Energy System Analysis in Kolkajen

In recent years, developers have come a long way in their ambitions to make buildings more energy efficient. In order to develop a fossil-free energy system for Stockholm Royal Seaport, the issue needs to be addressed at the area level.

Energy-efficient buildings need to be combined with, among other things, recovery of waste energy and increased local production of renewable energy, with the sharing and storage of energy playing a key role. Challenges exist in several areas, for example, improving the ability to utilise and seasonally store solar energy, optimising waste heat recovery, and redistributing energy from producers to consumers.

A preliminary study on a resource-efficient energy system for the Kolkajen phase was carried out and solutions for resource-efficient heat recovery from wastewater were evaluated. The possibility of locally optimising energy generation and energy use was also studied. The potential for Kolkajen was defined as follows:

• The possibility to install a hybrid system based on geothermal energy, heat exchange of wastewater, energy piles, and district heating.
• The energy system of the future is flexible and the resources used for energy production are local and renewable.
• The possibility to utilise heat from buildings with excess heat/cooling needs.
• The possibility to balance energy needs over time through a storage system.
• Reduce distribution losses and achieve greater energy recovery by utilising energy in wastewater locally.

Purpose and goals

The purpose of the preliminary study was to investigate the conditions for various types of energy and possible resource-optimised and cost-effective energy system solutions for a detailed plan in Stockholm Royal Seaport.

The purpose of the heat recovery study was to provide additional information for decisions on guidelines for heat recovery systems from wastewater ahead of land allocation.

Results and experiences

According to the preliminary study, the system perspective should be the starting point. The conclusions were that the conditions for geothermal energy are limited, as heat extraction from a relatively limited soil volume causes a significant temperature decrease in the ground, despite recharging to boreholes. Recovery from wastewater via a larger common facility with wastewater heat exchangers showed good potential. A possible solution could be heat collectors integrated into piles. This was considered an appropriate and innovative technology that would provide a significant amount of thermal energy at a limited additional cost. Due to a restructuring of the structure, the pile deck was removed and the solution was no longer relevant.

An important conclusion from the project was that the boundaries of the system must be carefully defined and that various stakeholders perspectives and interests are considered for decisions and choices. What appears to be a natural system boundary will differ from one actor to another, depending on the mandate, interests, and structural assets in the form of infrastructure. For the developers, the system boundary is at the property or area level, for a municipal administration it is at the city or district level, while a water company or energy supplier naturally relates the system boundary to its market. How system boundaries are drawn affects the results in the analysis, as well as assumptions made about the technical and economic characteristics and performance of the systems, now and in the future.

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