Stirling Engine

The two principal types of Stirling Engine, kinematic and free-piston. All Stirling engines have a two pistons (functionally speaking), one of which shuttles the working gas between the hot and cold zones and is known as a displacer, whilst the other is subject to the resulting pressure changes and does work to drive the engine. In the kinematic engine, these two pistons are physically connected by a crank mechanism, whereas in the free-piston engine, there is no physical linkage and the displacer oscillates resonantly. In theory the LFPSE (Linear Free Piston Stirling Engine) is much simpler as it contains fewer moving parts. In practice, the challenges of differential expansion and linear generator design have so far proved a major obstacle to commercialisation. For further discussion of the relative merits of these engine types see section on papers.
WhisperGen	Microgen	ENATEC	Disenco
The WhisperGen micro CHP unit is being marketed by the UK energy company, Powergen. It is a four cylinder unit which leads to smooth, vibration free operation, with noise levels similar to a domestic freezer. However, to reduce noise even further it should be installed within an acoustic enclosure, or alternatively located in a utility room (or garage). The MkV unit, incorporating a supplementary burner, will provide additional flexibility, making the unit suitable for larger homes. This variant will also incorporate an integral acoustic enclosure which will make kitchen installation possible, and is expected to be available in late 2006.	The Microgen unit, developed by BG Group from a US (Sunpower) design, is a LFPSE which is intended for wall-mounting and contains a supplementary burner which enables it to meet the full heating requirements for even larger homes. However, when operating with the supplementary burner, the electrical output as a percentage of fuel input is very low.	The ENATEC unit is also a LFPSE and based on another US (STC) engine. ENATEC is a Netherlands' consortium formed by Eneco, the energy supplier, the consultancy ECN, and ATAG a domestic appliance manufacturer. Following the demise of ATAG, the Japanese boiler manufacturer Rinnai, is now partnering the group, initially focussing on products for the Japanese market.	The Disenco unit is a kinematic design with an electrical output of around 3kWe, significantly higher than the other products. It is based on a design originating in Lund University and has recently been substantially redesigned by Ricardo in the USA. The high electrical output enhances payback of the unit (which is anticipated to be significantly higher then the other three products). This does, however, make the unit susceptible to the recoverable value of exported power from the unit unless it can achieve high utilisation such as in a small hotel.

For UK sales contact: whispergen@powergen.co.uk
For further details contact: WhisperGen	For further details contact: BG Microgen	For further details contact: ENATEC	For further details contact: Disenco
Electrical output 0.85 (nominal) - 1.2kWe (peak)	Electrical output 1kWe	Electrical output 1kWe	Electrical output 3kWe
Thermal output 6.0 (nominal) - 8kWt (peak)	Thermal output 4-40kWt	Thermal output 4-40kWt	Thermal output 9kWt
Application Individual family homes	Application Individual family homes	Application Individual family homes	Application Homes & small commercial
Supply only cost £1350 plus VAT	Supply only cost	Supply only cost	Supply only cost
Installed cost £3000 including VAT	Installed cost	Installed cost	Installed cost
Availability East Anglia, East Midlands, NW England - 2004 London, West Midlands - January 2005	Availability 2007	Availability 2008?	Availability 2009?