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
Despite expectations of product
availability as recently as late 2012, the decision by E.ON to abandon a
fully proven product as it no longer fitted their core strategy, may
have been the final nail in the coffin for this technology, particularly
given developments in fuel cell based micro CHP technologies.
For further discussion of the relative
merits of these engine types see section on papers.
The WhisperGen micro CHP unit comprises a four cylinder engine which leads to
smooth, low vibration operation, with noise levels similar to a
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.
Several hundred units underwent extensive field trials in Europe
and technical issues appeared to have been fully resolved.
E.ON announced forthcoming product launch in
November 2012, then just prior to actually doing so, decided to "focus
on core business", whatever that means.
EHE is now in receivership and there seems little
prospect of that technology becoming commercially available in 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
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 has developed their own variant of
micro CHP unit incorporating the MEC engine, now being manufactured in China.
The UK variant is manufactured by Baxi, part
of the BDR Thermea Group which also includes Remeha, De Dietrich and
Infinia (formerly known as STC) LFPSE was developed for incorporation in
micro CHP products manufactured by Ariston
(formerly MTS) and Bosch
in Europe as well as Rinnai in Japan.
Rinnai will also 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.
Although based on a virtually identical core
LFPSE as the MEC derivatives, this unit is more realistically housed
within an integrated floor-mounted unit incorporating a hot water
The Infinia engine previously formed the
basis of the ENATEC micro CHP unit, a joint venture between the Dutch
utility ENECO, ECN and appliance manufacturer ATAG.
As of 2013, there has still been no
commercial launch and it is believed that development has been
The Disenco unit is a kinematic design with
an electrical output of around 3kWe, significantly higher than the other
In January 2008, Disenco announced a
manufacturing partnership with Autocraft to produce the core engine,
with packaging by Malvern boilers and recently announced marketing deals
with Endesa and Centrica.
In early 2010 Disenco was placed in
receivership; the design has been taken over by Inspirit Energy who
expect to trial the unit in 2011.
In 2013, Inspirit still seem to be facing
funding difficulties and no product availability has been announced.
Supply only cost (UK)
Supply only cost (Germany)
only cost (Remeha variant)
NL 2010 €10,000* (less €4000
DE 2011 €11,000 (less €1,500 subsidy)
UK 2010 £6-8000 (depending on