During yet another one of those wonderful public service announcements on the radio I heard the claim that a compact fluorescent light bulb was typically “four to six times more efficient” than a traditional incandescent bulb. Leaving aside the issues of governments banning incandescents (why not tax electricity instead, and allow us the choice in how we conserve on use and CO2 emissions?) and leaving aside some people’s complaints that CFC wattages and lights are not comparable to incandescent ones I want to focus on the specific claim.
Suppose I take it as 100% gospel truth, and I have no reason to believe otherwise. I think this sort of thinking has us focus on a very small way of improving how much CO2 is emitted by our electricity production and/or how much energy we might conceivably save by various conservation strategies.
What the true measure of efficiency is, for me, is what percentage of the raw energy inputs end up being turned into useful work on the user end. Given that the modal electric outlet and light socket in the United States receives its electricity from coal-fired steam-turbine electricity generation plants, here is how I think of efficiency.
Coal has some amount of energy in it. In an idea world, 100% of that (potential) energy would be turned into work. However, we lose energy in every part of the electricity generation process. We lose energy during the coal combustion process as heat is lost up the exhaust pipes of the power plant. We lose energy (a lot of it) as the steam powers the turbine in the power plant. Most of the steam is lost as it escapes the teeth of the turbine. Then we lose energy as the turbine powers the dynamo via friction and heat losses. And then we lose energy in the transmission of the electric wires that run from the power plant to your outlet.
An optimistic estimate of the efficiency of this process is 36%. This assumes an 85% boiler efficiency, a 45% steam turbine efficiency and a 95% generator efficiency and no losses in transmission. Suppose a typical incandescent bulb is only 5% efficient. Then in this case the efficiency of the entire system is only 1.8%. Suppose a typical CFC bulb is five times more efficient, at say, 25%. As part of the closed system, then this would actually have a total efficiency of 9%. And yes, the CFC is still 5x more efficient than an incandescent bulb.
But, if we care about energy efficiency, consider that lighting makes up only a fraction of our energy use. So replacing 100% of incandescent bulbs with CFCs will not mean we save 5% of our energy and CO2 emissions, but a far small portion of it. Furthermore, think like a good economist. While it might make sense to replace all lights with CFCs to save up to x% of our energy loss, remember that energy is lost throughout the entire system. The only way “it makes sense” to use CFC’s is if to save a given amount of energy use and CO2 emissions this is the least costly way to do it. Is this possible? Sure. Is it likely? I don’t know. But think about steam-turbines for a minute. They lose over 55% of the energy applied to them. Just a small improvement in turbine efficiency would more than swamp efficiency gains from better light-bulbs. The right economic question is what cost we incur from doing each of these. Now, there is no reason to believe we cannot afford to make efficiency improvements throughout the entire system, as has happened anyway during the past 100 years.
Is there a better policy tool to “promote” the desired efficiency gains than mandating the use of a particular bulb? Of course there is. Let me discuss two points that are not often brought up in this discussion (many folks have done a fine job demolishing the sense of mandating CFC’s).