The history of the power plant

The hydropower plant Harteværket has a long history. The use of hydropower to generate electricity dates back to 1878, when it was first used.

The history of the resin plant begins around 1917, stretches up through the 20th century and all the way to the time we have today. But you can read much more about that in our timeline.

In connection with Harteværk’s 100th anniversary, a book has also been prepared, which is free to download for anyone who would like to explore Harteværk’s history to a greater extent.


The hydropower plant was planned by the Kolding engineer, M.Sc. Polyt Mikkel Thomsen, and is a bit of a stroke of genius.

The construction of the dam over Vester Nebel Å at Ferup forces the water in Alminde Å to run in the opposite direction of the river and the water is thereby raised in the Donssøerne.

From Donssøerne, the water is led on to Stallerup Sø and then via a canal under the motorway through an 80 meter long pipe to the plant’s turbines.

The water drives the turbines, which via the generators convert the falling force of the water into electricity.

These are largely the original turbines and generators that are used today to produce electricity at Harteværket.

The drop height is 25.4 meters (Denmark’s largest), and 6,000 liters of water flow through the pipe every second.

The pressure pipe is fitted with a shut-off valve, which means that if a hole is made in the pipe, the water supply is automatically closed.
Harteverket’s turbines are the original machines from 1920. The plant’s production depends on the amount of water.

The hydropower plant in Harte, called Harteværket, was built in the years 1918-1920, and was the first major plant of its kind in Denmark. The construction of Harteværket was started to cover a growing need for energy for lighting and industry.

It was also built to ensure electrification of the land around Kolding after the energy crisis during World War I. In its time, the plant could supply half of the city of Kolding and the surrounding area’s consumption of electricity.

The work is now owned by a foundation, and due to its cultural-historical value, it is protected. Today it functions as a museum and visitor center and periodically as a supplier of electricity to Kolding. The majority of the equipment is the original, which has been in operation for over 90 years, and still is – however with a limited amount of water, as part of the water has been returned to the original river course as part of a nature restoration project.


Januar – 1919

“Construction work begins”

When Harteværket was built in the years 1918-1920, several dams were built to get a sufficient amount of water and fall enough to drive the turbines to Harteværket.

When you move around the Danish country – especially by train and railway, you do not give the workers behind this so crucial infrastructure for Denmark’s development many thoughts.
Furthermore, one hardly considers how the excavation work was done with shovels and wheelbarrows by workers – the so-called “brushes”. They devoted large parts of their lives to this work. The brushes were then also known as ‘the rushing journeymen of the road’.

They are known especially as labor in connection with the construction of the railway network in Denmark. But the brushes were also behind the earthworks at Harteværket’s construction. Their contribution to the development of society at the beginning of the 20th century is thus massive, but as a business group they appear as a gray, anonymous mass of workers.

The brushes put an enormous amount of manpower into the large-scale construction work, which was the precondition for Harteværket to become a well-functioning hydropower plant. Their work effort must not be underestimated, but as a working group and a significant contributor to many of the great earthworks that were done at this time, it is thought-provoking how little one really knows about this workforce.

Among their achievements is the construction of the dams near Harteværket.

The largest of these was created at Ferup Lake. The lock house by the lake can still be seen out there. Thereby the two larger lakes at Dons were created, namely Dons Nørresø and Dons Søndersø.

Like several strategically placed artificial canals, they led the water the right way to Harteværket and further out into Kolding Å.

The water in Vester Nebel Å was raised, approximately where it was crossed by Troldhedebanen, so that the water went against its natural fall. In addition, by turning the water in Almind Å, the water was pushed east. Thereby it ran into the canal at Busholm Bridge to run through Søndersø and Skallebæk, which were cleaned, deepened and directed south to Stallerup Lake. Stallerup Lake had otherwise previously been attempted to be emptied in the interest of land reclamation.

“Drowning accident at Stallerup Lake”

A story that fills a lot in the story of Harteværket is the one about the five brushes that drowned in Stallerup Lake in the summer of 1919.

