The history of Harteværket

The hydroelectric plant known as “Harteværket” has a long history. The use of water for the sake of generating electricity goes all the way back to 1878 where it was used for the first time.

The history of Harteværket begins around 1917 goes through the 1900’s and reaches us today. You can read much more about that in our timeline.


In celebration of the 100-year anniversary of Harteværket, a book has been written about it in danish and is free for anyone, who wishes to explore the history of Harteværket in greater detail. Enjoy!


The planning of the hydroelectric plant was done by engineer cand. polyt Mikkel Thomsen from Kolding and is quite the stroke of genius.

The dam erected across Vester Nebel Stream at Ferup forces the water from Alminde Stream to run against its natural current and because of this, the water is dammed up in the Dons lakes.
From here, it is led towards Stallerup Lake and afterwards to the turbines of the plant through an 80-meter-long pipe going through a canal under the motorway.

Water drives the turbines. They then convert the energy of the falling water to electricity using generators.

Largely, the original turbines and generators are still the ones who produces the electricity of Harteværket.
Its falling height is 25.4 meters deep (Denmark’s steepest drop) and every second 6,000 litres of water streams through the pipes.
The penstock is equipped with a buckle valve which means that if the pipe ends up leaking, the water supply is automatically stopped.
The turbines at Harteværket are the original machines from 1920. The productivity of the plant depends on the volume of water.


The hydroelectric power station in Harte, called Harteværket, was built in the years 1918-1920, and was the first major plant of its kind in Denmark. Construction of the Harteverket was started to meet a growing need for energy for lighting and industry.

It was also built to secure electrification of the land around Kolding after the World War I energy crisis. In its time, the plant was able to supply half of Kolding city and upland consumption of electricity. The plant is now owned by a foundation, and due to its cultural-historical value, it is protected. Today, it serves as a museum and visitor center and periodically as a power supplier to Kolding. Most of the equipment is the original one, which has been in operation for over 90 years, and still is – though with limited water volume, as part of the water has been returned to the original river course as part of a nature restoration project.

January – 1919 – “Work on the plant begins”

As Harteværket was being built in the years 1918-1920, multiple dams were constructed to secure a sufficient volume of water and a steep enough drop to power the turbines.

When travelling through the Danish countryside – especially via train – you hardly think about the workers behind this crucial piece of Danish infrastructure.
Furthermore, you hardly consider how the workers dug it using nothing but shovels and wheelbarrows. These workers were in Danish called “børster” which can be translated to “brushes”. Back then the brushes were known as the “travelling workers of the country road“. They are especially known for their work related to the construction of the railways throughout Denmark. But the brushes were also behind the digging related to the construction of Harteværket. Hence, their contribution to the development of society at the beginning of the 1900’s is massive, but as a group they appear like a grey anonymous blob of workers.
The brushes put an enormous amount of energy in the big construction work which was the basis upon which Harteværket could become such a well-functioning hydroelectric plant. Their contribution should not be underestimated, but as a working group and as such an important contributor to so many of the great digging projects around this time, it is quite thought-provoking how little we actually know about this workforce.

Among their achievements, we find the construction of the dams near Harteværket. The biggest of these were built at Ferup Lake. The sluice house at the lake is still there.
In this way, the two big lakes at Dons were made. That is Dons Nørresø and Dons Søndersø.
Like with so many strategically placed artificial canals, the water was led towards Harteværket and out into Kolding Stream from there.

The water in Vester Nebel Lake was dammed up around the place where it crossed Troldhedebanen such that the water went against its natural drop. Furthermore, by turning the water at Almind Lake, the water was pushed eastwards. Hereby, it was led into the canal at the Busholm Bridge in order to run through Søndersø and Skallebæk where it was cleansed, deepened and turned south towards Stallerup Lake. Otherwise there were attempts at emptying the Stallerup Lake in the interest of reclaiming some land.

