Stirling generators on trial23 March 2001
Field trials are now well advanced on WhisperGen, in effect a personal power station. The small (single household sized) combined heat and power system runs quietly on most liquid or gas fuels and has been developed by Christchurch (New Zealand) company Whisper Tech Ltd. Known as MCHP (for Micro CHP) it has a DC portable variant, the PPS16, designed for use in and being sold mainly in marine applications. Both WhisperGen models use the same engine, a WhisperTech designed four cylinder double acting kinematic Stirling engine (illustrated, right). A co-generation system provides heat in the form of hot water suitable for water or space heating.
The WhisperGen's Stirling is an external combustion engine in which fuel is burnt in a continuous manner outside the engine's cylinders. Because it burns fuel continuously and not explosively, the engine operates very smoothly and quietly – noise levels are less than 50dBA during operation and exhaust emissions are at lower levels than those produced by a conventional generator. Other advantages include its multi-fuel nature. It can run on almost any liquid or gas fuel from natural gas, LPG and diesel, to oil and biogas. Its unique feature is the “wobble yoke” linkage, a patented development which overcomes some of the previous Stirling design problems, and has allowed the design of a compact, low vibration engine.
WhisperGens are available as AC or DC systems, each producing 750 We and 5-6kW of thermal output, although 1 kW versions are imminent. The DC system is being sold as a commercial product for marine applications in Western Europe, it is CE marked and distribution channels are now being established. The DC system is designed to charge batteries such as those used to provide power in remote homes, yachts or other mobile dwellings. In this situation the WhisperGen can be seen as a generator with a by product of heat. A system the size of the WhisperGen will provide enough electricity and heat to satisfy the requirements of the average remote area home.
The AC system, which is gas fired, is now being sold as a trial and demonstration system and is currently being evaluated internationally with systems operating in several countries including the UK, Netherlands, Denmark, Germany, USA and Korea. The system is designed to be grid connected and to export excess electricity directly to the network. It is intended for use in countries where central heating boilers are the norm. In these countries the unit can replace the central heating boiler and thus be considered as a heater with a by-product of electricity.