The accident happened on a Sunday, where work had been done in the morning, and where ten workers after dinner would sail a trip on the lake before having afternoon coffee. The boat capsized in connection with a change of oars, and all ten men smoked in the water. Some of the men managed to get the boat back on the right keel, five of them holding on to the boat while the other five drowned.

The story of the drowning accident on Stallerup lake has given us the opportunity to know the names of a few of the workers who suffered at Harteværket. Just as it has given us an impression of the solidarity which, after all, was among the workers, and which was directly expressed by the memorial stone erected at Harte Cemetery, which was paid for by the other earthworkers.

Juli 1919

Juli 1920

“The hard work is finished”

The resin plant was built just after the First World War and put into operation in 1920. At that time, many electricity-producing hydropower plants had already been established throughout the world. They started back in 1878 with the use of hydropower to produce electricity.

In Europe, the facilities were especially established where there were large drop heights and / or large volumes of water. The resin plant is thus built with known technology.

The whole project of buying land, building canals etc. cost 3.6 million. Today, this amount corresponds to approx. 1300 mio. When Harteværket was built, it obtained an indefinite right to the water with a regulating band of 1 meter.
The plant was then operated together with a steam power plant in Kolding city.

In its time, Harteværket could cover almost half of Kolding’s and the catchment area’s consumption of electricity, but today production accounts for only about 1% of consumption in Kolding city.
Although Harteværket today is only a smaller production unit compared to the central power plants, it is a larger power plant compared to the many local production units such as gas engines etc.

Despite the fact that Harteværket today only makes up a small part of the energy supply itself, it does have some properties in the form of rapid regulation that can be utilized.

In 2007, a nature restoration of Vester Nebel Å took place to ensure the fishing and plant environment in the rivers. This resulted in the water supply to Harteværket being reduced by 60%, but electricity is still produced at Harteværket.

The resin plant is today protected, both buildings and machinery, because the plant is a piece of industrial history. Most of the equipment is original, and has been in operation for over 90 years.
That is why it is said that the work is a living cultural heritage. You can read more about the protection of Harteværket here.
Harteværket is currently run by the Harteværket Foundation.

In 1920, when Harteværket was built, electricity production corresponded to almost half of Kolding’s and the catchment area’s consumption of electricity.

When Harteværket changed operations in 2007, the plant still produced an average of DKK 1.8 million. kWh pr. year.

The calculations for the plant’s electricity production have held true throughout the years and have only varied considerably this year with a lot of drought or precipitation. In 1980, when there was heavy rainfall, production, for example, was up to 3.42 million. kWh.

There are three turbines at Harteværket, where two of them have 525 HP and one has 300 HP. The turbines thus have a total of 1350 HP, corresponding to around 1000 kW.

At that time, a machinist, two machine assistants and two workers were attached to the operation of Harteværket.




Fiberglass pipes for protected hydropower plants. Aarsleff has performed a somewhat special task for Harteværket in Kolding. The hydroelectric power plant’s old downpipe was corroded and the hole like a Swiss cheese. The solution was to install a fiberglass-reinforced polyester pipe inside the 80-meter-long pipe. This happened in the year 2010.

The downpipe is a riveted steel pipe, which over time has become very corroded. Regularly new holes appeared in the pipe, which were closed with wooden sticks. Eventually, however, the wooden pegs were replaced by a bolt with a gasket if a patch was not welded on. This solution was not sustainable in the long run, so Rørteknik, Bolig og Industri received an inquiry about the problem.

Like a starry sky. The tube was cleaned inside, and during that process, about 500 new holes suddenly became visible, which with a look from the inside led the mind to a starry sky. We proposed to install a fiberglass pipe inside the existing pipe, so we got a corrosion-free pipe that can withstand the water pressure of 2.5 bar.

The proposal was accepted by the Danish Cultural Heritage Agency because we preserved the original pipe on the outside, and the agency even chose to support the project with 20 percent of the construction investment.

