ) = $0.137/lumen-year Total cost: $0.151/lumen-year

Compact fluorescent (Maxlite Micromax Spiral MLM20S) Cost for bulb: 1200 lumens, ~$6 ea. in qty. 1, 10000 hours, 20 W: $0.004/lumen-year Cost for power: (0.020 kW * 24 hours * 365.25 days * $0.20/kWh / 1200 lumens ) = $0.029/lumen-year Total cost: $0.033/lumen-year

Out of curiosity, I decided to compare a halogen bulb from the drugstore down the street and an LED bulb I found on the global netweb to the bulbs I have. The LED bulb is almost competitive with the CF on cost, but it only produces 60 lumens, so you'd need 20 of them to light a room, which would cost $500. They would last for eternity, but I think I'll wait a few years for the cost to drop before I buy those.

Halogen Cost for bulb: 830 lumens, $7 ea. in qty. 1, 2000 hours, 50 W: $0.037/lumen-year Cost for power: (0.050 kW * 24 hours * 365.25 days * $0.20/kWh / 830 lumens ) = $0.106/lumen-year Total cost: $0.143/lumen-year

LED (CC Vivid Plus) Cost for bulb: 60 lumens, $25 in qty. 1 (on sale, even!), 60000 hours, 1.3 W: $0.061/lumen-year Cost for power: (0.0013 kw * 24 hours * 365.25 days * $0.20/kWh / 60 lumens ) = $0.038/lumen-year Total cost: $0.099/lumen-year

Wind turbine costs

I've been arguing with my associate Ben about the relative costs of wind turbines. (We work at a GreenMountain, a renewable energy engineering firm near Boston, so this is what we do for fun.) We're both puzzled over the continued growth in the size of wind turbines.

Aldo da Rosa writes in Fundamentals of Renewable Energy Processes, Elsevier Academic Press, 2005 (pp. 599-600):

"For a given wind regimen, the amount of energy that can be abstracted from the wind is proportional to the swept area of the turbine. . . . The mass of the plant (in a first-order scaling) varies with the cube of the diameter. . . . Hence for the same amount of energy produced, the total equipment mass varies inversely with the diameter. Since costs tend to grow with mass, many small turbines ought to be more economical than one large one."

This is exactly the argument that Ben came up with last week. The flaw, as best as I can tell, appears to be that cost does not actually track mass. Historically, it appears that costs are dropping as mass increases.

(Chart removed because javascript was screwing up other scripts. It was just a falling line--just imagine looking at the right side of a silhouette of a mountain.)

The data above comes from Gil Masters' Renewable and Efficient Electric Power Systems, Wiley-Interscience, 2004 p. 372, with the 1981 data point added from an American Wind Energy Association paper, "The Economics of Wind Energy." Masters states that, "taller towers increase energy faster than costs increase," (p. 372), but he does not directly address mass scaling relative to area scaling. Masters also cites data from the Canadian Ministry of Natural Resources that estimates the annual operating and maintenance costs (~$2m) of a 60 MW windfarm at 3% of the capital costs (~$60m).

Let me add here (because I can hear fellow wind energy enthusiast Keith gnashing his teeth over TCP/IP) that if I had the data, I would prefer to see wind turbine values expressed as $/(kWh/year), rather than $/kW, where the kW rating calculated can be achieved at some high windspeed found only in Stillwater, Minnesota.

Deval Patrick appoints Microsoft lobbyist to technology working group

I voted for Deval Patrick for governor of the fine commonwealth, er, state that I live in; I was disappointed to see that he appointed the Microsoft Regional Director for Public Affairs, Brian Burke, to his technology working group. It's disappointing because Mr. Burke will likely attempt to overturn a great technology decision made by requiring that the state adopt OpenDocument format (recently published as an ISO standard) as its preferred format by January 1, 2007. This would mean that my government would no longer be paying so much for Microsoft Office when cheaper alternatives, such as OpenOffice, exist. It's true that OpenOffice has its flaws, but as a daily user of Microsoft's lovely office suite, I can verify that Microsoft Office does as well. (Why, for example, when I search Outlook's inbox, does it return results from my oldest email first?) The working group has a public meeting at 7 pm on Monday, December 11, 2006.