20.07 – 1919 – “The drowning accident at Stallerup Sø

An incident with a strong presence within the story of Harteværket was the story about the five brushes who died in Stallerup Lake in the summer of 1919.
The tragedy happened on a Sunday. After having worked the entire morning, ten workers decided, after eating lunch, to take a boat trip onto the lake before it was time for afternoon coffee. The boat ended up keeling over after changing oars and all ten men fell into the water. Some of the men succeeded in getting the boat back on the right track. Five of them held onto the boat while the remaining five drowned.
The story of the drowning accident at Stallerup Lake has given us the opportunity to know the names of some of the workers who toiled at Harteværket. It has likewise given us an impression of the solidarity shared among the workers, which expressed itself at the monument erected at the Harte Graveyard. Payed for by their fellow workers.

28.07 – 1920 – “Harteværket is complete”

Harteværket was built right after World War 1 and was put into service in 1920. Back then, many different electricity producing hydroelectric plants were already to be found throughout the world. The use of hydropower for the sake of producing electricity already began as far back as 1878.

Across Europe the plants were in particular established in places with great drops and/or great volumes of water. Thus, Harteværket was built using known techniques.

The entire project with the purchase of land, digging canals and so on ended up costing 3.6 million DKK which is the equivalent of around 1300 million DKK in current currency. This would be around 173.99 euros. When Harteværket was built, it attained the right to the water with a regulatory band of 1 meter for an indefinite period of time. In those days, the plant was run in cooperation with a steam power plant from within Kolding. At that time, Harteværket was capable of covering almost half of Kolding and the surrounding areas use of electricity, but today it only covers around 1 % of Kolding’s consumption alone.
Although Harteværket these days is a lesser production facility in comparison with the central power plants, it is still a big power plant in comparison with many of the local production units like gas motors and so on.
In spite of the small role Harteværket plays in powering the city, it still has some properties like fast regulation which can be used.


In 2007 Vester Nebel Stream was the target of a nature restoration project for the sake of securing the environment of fishes and plants within the lakes. This resulted in a 60 % reduction of water running towards Harteværket. Yet, the production of electricity at Harteværket continued.

These days Harteværket with its buildings and machines is protected due to it being a piece of industrial history. Most of the equipment is still the original ones and have been in use for over 90 years.
That is why the plant is said to be a living piece of cultural heritage. You can read more about the protection of Harteværket here: (note: it is only in Danish).
Harteværket is today run by Fonden Harteværket.
In 1920, when Harteværket had finished construction, its production of electricity covered almost half of Kolding and the surrounding area’s consumption.

When Harteværket’s output was lowered in 2007, the plant still produced 1.8 million kWh a year on average.
The calculations of its output have been more or less true through the years and its output has only really noticeably changed in years of great drought or rainfall. In 1980, where it rained a lot, the production was for instance all the way at 3.42 million kWh.
There are three turbines a Harteværket. Two of them have 525 horsepower while the last one has 300 horsepower. Together the two have 1350 horsepower which is around 1000 kW.
Back then an engineer, two assistant engineers and two workers were assigned the task of overseeing the operation of Harteværket.

2010 – Restoration

Fiberglass for a protected hydroelectric plant

Aarsleff has accomplished a somewhat special task for Harteværket in Kolding.
The hydroelectric plant’s downpipe had gotten corroded and was as full of holes as a swiss cheese.
The solution was to install a fiberglass-equipped polyester-pipe within the 80-meter-long pipe. This happened in year 2010.

The downpipe was a riveted pipe of steel which had gotten very corroded over time. Regularly, new holes appeared in the pipe and these were closed with wooden sticks. Over time the wooden sticks were replaced by a bolt with gasket or a patch was welded on. This solution proved not to be sustainable in the long term which led to the involvement of the company Rørteknik, Bolig og Industri regarding the problem.

Like a starry sky

The pipe was cleansed internally and during the course of this process, around 500 new holes were suddenly visible which from the inside made you think of a starry sky. We proposed to mount a pipe of fiberglass within the existing pipe such that you would get a pipe free from corrosion and capable of withstanding a water pressure of 2.5 bar.

The proposal was accepted by the national board of cultural heritage because we chose to preserve the original pipe. The board even chose to support the project by covering 20 percent of the investment.