Divided into sections. The pipe has a drop height of about 26 meters, is 80 meters long, and has a diameter of 1.75 meters. The new pipe is made of fiberglass-reinforced polyester with sand in the core. The pipe is divided into segments, where each segment is 2.3 meters long and has an inside diameter of 1.6 meters. For every fourth segment, the gap between the fiberglass pipe and the steel pipe was closed with concrete to limit buoyancy and the pressure when re-casting between the pipes.

35 sections installed. After a total of 35 pipe segments were installed, both ends of the pipe were laminated with fiberglass-reinforced polyester. The 2.5 meter long cut piece of steel pipe, which had been removed so that we could get into the pipe, was welded on again and the concrete was pumped in between the pipe pieces. In total, Rørteknik worked on the project for four weeks.

New foundations. Aarsleff was also involved in the project and was responsible for the excavation work and the installation of additional foundations. The pipe runs down a slope, half above ground, half down into a ditch. This made both the excavation and the casting under the pipe cumbersome. Aarsleff installed 11 new foundations to secure the pipe for the extra load. The slope presented challenges because it was impassable for, among other things, the concrete trucks. Therefore, we had to establish a comprehensive pumping system despite the limited amount of concrete we had to use.

After almost a whole century, Harteværket is still in operation. A nature restoration was carried out at Ferup in 2008, so that the course of Vester Nebel Å has been traced back to its original lease.

The electricity production at Harteværket has thus declined sharply, as the plant has lost 2/3 of the original annual amount of water. In recent years, very large amounts of wind power have entered the electrical systems. This has made electricity production more unpredictable and there has been a need for more flexibility in the system.

Here, the great regulating power of hydropower comes in handy. By operating the plant in a different way than before, utilizing the large regulating power of hydropower, this mode of operation compensates for the operating loss with the smaller amount of water.

Today, more than ever, there is a need for supplementary productions that are very flexible and can quickly regulate electricity production up or down in step with the wind or other imbalances in the electricity system.

The future of the work. In the future, the plant will work together with other smaller production units and thus form a larger power plant for regulation. In addition to payment for electricity production, the plant will in future receive payment to make its flexibility available.

Harteværket today

That's how it started

In the 1930s, salt was drilled at Harteværket.

It began with Denmark’s leading geologist in the 1930s, Dr. phil. Victor Madsen, after years of studies and geophysical studies, had formed a theory that salt had to be found in Denmark, and the place had to be Harte.

But there was no one who wanted to throw themselves into boreholes for the mineral, as one was not sure if it existed. Therefore, it could risk costing a fortune. As the Danish state did not want to risk a financial loss, advertisements were inserted in which the government invited lovers to, under certain conditions, start salt drilling.
The ad gave no result, but when the Danish engineer Karl Østman traveled to America in the early 30s, he met the engineer Frederick Franklin Ravlin. Ravlin had for a number of years succeeded in drilling for oil and became interested in the advertisement that Østman showed him.

Ravlin went to Denmark the following year, and here he met the director of the Geological Survey of Denmark, Dr. phil., Victor Madsen, dr. Hilmar Ødum (head of the drilling archive at DGU) and Prime Minister Thorvald Stauning. Here the contract was signed, and it appeared that Ravlin at his own expense and risk could be allowed to drill in the ground at Harte, but if he within two years found minerals of any kind, he could acquire the concession to Denmark’s underground in exchange for paying the state 7½% of the value of what would possibly be produced.

Salt extraction

The big day – the lump of salt. Ravlin traveled home and sent equipment and experienced drillers to Denmark, and work began on July 27, 1935.
The first real result was the famous lump of salt, which was drilled up on 13 November 1936 in the presence of dr. Victor Madsen, ass. geologist at the University of Copenhagen A. Noe-Nygaard and engineer Karl Østman, although its authenticity was later questioned.
Victor Madsen then prepared a document about the find and its circumstances and traveled to Copenhagen with the salt after having previously given a small informal speech, in which he expressed the joy that his theory of salt at Harte had held true. He also mentioned that the right to the subsoil and extraction of raw materials in Denmark now belonged to Ravlin.

