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

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 the 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.


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“, says 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.

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


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 – in total a 70,000 m2 installation in combination with a 200,000 m3 thermal pit storage – a huge thermal seasonal storage formed by a welded liner allowing 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.


Vojens District Heating took 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”, is the conclusion in Vojens.

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