Marstal Fjernvarme was in need of a new lid for their Pit Thermal Energy Storage (PTES) system, as the original lid was damaged due to moisture accumulation resulting in a significant heat loss. Since installation, Aalborg CSP's unique lid design has contributed to an increase in the plant's solar energy share from 45% to 55%.


Client:       Marstal Fjernvarme
Location:    Marstal, Denmark
Status:    Operational
Technology:     PTES lid
Area - PTES lid:     10,000m2
Expected lifetime:     25 years

From 45 to 55% solar energy share

In order to minimize the heat loss in their Pit Thermal Energy Storage (PTES) system and likewise increase the efficiency of their heat production, Marstal Fjernvarme decided to replace their original PTES lid solution. The original lid was damaged due to the accumulation of moisture in the insulation layers and therefore no longer able to retain heat, which resulted in a significant heat loss as well as a reduced efficiency. The new diffusion-open and sectionized lid design prevents accumulation of air, water and moisture inside the insulation and enables safe and efficient dewatering. By replacing the original lid, the district heating plant's solar energy share has increased from 45 to 55%. Marstal Fjernvarme has, likewise, gained a full-automatic plant which requires a minimum of maintenance and supervision.

New design improves insulation and minimizes heat loss

A diffusion-open construction allows vapor to diffuse out through the upper liner over the insulation. This improves the insulation capacity of the storage and reduces the heat loss. The lid is further divided into sections for better rainfall handling. The lid in Marstal consists of 12 sections and thus 12 pump wells. The original lid had only two pump wells, both located in the middle of the storage, and thus not enough capacity to pump larger amounts of rain away. 

The turnkey project in Marstal included design and installation of the complete lid solution including design of diffuser, liner work, installation of control system, electrical connections and rainwater pump system. The project was carried out by Arcon-Sunmark, but Aalborg CSP has since then acquired all know-how and intellectual properties related to the PTES technology. 


Andreas Zourellis
VP Sales - International
District heating / industrial solar technologies
Phone: +45 50 30 00 25