Dr. Madsen later divided the lump of salt into two pieces, one part is in Copenhagen, the other part he gave to Ravlin, who later gave it to a lady in the USA, who herself drilled for oil and had made a million fortune on it.

Now Ravlin put more effort into the work. He got more drilling materials and more crew sent over from America. The news of the salt discovery reached the world and resulted in the international company Gulf Oil Co. approached Ravlin to take over his exclusive rights. Ravlin initially said no, but Gulf kept pushing, and the company’s offer eventually assumed such a favorable scale that Ravlin accepted, subjecting himself to the state sanction.
Thus, Ravlin stepped out of the picture and returned to the United States after spending approx. one million kroner in Harte.

The authenticity of the lump of salt. When World War II began, Karl Østman claimed that the salt discovery was forgery and that he had bought the lump of salt in P. A. Kruuse’s material store in Odense. Ravlin had then placed it in the drill pipe himself. Karl Østman later recalled this statement on the grounds that it was to divert the Germans’ attention from the Danish underground.

Large salt deposits in the form of salt thirst have subsequently been found in several places in Denmark.

How does it add up?

Harteværket gets its water for electricity production from Dons Søerne.
The water exploits the effect of gravity. From a high place the water falls down to a lower level.
In its case, the water passes a turbine. The falling water causes the turbine to rotate about an axis, which in turn pulls a generator and produces electrical energy.

The water is led via canals into the plant.
Then it runs through the grate in the grate house. Here the water is cleaned of leaves, branches and other dirt so that it does not get into the turbines.
(The fish are led via a bypass around the turbines and out into Kolding Å).

In the first grate house at Harteværket, there was a coarse grate, which took the worst, but when you got new grate at smaller intervals in the grate house, the coarse grate was no longer necessary.

The lock gate (is in the black housing by the inlet channel) is always lowered a bit down into the channel.
The lock takes the really big things, such as a tree trunk. If these are not sorted out, it will destroy chains etc. in the grate house.

Once the water has been a trip through the grate house, it flows further down through the large red pressure pipe.

The water first comes down into the basement. Here the pipe splits in two, one pipe leads up to turbine 1, and the other pipe distributes to turbines 2 and 3.
Then the damper opens and the turbine starts when the water comes. The damper can be opened both manually and per. automatik.

In the turbine there are a lot of “blades”, which are connected to a shaft that leads to a flywheel that stabilizes the revs and the generator. It is the generator that forms the power.

The voltage generated by the generator is 380 Volts. The current from the generator goes via thick copper rails down into the basement under the plant.

Here, the energy is converted from 380 volts to 10 kV (kilovolts) or 10,000 volts, to be suitable for transporting over longer distances.

It happens in the 3 transformers, one for each generator.

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

From the transformer station “Harte” the power is sent partly up on the cable and overhead line network to other parts of the region, partly out to the 10 kV cable network around Kolding. From the 10 kV cable network, the energy is again transformed down before it reaches the household, namely to 230 and 400 Volts, which we can use in the ordinary appliances.

The amount of energy that the plant can produce depends on the number of turbines, which in turn depends on the amount of water that day. The production must be reported to NEAS Energy, which is responsible for selling it to the electricity market. It must be done before kl. 11.30, 24 hours in advance. For example, it is reported that tomorrow turbine 1 will run from 8 am to 4 pm.

NEAS Energy can then take control of the turbine at 8 o’clock the next day and generate the amount of power they need.

In recent years, very large amounts of wind power have entered the electrical systems. This has made electricity production more unpredictable and there has been a need for more flexibility in the system. Here, Harteværket’s good regulatory capabilities come in handy.

By quickly regulating production up or down in step with the wind or other imbalances in the electricity system, Harteværket helps to stabilize it – and can receive payment for it, in addition to the payment for energy.

