The national policy on energy for Denmark sees district heating as one of the major contributors to a fossil free heating sector. District heating can be produced with any type of primary energy and it is flexible for change from one source to another.

On the island Aero we find the city of Marstal. The district heating company is a co-operative owned by the citizens. Years ago they took up the challenge to reduce the fossil fuel for heating and focused on the energy from the sun.

Today district heating in Marstal is based 100% on renewable energy sources. They operate the second largest solar heating system in the world and generate 30% of the heat from solar energy whereas bio oil stands for 70%.

The existing solar heating system has a size of more than 18,000 square metres of solar collectors. In these years the system is further developed with an additional 15,000 square metres and a new thermal storage of 75,000 cubic metres. This extension has been named Project Sunstore 4.

Marstal has now 1,550 consumers of district heating and with implementation of Sunstore 4 in 2014 they will receive 55% of the energy from solar heat and 45% from locally produced biomass.

A control technique that controls the pumps according to the influx of light has been developed. This technique has among other resulted in an energy saving of 75 % for pumping power in addition to an increased efficiency of solar collectors, and today the technique is used by the majority of large solar heating plants.

LOGSTOR supplies the pre-insulated pipes to the city of Marstal.

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