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Consumer-oriented and sustainable production of electricity and heat play a major role not only in the private sector. Also in the larger power range is increasingly set to the on-site production of energy-efficient and simultaneous production of electricity and heat.

For this reason the project “Pellematic e-max – the electricity generating pellets heating for the medium power range” has been started with the goal to supply larger buildings with a high heat demand, with electricity and heat from pellets.

  • Project goal: development of an electricity generating pellet heating fort he medium power range.
  • 50-60 kW thermal power.
  • 4-5 kW electrical power.
  • Target group: commercial enterprises, hotels and residential complexes.
  • Technology: Stirling engine and the tried and tested a thousand times ÖkoFEN pellet heating technology

Structure of the electricity generating pellet heating
To integrate the Qnergy Stirling engine an own pellet boiler was designed which should gradually be adapted to the needs of the stirling engine. This pellet boiler has roughly a thermal output of 50 kW while providing an electrical output of about 4-5 kW.

To ensure a proper operation and the highest possible electricity yield it is important to keep the combustion conditions in the combustion chamber as constant as possible. For this reason a separate concept was developed for the regular incoming flow of the Stirling engine, which is designed to ensure that the Stirling engine is evenly supplied from all sides with heat.
In the future this pellet boiler with integrated Stirling engine shall be used especially in the mid-power range in interaction with other boilers. This electricity generating pellet boiler, which is designed for base load applications, should be used especially in larger buildings. In this field of application very high runtimes, related with a high anual energy yield, can be achieved.

These factors have a significantly positive effect on the payback time of the entire system. At steady energy prices and the use Pellematic e-max as base load boiler it can be relatively quick to achieve this payback rate. Pellematic e-max can be integrated as base load boiler in a cascade connection but also is available as sole heat source in multi-family houses or similar buildings.

Advantages of the Project Pellematic e-max

  • Energy-efficient heat and electricity generation at the place of use
  • Low emission and ecological: CO2-neutral energy balance for heat and electricity
  • As base load : long, continuous runtimes and thereby a predictable energy yield
  • Short payback time at optimum use and long run-times


The hermetically sealed free-piston Stirling engine of the company Qnergy works with helium as driving gas. The heat supplied from the wood pellets leads to a piston movement in the interior of the Stirling engine. This allows up to 5 kW of electrical power, completely maintenance-free and environmentally friendly. Depending of the heat supply or the temperature in the combuston chamber, the Stirling engine modulates ist electric capacity and adapts to the requirements.
The produced electric power needs to be rectified. The conversion of DC to AC (50 Hz) and the later three-phase feed into the public grid is carried out by an inverter from the company Fronius.

How it works

1. The head of the Stirling engine is heated with the flame of the wood pellets. This heat is then transferred to the working fluid of the Stirling engine (helium). This heating leads to a pressure increase.

2. With the heat supply and the cooling of the Stirling engine in the cooling circuit, a temperature and pressure difference is generated. Through this temperature difference, the helium in the Stirling engine expands and contracts again and thereby, the piston is set in motion and moves up and down.

3. This movement is converted by the linear generator directly inside the Stirling engine into electrical energy.

Further information