What is electricity?
Electricity is created when electrons flow through a conducting material, such as the copper or aluminium used in power lines.
Electrons are tiny particles that are part of all matter and are so small that they can move through wires.
In New Zealand, the energy in falling water is the main source of electricity generation; this is referred to as hydro generation. Most of our electricity is generated from hydro, averaging 59 percent of supply over the last five years.
Hydro generation works by holding water from a lake or a river in a dam and releasing it down a large pipe, called a penstock. When the water comes out of the penstock and hits the blades of the turbine, the force of the water causes the blades of the turbine to spin. A turbine is like a large propeller and it’s attached to a generator, which consists of huge magnets that spin inside massive coils of conducting wire. The magnetic field from the spinning magnets pushes the electrons through the wire coils.
The movement of the electrons through the wire is known as electricity.
The electricity flows from the generator into the national transmission network—also known as ‘the national grid’, or just ‘the grid’—and then on to all the houses and businesses that use electricity.
Wind turbines generate electricity in a similar way, but they use the energy from the wind to spin the turbine and generator.
Thermal generators create heat energy by burning fuel such as natural gas, coal or oil. Some thermal generators use the hot combustion gases to spin the turbine and generator directly, while others boil water to create high pressure steam which spins the turbine and generator.
Geothermal generators use the hot steam that is naturally produced under the ground in some parts of the country, mainly in the Bay of Plenty.
What do voltage, current, energy and power mean?
The force applied to electrons to push them through the conducting wire is known as voltage, and the rate of flow of the electrons is known as current.
If you think about water running through a pipe, voltage is the pressure applied to make the water flow and current is how much water is flowing through the pipe every second.
Energy comes in many forms, for example:
- your body takes chemical energy from the food you eat and converts it into mechanical energy in your muscles when you move
- chemical energy is stored in a torch battery, converted into electrical energy to power the light bulb and then into light energy to give you light
- electric heaters convert electrical energy into heat energy
- a car engine converts the chemical energy in petrol into kinetic energy—the form of energy contained in moving objects
- when you bike up a hill you have to push harder on the pedals because that extra energy is being converted into gravitational potential energy. The higher you go the more gravitational potential energy you have. When you race back down the hill, the gravitational potential energy is turned back into kinetic energy.
Power is a measure of how fast energy is being converted from one form (electricity) to another (heat from your heater).
Electrical energy is measured in watts (W), kilowatts (kW), megawatts (MW) or gigawatts (GW).
1,000 W = 1 kW
1,000,000 W = 1 MW
1,000,000,000 W = 1 GW
Kilowatt hours (kWh) are used to measure how much electricity a household uses over time; they’re often called “units” on your electricity bill. Larger electricity users such as large factories measure their consumption in megawatt hours (MWh) or gigawatt hours (GWh).
For example, a 1kW heater running for an hour will consume 1kWh of electricity.
Average households in New Zealand use about 8,000kWh of electricity per year.