HowStuffWorks "How much coal is required to run a 100-watt light ...

We'll start by figuring out how much energy in kilowatt-hours the light bulb uses per year. Although coal fired power generators are very efficient, they are still limited by the laws of thermodynamics. So the electricity generated per ton of coal is 0.4 x 6,150 kWh or 2,460 kWh/ton . Multiplying by 2,000 pounds/ton we get 714 pounds ( 325 kg ) of coal. That is a pretty big pile of coal, but let's look at what else was produced to power that light bulb. To produce this amount of electrical energy, the plant burns 1.43 million tons of coal.