By contrast, the heat rejected to cooling towers, rivers and the sea by central electricity generation is sufficient to heat most of the buildings in our cities. The idea of harnessing this waste heat is at the heart of combined heat and power (chp).
In basic terms, a chp plant is an installation where there is simultaneous generation of usable heat and power, usually in the form of electricity, in a single process. The elements of a chp plant comprise one or more prime movers, usually driving electrical generators, where the heat generated in the process is utilised via heat recovery equipment for a variety of purposes including industrial, or community heating.
Government recognised that harnessing waste heat would have huge advantages, in studies such as Energy Paper 35 (1979) which identified savings then of 30 million tonnes of coal, equivalent to more than a third of the output of the whole of the coal industry.
At that time, however, the concept of combined heat and power was opposed by the gas industry and also the electricity industry who viewed combined heat and power as a threat to their traditional markets. Now the concept is actively supported by the gas industry. It is still felt that there remains a certain ambivalence within the electricity industry, probably due to potential competition from embedded generation resulting in potential loss of revenue.
According to DTI figures, for every 1 MWe of chp operating in the UK, 1000 tonnes of carbon are saved annually. Reaching the government's current target of 10 GWe of chp would produce carbon savings of 6 million tonnes each year – more than 25% of the current shortfall required to achieve the UK's domestic target of a 20% CO2 emission reduction by 2010.
The government has been investigating institutional barriers to embedded generation and chp through the Embedded Generation Working Group (DTI) which has identified various conflicts of interest.
Resolution of such problems will be essential if embedded chp technology is to achieve the potential it offers.
The challenge for the UK's chp sector is that the government's policy, as with many aspects of sustainable energy, is often contradictory.
CHP needs more investment if it is to grow. One hurdle to this is the way in which the value of power and heat from chp is calculated. The UK follows the EU basis of treating electricity as the waste product and heat as the prime, valuable output. In effect, the heat subsidises the production of electricity.
From a consumer point of view, this means that heat is the more expensive, rather than the cheaper, product of chp and that the electricity is priced the same as that from normal suppliers.
To give an analogy of why the current methodology is flawed, imagine a car as a mobile chp plant. The method of valuing energy as outlined above is rather like deciding that a motorist who uses the waste heat from the engine to heat their car in winter is saving petrol.
The statistics are prepared on the assumption that if you did not have waste heat from the engine you would have to burn fuel in a boiler to heat your car. The imaginary fuel you would have burnt thus can be considered as reducing the fuel you have to use for your journey.
This methodology has been and continues to be under review within relevant government departments.
Equal treatment for chp
Many supporters of chp feel that it is not currently evaluated on the same basis as other CO2 saving technologies.
Comparison with insulation of buildings is one example. Insulation is due to be imposed through Part L at paybacks in excess of 16 years and we have legislation to impose minimum U values on retrofitting buildings. By contrast, chp must achieve payback of six years or less.
Investment in double glazing and external insulation are seen in normal public sector investments as a means to reduce energy and CO2 emissions under HECA programmes. They are usually public funded. Why not encourage of local authorities to treat chp and its piping infrastructure as normal expenditure?
Figure 1 shows the large differences in CO2 savings which can be achieved by either insulation or using chp. Not only are the CO2 savings much greater with chp, the capital cost is also lower. The figures are based on a feasibility study for a community heating chp project in Lambeth, London. The comparison made is between addition of insulation to an existing wall of U-value 2·2 W/m2K and heating from a 600 kW chp.
It is clear that what is an economic level of insulation for a building fed with very high carbon content electricity should be different to that for a building supplied with heat form chp. As the draft Part L is currently structured it does not allow for investment in chp to be traded off against investment in fabric measures.
Also, renewable electricity gets full climate change levy benefit on exported electricity. Electricity sales made from chp plant through licensed electricity suppliers is, however, still subject to the tax. This is a particularly significant challenge to the development of chp. For many users of chp the ability to export electricity and gain a fair market price is an important part of the financing of these schemes.