Divided into sections

The pipe has a falling height of around 26 meters, is 80 meters long and has a diameter of 1.75 meters. The new pipe was made of fiberglass with sand inside the core. The pipe is divided into segments where each segment is 2.3 meters long and has an internal diameter of 1.6 meters. For every fourth segment the space between the fiberglasspipe and the steelpipe is closed with concrete in order to limit the buoyancy and pressure, when they had to cast after, between the pipes.

35 sections installed

After all 35 segments of the pipe were installed, both ends of the pipe were laminated with polyester reinforced with fiberglass. The 2.5 meters long cut off piece of steelpipe was removed such that we could get into the pipe, weld it back onto it and have the concrete get pumped in between the pieces of pipe. All in all, the company Rørteknik worked on the project for four weeks.

New foundations

Aarsleff was also involved with the project and was behind the digging and installation of extra foundations. The pipe runs down a slope. One half runs over terrain while the other half runs down a ditch. That made the excavation and casting underneath the pipe bothersome. Aarsleff installed 11 new foundations to secure the pipe to the extra load. The slope provided several challenges seeing as it was impassable for the concrete cars among other things. Therefore, we had to establish an extensive pump-system in spite of the limited amount of concrete needed.

Harteværket today

After almost an entire century, Harteværket is still in operation. In 2008 a nature restoration project was done at Ferup such that Vester Nebel Stream’s course could be led back to its original level.

The production of electricity at Harteværket has as such been significantly reduced seeing as the plant has lost 2/3 of its original yearly volume of water. In later years much greater amounts of wind power has entered the electrical systems. This has made the production of electricity more unpredictable and a more flexible system has become necessary.

This is where the hydropower’s great regulatory capacity gets very useful. By running the plant in a different way than earlier by using hydropower’s great regulatory capacity, the losses of this method of management are compensated for with the lower volume of water.

Today there is a bigger need than ever before to have additional productions of energy capable of being flexible and which quickly can adjust its production up or down concurrently with the wind or other imbalances in the electrical system.

The future of the power plant

In the future, the plant will cooperate with several lesser production units and will thus create a bigger power plant to regulate. Aside from paying for the production of electricity, the plant will in the future receive payment for putting its flexibility at others’ disposal.

Extraction of Salt

During the 1930’s the area around Harteværket was mined for salt.

This is how it began

It all began, when the leading Danish geologist of the 1930’s, dr. phil. Victor Madsen, after yearlong studies and geophysical examination had made the theory that there had to be salt in Denmark and that Harte would be that place.

But no one wanted to begin digging for the mineral, when they were not even sure it was there. Therefore, they could end up losing a fortune on the operation. Since the Danish government did not want to risk an economic loss, advertisements were placed, in which the government offered those interested to start digging for salt under certain conditions.
The advertisement gave no results, but when the Danish engineer Karl Østman in the beginning of the 1930’s travelled to America, he met the engineer Frederick Franklin Ravlin. Ravlin had for a number of years had great luck in digging for oil and got interested in the advertisement, Østman showed him.
Ravlin went to Denmark the following year where he met the director of Danmarks Geologiske Undersøgelser (Denmark’s Geological Research, DGU) Dr. phil. Victor Madsen, Dr. phil. Hilmar Ødum (leader of the digging archive at DGU) and prime minister Thorvald Stauning. Here, the contract was signed and from this it appeared that Ravlin at a personal cost and risk was allowed to dig in the ground at Harte, but if he within two years found minerals of any kind, he could get the concession to Denmark’s underground as long as he payed the government 7½ % of the value of anything eventually found.

The big day – the lump of salt

Ravlin travelled home, found equipment and experienced digging personnel and sent them to Denmark. The work was commenced the 27th of July 1935.
The first proper result was the famous lump of salt although its authenticity later was called into question. It was found the 13th of November 1936 in the presence of Dr. Victor Madsen, assistant geologist at the University of Copenhagen A. Noe-Nygaard and engineer Karl Østman.
Accordingly, Victor Madsen drew up a document regarding the find and its circumstances and went to Copenhagen with the salt after first having held a small informal speech in which he expressed delight in how his theory about salt at Harte seemingly was correct. He also mentioned that the right to the underground and extraction of raw materials in Denmark now belonged to Ravlin.
Dr. Madsen later split the lump of salt in two pieces. One of them being in Copenhagen while he gave the other piece to Ravlin who later gave it to a woman in USA, who herself drilled for oil and later made a fortune out of it.

