Combined heat and power (CHP) is the generation of
and useable heat at the same time. It is also known as cogeneration.
When some of the generated heat is used in adsorption/absorption
chillers for cooling, it is known as tri-generation.
The key benefits of using CHP systems are energy
efficiency (and the associated carbon savings) and energy security.
conventional power stations, both electricity and heat are generated.
However, the heat is simply wasted, it is only the electricity that is
seen as a useful product. This has a substantial impact on the
efficiency of the system as so much of the energy in the fuel consumed
is simply lost. For example, in the UK, the efficiencies of gas power
stations are around 50%, coal-fired stations have even lower
efficiencies, around 38%. In contrast, in CHP systems, rather than
being wasted, the heat is captured for use. In this way, efficiencies
of up to 80% can be reached.
CHP systems are also available at a wide
range of scales and so are
particularly suited to local use. This produces further efficiency
benefits as transmission losses are reduced.
conventional power generation with its associated heat losses, carbon
savings of up to 30% can be made using CHP with the same fuel source
simply due to the increased system efficiency.
systems with different fuel sources, renewables based CHP systems in
particular can offer substantial carbon savings.
are also often associated with a reduction in other pollutants as less
fuel overall is being used to produce the same amount of useful energy.
security can be also be enhanced by CHP systems through more efficient
fuel use (less overall fuel is needed) and diversification of energy
recognition of the benefits of CHP, there are several Government
financial incentive schemes as well as Government policies to encourage
the use of CHP.
The financial incentive schemes vary with
the scale and CHP technology. For renewable fuel systems examples
include the Renewables Obligation (RO) which gives tradeable
certificates for the electricity generated, the Renewable Heat
Incentive (RHI) which provides payments for 20 years on the heat
generated and the Feed in tariff (FiT) which provides payments for 20
years on the electricity generated.
For more details of the renewable incentive
schemes, please visit our RHI and ROCs
quality renewable and non-renewable CHP systems are also eligible for
Enhanced Capital Allowances although these cannot be claimed in
conjunction with the RHI.
Increasing recognition of the benefits
of District Heat Networks (DHN) has also led to incentive schemes that
benefit CHP systems indirectly as they are so suited to DHN use. For
example, the Scottish Government’s District
Heating Loan Fund.
systems are particularly suited to sites where there is a consistent
need for both low-grade heat (<100 °C) and electricity. Many
are sized to meet the heat needs on site and connected to the low
voltage electrical distribution system so any excess electricity can be
exported to the grid.
At the end of 2015, the installed CHP
capacity in the UK stood at 5,692 MW of electrical output from 2102
installations. Of these installations, 383 schemes (85% of electrical
capacity) are in the industrial sector and 1,719 schemes (15% of
capacity) are in the agricultural, commercial, public administration,
residential and transport sectors (figures from the DECC, Digest of UK Energy Statistics).