Environmental Engineering Reference
In-Depth Information
Although the technology used in power plants is highly complex, the process of energy
conversion from a fuel to an electrical appliance is surprisingly simple. Whether fuelled
by coal, oil, natural gas or uranium, a power plant converts the energy stored in the fuel
into heat. The heat released is immediately used to turn water into steam at temperatures of
around 500 degrees Celsius. The superheated steam is carried, via a network of pipes, to a
turbine, where it drives blades that are connected via a shaft to a generator. Technologically
speaking, this generator is like a supersize bicycle dynamo, in which rotating magnets
convert the mechanical energy of the rotating shaft into electricity. The electricity enters
the grid and travels at the speed of light to homes, offices and factories, where it is again
converted into light and heat or used to power machines and electronic devices.
Some renewable technologies (biomass and concentrated solar power) exploit the same
'boiling pot and dynamo' principle, converting heat to motion and motion to electricity,
though the scale is usually much smaller. While a coal power plant may exceed 1,000
megawatts of capacity, biomass power plants with more than 100 megawatts of capacity
are rare, as are concentrated solar power (CSP) plants with more than 5 megawatts. Wind
and hydroelectric plants dispense with heat generation entirely, though the latter stage (the
conversion of mechanical to electrical energy) is similar.
Energy, Power and Capacity
Which contains more energy - a plate of cookies or a small hand grenade? The answer,
counter-intuitively, is the plate of cookies. One hundred grams of cookies have an energy
content of about 1,500 kilocalories (6,279 kilojoules), three times more than the same
amount of TNT. The TNT releases a smaller quantity of energy than the cookies, but does
so in a far shorter period of time. It contains less 'energy' than cookies but has much more
'power'.
The joule (J) is the unit used to measure energy, while the watt (W), defined as 1 joule
per second, is used to measure power (
Chapter 1
). However, in addition to the joule, there
is alternative unit measure of energy, which will be familiar to anyone who has had the
privilege of receiving an electricity bill: the kilowatt-hour (kWh).
Every externally powered device, from a domestic electric heater to a nuclear power
plant, has a nominal power capacity, describing the maximum power at which the device
can operate continuously. A washing machine with a nominal power intake of 1,000 watts
changes its energy consumption during operation. It goes from 100 watts when pumping
