Micro CHP - Baxi Ecogen, cost £10,000

Although not technically a form of renewable energy, combined heat and power (CHP) is a process in which both heating and electricity are produced at the same time. Large CHP units have been operating on an industrial/community scale since the 1970s – indeed gas-fired power stations essentially employ CHP engines to produce electricity, although they do not make use of the heat generated.

The European Cogeneration Directive defines micro CHP as all units with an electrical capacity of less than 50kW – this has become economically viable more recently, with rising energy prices and advances in technology. A micro CHP unit designed for individual buildings replaces a normal gas central heating boiler, additionally providing some electrical output.

Types of CHP

The most common form of micro CHP employs an internal combustion engine – they are tried and tested, and noisy and dirty. They are generally used in small commercial premises and in large residential developments such as care homes.
  
Current developments in micro CHP technology centre on Stirling engines - these are external combustion engines, which allow continuous, controlled combustion resulting in very low emissions and high efficiency. Compared to internal combustion engines, Stirling engines need less maintenance, are more efficient, and are quieter – making them more suitable for domestic applications.
 
At present, only 1 wall-hung micro CHP unit has been accredited, the Baxi Ecogen.This is a similar size to a conventional boiler, although twice the weight and so needs to be installed on a load-bearing wall. (There are many more in the pipeline).

Fuel sources  

In the future, CHP units are likely to be powered by fuel cells, which are very efficient, very quiet, and have very low emissions. Fuel cells convert hydrogen and oxygen directly into electricity without the need for an engine - heat is produced as a bi-product of the electrochemical process - with clean water as a waste product.
    
Until such a day, natural gas is the most common form of fuel for micro CHPs – although engines are being developed which can use sustainable fuels such as biomass, wood gas, or solar thermal.

Benefits

Micro CHP enables greater autonomy, and electricity can be sold to the grid through the FIT scheme. 
 
Under the FIT scheme, the first 30,000 people to install micro-CHP will be paid for every kWh of electricity generated and an additional figure for any unused electricity exported back to the grid. This feed-in tariff payment will continue for 10 years and is index linked.
 
Micro CHP is also an eligible measure under the Green Deal.
 
Micro CHP has the potential to provide large carbon savings over oil and grid electricity, and in the not too distant future over gas too. Unlike large power stations which must run all the time, with micro CHP electricity is only generated when heating is required - this is typically at times which correspond with peaks in electrical demand.

Installation

Installation of micro CHP is easy - there is very little difference between a micro-CHP installation and that of a standard gas boiler, and if you already have a conventional boiler then it plugs straight into your current heat distribution system. The installer must be approved under the Microgeneration Certification Scheme. Similarly, servicing costs and maintenance frequency are estimated to be similar to a standard boiler – although a specialist will be required.
 
 
Micro CHP is at present in its infancy, however it is likely to replace most if not all conventional boilers in time – watch this space!  
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