Power plants (power stations)
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!
A power station is really a machine 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 convert 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. That means power plants are not very efficient: in a typical plant running on coal, oil, or gas, only about 30–40 percent of the energy locked inside the fuel is converted to electricity and the rest is wasted.
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.
Furnace: The fuel is burned in a giant furnace to release heat energy.
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.
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 (the energy of something moving). 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.
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 small amount of the water used escapes as steam from the towers themselves, but huge amounts of heat and energy are lost.
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.
Electricity cables: The electricity travels out of the generator to a transformer nearby.
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.
Pylons: Hugh metal towers carry electricity at extremely high voltages, along overhead cables, to wherever it is needed.
Step-down transformer: Once the electricity reaches its destination, another transformer converts the electricity back to a lower voltage safe for homes to use.
Homes: Electricity flows into homes through underground cables.
Homes: Electricity flows into homes through underground cables.
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!
A typical, old-fashioned coal power station is only 35 percent efficient (it wastes about 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. Combined heat and power (cogeneration) plants are another improved design, in which waste energy is used to heat hot water. 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 make renewable energy: they’re more environmentally friendly because they don’t use up Earth’s limited supplies of fossil fuels, and (in theory) we could use them forever without damaging the planet. The trouble is, the huge dams that hydroelectric power plants need are usually very destructive to build. The Three Gorges hydroelectric dam on the Yangtze river in China, which took almost a decade to build from 1994 to 2012, has displaced around 1.2 million people from their homes. Other hydroelectric projects have caused major damage to rivers.
Back in 1831, British chemist Michael Faraday (1791–1867) found that when he rotated a copper disc between the poles of a magnet an electric current was produced. Electric generators, from the tiny dynamos on bicycle lamps to the massive machines producing electricity for entire cities, still work in exactly the same way today.
When a loop of metal rotates in the magnetic field produced by a magnet, an electric current is induced (generated) in the metal. If the coil is connected by terminals to a load, such as a flashlight bulb, the current will flow through the lamp and make it light up. The amount of current produced depends on how big the coil is, how strong the magnets are, and how fast the coil is turned.