Chapter 10, electricity supplies
At present, most of the world’s electricity is generated using the energy released from burning fuels, but this is having a serious effect on the Earth’s atmosphere. Electricity produces radioactive waste and so causes environmental problems. There is an increasing interest in the use of renewable energy sources to generate electricity. This was very expensive until now, and they also have environmental impact.
Electricity is a secondary energy source: it has to be generated using a primary source of energy. With renewable energy sources, there are no fuel costs.
Decisions about how to generate electricity involve weighing up technical, environmental and economic considerations.
What energy sources are used to generate electricity in the UK?
[Figure 10.3 is an important one]
Power stations that use fuels as their primary energy source are not very efficient. Gas-fired power stations are 50% efficient, and coal-fired power stations and nuclear power stations (which use steam) have an efficiency of 40%. Since most electricity in the UK is generated using fuels, fuel-burning power stations should be made more efficient.
How can fuel-burning power stations be made more efficient?
In a fuel-burning power station, heat is produced when the fuel is burnt and this is used to boil water to make steam. This then drives a turbine. Once the steam has passed through the turbine blades, it is condensed back to water, to draw more steam through. The cooling water used to do this is heated in the process. In any fuel-burning power station, a lot of the heat produced by burning the fuel is carried away by this cooling water. As a result, the efficiency of the power station is low.
A power station can never be 100% efficient. This is because some of the heat always has to be transferred to a cold reservoir to keep the process running. The maximum efficiency using 500*C is 60%.
Are nuclear fuels greener than fossil fuels?
Most electricity in the UK is generated using fossil fuels, and this will also happen in the future. Existing nuclear power stations reduce the amount of carbon dioxide being released into the atmosphere by as much as it would be if 70% of cars were taken off UK roads. There are three possible sources of radiation risk to the general public:
• From the routine leakage, however slight, of radioactive materials into the immediate environment. This mainly affects people who live close to nuclear power stations or to plants which process nuclear fuel.
• From the waste produced by nuclear power stations, some of which has a long half-life and will remain dangerously radioactive for hundreds of years. The people who might be at risk from this depends on where, and how, the waste is stored.
• From accidents which release radioactive materials into the environment. Depending on the scale of the accident and weather conditions the effects of this might be local or spread over a wide geographical area.
The problem of radioactive waste
Nuclear power stations produce three main types of radioactive waste:
• High-level spent fuel rods; solidified waste from reprocessing fuel rods;
• Intermediate-level cladding that surrounds fuel rods, filters and residues from effluent treatments; worn-out items of equipment from nuclear power plants;
• Low-level protective clothing; rubble and steelwork from decommissioned nuclear power plants.
So far, however, no country has managed to find a safe underground site for its high-level or intermediate-level nuclear waste.
A major reason for opposition to nuclear power is the fear of serious accidents and the scale of radioactive contamination that these might cause. This fear is based on two sorts of reason.
First, there have, in fact, been quite a number of nuclear accidents. Secondly, it is never possible to anticipate all of the things that might conceivably go wrong or to make every aspect of the process completely fail-safe. Furthermore, people are involved at various stages in the process and it is never possible to rule out the possibility of human error.
How will the UK’s electricity be generated in the 21st century?
The amount of electricity generated in the UK from nuclear fuels will decline during the early years of the 21st century. The only alternative to fossil fuels will come from renewable energy sources. One reason why the move towards other renewable energy sources has been very small and very slow is that the cost of each unit of electricity generated using these energy sources has tended to be greater than for conventional power stations. The cost of generating a unit of electricity by each of the available methods is not determined solely by technical considerations, such as the efficiency of the generating equipment. So those in favour of renewable energy sources are working hard to improve the technology so that the cost of each unit of electricity generated is more or less the same as the electricity generated by power stations which use fuels as their primary energy source – even under the current economic rules.
Developments in renewable energy sources.
In the 1990s, there was a rapid growth in the number of wind generators in the UK. Wind generators are expensive at the moment, but they will successfully develop them, and they will be cheaper in the future. The growth in the numbers of wind generators in the UK is likely to continue into the 21st century. There is, however, a limit to the proportion of UK electricity that can be generated in this way.
The harnessing of energy from waves for generating electricity is not so well advanced as harnessing energy from the wind. The UK government was against the idea of using waves for energy, because of the costs. Researchers continued to make considerable progress mainly using scale models in large wave-tanks. After trying 16 years to introduce it, the British government was once again prepared to support it.
Solar cells have been used for many years to generate electricity directly from the Sun’s rays. The cells are usually made from crystalline silicon which means that manufacturing them is not only quite expensive but also requires a considerable amount of energy. It can also be made from amorphous silicon. This is much cheaper, but less efficient. There are also cells from titanium oxide and dye. These cells are more efficient than silicon cells and cost only on-fifth as much.
Electricity generation in developing countries.
In developing countries, generating electricity in large power stations and then distributing it to these villages is uneconomic. Nevertheless, access to some electricity can significantly enhance the quality of life of the people who live in these rural areas. What is needed in such situations is a method of generating relatively small amounts of electricity cheaply and reliably using technology that is appropriate to local circumstances.
The unit normally used to measure amounts of energy supplied by electricity in domestic situations is the kilowatt-hour (kWh). It is the amount of energy required to run a 1 kW device for 1 hour. 1 terawatt-hour (TWh) = 1 billion (109) kWh.
→ Study the figures and the red parts in the book!
Chapter 10 - Electricity Supplies0
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- 4e klas tto vwo | 1169 woorden
- 25 juni 2009
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