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Using electricity Electrical efficiency
Generating and distributing electricity

Although electricity is very convenient we aren't always conscious of the waste associated with its use. In 2002, the UK used 3.6 ×1011 kWh of electricity. About 85% of this was generated using fossil fuels. Burning these fuels has an environmental impact releasing carbon dioxide (a greenhouse gas) and sulphur compounds into the atmosphere. Fossil fuels are finite resources and any waste in the system means that we are consuming them more quickly than our great grandchildren would like.

Graphic of transmission system.
Picture 1.1 Roll over the blue dots in the drawing to reveal energy losses and the environmental impact of our use of electricity. Click here to see the whole table.

Using electricity

The distribution system loses (as heat) about 8% of the energy that is supplied to it - i.e. it is 92% efficient. The generation system is less efficient. A conventional power station is about 35% efficient  – although modern combined heat and power (CHP) plants can have efficiencies approaching 60%. Most of the losses in the power station are inherent in the thermodynamic processes with the generators being about 92% efficient.

So, by the time we use the electricity, it only represents about 33% of the original energy content of the fuel. There is then a further loss in the appliance that we use. For a standard motor, this would be about 12%, making the whole system about 28% efficient.

If we can improve efficiency, then this reduces the cost, the environmental impact and the rate at which we are using up precious fossil fuel reserves. Efficiency can be thought of as the third fuel – an alternative to alternative energy sources.

Photo of transformer coils
Picture 3. Copper electric motor windings, transformer coils and microcircuit.
Comparing losses

The overall efficiency for electricity generation and use may seem very low. But it has to be compared with uses of other fuels. In a car, about 15% of the primary energy of the fuel is available at the wheels – not including the losses involved in transporting petrol from refinery to the point of use. A domestic gas boiler has a thermal efficiency of about 70 % – again neglecting the energy required to pump gas around the country – but much of the heat output merely heats up building voids and structure so the useful output is much lower.

Not only must new energy sources, particularly renewable ones, be developed, but we must improve the efficiency of use of existing resources. And copper has a vital role to play in improving the efficiency of electrical appliances and electricity distribution.

Reducing losses
Electrical engineers have to consider energy efficiency when they are designing new systems. When electric currents flow and when magnetic fields change, there are energy losses – things get hot when we don’t want them to. This waste costs money, and results in increased environmental damage.

60% of all the copper produced worldwide is used in electrical applications. It is used in

  • electric motors and generators
  • transformers
  • wires and cables
  • printed circuit boards
  • microchips.

Question 1
a) i. How many tonnes of carbon are released into the UK atmosphere per year due to electrical waste (including other losses in transformers)?

ii. The UK population is about 60 million. What is this figure per person?

b) At 99.5% efficient, transformers are the most efficient part of the distribution system. However, they still waste the equivalent of100,000 tonnes of oil per year.
i. Imagine we improved their efficiency to 99.7%. How much oil equivalent would this save?

ii. Transformers with this efficiency already exist. However, the old ones are not being replaced as a matter of course. Why do you think this is so?

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Component Description % efficiency Annual wastage in UK
billion
kWh		 Million
TOE		 Million tonnes
carbon dioxide
Thermodynamic
restraints		 A traditional fossil fuel power station burns the fuel to boil water into steam. The steam drives turbines to turn the generator. The steam is then cooled to condense it back into water. There is no way of avoiding the need of this system to heat up the surroundings. It will always be inefficient. 38
 800 68.8 408
Table 1. Losses in the electricity system. The unit tonne of oil equivalent (TOE) is a useful way of comparing energy use - relating it to fuels. 1 TOE equals 11,634 kilowatt–hours. In the UK, 1 kWh produces 0.51 Kg of carbon dioxide; this takes into account the different ways in which electricity is generated (15% is generated without producing any carbon dioxide).
Component Description % efficiency Annual wastage in UK
billion
kWh		 Million
TOE		 Million tonnes
carbon dioxide
Generators In coal, oil and nuclear power stations, the generators are turned by the steam turbines. From this movement, they generate a voltage which can drive a current into the transmission system. 92
 39 3.4 19.9
Table 1. Losses in the electrcity system. The unit tonne of oil equivalent (TOE) is a useful way of comparing energy use - relating it to fuels. 1 TOE equals 11,634 kilowatt–hours. In the UK, 1 kWh produces 0.51 Kg of carbon dioxide; this takes into account the different ways in which electricity is generated (15% is generated without producing any carbon dioxide).
Component Description % efficiency Annual wastage in UK
billion
kWh		 Million
TOE		 Million tonnes
carbon dioxide
Generator
transformers		 Transformers are used to step the voltage up at the power station and to step it down close to the end-user. The transformers at the generator end are usually state of the art and highly efficient. 99.5
 2.2 0.2 1.1
Table 1. Losses in the electricity system. The unit tonne of oil equivalent (TOE) is a useful way of comparing energy use - relating it to fuels. 1 TOE equals 11,634 kilowatt–hours. In the UK, 1 kWh produces 0.51 Kg of carbon dioxide; this takes into account the different ways in which electricity is generated (15% is generated without producing any carbon dioxide).
Component Description % efficiency Annual wastage in UK
billion
kWh		 Million
TOE		 Million tonnes
carbon dioxide
Distribution
system		 This includes the step down transformers and the cables, which carry the electric current from the power station to the end-user. All the wires have electrical resistance and therefore get hot, wasting some of the energy as low grade heat in the atmosphere. 92
 35 3.0 17.9
Table 1. Losses in the electricity system. The unit tonne of oil equivalent (TOE) is a useful way of comparing energy use - relating it to fuels. 1 TOE equals 11,634 kilowatt–hours. In the UK, 1 kWh produces 0.51 Kg of carbon dioxide; this takes into account the different ways in which electricity is generated (15% is generated without producing any carbon dioxide).
Component Description % efficiency Annual wastage in UK
billion
kWh		 Million
TOE		 Million tonnes
carbon dioxide
End use
e.g. motor		 We use electricity for heating, cooking, driving things (motors) and electronic appliances. All of these have inefficiencies - usually wasting energy as low grade heat. 88
 49 4.2 24.9
Table 1. Losses in the electricity system. The unit tonne of oil equivalent (TOE) is a useful way of comparing energy use - relating it to fuels. 1 TOE equals 11,634 kilowatt–hours. In the UK, 1 kWh produces 0.51 Kg of carbon dioxide; this takes into account the different ways in which electricity is generated (15% is generated without producing any carbon dioxide).
Component Description % efficiency Annual wastage in UK
billion
kWh		 Million
TOE		 Million tonnes
carbon dioxide
Total
(electrical total)		 The total efficiency is low. Notice that, for similar percentage losses, the actual losses get smaller later on in the system. This is because there is less energy being transmitted at the later stages. 28
(74)
 930
340		 79.9
(28.9)		 474
(171)
Table 1. Losses in the electricity system. The unit tonne of oil equivalent (TOE) is a useful way of comparing energy use - relating it to fuels. 1 TOE equals 11,634 kilowatt–hours. In the UK, 1 kWh produces 0.51 Kg of carbon dioxide; this takes into account the different ways in which electricity is generated (15% is generated without producing any carbon dioxide).