Although the principle of combined heat and power generation is attractive, practical problems have hindered its application. In the U.K. the scope for ‘small scale’ combined heat and power (total energy) systems has been improved markedly by the introduction of new Electricity Board regulations which allow the operation of small a.c. generators in parallel with the mains low voltage supply. Following this change, Serck have developed a standard total energy unit, the CG100, based on the 2.25 1 Land Rover gas engine with full engine (coolant and exhaust gas) heat recovery. The unit incorporates an asynchronous generator, which utilising mains power for its magnetising current and speed control, offers a very simple means of generating electricity in parallel with the mains supply, without the need for expensive synchronising controls. Nominal output is 15 kW 47 kW heat; heat is available as hot water at temperatures up to 85°C, allowing the heat output to be utilised directly in low pressure hot water systems. The CG100 unit can be used in any application where an appropriate demand exists for heat and electricity, and the annual utilisation will give an acceptable return on capital cost; it produces base load heat and electricity, with LPHW boilers and the mains supply providing top-up/stand-by requirements. Applications include ‘residential’ use (hospitals, hotels, boarding schools, etc.), swimming pools and industrial process systems. The unit also operates on digester gas produced by anaerobic digestion of organic waste. A larger unit based on a six cylinder Ford engine (45 kWe output) is now available.