Solar Heating World Champ

Seasonal heat storage boosting the effect of the world’s largest solar heating plant

The small Danish city of Vojens is perhaps best known for their accomplished ice hockey team, as well as Vojens Speedway Center, founded by the winner of several world championships, Ole Olsen. Now, the city wins gold in solar heating as well.

Sunrays equal cost savings

“The pleasure of going to work is particularly great when the sun is shining, because I know how the sunrays are saving our customers money,” Arne Holm says. He is the Business Manager at Vojens District Heating Plant, which runs the world’s largest solar heating plant, and the world’s largest thermal pit storage.

It all began when Vojens District Heating Plant decided to cut down their C02 emission and their consumers’ heating bills at the same time. The solution was a largescale solar installation – extremely large-scale. They aimed to cover 50% of the total annual heating with solar heat. In cooperation with advisers they figured out how to reach the goal.

Key plant data

• Collector area (effective): 70,000 m²
• Number of solar collectors: 5,439
• Storage capacity: 200,000 m³
• Share of annual heat demand: app. 45%
• Calculated peak capacity: 49 MW
• Calculated annual production: 28,000 MWh

Highly professional

Arcon-Sunmark was chosen as the supplier after an extensive selection process. In 2012 a 17,500 m² plant including a 3,000 m³ steel tank became reality. The results were so impressive that an extra 52,500 m² were added only a couple of years later, in 2014/2015.

By now, the collaboration has led to a 70,000 m² installation, and a 200,000 m³ thermal pit storage, for storing excess solar heat for periods of time where the sun delivers less energy. The storage is excavated in an old gravel pit. The large water volume is separated from the district heating water by a heat exchanger. A huge thermal seasonal storage formed by a welded liner allows the energy to be stored from summer to winter.

The total installation delivers 49 MW of peak effect, covering nearly 50% of the total heating demand. The remaining part is produced by three gas engines, a 10 MW electric boiler, an absorption heat pump, and gas boilers.

“The collaboration with Arcon-Sunmark has been incredibly positive and even better than I had hoped. Everything has progressed in a highly professional manner – from the moment I received the first reading material through the planning to the installation itself. Everything is under control. At times they have even been ahead of schedule,” Arne Holm says.

Low maintenance

Vojens District Heating Plant has taken advantage of the low interest rate and financed the investment with a loan offering an interest fixed over 25 years. That means stable energy prices and a great security: “Knowing our prices this far into the future is a big relief. And the awareness that the maintenance is going to stay at a minimum, really allows us to reap the benefits”, Arne Holm concludes.

Source: Arcon-Sunmark