© NEP Solar, 630 m² Parabolrinnenkollektoren bei der Fromagerie de Saignelégier (CH)

Parabolic Through Collectors in Cheese Production

The company Fromagerie de Saignelégier SA is part of the Emmi-Group. With their ten employees, five of whom are cheese makers, they produce 40 % of the worldwide production of Tête de Moine – a cheese speciality made of fresh-milk that is traditionally produced since 800 years. Certified cheese dairies produce only 2,150 t of this cheese in total each year. The production site of Fromagerie de Saignelégier is seated in the Swiss canton of Jura at an altitude of 1,000 m.

Ca. 3,000 cheese wheels of 700…900 g each are moulded daily using 30,000 l of fresh milk. Each year the company produces around 1 million cheese wheels with a total mass of about 860 tons. The company’s production has used two oil boilers, which consumed 200,000 l of fuel oil per year. In order to preserve the environment and lower the production costs, the company decided to build a solar process heat plant with an area of 630 m2. The concentrating parabolic through collectors were installed on the company’s new warehouse in 2012. The photograph shows the collectors on top of the new building in which the cheese wheels are stored for ripening.

Seventeen Poly Through 1800 collectors by the company NEP with an aperture-area of 37 m² each are capable of a maximum performance of 360 kWth, which approximately equals 50 % of the company’s peak load. Since concentrating collectors cannot pick up diffuse or reflected radiation but only direct radiation, their mirrors need to track the sun’s direction in order to point the bundled radiation directly at the absorber-pipe. Therefore, the collectors’ position is readjusted automatically every ten seconds.

© Fromagerie de Saignelégier Parabolrinnenkollektor
The solar heat is directly fed into the return flow of the pressurised heating network, so the fossil-fuel-heater only has to be switched on when solar radiation is not sufficient. Spare heat can be stored in the 15 m³ buffer tank.

Because the outside temperature can drop below -20 °C, the solar system is run with a water-glycol mixture. The collectors provide a temperature of about 120 °C. The company’s pressurised hot-water-network is directly fed via a plate heat exchanger; it is operated at 105 °C and has a return temperature of 75 to 95 °C. When the plant can supply the minimum target temperature of 110 °C, it can cover a share of the heat demand of all the company’s thermal processes; only then is it operated. The regulated maximum temperature of the solar hydraulic is 130 °C. In order to level out uneven load profiles, an additional short-term-store with 15 m3 of volume has been integrated into the hot-water-network.

Each year the cheese dairy saves up to 30,000 l of fossil fuel in total, which spares the environment 76 tons of CO2. The solar plant’s system yield of up to 255 MWh/a equals a solar fraction of 15 % in relation to the whole heat demand of the cheese dairy.

The company financed the plant on its own. They invested ca. 375,000 € in the plant after funding. Amortisation periods of up to twelve years were acceptable since Fromagerie de Saignlégier is a traditional company planning for the long term. Therefore, a process heat plant with concentrating collectors became possible at the production site despite the relatively low amount of direct radiation with 1060 kWh/m²a.