CHP can be considered an old practice. In 1868 the construction of a newly opened sugar beet factory was reported in the tecnhical press of the time. Whereas details of the process equipment was extensively covered, the reciprocating steam engine providing power and exausting steam to the process attracted little comment as being normal practice. However, despite of being a known practice, in the UK there was no major interest in the widespread use of CHP until the last two decades of the twentieth century.
From 1973 with an increase in real energy costs resulting from OPEC action, the efficient use of energy began to receive attention in all the industrial countries. This often resulted in tax incentives, grants and other legislation to encourage CHP. In the UK, 1983 saw the Energy Act followed by Department of Energy part-funding of extended surveys and of installations providing an efficient use of energy.
Basically these were the factors that have significantly contributed to a bigger interest in local generation of electricity with high efficiency obtained by taking advantage of concurrent heat demands (CHP).
In this section some statistics regarding the use of Combined Heat and Power (CHP) in the UK
are presented.
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The change in the installed CHP capacity over the last twenty years is shown in Chart 1. Since 1988 the installed capacity suffered a constant increase and in 1996 the capacity is almost doubled.
In 1996 the total number of sites with CHP was 1336 with a total installed capacity of 3562 MWe. The electricity generated was 19081 GWh , at about 6% of electricity used by fuel industries and final users. The heat to power ratio was approximately 4:1. Along the past few years there has been a reduction in this value, due to industry demand for plant with a lower heat to power ratio and an increased incentive to export electricity.
From 1993 to 1996 the average load factor increased from 56 to 61%. This is due primarily to a greater utilisation of some large CHP schemes.
The target established by the government for the year 2000 is to achieve 5000 MWe of CHP
installed capacity. This requires an installation rate of 270 MW per year of new CHP capacity,
each year, for the period 1991-2000.
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The distribution of CHP sites and electrical capacities per economical sector is summarised in Table 1. There is an approximately an inverse relation between the number of sites and the electrical capacity, when going from industry to services sector. The industrial sector represents 86% of the CHP electrical capacity. On the other hand, 74% of the sites are commercial, residential and public sector buildings.
| Sector | Number of Sites | Electrical Capacity (MWe) |
| Industry | 304 | 3068 |
| Transport, commerce and administration | 671 | 185 |
| Other (*) | 361 | 309 |
| Total | 1336 | 3562 |
It is difficult to say accurately how many district/community heating schemes there are today and how many homes are served, as the last detailed assessment was carried out in 1984 - this survey found 780 individual schemes, serving 300,000 homes, representing 1.5% of the UK housing stock at that time. However it is estimated that currently the percentage of homes heated in this way had increased to 2% and that the maximum heat output capacity of the existing district heating schemes is about 120 MW.
Such systems only offer scope for significant environmental benefits when they operate in
association with CHP. Particularly extensive CHP-based schemes have been established in
Sheffield, Doncaster, Nottingham and a number of South London boroughs.
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It can be seen from Table 2, that the vast majority of the 1336 CHP schemes in operation are less than 100 kW (50% of sites) and between 100-999 kWe (34% of sites). However the schemes larger than 10 MWe make 79% of the total electrical capacity. As the capacity size range increases, the number of sites decreases while the total electrical installed capacity significantly grows.
| Electrical Capacity Size Range | Number of Sites | Electrical Capacity (MWe) |
| Less than 100 kWe | 674 | 37.1 |
| 100-999 kWe | 454 | 111.8 |
| 1-9.9 MWe | 144 | 587.5 |
| Greater than 10 MWe | 64 | 2825.9 |
| Total | 1336 | 3562.4 |
The total fuel consumption in 1996 was 111,299 GWh and the overall plant efficiency was 75%. The overall plant efficiency increased since 1993, when its value was 71%.
The distribution of fuels used for CHP in 1996 is shown in Chart 2. Natural gas dominates, with 46% of total fuel use. The percentage of natural gas use is growing, while coal use percentage is decreasing. CHP schemes accounted for 6% of UK gas consumption in that year. On the chart, renewable fuels include: sewage gas, other biogases, clinical waste, municipal waste. Other fuels include: process by-products and uranium.
The proportion of electrical capacity in 1996 per type of CHP scheme is provided on Chart 3. Back pressure steam turbine has the largest proportion. The amount of combined cycle gas turbine based plant has significantly increased over the last ten years. Statistics show a trend to replace steam plant with gas turbine based units. In terms of numbers, the largest segment is for reciprocating engines. Several reciprocating engine schemes have installed in the past ten years, but the average size of these plants are is under 1 MWe.
In terms of electricity generated during 1996, the bigger portion was generated by CHP combined cycle schemes (about 32%), immediately followed by back pressure turbine plant (about 31%). As to the heat generation, 54% came from back pressure steam turbine plant and 13% from combined cycle schemes.
The main reference was the Combined Heat and Power Association Web Page, in particular the document "Statistics for Combined Heat and Power in the UK"at http://www.energy.rochester.edu/uk/chpa/statistics/1997.htm
Comment
It describes the results of a study prepared by ETSU (Energy Technology Support Unit) to DUKES
(Digest of UK Energy Statistics) on UK energy statistics related to CHP.
The information provided is fairly detailed and extensive. It is comprehensively reported,
but requires considerable attention and time to fully understand the figures.
Adequate for someone with a previous reasonable good knowledge on the subject or who wants to
acquire it. May be confusing for a person that just wishes to get a general idea of the main
figures.
Nash, F.
"Cogeneration-CHP in industrial and commercial applications",
?Publication?,
World Wide Web Virtual Library for District Energy
http://www.energy.rochester.edu/
