DESCRIPTION

Combined heat and power generation (CHP) is an important technology
for efficient fuel use and can use biomass as the fuel, however there are
currently few examples. The system produces electricity that can be used
in building or exported to the grid, and heat for space, water and even
process heating. Systems must be ‘heat lead’ for high efficiency, which
best suits applications to situations where there is a significant demand for
heat for long periods of time, such as hospitals, hotels and leisure centres.
Excess summer heat can be used for cooling via absorption chillers.
For building applications in London, the best system for using biomass
for CHP is thought to be gasification, whereby the biomass is converted
into a gaseous fuel that is used in an internal combustion engine driving
an electric generator. Wood biomass can be converted to gas with a
‘gasification’ system but subsequent cleaning of the gas is required
before it can be reliably used in the engine. This process is likely to
require a flue to the height of a conventional chimney. There is one
example of this type of system at BedZED.

Traditionally, biomass can been burnt as in a traditional power station to
generate electricity by the steam cycle but such plants are normally too
large for most developments. Other biomass CHP systems are
based on gas from biomass digesters and landfill gas, and the use of
biodiesel and ethylene. None of these are currently available on a domestic scale, although Baxi expects to launch a domestic version in 2009. Where biomass CHP applications are possible, the biomass fuel used is considered as carbon neutral, i.e. responsible for zero carbon emissions.

WHERE CAN BIOMASS CHP BE USED?

Biomass CHP is theoretically suitable in any situation where conventional
CHP is viable, i.e. those buildings where there is a high demand for heat
for most of the year - hotels, hospitals, leisure centres and some
industrial premises. CHP can be successfully used in residential and office
developments if the heat can be shared with adjacent buildings with high
heat or cooling requirements.

COST RANGES

The costing of biomass CHP is at present very difficult due to lack of
reliable commercial products and installations in the UK. Specific
quotations are required as technologies become available. The biomass fuel
is likely to be an equivalent price to conventional fossil fuels, if not more
expensive. This may change over time as fossil fuels get more expensive
and as the market for biomass develops. Suppliers should be contacted for
up to date costs.

OUTPUT RANGES

There are no inherent limitations on the range sizes of biomass CHP,
though at present the systems available are only for large communal
systems. Individual house microCHP systems will come on the market towards the end of the decade

TECHNICAL FEASIBILITY ISSUES OR CONSTRAINTS

See biomass section for details of general issues relating to biomass. In
addition, for CHP, there are currently many technical constraints on the use
of gasification biomass CHP. No reliable systems are available at present
though prototype systems are being used and tested.

MAINTENANCE REQUIREMENTS

Maintenance requirements are currently unknown but likely to be high
due to the technical complexity of the machinery involved.

ADDITIONAL BENEFITS OF TECHNOLOGY

CHP has the advantage of being able to supply power in the event of
failure of the grid supply. Also CHP can be used with ‘private wire’
systems in certain circumstances with consequential cost benefits.

PLANNING AND LEGISLATIVE ISSUES

CHP systems can be housed in separate buildings or within the building it
is to serve and therefore are not visible. However, the combustion gases
will require an external flue usually terminating above the ridge-line of the
building. This part of the system will be visible and should be designed to
be as unobtrusive as possible. Planning permission may be required.
There are regulations relating to connection to the grid.

LINKS TO SOURCES OF MORE DETAILED TECHNICAL INFORMATION

• Companion Guide to PPS 22: The technical annexes, available at
www.odpm.gov.uk/planning.

• Beddington Zero (Fossil) Energy Development, Toolkit for Carbon
Neutral Developments - Part II by Nicole Lazarus, Bioregional
Development Group, www.bioregional.com.

• CHPA, www.chpa.co.uk/biomembrief.html.

• British Biogen, www.britishbiogen.co.uk/bioenergy/chp/chp.htm.

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