CHP stands for ‘Combined Heat and Power’ and describes a fuel-fired engine driving an electrical generator, with heat being recovered from the engine for space heating use.
Gas-fuelled engines are usually used in CHP, but other fuels, including renewable fuels, can also be used. The electricity generated by the CHP unit can be used on site or exported to the grid.
Whilst the overall fuel efficiency of a conventional generator is only 25-30%, the efficiency of a CHP unit can be over 90%. This is because the heat that would usually be wasted from the engine exhaust and cooling jacket is recovered.
Because the electricity and heat produced has a higher value than the fuel going into the engine, overall economics can be more favourable than just using a high efficiency boiler. However, CHP is expensive to buy and maintain.
For growers, there is an additional benefit too. The CO2 from the engine exhaust can be used for greenhouse atmospheric enrichment. CHP works out best when the greenhouse has a long heating season and where significant electricity consumption exists on site — e.g for lighting.