How does a domestic micro-CHP boiler work?
Posted by Sharon Russell-Verma on 8 January 2016 at 12:15 pm
Micro combined heat and power (Micro-CHP) technologies generate both heat and electricity at the same time. They have a small fuel cell or heat engine which drives a generator and provides electric power and heat to a building.
At a district scale, marine marine diesel engines modified to run on natural gas are already providing heat and electricity to blocks of flats and retail units, with a recent example in Milton Keynes.
On the micro scale CHP has only recently started to roll out in the UK following numerous false starts, early reliability issues and high unit and installation costs.
Most micro-CHP systems operating today run on mains gas or LPG because it’s cheap, it burns easily and it’s accessible. Although natural gas is a fossil fuel, the technology is still considered to be low carbon due to the fact that it can be more energy efficient than simply burning fossil fuel. They are mainly used in homes or small buildings as their electricity generating capacity is relatively small.
The micro-CHP system itself is similar in size and shape to domestic boilers and can be mounted on a wall or on the floor. It can be up to 92% efficient and this is possible because otherwise lost exhaust heat energy is converted into useful electricity by the boiler.
Normally energy escapes as heat when electricity is transmitted through cables and the further electricity has to go, the greater the energy losses. In fact up to to 7%-12% can be lost between a power station and individuals’ homes. Hence, micro-CHP systems can be extremely efficient in the respect that the electricity they generate can be used on-site.
On average a domestic micro-CHP unit will produce 1KW of electricity, with the maximum for a domestic property being 50KW and if you generate more than you can use, any extra electricity can be sold back to the grid.
There are two domestic Micro-CHP boiler technologies available today:
(i) The stirling engine is one of the most popular available to the domestic market such as the Baxi Ecogen. It works as follows; when heat is demanded a magnetic piston drives up and down within a generator coil to produce 1kW of electricity to power appliances.
(ii) The fuel cell is to perhaps the most exciting and futuristic. It works by taking energy from fuel at a chemical level rather than burning it and because of this it can offer better energy efficiency and higher rates of electricity generation to heating rates. Although the technology is still at early stage, Viessmann have launched a consumer unit in Germany.
Advantages of micro-CHP
So why would you install a micro-CHP in your home rather than a conventional boiler? Well there are some advantages of micro-CHP
- When the micro-CHP is generating heat, the unit is also generating electricity which can be used in your home or exported to the grid.
- According to some manufacturers you could save up to £600 on your annual fuel bill.
- Installation is easy. In fact, there is very little difference between a micro-CHP installation and a standard boiler. If you already have a conventional boiler then a micro-CHP unit should be able to replace it directly as they’re roughly the same size. All installers must be approved under the micro-generation scheme.
- Servicing costs and maintenance are estimated to be similar to a standard boiler, although you will need a specialist installer.
- Installing a micro- CHP system in your home also benefits the environment due to the reduction in CO₂ emissions compared to grid electricity and standard boilers. Nearly 73% of CO₂ emissions in the home come from heating and hot water.
- Micro-CHP is eligible for FITs so you will earn money for each kWh of electricity your system generates and if you export excess electricity to the grid you will receive an export tariff.
A future role for micro-CHP
With electricity prices rising, it makes economic sense to consider installing a micro-CHP in your home, as it will not only efficiently heat your home, but it will also provide hot water and some useful low cost electricity. In addition, CHP can help with security of energy supply: the electricity generated by micro-CHP units, together with smart grids and energy storage solutions, could help the national grid cope with the peak load requirements. And having a secure energy supply is vital to everyone.
More information about Combined Heat and Power (CHP) on YouGen.
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