by Linda Bertelsen
Vraa Varmeværk Solfanger

Photo above: Solar collectors and storage tank at Vraa Heating Plant

Locally produced excess heat contributes to the transition towards becoming 100% fossil-free in the municipality of Hjoerring, Denmark. It contributes to increasing independence from international energy prices and crises. At the same time, a much stronger connection is created between the companies and the local society. This is a real win-win situation: The price of district heating decreases, and the companies achieve a greener profile and increased goodwill from the local society.

By Poul Rask Nielsen, Senior Project Manager, Hjoerring Municipality

Published in Hot Cool, edition no. 4/2024 | ISSN 0904 9681 |

Strategic energy planning

The municipality of Hjoerring works consciously to create the conditions for being an attractive settlement for citizens and businesses including good infrastructure (heating, electricity, water, IT, and transport). In the strategic energy planning, the focus is on the production of energy in the municipality being green, based on local energy resources: Electricity, hydrogen, and heat from wind turbine and solar cell parks, biogas plants, as well as excess heat from cold stores and freezers, hydrogen and biochar production. Recently, the city council has approved the initiation of planning work around 22 solar photovoltaic plant (PV) and wind farms totaling 1.7 GW, as well as a significant expansion of the seven existing large locally owned biogas plants.

Map of Hjoerring Municipality

The municipality of Hjoerring’s perspective

  • 64,000 inhabitants

  • 11 district heating plants, all owned by the citizens as co-operatives. Organized through voluntary boards, elected at annual meetings.

  • 66% of the homes are connected to district heating.

Most unconnected homes are located in the countryside and heated with individual solutions. A few villages are heated by natural gas. In the next few years, a transformation to individual electrically powered heat pumps is taking place. Some villages recently switched to district heating in connection with the international energy crisis.

A view from the mayor’s desk over the municipality

Cheap locally produced district heating provides independence from fluctuations in international energy prices. It contributes to developing the local society, which rests upon an economically strong and stable foundation. The use of surplus heat from local industry increases cohesion between the local society and industry. It is a win-win both from the perspective of the heat consumers, who get cheaper heat, and the perspective of the companies, who secure both a financial side income and goodwill from their production. The case below from the city of Vraa also shows that new jobs are being established and job creation is taking place in the local society, where previously, for many years, there has been the classic migration from rural areas like Hjoerring towards the larger cities.

Soren Smalbro, Mayor of Hjoerring, Denmark

Soren Smalbro, Mayor of Hjoerring

quote“It would be great if all the municipality’s district heating companies in the future would be connected by a common transmission grid.
I expect in the future, with the development that is on the way, there will be far more industrial surplus heat than today. With the transmission grid, it will be possible to use the cheapest heat source as a supplier to the municipality’s 11 district heating plants. Perhaps central heat storage should also be established, which will collect and store the fluctuating heat production throughout the year.
The accumulated heat can be stored for use in the coldest winter months. Cheap heating based on locally produced green energy is an important part of the central infrastructure, which helps to create the foundation for a municipality to a strong development for both citizens and businesses.”

Energy Park Vraa - map with geographic location

Map with geographic location of Vraa town and energy park (top-right)

Energy Park Vraa

Just outside the city are two well-established large biogas plants. One of them has also recently built a pyrolysis plant. A transmission district heating grid has been established from the two biogas plants to the city’s district heating plant. Both supply excess heat as derived effects from the production of biogas and pyrolysis. In addition, there is a solar park and a wind farm on the way, which are expected to be established within the next two years. Both biogas plants have major expansion plans in the near future.


Vraa Heating Plant

The district heating plant in Vraa is being transformed to use locally produced energy and is being electrified. The goal is heating with 100% renewable energy by the end of 2024.

bilag 5 - Fordeling2022

2022 – Red: Natural gas Yellow: Solar heat Grey: Electric boiler (electricity) Green: Heat from Green Gas

The heat demand is generally growing, and natural gas must be phased out at the same time. It is, therefore, interesting to connect excess heat to the mix of heat sources.

Economically, excess heat is interesting; it is affordable both in terms of investment and heat delivery. The excess heat supplier makes the investment in the transmission grid, and once paid for, the supply of the heat must be renegotiated.

The disadvantage of using an external heat supplier is that the supplier has no obligation to supply. Therefore, the supplier is responsible for investing in the district heating transmission grid.

Pt. the heating plant has an application pending with the municipality for the establishment of a heat pump that must be powered by locally produced green electricity from the nearby energy park. A memorandum of understanding has been drawn up on the purchase of electricity from the future wind turbines.

Chairman Vraa Fjernvarme, Niels Henrik Nielsen

Chairman Vraa Fjernvarme, Niels Henrik Nielsen


quote” We would like to become 100% free of fossil fuels. At the same time, we have a city that is growing with new homes and businesses. Today, almost all homes and businesses in Vraa are heated by district heating.
Today, heat production takes place in a mix of different sources: solar collectors, electric boilers, excess heat from the two biogas plants, accumulation tanks, and a natural gas boiler as backup and for peak load production in the coldest months.”

Vrejlev Bioenergy

Vrejlev Bioenergy originated from a larger farm that established a biogas plant a few years ago. The plant has been continuously expanded and today supplies upgraded biogas to the national natural gas grid. Together with the other large biogas plants in the area, they have established a company that plans to sell biogenic CO2.

The company is now being further developed with a pyrolysis plant that produces biochar from fibers, which are a residual product from biogas production. Biochar binds CO2 and can be returned to the soil, where the carbon is bound for hundreds of years. The new facility will be commissioned in April 2024.

One of the residual products from biochar production is waste heat. From the beginning, surplus heat was planned for the local district heating plant “Vraa Varmevaerk.” A district heating transmission line of 2.8 km has been established, where Vrejlev Bioenergy owns the transmission pipe. Vrejlev Bioenergy owns the transmission pipe – and not Vraa Varmevaerk – because Vrejlev Bioenergy does not have an obligation to supply district heating.

Therefore, it would be too risky for Vraa Varmevaerk to take the investment up front. The transmission pipe has depreciated over five years. Vrejlev Bioenergy can initially supply 1.6 – 1.7 MW/year and more in the future. The heat is distributed throughout the year. In the period from May to August, the company cools the heat away, as the district heating company covers the summer heat demand using its own solar panels.

CEO Thomas Kjær Vrejlev, BioenergiCEO Thomas Kjær, Vrejlev Bioenergy, points out that it is a trust-based agreement between his company and the Vraa Varmevaerk – it is a win-win for both Vrejlev Bioenergy and Vraa Varmevaerk. The district heating consumers get cheaper locally produced heat, and Vrejlev Bioenergy gets local goodwill.

As CEO Thomas Kjær says, “We live here and give back to the local community as a “thank you” for being allowed to fill the landscape with our plant and many lorry transports”. If CEO Thomas Kjær looks into the future, he wishes, like the mayor, to have established a district heating transmission grid between several heating plants. So that he can supply excess heat all year round and not have to spend money on cooling in the summer.

At the same time, he sees opportunities to deliver far more excess heat from various sources in his company. For example, the amount of excess heat could be increased by cooling the slurry before it is brought out to the field if a heat pump is connected.

For further information, please contact: Poul Rask Nielsen, at poul.rask.nielsen@hjoerring.dk

“Industrial surplus heat boosts local develment – the case of Hjoerring Municipality” was published in Hot Cool, edition no. 4/2024. You can download the article here:
Industrial Surplus Heat as Part of Local Development - the case of Hjoerring Municipality, Hot Cool article by Poul Rask Nielsen

meet the author

Poul Rask Nielsen
Senior Project Manager