Innovative combined heat and power plant in Brønderslev combines new technologies

Bronderslev 4

Brønderslev receives heat and electricity from a state-of-the-art energy plant that uses local wood chips and solar to supply the city with district heating. The plant has been expanded with 5 km of CSP solar collectors, and two chip boilers supply the energy to an ORC turbine. Furthermore, the plant's electricity needs are partly covered by electricity produced through its own solar cells.

February 23, 2022
  • SDG: #7, #11, #12, #13
  • SECTORS: Energy
  • COUNTRIES: Denmark
  • CLIENT: Brønderslev Forsyning

The combined heat and power plant in Brønderslev is the first of its kind in Denmark. The unique combination of chip boiler with ORC turbine utilises wood chips for the production of electricity and heat. During the summer months, the wood chip boilers can be shut down and the unique solar collectors take over heat production.

Furthermore, the plan is for the solar collectors to be connected to the ORC unit, so that in the future they will also be able to produce electricity from the sun's rays. This will be the first time in Denmark that electricity is produced via solar troughs. In this way, Brønderslev will in future be much less dependent on fossil natural gas. Already in 2020 more than 2/3 of the heat production was based on renewable sources.

NIRAS has been the client's consultant at the innovative facility in Brønderslev, which has cost approx. DKK 350 million. NIRAS is still the consultant at Brønderslev, and work is currently underway on further optimisation of the plant for maximum utilisation of all potential through the use of heat pumps for cooling the boiler hall, etc.

Innovative facility

The system works in such a way that the chip boilers or CSP solar collectors heat a thermal oil that is passed on to an ORC turbine. The ORC turbine converts the oil’s heat into electricity and district heating. Electricity is allocated to the electricity grid and the heat is sent out to consumers. Biomass boilers, which are used during periods when the sun is not a sufficient energy source, are supplemented by existing units such as electric boilers, natural gas cogeneration engines and boilers.


  • A solar trough is a large solar collector (CSP solar collector). The solar troughs in Brønderslev are shaped like satellite dishes and consist of computer-controlled mirrors that follow the sun from sunrise to sunset.
  • CSP stands for Concentrated Solar Power. The technology concentrates the sun's rays up to 80 times.
  • ORC stands for Organic Rankine Cycle. In short, an ORC turbine is in principle the same as a steam turbine - but a silicone oil is used instead of water (steam) to drive the turbine.

"We are not dependent on one energy source. With our plant, we can utilise solar energy and biomass, so we can produce whatever is best on the day. This means we are very robust relative to the price increases that we see in electricity and gas in the rest of the sector "

Thorkil Neergaard, director of Brønderslev Forsyning.

This is not the first time that the sun's rays have been converted into electricity, but it usually happens via solar cells. The innovative thing about this solution is the possibility of co-production of electricity and heat through the solar troughs. Subsequently, the plant has also established solar cells to be able to produce electricity for internal use at the plant.

The combination of both the chip boilers and the solar collectors, connected to the ORC unit so that electricity and heat can be produced, is new. In order for the flue gas from the boilers to be discharged as cold as possible, thus optimising the use of the energy content of the wood chips, the flue gas is cooled in two heat pumps and can be discharged with a temperature of 16 ° C. Thus, an efficiency of more than 100% is achieved on the utilisation of the energy content of the wood chips.

With its heat production, Brønderslev Varmeværk can play a role in the electricity market, both as a producer and a consumer, to the benefit of heat consumers. The plant has been able to maintain favourable prices for heat consumers after the new units have been brought into use.

"Brønderslev has got a world-class wood-fired CHP plant, which is among the world's most efficient in terms of total efficiency"

Jørgen Røhr Jensen, project manager at NIRAS.

Millions in support for the project

The ambitious project, launched with NIRAS as consultant, means that Brønderslev Varme has largely switched to renewable energy from natural gas heating. Due to its unique design the plant has received a grant of DKK 20 million via the Energy Technology Development and Demonstration Program (EUDP).

This is the first time that the supply industry in Denmark can boast of this type of plant. Even in the wider European context the plant's technology is very advanced.

Bronderslev 7

Many disciplines in play

NIRAS has provided consultancy to Brønderslev Forsyning throughout the process, and there have been many disciplines in play along the way. The consultancy provided has addressed the environment, construction, machinery and electricity.

In addition, NIRAS has advised on dealing with the relevant authorities, prepared tender material, managed the entire tender process and supervised. NIRAS has also been responsible for construction management and financial management during the implementation of the project.

A plant with real muscle

  • The 40 rows of CSP solar collectors (5 km) in Brønderslev have a total power of almost 17 MW.
  • In addition there is the ORC system that can convert 20 MW of thermal energy into 4 MW of electricity and 15 MW of heat.
  • Flue gas cooling and two heat pumps on the flue gas, together providing 6 MW of heat.

Reach out

Jørgen Røhr Jensen

Jørgen Røhr Jensen


Aalborg, Denmark

+45 4010 4383

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