When the water level is about to be down in the lakes, we report the turbine out of the market again, the day before.
Previously, the turbines were inspected every evening and twice every day on weekends. But due to savings, this is no longer done. However, there are alarms on, so if something happens, the turbine disconnects from the mains and shuts down by itself.

A little bonus info: A generator is built according to the same principles as an electric motor. When there are enough revolutions in the generator, it produces current equivalent to the electric motor turning when you put power to it. It can be compared to an old-fashioned bicycle dynamo. The more you step on the pedal, the more your lamp lights up.

Turbine 1 and 3 are twin turbines and No. 2 is a single turbine. Gemini means that there are two sets of slats.
The slats wear out and must be renovated after several years of use. When they wear, they lose power. This means that the effect of the water flow becomes smaller. It can be clearly felt when new ones come in.

The plant consists of three Francis hydropower turbines, which use a special technology that is ideal for a “small” hydropower plant such as Harteværket, as a lot of energy is generated by a relatively small amount of water.

The two large turbines generate 350 kW per piece. per hour, and uses 2400 liters of water per second. The small turbine generates 250 kW per hour and uses 1200 liters of water per second.

The installed power on the generators is approx. 1300 kW.

The maximum performance is approx. 1000 kW.

It is the original turbines and generators that are still in operation.

All technology at Harteværket is thus 100 years old. The only replacement that has taken place is of the grate house which is located at the top of the hill, where the water is filtered for fallen leaves etc. before it is led down to the turbines. The grate house was replaced in 1947.


Fishing in the area was an important source of income for e.g. the peasants. In 1896, some farmers chose to shift production from pork and meat to trout and carp.
Earlier in the story, the fishing belonged to the royals at Koldinghus Castle, but in some cases others were allowed to fish by King Christian the Fourth. It was not until 1767 that fishing became private property for the first time.

The method. A distinctive method was especially used before 1864, namely the so-called seesaw fishing. It is believed that the method originated in the Rhine somewhere in Germany, and that the Kolding area is the only place in the country where the “rocker” was used.

The tilting yarn consisted of a solid support post (tilting pole), which was dug far down in the river bank and braced with three buried oblique struts. On top of the pole was a fork (the turner) fastened with a bolt. The rocker bar, which was 24-30 feet (7.32-9.14 m) long, was held in place by a clamp on each side of the turner.

Rocker Net fishing

The tilting rod could then be easily swung in towards land, at the same time as the fisherman used his weight to tilt the rod up, so that the device was lifted up the water.

A loop connected to the lashing yarn was attached to the rocker bar. It was on all four sides stretched out over a strong corpse, which in turn was attached to the hangers, which were made of young beeches crossing each other. In addition, some liners were attached to hold the hangers in a fixed position. The mesh size was between 2 and 11/4 inches (5-7 cm).

Yield. The yarn was arranged so that it filled the entire sob. As soon as it was lifted, one probably got some of the fish that were over the net. In the actual lifting, the net was gently raised slightly, but if there was no catch, the net was slid back again. If there was a catch, the trout would search towards the deepest point of the net while the net was being lifted and therefore the fish rarely escaped. Conversely, the large meshes ensured that fish under 40 cm were sorted out, so that only a few brown trout, Greenlanders and small sea trout were caught.

The effectiveness of the method was underlined by the fact that the maximum catch in one night was stated to be 1800 pounds (816.5 kg) distributed among 40 seesaw fishermen. This corresponds to 20.4 kg per rocker yarn.

The influence of nature. In the gloom and darkness of the night, the gillnet fishermen stood along Vester Nebel and Kolding Å, while the nets were tilted gently up and down at three-quarter minute intervals. From Trudsbro and down there were between thirty and forty yarns. During the sea trout’s hauling period (July-Oct.), People fished in the caves (hauls), where the river is deepest, and they were especially active when the weather was turbulent with northeasterly winds and high tides in the fjord. Therefore, there were shelters along the creek to crawl under during storms. In circumstances with turbid water after rain (flood), the fishing could also be carried out during the day.