Buildings

Combined Heat and Power Generation

In conventional power plants, only one third of the energy consumed is fully utilised. Combined heat and power (CHP) systems provide a viable, environmentally friendly alternative. CHP plants work on the principle of combined heat and power generation, whereby the energy consumed is simultaneously transformed into both electricity and useful heat. As a result, up to 40% of the primary energy can be saved compared with centralised power generation and decentralised heat generation.

In addition to medium-sized and large CHP units, German companies also offer "mini CHP systems" with a capacity of up to 30 kWei (electric power) and 200 kWth (thermal power). Mini CHP units essentially comprise a combustion engine, a power generator and a system of heat exchangers.

The electricity generated in the generator can either be used in the building directly or fed into the public grid. The waste heat generated by the combustion engine is recovered by heat exchangers and can be used for heating purposes. The heat is usually stored in a buffer storage unit until needed.

The size of a mini CHP depends on its capacity but is not generally larger than a standard boiler. The engines also make very little noise and therefore can easily be installed in basements. The capacity of a mini CHP unit can provide enough thermal heat for a large single-family house or multiple family dwelling. The greater the heating load required, the greater the amount of electricity generated and the sooner the cost of the CHP system will be recovered.

Mini CHP units can be used in residential buildings, in recreational buildings (including hotels, guesthouses and restaurants), public buildings or healthcare facilities (including hospitals, care homes and health centres), in other words, wherever heating is required on an ongoing basis. In addition, standalone mini CHP systems without a connection to the grid provide an attractive alternative to traditional power generators in isolated areas.

German legislators recognised the environmental benefits of CHP systems many years ago and implemented appropriate measures such as the Heat-Power Cogeneration Act (KWK) and the Energy Saving Ordinance (EnEV) to promote and extend the use of combined heat and power generation. Electricity tax is not applied to the consumption of electricity generated by CHP, while the fuel used to generate the electricity is exempt from energy tax.

Germany currently has some 2,500 CHP units with electrical capacities of between 50 kWei and 2 MWei. Since 1990, the electrical power of CHP engines has increased in Germany from 500 MW to more than 4,100 MW, which represents 3.5% of the national energy supply. Experts predict a further increase to 10%.

In other words, a large number of manufacturers and a wealth of expertise have been present in Germany for several years. German manufacturers are continually pushing the boundaries of their technological innovations to make them even more effective and to identify new applications. These include, for example, the use of micro gas turbines to drive mini CHP systems.