Power plants (power stations)

Last updated: December 9, 2009.

When Thomas Alva Edison (1847–1931) constructed one of the first power stations in Pearl Street, New York City, in 1882, he revolutionized the way people used energy. Once energy had to be produced where and when it was needed. But a power station separates the producer of energy from the consumer, using electricity as a go-between. This makes it possible to generate electricity in Detroit that will be used in California or to use cheap energy produced at quiet periods during the night to produce electricity for peak periods during the day. How do power plants actually work? Let's take a closer look!

Photo: A typical coal-fired power plant. Photo by Warren Gretz courtesy of US DOE/NREL (US Department of Energy/National Renewable Energy Laboratory).

How does energy get from a power plant to your home?

The heart of a power station is a large generator that extracts energy from a fuel. Some power stations burn fossil fuels such as coal, oil, or gas. (Nuclear power stations produce energy by splitting apart atoms of heavy materials such as uranium and plutonium.) The heat produced is used to turn water into steam at high pressure. This steam turns a windmill-like device called a turbine connected to an electricity generator. Extracting heat from a fuel takes place over a number of stages and some energy is wasted at each stage.

1. Fuel: The energy that finds its way into your TV, computer, or toaster starts off as fuel loaded into a power plant. Some power plants run on coal, while others use oil, natural gas, or methane gas from decomposing rubbish.
2. Furnace: The fuel is burned in a giant furnace to release heat energy.
3. Boiler: In the boiler, heat from the furnace flows around pipes full of cold water. The heat boils the water and turns it into steam.
4. Turbine: The steam flows at high-pressure around a wheel that's a bit like a windmill made of tightly packed metal blades. The blades start turning as the steam flows past. Known as a steam turbine, this device is designed to convert the steam's energy into kinetic energy (movement). For the turbine to work efficiently, heat must enter it at a really high temperature and pressure and leave at as low a temperature and pressure as possible.
5. Cooling tower: The giant, jug-shaped cooling towers you see at old power plants make the turbine more efficient. Boiling hot water from the steam turbine is cooled in a heat exchanger called a condenser. Then it's sprayed into the giant cooling towers and pumped back for reuse. Most of the water condenses on the walls of the towers and drips back down again. Only a tiny amount of the water used escapes as steam from the towers themselves, but huge amounts of heat and energy are lost.
6. Generator: The turbine is linked by an axle to a generator, so the generator spins around with the turbine blades. As it spins, the generator uses the kinetic energy from the turbine to make electricity.
7. Electricity cables: The electricity travels out of the generator to a transformer nearby.
8. Step-up transformer: Electricity loses some of its energy as it travels down wire cables, but high-voltage electricity loses less energy than low-voltage electricity. So the electricity generated in the plant is stepped-up (boosted) to a very high voltage as it leaves the power plant.
9. Pylons: Hugh metal towers carry electricity at extremely high voltages, along overhead cables, to wherever it is needed.
10. Step-down transformer: Once the electricity reaches its destination, another transformer converts the electricity back to a lower voltage safe for homes to use.
11. Homes: Electricity flows into homes through underground cables.
12. Appliances: Electricity flows all round your home to outlets on the wall. When you plug in a television or other appliance, it could be making a very indirect connection to a piece of coal hundreds of miles away!

Photo: Left: Power station transformers.
Right: Transmission line (pylons).
Both photos courtesy of US Department of Energy.

Making power the modern way

A typical, old-fashioned coal power station is only 35 percent efficient (it wastes over two thirds of the energy in each lump of coal), but new designs such as combined cycle power stations may be up to 50 percent efficient. Unlike in a traditional power station, hot exhaust gases produced in a combined cycle power station are not allowed to escape and waste energy, Instead, they are used to produce steam and drive a second turbine and generator. This design is up to 15 percent more efficient than a traditional power station.

Generating electricity does not always mean burning fuel. In a hydroelectric power station, the energy of rushing water is directed at a large vaned water turbine connected to an electricity generator. The water may be released from a large dammed reservoir to satisfy peak electricity demand during the daytime and pumped back up into the reservoir when electricity is cheaper at night. This is known as pumped storage. Hydroelectric power stations are environmentally friendly, but their huge dams can still be very destructive. The Three Gorges hydroelectric dam being constructed on the Yangtze river in China will displace around 1.5 million people from their homes.

Photo: Ice Harbor hydroelectric dam produces electricity when water rushes through its turbines. Photo by US Army Corps of Engineers courtesy of US DOE/NREL (US Department of Energy/National Renewable Energy Laboratory).