Buzz
Important Points to Remember
- To keep a 100-watt light bulb on continuously for a year, 876 kWh of electricity is needed, which equates to burning around 714 pounds (325 kg) of coal in a coal-powered plant.
- Coal power plants operate at roughly 40 percent efficiency, meaning only 40 percent of the coal's thermal energy is converted into electrical energy.
- In addition to electricity, coal combustion releases harmful pollutants such as sulfur dioxide, nitrogen oxides, and carbon dioxide, contributing to issues like acid rain, smog, and global warming.
We begin by calculating how much energy the light bulb consumes annually in kilowatt-hours. By multiplying its power usage of 0.1 kW by the total hours in a year (8,760 hours), we get a total of 876 kWh.
Coal has a thermal energy content of 6,150 kWh per ton. Despite the efficiency of coal-fired power plants, only about 40 percent of the thermal energy from coal is converted into electricity. Thus, the electricity produced per ton of coal is 0.4 x 6,150 kWh, which equals 2,460 kWh/ton.
To determine how much coal was used for our light bulb, we divide 876 kWh by 2,460 kWh per ton, which gives 0.357 tons. By multiplying that by 2,000 pounds per ton, we get a total of 714 pounds (325 kg) of coal. This is quite a substantial amount, but let's explore what other byproducts were created in the process of powering the light bulb.
A standard 500-megawatt coal-fired power plant generates billion kWh of electricity annually, enough to power 4 million of our light bulbs continuously throughout the year. To produce this electricity, the plant consumes 1.43 million tons of coal, and it also emits these pollutants:
Sulfur Dioxide
- Primary contributor to acid rain
- Total produced by the plant: 10,000 Tons
- For one light bulb operating for a year: 5 pounds
Nitrogen Oxides
- Contributes to smog and acid rain
- Total produced by the plant: 10,200 Tons
- For one light bulb operating for a year: 5.1 pounds
Carbon Dioxide
- Greenhouse gas believed to contribute to global warming
- Total produced by the plant: 3,700,000 Tons
- For one light bulb operating for a year: 1,852 pounds
The power plant also releases trace amounts of nearly every element on the periodic table, including the radioactive elements. In fact, a coal-fired power plant emits more radiation than a (properly functioning) nuclear power plant!
