Combined heat and power suits users with a year-round requirement for both heat and power.
Taken from the government publication CHPQA Standard volume 5:
CHP can make significant fuel, cost and emissions savings over conventional,
separate forms of power generation and heat-only boilers. The generation and supply
of electricity from power stations is generally at an efficiency in the range 25-50%,
based on the Gross Calorific Value (GCV) of the fuel and including transmission and
distribution losses. This means that 50-75% of the energy content of the fuel is not
usefully employed. This unused energy is rejected as heat directly to the atmosphere
or into seas or rivers. The generation of electricity and the recovery of heat in CHP
Schemes typically achieves overall efficiencies of 60-80%, and sometimes more.
Unlike conventional methods of electricity generation, some of the heat cogenerated in
a CHP Scheme is put to good use, typically for industrial processes or for space
heating and hot water in buildings. The heat used in this way displaces heat that
would otherwise have to be supplied by burning additional fuel, and so leads directly to
a reduction in emissions. The deployment of CHP is a particularly cost-effective
approach for reducing CO2 emissions and therefore plays an important role in tackling
This is perhaps the best way you can help the environment while also reaping the benefits of half price electricity and an RHI uplift payment, as if you needed any more encouragement to do the right thing.
Which type of CHP should I choose?
The three main renewable types are:
- Biomass gasification CHP
- Steam Heleix
- Organic Rankine Cycle
The gasification type, in simple terms, cooks wood to release wood gas, which is then captured and fed into an internal combustion engine (modified petrol engine like you find in a car) which drives a generator. The cooling water of the engine and exhaust provides the heat you need, and the generator the power. The drawbacks are that they are temperamental, very fussy about the fuel quality and moisture content and the gas they produce is very dirty when compared with other sources of gas. This leads to the engine needing a lot of attention, such as filters changed every few days, engine oil change every week or so, and an engine overhaul once a year, not to mention engine replacement every four years or so. Imagine running your car engine night and day at 6,000 rpm for 8,000 hours straight for 333 days of the year. Does that sound like it would be trouble free?
Steam heliex relies on a steam generating boiler. It’s a much more reliable and relatively trouble free process compared to the gasification CHP. The drawbacks are the steam biomass boiler is very expensive, with a complex control system, and creating steam with biomass is relatively inefficient when compared to running a low temperature hot water boiler. It’s also potentially far more dangerous if anything goes wrong.
Organic Rankine Cycle (ORC) uses a fairly standard and hence much cheaper (than steam generating) biomass boiler to heat a thermal oil, in a similar process to a refrigeration cycle, which causes the thermal oil to boil and turn into a gas to drive a turbine, which creates power, then when the gas cools it turns back into a liquid again to be re-heated. Once the process has used the heat it needs to generate power, the water then is circulated around your heating system and back to the boiler.
We choose to install ORC because:
- Lower capital cost makes payback quicker
- Low maintenance requirement makes for cheaper running costs
- Fewer moving parts and lower pressures in the biomass system makes for good reliability
Our ORC manufacturing partner is Enogia in combination with the Gilles industrial boiler range, which can run on very low grade fuel to give you the lowest running costs, combined with the best returns.