CHP units generate simultaneous thermal heat and electrical power. They normally comprise an engine driving a turbine (similar to a generator) producing electricity. Unlike a generator though where the resultant heat is rejected and therefore wasted, the CHP recovers the heat through a water cooling system. This makes the system very energy efficient. This heat can then be used for heating and hot water similar to a boiler heating system.
Not only does CHP enable the conversion of a high proportion of waste heat to usable heat but also it is very efficient because power is generated close to where it is being used and thus electricity transmission losses are minimised.
CHP has been used for many years in commercial and industrial applications, for example, in hospitals and hotels where there is a continuous demand for both heating and electricity. In these cases, they are normally used in conjunction with standard boilers so that when they are shut down for maintenance or when electricity generation is not required, the standard boiler runs to provide hot water and heating.
Now though, micro CHP, smaller units for residential use are becoming more popular and more widely used.
On a residential level in Portugal, the CHP has two very useful applications: firstly in remote locations where mains electricity is not available, it can be used as a generator for providing electricity for the house whilst at the same time producing heat for the heating or sanitary hot water systems. Secondly where mains grid power is available, it can be used to generate electricity to sell back to the grid whilst once again producing heat for the heating or sanitary hot water systems. With the new legislation in Portugal for selling electricity back to the EDP grid, this latter solution makes the CHP system far more viable.
The normal fuel for CHP units is gas or oil but more recently, the units are now available with other types of burners including wood, waste products and biomass. Biomass pellets are a carbon neutral fuel (the carbon dioxide released during combustion is balanced by that absorbed during production).
The combination of biomass with CHP is extremely attractive because it involves a very efficient system combined with an environmentally friendly fuel.
The drawbacks with CHP units for residential applications are twofold:
*
Initial cost – a typical domestic CHP unit generating about 5 KW of electrical power and 10 KW of thermal power would cost in the region of €15,000.
*
Running times - CHP units work most efficiently when there is a continuous demand for both electrical energy and thermal energy. In winter, this should not be a problem as heating is necessary and the electrical energy can always be sold back to the grid if not consumed, but in summertime it may be difficult to run the CHP as there may be no thermal demand (except for hot water which is minimal particularly if solar panels are fitted) or unless the heat is dumped into the swimming pool. It is not possible to run the CHP without thermal demand as the heat must be rejected in some way.
