Electricity Generation PDF

Electricity Generation Observations: hand crank generators Observations: Model Steam Turbine Combustion Process Fuel + O2 → CO2 + H2O How is electricity produced by a generator? The burning coal heats the fluid. The fluid (steam, water, wind) rotates a turbine. The turbine drives or is...

Electricity Generation Observations: hand crank generators Observations: Model Steam Turbine Combustion Process Fuel + O2 → CO2 + H2O How is electricity produced by a generator? The burning coal heats the fluid. The fluid (steam, water, wind) rotates a turbine. The turbine drives or is a attached to a generator. The generator produces electricity. Law of Conservation of Energy Electrical energy 825 J Conservation means that the electrical energy needed to run the hair dryer doesn’t go away, instead it is changed into other forms. Add up these other forms of energy and they will equal the original amount of electrical energy required. Efficiency According to the second law of thermodynamics, at each energy conversion some energy is degraded to low-quality waste heat and lost to the environment. When an energy system is more efficient, it means that more energy contained in the fuel is ultimately converted to useful energy that can be converted to other forms. For example, coal and natural gas are forms of chemical bond energy that ultimately becomes electrical energy used in our homes. The more energy exchanges that take place in the system, the less efficient the system. These forms of chemical bond energy contain a certain number of BTU (british thermal units) that can be converted to calories. A calorie is the amount of energy needed to raise a gram of water 1 degree centigrade. 1 calorie = 0.00396573 BTU 1 BTU = 252 calories Energy efficiency, E, can be calculated as a percentage: E = Energy Produced x 100% Energy Consumed Practice Calculate the efficiency of the Coalville Power Plant. The plant generates 64,423 megawatt hours (64,423,000 kilowatt hours) of electricity by burning 31,796,825 metric tons (35,050 tons) of coal. 1 kwh = 3413 BTU BTU value of coal = 9800 BTU/lb 2000 lb = 1 ton Solution When calculating the energy efficiency E of an electrical power plant, the BTU produced (electrical output) are compared to the BTU contained in the fuel being burned. The calculation requires converting megawatt hours (MWh) to kilowatt hours (kWh). E = (64,423MWh)(103kWh/MWh)(3413 BTU/kWh) x 100 = 32% (35,050 tons of coal)(2000 lb/ton)(9800 BTU/lb) The coal burning plant is 32% efficient, meaning that 68% of the energy in the coal is lost as waste heat. Energy efficiency is the product of all individual efficiencies (35%) x (90%) x (5%) = 1.6% efficiency The conversion of coal into the light of an incandescent light bulb is only 1.6% efficient. Try it! Compare the efficiencies of two systems: Calculate the overall efficiencies of the two systems shown in the table. Power Plant Transmission Light bulb Coal to 90% Compact electricity (35%) fluorescent (20%) Natural gas to 90% LED (light electricity (50%) emitting diode) (25%) Solution Coal to Electricity: 35% x 90% x 20% = 6% Natural Gas to Electricity: 50% x 90% x 25% = 11%