Project Summary: How micro CHP boilers can be used to heat your home and provide low carbon electricity, find out all about their benefits, installation methods and costs.
Micro CHP systems are combined heat and power systems small enough to be fitted into the average home.
They are fitted in place of your boiler and use either mains gas or LPG (Liquid Petroleum Gas) to heat water for use in a water filled central heating system and to provide hot water.
Whereas industrial CHP systems generate electricity and heat as a by-product of that generation, micro CHP systems operate the opposite way by generating heat and generating electricity as a by-product of that heat generation. Whilst they are generating hot water, the waste heat this produces is used to generate electricity, normally in a ratio of about 6 units of heat to 1 unit of electricity.
What all this means is that micro CHP is classed as a low-carbon technology because it generates electricity by using a waste product rather than burning more fossil fuels. Because of this, domestic CHP installations are eligible to be paid (11p/kWh) under the FIT (Feed-In Tariffs) Scheme.
Typically the monetary benefits with an average system are:
There are several different types of CHP system available, however only one has been fully developed as a micro CHP system for the domestic market: the Stirling engine. Stirling engines produce heat and electricity typically in a 6:1 ratio. A standard system produces around 1Kw of electricity an hour, supplying 46% of an average home’s electricity needs.
Other CHP systems include the commercially used internal combustion engine and newer fuel cell systems which take energy from a fuel through a chemical process rather than combustion.
In a standard micro CHP system you will use a condensing boiler to heat your water-filled central heating and hot water. The steam that this produces is used to drive a Stirling engine to generate electricity.
A Stirling engine is essentially a sealed box, usually containing one or more linked, gas filled tubes, each containing a piston. One tube is exposed to a heat source, and the other to a cooling source. There is a fixed volume of gas in the tubes, so if the gas expands or contracts it moves the pistons. The gas can be expanded or contracted/compressed in the system by the heating and cooling sources.
The heating and cooling of the gas drives the pistons alternately up and down. The engine is connected to an electrical generator which uses the pistons’ energy to generate an electrical current. The design of the Stirling engine means that it is very efficient at converting heat into electricity, as well as being fairly quiet.
According to the Carbon Trust homes most suited to a micro CHP system are typically larger or older properties with solid brick walls where insulation is not worth the investment. This is because smaller, better insulated homes have a lower heating requirement which means that less electricity is generated by the system.
The installation process for micro CHP systems is very similar to the process for standard boilers, and so should be fairly simple to carry out, particularly if it is simply replacing a conventional boiler.
There are a few things that should be considered:
The installation time for a micro CHP system should be similar to that of a boiler. If you are incorporating additional building work you will have to consider the time that this will take also.
To be eligible for FIT scheme payments you will need to hire an MCS accredited installer and the installer will have to use MCS accredited parts in the installation. When your installer has finished the work they will give you a certificate stating that your installation is MCS compliant. Green deal installations will need to be carried out by a Green Deal installer.
A micro CHP system for an average house will cost around £4,000-£6,000 including installation. It should deliver an energy saving totaling around £60 a year, in addition to Export Tariff payments of £30 and Generation Tariff payments of around £180 a year through the government’s FIT scheme. These tariff values are available to the first 30,000 households to install micro CHP technology. The lifetime for the CHP system is at least 15 years, and the tariff value is fixed when you start receiving payments as well as being index linked. To find out more about FIT take a look at our Feed-In Tariffs (FIT) project page.
The government’s newly launched Green Deal can pay for the up front costs of a micro CHP installation. The money that you save using the system is then used to pay back the loan every month. This should make the installation ‘free’ to you as you spend no additional money. Whilst this represents a great deal you will save more money if you pay for the installation yourself as the Green Deal charges around 7% interest on the payments. You can visit our Green Deal project page to find out more about this scheme.
In terms of maintenance, your installer should be able to give you more information regarding any procedures that need to be carried out. Maintenance should be similar to that of a boiler but you will need a specialist to carry it out, and a professional service needs to be performed every year as with your conventional boiler.
In addition to the £270 a year saving your system will deliver there are other benefits:
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