Electric Power Generation EES 205 Electricity in the form of atmospheric lightning is a frightening and beautiful phenomena. We generate electricity in less dramatic and much more controlled forms.

Power Plant Most electric energy in the US is generated in large power plants. Most of these plants use the energy stored in coal or other fossil fuels to produce electric energy.

How a Power Plant Works Diagram shows the elements of a power plant that uses fossil fuel. Fuel (usually coal) is burned (a chemical reaction that changes carbon to carbon dioxide and releases energy in the process) to produce heat. (Coal consumption also produces waste in the form of ash, air pollution, and CO2). The heat raises the temperature of water to produce steam. (So, stored chemical energy has been released and transformed to thermal energy by producing steam.) The steam then drives the steam turbine. It causes the blades of the turbine to turn – the turbine spins on its axis (So, thermal energy has been transformed to mechanical energy.). The shaft of the rotating steam turbine is connected to the shaft of the electric generator; so, the steam turbine causes the electric generator to turn. The turning generator causes the generator to produce electric power through electromagnetic induction. (Mechanical energy has been transformed to electric energy). Electric energy is distributed to the end user by the electricity transmission and distribution system – the grid. In this example, electric energy is converted to thermal energy in the toaster. Be sure that you understand this figure. It is very important. Also, notice all the ways that the chemical energy stored in the fuel is lost – some energy goes up the smokestack, some is lost in the condenser, some is lost in the generator, and some is lost in transmission and distribution. 2/3 of the energy released by burning the fuel is lost and not delivered to the end user.

Fuel Almost 50% of electric energy is generated by burning coal. Another 20% comes from natural gas and another 20% from nuclear. So 70% of electricity comes from burning fossil fuel. But coal is the largest source of primary energy for producing electricity.

Coal-Burning Power Plant: Bridgeport Harbor Generating Station The Bridgeport Harbor pwer plant burns coal to make electricity. It is typical of coal-burning power plants. However, most New England plants use natural gas rather than coal.

Coal Mine Most coal comes from surface mines – strip mines

Coal Train Coal is transported by train to power plants.

Coal Pile Coal is stored at the power plant. Coal is stored chemical energy.

Coal-Fired Boiler The coal is pulverized and then burned in the power plant.

Steam Turbine The steam generated in the boiler, turns the steam turbine blades.

Electric Generator The turbine is connected to the generator and the rotating turbine shaft turns the generator. This produces electricity by electromagnetic induction.

Electric Generator An electric generator uses mechanical energy to rotate wires in a magnetic field. The motion of the wires in the magnetic field causes electric current to flow in the wires. This is electromagnetic induction.

Plant Output A coal-burning power plant converts chemical energy stored in the coal into electric energy. The electric energy is transmitted through transmission wires that connect the plant to the electric power grid.

AC Power The power on the grid is AC (alternating current) not DC (direct current). AC power can be stepped up to higher voltage or down to lower voltage using a transformer.

Voltage and Current Voltage (V) is like the height of a waterfall. The higher the voltage, like the higher the water waterfall, the more power it delivers. Electric current (I) is the flow of electrons in wires; electric current is similar to water current. The product of voltage and current equals power (P = I x V). High voltage and high current produce high power, just like a high waterfall with a large flow of water produces high hydropower.

Electric Grid The US grid is a collection of regional grids. Some regional grids are interconnected, but others like the Western grid and the Texas grid (ERCPT) are not connected with other regional grids. The grid is part of the US infrastructure that needs to be upgraded.

Grid = Transmission & Distribution The grid connects the end user to the power plant.

High Voltage Transmission Transformers step up the generator voltage from the 1 kV range to 100 kV range. Less energy is lost by transmitting at high voltage.

Power Substation Transformers at substations step down voltage from the 100 kV range to the kV range for safe neighborhood distribution

Power Pole Transformers on power poles drop the voltage down to 240 Volts AC for home use.

Kilowatt-Hour Meter . Watt-hour meters measure and record energy use. Most house appliances use AC. Some household devices use 240V and some use 120 V.

End Use . This household appliance converts electric energy into thermal energy to make toast.

Issue #1 - Efficiency Power plants turn the energy stored in fuel (e.g. coal) into electric energy. The efficiency of this transformation process is always less than 100%. Some energy is always dumped into the environment as waste heat. Typically coal plant efficiency is 33% (1/3), but new plants may be 50% (1/2) efficient. High efficiency plants conserve energy and reduce CO2 emissions.

Efficiency Electric Power Out Thermal Power In So, if a power plant releases thermal energy (by burning coal) at the rate of 1,500 MW and produces 500 MW of electric power, then 500 MW Efficiency = ----------------- = 1/3 = 33% 1500 MW This is the definition of efficiency: power out/ power in. So, if the 500 MW power plant has to produce 1500 MW of thermal energy (by burning coal) in order to produce 500 MW of electric power, then it has to throw away as waste heat 1500 MW – 500 MW = 1000 MW. Higher efficiency would mean that less coal has to be burnt to produce the same amount of electricity.

Issue #2 – Air Pollution The main air pollutants associated with burning coal are sulfur dioxide which comes from sulfur impurities in coal and nitrogen oxides which come from oxidizing atmospheric nitrogen (air is 80% N2) in the combustion process. The emission of these gases leads to acid rain and photochemical smog, respectively.

Cap and Trade “Cap and trade” is a policy designed to reduce acid rain by reducing SO2 emissions from the 3,208 Electric Utilities in the US. Utilities are assigned allowances - permission to emit a ton of sulfur dioxide. Total allowances add up to the “cap”. The cap is lowered every year. Utilities can either use their allowances, sell unused allowances to other utilities, or buy allowances from other utilities. This market system leads to the most economical way to reduce emissions.

Issue #3 – Global Warming Since 70% of electricity is generated by burning coal, natural gas, and oil, electricity generation produces CO2 and other greenhouse gases as a byproduct. These greenhouse gases are leading to climate change.

Carbon Capture and Storage Several strategies and technologies can help reduce the climate impact of fossil fuel generation. These include switching from coal to natural gas (natural gas releases less CO2 per kWh of electricity), generating electricity using nuclear energy and renewable energy, and sequestering CO2 underground or in the deep ocean.

Conservation Reducing the demand for electricity is the least expensive way to reduce the problems associated with generating electricity.