Wood Chips and Organic Milk from Bavaria

The dairy farm “Zum Marx”, run by the family Westenrieder and their two employees, dries wood chips and hay and produces organic milk as well as further dairy products for sale.

The company’s complete heat demand is covered by a solar plant, which was installed in 2015, and a wood chip boiler. The energy system uses air collectors and 160 m³ of wood chips per year, which are dried by the solar plant. The collector field with CCS+ air collectors by the company CONA and an area of 156 m² has a thermal power of up to 114 kW and was integrated into the rooftop of the drying facility.

Besides wood chips, also hay is dried with the solar process heat plant during the summer months. At night, as well as on cloudy and rainy days the hay is aired in intervals in order to avoid germination and fungi growth. If necessary, the air used for that purpose can be post heated by the wood chip boiler, which ensures a high quality of the drying good. The wood chip boiler runs very efficiently because there is only a small amount of residual moisture in the solar dried fuel. On sunny days or such with unsettled weather however, the solar heat produced by the air collectors is sufficient to dry hay and wood chips and therefore the boiler is not required.

The wood chip drying, using two chambers with a volume of up to 70 m³ each, is not only done to meet the company’s own heat demand but produces fuel for 15 further wood chip boilers. The wood chips’ gain in energetic value achieved by drying is at approximately 200 kWh/m³, whereas the electrical energy required for the drying process is only around 3 to 4 kWh/m³, which equals ca. 0.6 to 0.8 €/m³.

The solar drying plant supplies temperatures of up to 65 °C. Although the air collectors can reach even higher temperatures depending on the solar radiation, the drying itself can be done at temperatures significantly lower than 65 °C: In order to dehydrate the drying good efficiently, the solar process heat plant has to heat up the ambient air only by 5 K. Hence, at ambient temperatures of 5 °C the drying is possible at only 10 °C. Therefore, the solar plant achieves a high energy yield in the course of a year.

A heat resistant fan sucks ambient air through the air collectors and feeds the heated air into an air mixing box where a certain amount of ambient air is mixed in to ensure the temperature limit of max. 40 °C for the hay drying process. From this box the drying air is blown through the drying good from below by high performance fans.

System scheme of wood chip and hay drying at the family business Westenrieder

The family Westenrieder’s energy demand for drying about 2,500 m³ of wood chips yearly is covered completely by the solar plant. Depending on the weather, 70 to 80 % of the heat required for hay drying comes from solar energy; the wood chip boiler covers the remaining demand.

The solar drying system’s yield has been monitored since the system’s implementation. With 660 kWh/(m²a) it equals 97 % of the outcome expected by simulations and makes for a total yield of the solar plant of 103 MWh/a. Thus, with the solar plant alone ca. 10,300 litres fuel oil can be saved, which equals around 33 tons of CO2-emissions per year. Taking into account the gain in energetic value of 200 kWh/m³ wood chips, the energetic surplus value generated by the solar plat rises to about 600 MWh/a, which equals ca. 60,000 litres of fuel oil per year.

The Turnkey-costs of the solar process heat plant were at around 30,000 € including the funding of 50 %. Therefore, over a period of use of 20 years, a very low heat production price of about 20 €/MWh can be achieved. . Considering the wood chips’ gain in energetic value, the costs are even only at 5 €/MWh. Also, with no regard to energy costs for conventional fuels, the solar process heat plant amortises itself in only five years due to the sell-off of around 2,340 m³ of dried wood chips per year.

If you are interested to take a look at the plant of the dairy farm Marx, you can sign up for an one site visit.