Putting a value on chp
The introduction of the new electricity trading arrangements (NETA) has caused problems for many renewable energy sources. The impact of NETA has been significant. Recently gas prices have risen and the value of the electricity exported from chp schemes, the key to the CO2 displacement, has fallen even further in value.
It was difficult in the past to explain to tenants why the value of the electricity from their chp, connected to the same transformer as other central supplies of electricity, was worth less than 3 p/kWh when they were paying over 6 p/kWh.
The value of electricity from chp and the value of embedded generation to the country is thus key to the development of community heating chp.
In the short term a simple and effective solution to get chp running would be to simplify the rather impractical current trading arrangements for electricity from community heating chp, and recovery by the chp operator of climate change levy benefit which results in dilution of the levy benefit .
An alternative method would be to separate out the trading of chp electricity from the levy. The meter reading of exported electricity could then be used to pay the chp operator the levy assistance for community heating of 0.43 p/kWh exported.
These measures would assist in achieving the very significant CO2 savings.
CHP and nuclear power
The steam passing through the turbines when you visit a nuclear power station is little different to the steam in the turbines in a conventional power station. The only difference is the steam has been heated by a nuclear reaction with intermediate heat exchanges between the nuclear reaction and the steam. The steam still has to be condensed in order to produce the power, and vast amounts of waste heat goes to the French rivers, or the sea off the English coast.
Nuclear power stations, in their conversion of heat to electricity, are far less efficient then conventional power stations, producing a lot more waste heat for every unit of electricity produced.
It would be possible to use the waste heat to heat cities. The cooling water, instead of travelling a relatively short distance over a relatively short time to the sea, river or a local cooling tower, would be contained in large pipes feeding the cities. The rate of flow of the water is only about 3 m/s. If, as is the case in Aahus in Denmark, the coal fired chp plant is approximately 30 km away from the city, this option then becomes worth evaluating as a long term option.
Nuclear power inevitably becomes a public sector project as in practice no private organisation can obtain the insurance cover and the returns are insufficient for private sector investors. There is also the link between capital cost and safety levels.
Work carried out as part of the government's evaluation of city wide chp schemes and research by the Greater London Council, to evaluate the option of heating a large area of London with coal fired chp, compared favourably to the building of Sizewell C.
If the government is considering a really sustainable future, then it would do well to give priority to the development of citywide chp and large low temperature hot water grids as used in Denmark, utilising gas fired combined cycle chp to develop such systems.
This then provides the long-term infrastructure for cities to be heated from any chp source, including nuclear chp.
This option is vastly preferable to the scenario postulated by the electricity industry in the 1970s of a future where all buildings are heated electrically from nuclear power using direct electric heating and electric heat pumps. Such a scenario which would actually lower the temperature in cities in winter and result in many more nuclear power stations compared to the chp option.
CHP, wind power and solar power
CHP has a considerable advantage when used in conjunction with solar energy and wind power. CHP, particularly very large chp power plants of between 100-300 MW of electrical capacity, has the ability to change the mode of operation with no loss of performance, from producing just electricity only to producing electricity and heat in varying proportions.
During a day, the peak demands for electricity and for heat do not coincide. Heat storage is very cheap compared to electricity storage. This flexibility means that chp plants are normally always available at times of peak demand.
It is possible to use chp in conjunction with other renewable energy sources. For example, large chp generators, working with wind generation, can offer an overall service by reducing the electrical output from the chp plant and producing more heat when the wind power is at its peak .
CHP is available at times of system peak, and hot water grids are compatible with all forms of waste energy, so chp should be thought of as a technology which compliments, rather than competes with, renewable energy.
CHP offers a range of benefits and applications for consumers, industry and the environment. But a better approach to measuring these benefits is required if chp is to fulfil its potential.
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Building Sustainable Design
Postscript
William Orchard is partner in building services consulting engineering company Orchard Partners. He was first chairman of the Combined Heat and Power Association, and has advised the government on development of chp. Find more information on chp at www.chpa.co.uk