By Søren Bjørn-Hansen

The sales figure was promising at the time in September 1981. At a general meeting, the then chairman of Thisted Varmeforsyning, Erik Poulsen, described the bright prospects of retrieving geothermal heat from the Thyland underground:

"If it goes as planned, by the mid-80s there will be no more need for oil to heat homes in Thisted," he said.

Three years later, on a cold and wet November day, the so-called demonstration facility was inaugurated. At that time, a new and quite young chairman had joined the heating supply: Lars Toft Hansen.

In the commemorative booklet 'Towards the future', which was published in connection with the 50th anniversary of Thisted Varmeforsyning, there is a picture of him, with a slight grimace, taking a sip of the salty geothermal water that the plant has just raised . He was, and still is, excited about this new source of energy.

"You won't get more sustainable energy," as he says when we meet him today in a meeting room a few meters from where it all began.

It was Dong (now Ørsted) who, at the beginning of the 1980s, had proposed testing geothermal energy in the area. At the time, the Thybos said yes thanks to laying land for one of two test plants in Denmark.

But the geothermal adventure was not initially the success that his predecessor had promised. There were several bumps in the road. Firstly, they could not get enough of the 90 degree hot water down to the three kilometer depth the drilling was originally planned for. Instead, they had to make do with the 45 degree warm water at a depth of 1250 metres. It required a heat pump with a rather large electricity consumption at the time – equivalent to a thousand tonnes of coal per year – at a time when the electricity tax had just increased (see box for more on how geothermal works).

Secondly, it had been agreed with Dong that the price of the geothermal heat could only be reduced by 15 percent compared to the oil price.

And thirdly, the plant supplied only seven percent of Thisteds Varmeforsyning's total consumption. So there was a long way to go before the promising words from the previous chairman.

The chairman took a bet

But Lars Toft Hansen held firm. When Dong later chose to phase out the geothermal activities and offered Thisted Varmeforsyning to take over the plant, he could have decided to go back to the fossil heat production that was in place before geothermal came along, but he went the opposite way.

Thisted Varmeforsyning took over the facility, raised DKK 5,3 million from the EC and invested DKK 7,6 million of the heat supply's own funds in a new, 40-tonne heavy Japanese so-called absorption heat pump, which did not itself use energy, but 'borrowed' it from hot water heated with gas and waste incineration.

This new plant now covered 20 percent of the heat supply's needs – and saved 23.000 tonnes of heating oil per year.

"Here it was hardly without significance that the chairman, engineer Lars Toft Hansen, professionally took a strong interest in the use of geothermal energy for district heating," as the memorial reads.

This interest has been confirmed by the chairman for 39 years. In fact, he is so interested in it that he integrated it into his daily work as an engineer in a local company, where he became a partner. He started working as an advisor on geothermal projects far from Thy. He went to Poland, the former East Germany and Lithuania. In several of the places, they have been able to bring up 90 degree hot water from a depth of three kilometers, and the new heating systems have functioned as a direct replacement for coal and brown coal, which, in his words, created terrible conditions with smoke and pollution.

"So they were very happy about it".

A new geothermal era on the way?

They now also did that in Thisted. After betting on the new heat pump from Japan, the locals could quickly read the effect in their heating bills, which became significantly smaller.

"They could see that it was a good idea. So... I'd say it's been some... At least after a few years... actually boring AGMs. Because there were no problems. It wasn't there," observes Lars Toft Hansen with a smile.

The journey in Thisted was not even over. In the year 2000, they bet again, now with a little more certainty in their stomachs, and expanded geothermal production with the help of more efficient submersible pumps that simply pumped up more hot water. Today, geothermal energy typically covers eight percent of the heat that is needed. The waste incineration on the side delivers its share of 60 percent, while straw and natural gas account for the rest. However, it fluctuates a lot, how much geothermal covers (see fact box).

