If all the solid waste of 230 million tonnes were burned in waste-to-energy power plants that are 20% efficient,
a) how many kilowatt-hours of electrical energy could be produced in a year? Compare this quantity with the total U.S. electrical energy production of approximately 3.8 trillion kWh annually.
b) what would be the equivalent average electric power output from all these waste burning power plants? how many 1-GW coal-fired plants could they displace
To calculate the electrical energy that could be produced from burning 230 million tonnes of solid waste in waste-to-energy power plants, we need to consider the efficiency of these plants.
a) First, we need to convert the weight of the solid waste to kilograms. Since 1 tonne is equal to 1000 kilograms, 230 million tonnes is equal to 230 billion kilograms.
Next, we calculate the energy generated by the waste-to-energy power plants. Given that these plants are 20% efficient, we can multiply the weight of the waste by the efficiency to get the energy produced. So, 230 billion kilograms multiplied by 20% gives us 46 billion kilograms of waste converted to energy.
To convert this energy into kilowatt-hours (kWh), we need to know the energy content of the waste. Let's consider that the average energy content of solid waste is around 6,000 kilocalories per kilogram. Converting kilocalories to kilowatt-hours, we divide the energy content by 860 to get an approximate value. So, 46 billion kilograms multiplied by 6,000 kilocalories/kg, divided by 860 gives us approximately 320 billion kWh.
Now, to compare this to the total U.S. electrical energy production, which is about 3.8 trillion kWh annually, we divide the energy produced from waste by the total U.S. production. So, 320 billion kWh divided by 3.8 trillion kWh is approximately 0.084, or 8.4% of the total U.S. electrical energy production.
b) To calculate the equivalent average electric power output, we divide the energy produced from waste (320 billion kWh) by the number of hours in a year (8,760 hours). This will give us the average electric power output in kilowatts. So, 320 billion kWh divided by 8,760 hours is approximately 36.5 million kW.
To calculate the number of 1-GW (gigawatt) coal-fired plants the waste-to-energy power plants could displace, we divide the average electric power output by the capacity of one coal-fired plant. Given that 1 GW is equal to 1 billion watts, we can divide 36.5 million kW by 1 GW to get approximately 36.5 coal-fired plants.
Therefore, the waste-to-energy power plants burning 230 million tonnes of solid waste could produce approximately 320 billion kWh of electrical energy in a year. This represents around 8.4% of the total U.S. electrical energy production. The equivalent average electric power output would be approximately 36.5 million kW, which could displace approximately 36.5 1-GW coal-fired plants.