I had read this interesting article on the site of the energy company in Turku, but I did not have time to write about it until now.

Located in the southwest of Finland, with a population of about 200 thousand inhabitants, Turku is one of the bigger cities in the country. I think the 6th biggest. 

Turku has plans to get carbon-neutral by the year 2029. It is not an easy task by any measure. But the city had booked big gains in that direction.

One of them, is a network of heat transfer tunnels conveying heated water from the source to the distribution points in the city. It is not shorter than 14.5 kilometres. The tunnels run from the source by the Naantali power plant all the way to Luolavuori. In some parts its diameter is as big as letting you ride a van and in other parts a motorcycle. Other than this main artery, there are smaller distribution tunnels and eventually pipes.  The water conveyed by this tunnel network is quite high. It is written that it reaches 120 degrees (C) in winter and 80 in summer. More than enough to heat the houses.

I know you would be asking about the carbon neutrality feature. Well, over the year, the Naantali power plant had been making transition from fossil-fuels to renewable energy usage. According to Turku Energia, in 2020 only 10% of the fuel will come from fossil fuel and the 90% from renewable sources.

I am not writing this for bragging about how great our infrastructure it. I only wanted to give an example of additional tunnel use, hot water, for utility companies. I would expect such tunnels to increase in numbers in the common decades, especially in Europe.

Regards.