Now Ravlin put more effort into the work. He got more digging materials and a larger crew from America. News of the discovery of salt reached out into the wider world and resulted in the international company Gulf Oil Co. enquiring Ravlin about taking over his exclusive rights. At first Ravlin said no, but Gulf kept asking and eventually, the offers were so favourable that Ravlin accepted since he after all were limited by the terms imposed by the government.
Thus, Ravlin stepped out of the picture and went back to the USA after having spent around one million DKK in Harte.

The authenticity of the lump of salt

When World War 2 began, Karl Østman claimed that the discovery of salt was fake and that he had bought the lump of salt at P. A. Kruuse’s chemist shop in Odense. Afterwards, Ravlin had put it into the drill pipe himself. Karl Østman has later recanted this claim with the justification that he said it to redirect the attention of the Germans from Denmark’s underground.

In later years, great discoveries of salt have been made in the form of salt domes throughout Denmark.

The Turbines

How do they work?

Harteværket gets its water for the production of electricity from the Dons Lakes.
The water utilises the effects of gravity. It falls from a high place towards a lower place and during this drop, it passes through a turbine. The falling water makes the turbine rotate around a shaft which then winds a generator and produces electrical energy.
The water is led by a canal towards the plant.
Subsequently, the water runs down a grate in the screenhouse. Here, the water is purified of leaves, twigs and other filth such that it will not get into the turbines.
(The fishes are led through a circulation around the turbines and into Kolding Stream).
In the first screenhouse at Harteværket, there was a coarse grating which took the worst of the filth, but when new grates came with smaller spaces in the screenhouse, the coarse grating was no longer necessary.

The sluice gate (which is in the black house at the inlet) is always slightly lowered into the canal.
The sluice takes the big things like a tree trunk for instance. If they are not sorted out, they will damage chains and more in the screenhouse.
When water has been through the screenhouse, it will run further down the big red pressure tube.

Firstly, the water runs down into the basement. Here, the pipe splits in two where one pipe leads to turbine 1 while the other pipe distributes it to turbines 2 and 3.
Afterwards, the gate opens up and the turbine is put to work as the water arrives. The gate can be opened either manually or automatically.
In the turbine, a lot of “shovels” are connected with a shaft leading towards a flywheel which stabilises the rotations and the generator. The generator is, unsurprisingly, the one that generates the electricity.

The voltage, the generator creates, is at 380 Volt. The electricity from the generator passes through thick copper tracks down into the cellar beneath the plant.

This is where the energy is transformed from 380 Volt to 10 kV (kilovolt) or 10.000 Volt such that it lends itself better for transportation over great distances.

It happens in the 3 transformers. One for each generator.

The red 10 kV cables then transport the energy to the transformer station “Harte” (the big black building, you can see from the parking lot).

From the transformer station “Harte” the electricity is partly sent up into the cable and overhead line network towards other parts of the region and partly out into the 10 kV cable around Kolding. From the 10 kV cable network, the energy is once again transformed, this time into 230 and 400 Volt, before it enters the household such that it can be used in the ordinary appliances.

The amount of energy, the plant is capable of producing, depends on the number of turbines. They in turn depend on the amount of water on that day. The production must be reported to NEAS Energy who are responsible for selling it to the electricity market. It should happen prior to 11.30 AM the day before. It could for example be reported that turbine 1 runs from 8 AM to 4 PM tomorrow.

NEAS Energy can then take over the operation of the turbine 8 AM the day after and generate the amount of electricity, they need.

In later years, very large amounts of wind power enter the electrical system. This has made the total production of electricity more unpredictable and made it necessary to have some more flexibility in the system. This is where the good regulatory capacities of Harteværket get useful.

By quickly regulating the production up or down in accordance with the wind and other imbalances in the power system, Harteværket contributes to stabilising it and receives payment for it beyond the payment for the energy itself.

