CHP (Combined Heat and Power)
CHP (Combined Heat and Power), also known as 'Cogeneration' is the simultaneous generation of useful heat and electricity through the process of combustion. This generates electricity whilst retaining the by-product heat.
This excess heat may also be used as a cooling mechanism, a process called 'Trigeneration'; which works using the same principles to that of a Fridge. The process of CHP is complex, and currently there exists a large amount of confusion as to what CHP is and how this produces electricity. Be sure to read how CHP works.
CHP has enormous potential to delivering small scale electricity generation within the home, reducing reliance on fossil fuels. If CHP is provided both on industrial decentralised sites and within communities, than according to Government figures, output in excess of double that proposed by the Nuclear Programme may be achieved.
CHP is relatively straightforward to install, and adaptable to existing homes of all ages and types; although its efficiency is higher within the larger home.
CHP Energy Source
There are currently two main varieties of domestic micro CHP.
- Stirling Engines
- Fuel Cells
Stirling Engines produce between 6Kw/h and 10Kw/h of heat for every 1kw/h of electricity. Generally, the more heat that is produced, the more electricity that may be derived, resulting in lower emissions and financial savings.
These CHP systems currently require use of natural gas to operate, however there are a number of alternatives which use Biomass (woodchips, straw bales) as a fuel source, resulting in zero carbon output.
Fuel Cells are as yet currently still in development, however there are plans by Ceres Power and British Gas to launch one by 2011. Fuel Cells produce heat and electricity in equal proportions, primarily suited to 3-4 bedroom houses. Please see The Rise of Fuel Cell CHP for more information.
Is it worth it?
Advantages of CHP
- According to the producer 'Baxi' householders may save £200-400 a year in electricity.
- Carbon Trust confirmed CO2 emissions may be reduced by 5-10%, or between 200-800kg per year in comparison to high efficiency condensing boilers.
- Electricity may be fed back into the grid, providing additional revenue. A recent amendment to the Energy Bill has resulted in a "feed in tariff" allowing higher market rates to be attained.
Disadvantages of CHP
- Cost remains high, at approximately £1500 more than traditional condensing boilers, with a 20 year payback period. However manufacturers are expecting this figure to fall below £600 with a payback of 7-15 years.
- Stirling engine CHP micro systems are generally suited to larger, older houses as they require higher and more consistent energy demands to be effective.
- May be ineffectual in responding to dynamic requirements of users particularly coping with seasonal variations; often producing excess heat during the summer period.
- Smaller, better insulated homes may see reduced emission savings to below 5%, or under 100kg a year.
Finance available
There are a number of financial incentives for choosing CHP; these include:
Eligible for Enhanced Capital allowances (ECAs) - Allowing you to claim 100% first year capital allowances. To qualify, system needs to be accepted into the CHP Quality insurance scheme.
VAT reductions - Only applicable for certain domestic CHP systems. This currently stands at 5%
ROCS (renewable obligation certificates) - For biomass fuelled CHP
CHP qualifies for financial support within the Low Carbon Buildings programme (LCBP).
Future use of Micro CHP
It is estimated that Micro CHP used in Homes will provide 20% of the UK's electricity generating capacity, substantially more than that obtained from Solar Panels.
However their use in achieving Carbon Zero new homes by 2016 may be questionable, as current Stirling engine versions currently rely on use of Natural Gas; restricting their use to Retro-fitting.
There is currently ongoing research into differing fuel sources for CHP systems; these include Biomass, to use of Woodchip from sustainably sought forests.