Stirling Engine

Stirling Engine | Rankine Engine

There are two principal types of Stirling Engine, kinematic and free-piston. All Stirling engines have 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

MEC (Microgen)

Infinia (STC)

Disenco

The WhisperGen micro CHP unit is marketed by the UK energy company, E.ON (formerly Powergen).

It is a four cylinder unit which leads to smooth, vibration free operation, with noise levels similar to a domestic freezer. The MkV unit, incorporating a supplementary burner, was introduced in 2005 to provide additional flexibility, making the unit suitable for larger homes. This variant also incorporated an integral acoustic enclosure which made kitchen installation possible.

In January 2008, WhisperGen announced the establishment of a joint venture (EHE) with Spanish white goods manufacturer Mondragon CC to mass produce units for the European market.

The Microgen unit, developed by BG Group from a US (Sunpower) design, is a LFPSE which is intended for wall-mounting; it contains a supplementary burner which enables it to meet the full heating requirements for even larger homes.

Following disposal by BG Group in 2007, development of the Microgen unit was taken over by MEC, a consortium of gas boiler companies (Viessmann, Baxi, Vaillant, Remeha) and Sunpower. Each of the boiler companies is expected to market their own variant of micro CHP unit incorporating the MEC engine, currently being produced in Japan, but with mass produced units likely to be manufactured in China.

The Infinia (formerly known as STC) LFPSE is now being used by MTS, Bosch and Enatec in Europe as well as Rinnai in Japan.

Rinnai will produce the LFPSE module for integration into micro CHP packages by the other partners for the European market, with a trial of 1000 units planned for 2008-2010. Rinnai will also produce a packaged unit 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. The high electrical output enhances payback of the unit (which is anticipated to be significantly higher then the other three products), although this makes 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. In January 2008, Disenco announced a manufacturing partnership with Prodrive to produce the core engine, with packaging by Malvern boilers and recently announced a marketing deal with Endesa, owners of Scottish Power.