When the water level in the lakes is low, the turbine is opted out of the market the day before.
Previously, the turbines were supervised every evening and two times each day of the weekends. But because of cutbacks this is not done anymore. There are, however, alarms turned on such that if anything happens, the turbine is automatically disconnected from the electrical system.

Some bonus info:

A generator is built from the same principles as an electric motor. When enough rotations occur in the generator, it produces levels of electricity matching what an electric motor produces when powered. You could compare it with an old-fashioned bicycle-dynamo. The more you press the pedals, the more your lamp will glow.

Turbines 1 and 3 are twin turbines while number 2 is a separate turbine. Twin means that there are two sets of lamellae.
The lamellae get worn out and must get renovated after several years of service. When they are worn, they lose their power. This means that the effect of the water’s flow is lessened. Nowhere is this more evident than the time, new ones get installed.
The plant consists of three hydropower turbines of the Francis type, which uses a special kind of technology ideal for a “small” hydropower plant as Harteværket seeing as it generates a lot of energy from a relatively small amount of water.

The two big turbines each generate 350 kW an hour and use 2400 litres of water a second. The small turbine generates 250 kW an hour and uses 1200 litres of water a second.

The installed effect of the generators is around 1300 kW.

Their maximum performance is around 1000 kW.

The original turbines and generators are still in operation.

Thus, all technology at Harteværket is at least 100 years old. The only thing replaced is the screenhouse at the top of the hill where water is filtered from filth before getting led down towards the turbines. The screenhouse was replaced in 1947.

Tilt yarn fishing

The fishery in the region was an important source of income for the farmers among others. In 1896, some farmers chose to convert their production from pork and meat to trout and carp.
Previously, the fishery belonged to the royals at Koldinghus Castle, but in certain cases others were allowed to fish by king Christian the fourth. Not until 1767, did the fishery enter private ownership for the first time.

The method

A quite distinctive method of fishing was in particular used before 1864. The so-called “vippegarns”-fishing. It can loosely be translated as “tilt yarn fishing”. The method is thought to have its origin in the Rhine somewhere in Germany and that the Kolding region is the only place in Denmark where the “tilt” was used.

The tilt yarn consisted of a solid support pole (“tilting pole”) which was dug far down into the brink of the lake and shored up with three buried braces. Atop the pole, was a fork (the “vrier”) fastened with a bolt. The tilting rod, which was 24-30 feet (7.32-9.14 meters) long, was kept in place by a cleat at each side of the fork. The tilting rod could easily be swung towards land at the same time as the fisher used his weight to tilt the rod upwards such that the contraption was lifted out of the water.
A noose connected with the tilt yarn was fastened at the top of the tilting rod. It was on every four sides stretched over a strong net, which again was fastened to the brackets made of young beeches crossing each other. Furthermore, some lines were pinned down to keep the brackets in place. The size of the machine was between 2 and 11/4 inches (5-7 cm).


The yarn was arranged in such a way that it filled the entire hull. As soon as it was lifted, one presumably got a lot of those fish swimming above the yarn. In the lift itself, the yarn was slowly raised a bit, but if there was no catch, the yarn was let back into the water. If there was a catch, the trout would seek the deepest point of the yarn while the yarn was lifted. This therefore meant that the fish seldomly escaped. On the other hand, the big meshes ensured that fish under 40 cm were sorted out such that only a few brown trouts, sexually immature and/or small sea trouts were caught.

The efficiency of the method was underscored by how the greatest catch on one night was noted as being 1800 pounds (816.5 kg) distributed among 40 fishers. This corresponds to 20.4 kg per tilt yarn.

The influence of nature

In the dark of night, tilt yarn fishers stood along Vester Nebel and Kolding Stream while the yarn slowly was tilted up and down every 45 minutes. From Trudsbro and on, there was between thirty and forty bits of yarn in use. During the waking season of the sea trouts (from juli to oktober), the fishing was done in the deepest part of the lake. Especially, when the weather was a bit too stormy with northeastern winds and high water in the fjord. This is why shelters were put up along the lake. In cases of muddy water after a rainfall, the fishing could also be done during the day.