Question: how much coal is required to run a power station?
Answer: One KW is 3600 kj per hour. Therefore, at 21% efficiency, we need a heat input of about 7,560 kj/hr (3600/21%) - therefore for producing 1 kw/hr electriccity, we need 7,560/20,000 or 0.378 kg of coal. For a megawatt/hr we would need 0.378 x 1000 = 378 kg of coal - we can round it off to 400 kg.