Saturday, April 11, 2009

Compact Fluorescent Lights: Bad for the environment or just more posturing by boneheads?

I'm sure you can guess the answer from the title of this post, but I should still go through the motions. :)

I saw this article today, which argues that CFLs are not as good for energy consumption as advertised due to the way certain components within the bulb affect the actual power draw vs the observed power draw. In short, CFLs take a little less than 100% more energy than claimed because of the way the electronics are built. This is mostly true (I haven't checked the actual values, just the basic physics/electronics), but you won't see the cost; it's a loss to the power company.

Does this mean the CFLs are another "greenwashing" for all us gullible fools out there who don't know anything and just glom onto whatever feel-good behavior is the fad-of-the-hour?

We can use math to answer this question.

Let's take the example of a 100 watt incandescent bulb most of you probably have in your house somewhere. I can easily find a 23 W CFL that outputs as much light as a 100 W incandescent. The CFL costs $2.00 per bulb, while the incan costs $0.28. The CFL is rated to last 8,000 hours. The incan is rated to last 1950 hours.

Assuming typical usage of 3 hours/day, we can expect the CFL to last 7.3 years and the incan to last 1.78 years. The difference in rated hours means the cost of replacing those incans would add up to $1.15 over the life of the CFL.

Let's go back to that article and assume the actual power usage of the CFL is 46 W instead of 23 as advertised. 46 W *8000 hours = 368000 Wh over the lifetime of the bulb. That's 368 kWh. For the incans, the usage would be 100 W * 8000 hours (assume we instantly replace the incan after it burns out and use the next ones until we reach 8000 hours of use) = 800000 Wh, 800 kWh.

The average cost of electricity in the US is about $0.11/kWh. The lifetime cost of the electricty (of which you'll only see ~50%) CFL is $40.48, giving a total cost of $42.48 (except your cost is only $22.24 because the extra power is dissipated in the power lines). The incan electricity cost is $88.00 (you'll see all of this cost), giving a total cost of $89.15.

Okay, great, so a CFL still uses less energy and the problem with the power can be fixed with a couple of additional electronics---if you're handy with a soldering iron, you could do this yourself.

What about the mercury problem you've heard so much about recently?

Well, a first generation CFL has about 4 mg of mercury, none of which is released to the environment if the bulb is not broken. For comparison, old thermometers contain about 500 mg of mercury. Newer CFLs have 1.4 to 2.5 mg of mercury per bulb. Incandescents have none.

Does this mean we should stop allowing CFLs because of the mercury problem?

No. Once again, some simple math can answer the problem.

First, as the CFL is used, the mercury vapor becomes chemically bound to the glass, leaving only about 14% to be released, assuming breakage, at the end of the life of the bulb. The EPA (this links to a PDF) estimates that if all 290 million CFLs sold in 2007 were destroyed in a landfill (each one broken), they would add about 0.16 metric tons of mercury to the environment. That's 0.16 per cent of the mercury released by humans.

Electricity generation is the main source of mercury emissions in the US. The average mercury emissions from electricity generation in the US is 0.012 mg/kWh. The CFL above would, if broken and assuming 4 mg of mercury in the original bulb, add about 0.012*368+0.14*4 = 4.98 mg mercury. The incandescent bulbs would produce 0.012*800 = 9.6 mg mercury. Here, the total electricity use of the CFL should be used, rather than the 23 Watts advertised.
Again:







CFL (26 W)Incan (100W)
Hg (mg)4.989.6
Electricity (kWh)368800
Cost ($)42.48 (or $22.24 if we only count your costs)89.15
Lifetime (hours)80001950


There's absolutely no reason not to go to CFL. Also, many places are recycling the CFLs for free now, which takes care of the "mercury problem" as well. The bright (ha!) ones among you will notice that even if you broke the CFL right after you bought it (using zero electricity), you won't reach the amount of mercury released due to electricity generation needed to run the incandescent bulb for 8000 hours. Even if you were a moron and bought two CFLs, broke one and used the other, you'd still release less mercury.

Note that I have not discussed the energy costs in producing the bulbs. I don't know those numbers and don't feel like looking them up right now. I am sure it takes more energy to make the CFLs right now, but am NOT sure that extra energy cost is enough to make up the difference in energy or mercury costs compared with the incandescent bulbs.

4 comments:

Grumpator said...

I love that you do all this work for me! Very helpful. You work for your cookies!

Jennifer said...

Yes, but you still haven't discussed how many people it takes to screw in a CFL vs. a standard lightbulb. That's the the most important question!

I am Moses. said...

This is a family-friendly blog, but here goes...

How many Harvard grads does it take to screw in a CFL? One. They just hold bulb to the socket and the universe revolves around them.

How many hippies does it take to change a CFL? Two. One to install the bulb and a second to say, "hey, man look at all the colors."

How many men does it take to change a CFL? At least seven. One to do the work, one to supervise, one to bring the beer, one to bring the bratwurst, one to nap, and one to talk about how he could do it better, one to explain why an incandescent would be easier to change.

How many republicans does it take to change a CFL? None. Let the commies stay in the dark for being disloyal to the incandescent bulb industry.

How many democrats does it take to change a CFL? None. They wouldn't be caught dead near such a politically dangerous topic.

How many environmentalists does it take to change a CFL? None. CFLs never need to be changed.

deborah said...

Loved the "How many jokes....Glad to hear that after all that science it appears that the CFL are the best we have right now.