The renewed enthusiasm for compact fluorescent lamps (CFL’s) highlights a persistent inefficiency in resdiential energy conservation programs. The underlying tension is between an understandable desire to get people to do the right thing and the complexity of the science involved (though the science is no more than high school physics). A regional, climate-aware strategy for public education and subsidies for residential conservation, instead of our shotgun appeals for everyone to turn off lights and take shorter showers (OK, water conservation matters) could greatly amplify the effect of policy. Here’s why:
Substituting a 23w CFL for a 100w incandescent lamp saves 77 watts in your house, but about 135w of fossil fuel (what causes global warming) considering the losses in the electric generating and distribution system and that US electric generation is about 70% fossil fuel. However, this is only true if you are neither air conditioning nor heating your house. [Energy wonks: I know, peaking versus baseload issues and regional generation mix fuzzes up this analysis. But it doesn’t change the overall lesson.]
In heating season where there is one, which includes most of the US and all of Canada for most of the year, a lot of the saving from the CFL (or almost anything you do indoors) is illusory, because your thermostat just runs your boiler or furnace a little longer to replace those 77 watts. The tradeoff is
With CFL: 77w x 1.54 (for a 70% efficient heater) = 119 w
+ 23w x 1.75 (fossil fuel used per electric watt ) = 40w
= 159w total fossil energy
With incandescent: 100w x 1.75= 175w total fossil
So the fossil fuel saving is only 16 watts. This is nothing to sneeze at, but far below the savings the CFL would appear to provide. [Big buildings like offices and stores air condition almost all the time, and most have already rationalized their lighting to fluorescent and HID.]
If you’re among the few who heat with resistance electricity (as distinct from a heat pump), neither the CFL nor sitting in the dark saves either energy or carbon: you might as well heat your house with light bulbs as with your electric baseboard strips, though you will save some money buying bulbs if they’re CFLs. Forget about the lights and look into insulation and weatherstripping.
In an air conditioned house, the CFL is much better than it looks, because every 100 watts of energy released in such a house demands another 30 watts to carry it outside with an efficient air conditioning system, more with an old one. Sparing you the calculations: replacing a 100w incandescent with a 23w CFL saves 175 watts of fossil energy input to the power grid, which is a really big deal, both for the planet and for your pocketbook. The only thing better than that is turning off the CFL, which saves another 53 watts.
Every CFL used in an air conditioned house is more than ten times as global-unwarming as in a heated house, and a third again as good as in an unheated one, and more than twice as good as the wattage label implies. If we’re going to spend public money getting people to save energy, we can get a lot more bang for the buck by spending it where it will matter most.
The basics of home energy conservation are not mysterious, and we’ve known them since the seventies. Northerners, what you really need to attend to is the roof, walls and windows of your house. Every watt-hour you can keep from leaking out is really saved; every watt-hour you can catch from the sun through a window is free; fussing about indoor electric consumption is more of a hobby (except in the summer). Want something easy? Put on a sweater and turn down the thermostat!
Southerners, you need to attend to that envelope to keep heat from coming in (got awnings? They’re a gold mine!). It’s you that have the big low-hanging fruit to harvest from electricity conservation, including CFLs, turning off the lights, using a whole-house fan at night, and the like. And turn up the thermostat!
State energy commissions and environmental NGOs: focus your programs on high-payoff behavior in the right places.