October 31st, 2007 by jayb
Switching to compact fluorescent lightbulbs (CFLs) is one of the single most effective steps you can take to reduce carbon dioxide emissions and save money at the same time. Yet CFLs contain a small amount of mercury, a highly toxic element. Do CFLs increase the amount of mercury in the environment?
Most of the mercury in the environment that has been spread by human activity comes from burning coal in coal-fired power plants. Coal contains a small amount of mercury that when residing in the coal is harmless. When the coal is burned to power electricity generators at a power plant, the mercury gets put into the air where it settles onto land and water and makes its way into our food supply.
The situation is acute enough that the EPA advises Americans to not eat fish more than twice a week and not at all if you are pregnant.
Coal-fired power plants create tremendous amounts of inexpensive electricity for us but we now know that the tremendous amounts of carbon dioxide make a big contribution to global warming and the mercury is making portions of our food supply inedible.
Compact fluorescent lightbulbs are highly energy efficient bulbs that go into the same fixtures that incandescent bulbs use. They create the same amount of light as incandescents while using only 25% the electricity. That means we put 75% less CO2 and mercury into the air per bulb and we pay 75% less on our electric bill for lighting.
However, in order for CFLs to perform their magic act, they contain an average of 5 milligrams per bulb. Last year 150 million CFLs were sold. They'll last an average of 5 years. CFLs should be recycled when they burn out and the number of recycling locations for CFLs is growing quickly. But let's assume that none of them get recycled. What would be the net impact on the level of mercury in the environment?
CFL Mercury Calculation
150 million CFLs thrown in the regular trash would put 1,653 pounds of mercury into the waste stream. As they use electricity, the CFLs also cause mercury to be put into the air from coal burning power plants. Let's calculate how much:
Start with the EPA's eGRID2006 version 2.1 which contains electricity generation and emissions data by state for the year 2004. According to the eGRID data, we generated 3.9 billion megawatts in 2004 from all US power plants and we emitted 106,041 pounds of mercury. That is 0.00002695 pounds of mercury per megawatt hour of electricity use. Let's assume the CFLs are 25 watts (100 watt incandescent equivalent) and that they are used for 6000 hours. (Manufacturer's typically rate CFLs at 6000, 8000 or 10000 hours lifetime.) 25 watts times 6000 hours times 150 million CFLs equals 22,500,000 megawatt hours of electricity. 22,500,000 MWh times 0.00002695 pounds of mercury per megawatt hour equals 606 pounds of mercury.
CFL Summary (150 million CFLs)
1,653 pounds of mercury in the bulbs.
606 pounds of mercury from the electricity to run them.
2,259 pounds of total mercury (assuming 0% CFL recycling)
Incandescent Mercury Calculation
Incandescent bulbs do not contain mercury so the incandescent calculation is just about the mercury that comes from the electricity used to run them.
150 million incandescent 100 watt bulbs used for 6000 hours = 90,000,000 megawatt hours of electricity. (Note that incandescent bulbs do not last anywhere near 6000 hours so to keep 150 million fixtures running for 6000 hours will take alot more than 150 million incandescent bulbs. But that is not relevant here because this is not a cost calculation but an electricity used calculation.)
90,000,000 MWh times 0.00002695 pounds of mercury per megawatt hour of electricity equals 2,425 pounds of mercury emitted.
Mercury from the CFLs and their use = 2,259 pounds
Mercury from incandescent bulb usage = 2,425 pounds
Switching to CFLs reduces the mercury put into the environment by 165 pounds or 7% assuming not a single CFL gets properly recycled.
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