Energy: our power station

Autonomous heat and electricity supply

The planning and realisation of our own power station Zündholz is a milestone on the road to achieving our goals. Its commissioning in 2010 brought us one step closer to our fulfilling our vision; we wish to work, produce, heat and build in a climate-neutral manner. Our power station produces electricity for around 1,200 households, and heat for timber drying, pellet production and the heating for our workshops.

Zündholz power plant

Lehmann Holzwerk AG uses Swiss wood sustainably and ensures maximum value by using waste as a source of energy.

Electricity is produced in our Zündholz wood power plant through the cogeneration of heat and power by means of an Organic Rankine Cycle (ORC). ORC is very similar to the thermodynamic cycle of a normal steam turbine. The main difference is that it uses a silicone oil instead of water. The vaporised silicone oil drives the turbine and operates at a temperature of 312 degrees and 11 bar. This allows a very efficient use of the heat source at a low temperature and operating pressure to generate power. The efficiency of the ORC unit is about 18% and behaves consistently within a partial load range. The plant produces an annual 5,000 MWh of electricity.

Wood as fuel

The heat needed to operate the wood power plant is obtained solely by burning waste wood from our own timber works and from the surrounding forests; about 55,000 cubic metres of wood chips is required. A trough chain conveyor is used to deliver the chips to the heater. It has an output of 6 MW.

At the outlet of the ORC unit, 75% of the heat is fed into the Erlenhof’s district heating grid to provide ecological heat generation for all operations on the Erlenhof. This achieves an overall efficiency of almost 90%.

Partners

The Zündholz wood power plant is a joint venture between Lehmann Energie AG, a subsidiary of Lehmann Holzwerk AG, and St. Gallisch-Appenzellische Kraftwerke AG (SAK). The firm in Gossau has responsibility for fuel preparation and firing, while SAK operates the ORC unit and generates the electric power. A perfect balance between each partner’s core skills. For SAK, a partnership on the Erlenhof is an important commitment to the sustainable use of wood as a source of energy.

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