How much mercury is emitted per unit of electric energy?
Wisconsin, like the Mid-Atlantic region, relies most heavily on coal-fired electricity generation, except during rare summer peaks. In a report2 for the State of Wisconsin, Table 1-3 shows emissions of about 0.05 pounds of mercury per gigawatt hours (GWh) (1,000,000 kilowatt hours [kWh]). Using common conversion tables, this is equivalent to 0.023 milligram (mg) per kWh. This electrical generation also produces other pollution such as oxides of sulfur and nitrogen and global-warming gases. A coal-fired generating station emits about two pounds of carbon dioxide (CO2), the most common global-warming gas, for each kWh of electricity. We can also choose higher-cost electricity produced from alternative energy, such as wind.
How much mercury do CFLs and conventional lamps contain?
In an article entitled “Mercury Use in Lighting,”3 Table 2 shows that 66 percent of CFLs contain 0 to 5 mg of mercury, 30 percent contain between 5 and 10 mg, and 4 percent contain between 10 and 50 mg. Assuming that each lamp in its cluster has the middle level of mercury, the level computes to 5.1 mg of mercury.
The two examples below provide a comparison between a CFL and a conventional lamp. (An mg is 1/1000 of a gram. A microgram is 1/1000 of an mg.
Ten 100-watt conventional lamps have a lifetime equal to one CFL.
Each conventional incandescent lamp lasts 1,000 hours. The 10 lamps then consume 1,000 kWh (100w x 10,000 hours) over their lifetimes. To supply these lamps, power plants will emit about 23 mg of mercury and 2,000 pounds of CO2. A consumer will spend $5 to buy these lamps (50¢ each) and $100 in energy costs to power them at 10¢ per kWh for a total of $105. The light output is 1,500 lumens or about 15 lumens per watt. Note: Conventional bulbs may contain lead solder, and lead is a powerful toxin as well.
One 23-watt CFL has the equivalent output of a 100-watt incandescent lamp.
The lamp lasts 10,000 hours and consumes 230 kWh over its lifetime. To supply that lamp, power plants will emit about 5.2 mg of mercury and about 460 pounds of CO2. Improper disposal of the lamp (for example, if it is consumed in a municipal incinerator) will result in 5.1 mg of mercury entering the environment. In this case the total emissions will be 10.3 mg mercury or about half of the emissions using conventional lamps.