The district heating grid operator Nahwärme Eibiswald heats its district heating grid via a wood chips heat plant.

Wood chips are 100% CO2 free but are still subject to fluctuating purchase prices. As the biomass boiler could not be operated in the low-load range, an alternative had to be found. While an oil boiler was out of the question, a solar option with a constant heat price was an attractive alternative. In 1997 Nahwärme Eibiswald installed its first district heating solar plant. With the installed collector area of 1,150 m²/12,379 ft² and solar heat storage volume of 105 m³/27,740 gal, Nahwärme Eibiswald was able to cover up to 90% of its heat demand via the solar thermal plant during the summer months.

Over the years the district heating grid and its energy demand grew constantly, resulting in a necessary extension of the existing solar system to keep a high solar heat coverage during the summer months. In 2012, an additional 1,115 m²/12,000 ft² of advanced high-temperature flat plate collectors were installed. The hot water storage volume was increased by 60 m³ / 15,850 gal.

SOLID evaluated the existing heat demand profile, and solar yield data of the initial solar plant, as a basis for the engineering of the solar extension.

The existing local wood chips drying plant (operated via circulation of outdoor air) was upgraded with an air-water heat exchanger, and integrated into the solar supply system. In this case, valuable solar heat overproduction can be used for the drying process.