This Thai success has probably been copied elsewhere in Denmark, one might think. But no, it isn't. At the time of writing, there are only two other, rather small plants – in Sønderborg and on Amager. How it can be, Lars Toft Hansen has a suggestion: the story of the large-scale and severely neglected geothermal project in Kvols outside Viborg. It should have been the largest geothermal plant in mainland Europe at the time, but when the drilling started in 2009, they must have received bad advice, he estimates. They began by drilling deviated (crooked) and therefore ran into major technical problems with the geology.

The initial budget of DKK 12 million was increased several times, and in 2012 there was no more money. The bank closed the box.

It put a huge scare into the lives of everyone who had to dream of geothermal energy on Danish soil. Lars Toft Hansen even estimates that they were very close to succeeding when the project was abandoned.

“When they stopped, they were down at the desired layer. If you had come down to it, you would probably have had a rather large insurance sum paid out. DKK 70 million. Then we would have been somewhere else today, I think”.

In addition, there is another important reason for geothermal's dormancy: Denmark's rate on gas. Successive governments throughout the 1970s and 80s insisted on pushing gas out into as many corners of the country as possible to provide the best economy for drilling in the North Sea.

But in these years the tide is turning for geothermal energy, partly because we as a society are in the process of phasing out fossil energy sources, including gas. A quick google search reveals a number of more or less advanced geothermal projects, all started very recently.

Aarhus in January 2022, Copenhagen October 2022, Skanderborg/Hørning November 2022, Holbæk December 2022 and a new project in Sønderborg April 2023. All projects are run by the new company Innargi, which is owned by AP Møller Holding, ATP and Nrgi. And they are also active in Poland and Germany.

Lars Toft Hansen is not familiar enough with these new projects to want to assess them separately, but he would like to say a few words about geothermal's general potential:

“The thermal potential is enormous. It can cover Denmark's entire district heating consumption. But there must be economy in it as well, so I can see the larger cities first covering 20-25-30 percent of their heat consumption".

And if there was any doubt: It would be a definite quantum leap for Denmark's green transformation. You just don't get words like that out of a thybo. Although it was here in Thisted that he proved the value of geothermal energy.

How geothermal works for district heating
The Earth's core consists of magma. Thousands of degrees of hot liquid rock, which we see at the earth's fracture surfaces in the form of volcanoes. But the heat is always there.
In some places near these fracture surfaces it is close, as in Iceland. Here you can use the heat easily with very high temperature of water not very far down in the underground. This means that it is neither particularly difficult nor expensive to use the water both for heat and for electricity production, because the steam can drive turbines.
In other places, such as in Denmark, you have to go down a long way to reach such high temperatures. Here, you operate instead with low-temperature geothermal energy, where you have to use heat pumps to optimize the utilization of the heat. It makes it harder and more expensive, but it still makes sense.
Both at high and low temperatures, the use of geothermal energy requires a borehole that brings the water up to the surface. In most places, you will make another bore that sends the water back, but in some places, such as at the Blue Lagoon in Iceland, you just bring the used water to the surface, from where it slowly seeps back.

Geothermy in Thisted Varmeforsyning
Since the late 90s, Thisted's heating supply's focus on geothermal energy has been good business for the 6000 customers on the district heating network. The average annual heating bill for a detached house of 130 square meters was DKK 2022 in 9.988. In the rest of Denmark, according to Statistics Denmark's net price index, the average expenditure was DKK 15.404.
In practice, it is only during the winter months that the geothermal plant is in use, because the baseload of the heat supply is the waste incineration plant. Seen over a year, waste cogeneration supplies just over 60 percent, straw heating accounts for approximately 24 percent, while geothermal accounts for around 8 percent. The rest is accounted for by a very small amount of biomass and gas. However, it fluctuates a lot from year to year as to how much geothermal covers. If it is a mild winter, as at the last count, waste incineration carries a larger share. If the winter is hard, they can reach 20 per cent. Over time, the district heating network is spread out to more customers and this results in a greater heating demand.

Søren Bjørn-Hansen is a journalist and part of the journalist community Klimajournalisterne.

This article is part of our project 'Yes in my backyard', where we focus on how people help drive the green transition in their local communities.