Air Collectors for Hay-Milk from the Bavarian Forest

The agricultural family business Mühlbauer in the Bavarian Forest switched their production to hay-milk and simultaneously installed a drying plant heated by air collectors. The goal was not only to secure the business’s livelihood but also to contribute to animal welfare. Natural hay rich in herbs promotes the health of the cows, which in turn give more milk of very high-quality rich in Omega-3 fatty acids.

The yearly demand of around 360 t of quality hay (dry material) for the 70 cows is yielded on 30 ha of grassland. Depending on the weather conditions during the year, up to four cuts yearly are processed in the new drying plant after pre drying for one to two days on the field. It is necessary for the hay to consist of at least 87% dry substance in order to avoid germ growth at the store. The amount of heat required for drying is produced primarily by an air collector plant with an area of 360 m2 by GRAMMER Solar.

The collector area is inclined by 20 ° and oriented 10 ° west. The plant has to heat up 10,000 to 35,000 m³/h of drying air to a temperature of 50 °C. When solar radiation is sufficient, fans suck the ambient air through the air collectors. By that, the ambient air heats up and it’s relative humidity decreases. When the radiation is too low, an additional heater fuelled by wood chips can be used. If necessary, an additional dehumidifier can be applied to prevent the hay from growing mildew and germs.

Bulk drying with air collectors (Source: (GRAMMER Solar))

Since the solar plant is used not only to dry hay (heat demand of ca. 125 MWh/a) but also to dry wood chips from the company’s own production (ca. 125 MWh/a) and other agricultural goods (ca. 105 MWh/a), a high specific solar yield of 675 kWh/m²a with 70 % of the energy required for drying processes covered by solar energy is possible. Furthermore, a photovoltaic plant provides the majority of the electricity required by the solar process heat plant. Hence, the running costs for the family business are very low and predictable.

Due to the high solar yield and the low investment costs of around 65,000 € including process integration and funding, very low heat production costs of circa 20 €/MWh are achieved. Therefore, the plant is very attractive also in economical terms.

With this solar plant, the family business makes a noteworthy contribution to the energy transition. They also support the conservation of the cultural landscape by cultivating meadows rich in herbs and flowers instead of large-scale cultivation of corn. Compared to conventional milk production, the business furthermore achieves higher profits per litre with the production of hay milk, which is an additional economical advantage.