The Pit Thermal Energy Storage (PTES) market is in rapid growth and Aalborg CSP has now secured its second contract in less than 10 months. The PTES solution using Aalborg CSP’s low-cost energy storage technology is to be installed at Dronninglund Fjernvarme (Dronninglund District Heating), Denmark. The contract is an upgrade of an existing PTES installed in 2015, where accumulation of water within the insulation layers had caused damage beyond repair.

After a public tender with a special focus on re-using as much of the previous insulation as possible in order to reduce the environmental footprint as well as the cost for the heat consumers in Dronninglund, the contract was awarded to the Danish energy storage and solar energy specialist, Aalborg CSP.

For the project at Dronninglund Fjernvarme, Aalborg CSP is applying the Lloyd’s certified PTES lid and energy storage solution, which has been achieved for the low-cost, high-quality and bankable solution for scalable low-temperature energy storage.

Best solution at lowest price solves challenge

Danish energy storage and solar energy specialist, Aalborg CSP has now secured the second PTES contract in less than a year. The project is to be installed in Dronninglund, Denmark, where Dronninglund Fjernvarme required an upgrade of an existing PTES containing less reliable lid solution. As water accumulation within the insulation layers of the existing PTES from 2015 proved to be unrepairable, Dronninglund Fjernvarme searched the market for the ideal solution to solve the challenges.

Chairman of the Board at Dronninglund Fjernvarme, Svend Bøgh explains -” Our existing lid construction was unable to do the job any longer and had to be replaced. Following the public tender, we decided to go with the attractive economical while still high-quality solution. We are pleased that Aalborg CSP won the EPC tender with their certified PTES technology, which for Dronninglund Fjernvarme gives us high comfort and trust in terms of a long-term and reliable solution”.

There is a rapid growth in demand for low-temperature reliable storage solutions like the PTES technology. After installing a similar PTES lid in Marstal, Aalborg CSP has experienced profound interest for the lid technology, and has therefore been working intensely on optimizing the solution in order to be able to provide future customers with not only a state of the art technical solution, but also the lowest possible price.

”We are proud of the trust that Dronninglund Fjernvarme has bestowed on us and the unique technical solution, which we have optimized during the COVID-19 lockdown. Despite the difficult market conditions for raw materials, we have succeeded in offering the technically optimal solution of a state of the art system at an attractive price; all due to extremely hard work from the Aalborg CSP team and our suppliers”- states CEO of Aalborg CSP, Svante Bundgaard.

Re-using material reduces environmental footprint

Given the background for the new PTES, a large amount of old insulation was suitable for reuse and as such it was possible for Aalborg CSP to recycle these materials in the best way. Hence, a key element within the offered solution became cost optimization and re-integration of the old insulation material.

“In a time of increased focus on sustainability, it was important for us to recycle as much of the materials as possible to reduce the environmental footprint as well as to offer Dronninglund Fjernvarme the least expensive solution. The recycling of the old materials combined with the new lid technology, ensures Dronninglund Fjernvarme the best insulated storage to date”- says Product Manager PTES from Aalborg CSP, Morten Vang Bobach.

Power-to-X with PTES is an essential part of the future integrated energy sector

Green investments in PTES solutions are an essential part of the future infrastructure and is paving the way for flexible and efficient sector coupling of electricity and district heating. If determining heat as X in a "Power-to-X" contexts, it is crucial that the excess green energy is used in an optimum way. In this connection, PTES is an ideal technology, as it is commercially tested, scalable and in-expensive compared to all other PtX alternatives. Likewise, a PTES may also be utilized for collecting and storing the surplus heat that is currently being discharged from chimneys or otherwise cooled away.

“The technology is scalable and hence, the PTES technology is an important part of the sector coupling of the future, where the need for in-expensive and reliable storage of excess energy increases. At the same time, the PTES technology is ideal in joint operation with heat pumps, electrical boilers and solar systems thereby optimizing the performance of all technologies in the integrated energy systems.” - Svante Bundgaard determines.

Third party certification provides customer assurance regarding PTES technology’s bankability.

Earlier this year Aalborg CSP received a Technology Qualification Certificate from Lloyd's Register declaring that the unique lid technology for PTES meets all necessary requirements in terms of design and functionality as well as sustainability. Multiple resources have been invested in solving key issues concerning the lid design as well as making it cost-effective, thereby creating a state of the art, low-cost, high-quality and bankable solution.

The Lloyd’s Register certification underlines the fact that the most in-expensive energy storage technology in the world can now be considered as a fully commercialized solution and thus a safe investment in low-temperature energy storage for district heating plants and utilities worldwide.


Client: Dronninglund Fjernvarme A.m.b.a.
Capacity of PTES energy storage: 5,500 MWh
Area – PTES-lid: 8,281 m2
No. of customers: Approx. 1,400
Location: Dronninglund, Denmark
Expected lifetime of lid: 25 years
Included in an integrated energy system with: solar heat, heat pump, gas boiler and gas engine