Inside Finland's underground tunnels that could be used to store renewable energy

The Finnish capital, Helsinki, has a long history of subterranean construction, with a vast network of civil defense shelters built during the Cold War. Helsinki is also looking to its underground tunnels as a potential source of renewable energy.

‌The city is home to a wide variety of subterranean spaces, from the spiritual, to some of the most unusual gallery spaces the world has to offer, to those underground facilities, they hope they never need.‌ Now, there are plans to harness some of the waste energy generated in the freezing winter months in the spaces underneath the city.

‌Hewn directly into the rock of the city's Toolo neighborhood is one of Helsinki's top tourist attractions as well as a place of worship. With more than 500,000 visitors annually the Temppeliaukion kirkko's church service manager, explained to CGTN that the underground construction gives the chapel a special feel.

‌"So, if you are a religious person, you can easily feel that connection. But also, if you are not, many people come here and say, oh, this is a fantastic feeling that I am experiencing here."

 Heli Suhtala Uralic told CGTN that she knows the benefits underground heat storage can have.

‌"So I'm all for it. And I think Temppeliaukion church is a good example of how it could work. Because we don't have much heating here. We just had -20 last week. Centigrade outside. But we don't have heavy heating here, and, I'm standing here without a coat or anything."

Tomi Rask was CGTN's guide, he is a paramedic and Civil Defense Instructor, he filled us in on the scale of the shelter network across Helsinki.

‌"We have, civil defense shelters, over 5,500 and, sheltering places for over 900,000 persons within Helsinki. And Helsinki is only 650,000 strong. So we are quite good on that perspective."

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‌But when it comes to the idea of doubling up shelters for heat storage, the process requires storing that heat in water, which can cause space issues if these facilities' were ever needed for their primary function in civil defense. Rask told CGTN that could change as the tech develops.

‌"Tomorrow's technology will probably bring some things (inventions) so we don't need to store the heat in water. Then we can store the heat in something else like bedrock, for example, or sand. They are testing now on some parts of the world."

‌It's the service tunnels that run under the city center where developers have submitted plans for projects that could include waste heat recovery and even exploration into the next generation of geothermal heat.

The Finns have developed a real talent for finding not just functionality but architectural beauty below the surface.‌ There are few better examples of Helsinki's underground cultural spaces than the Amos Rex art museum. The museum, which opened in 2018, was constructed under the Finnish capital to protect old buildings above ground. The 9.5-meter high subterranean domes allow visitors to feel completely immersed in exhibitions like that of Japanese artist and composer Ryoji Ikeda.‌ 

CGTN delved 20 meters under the bedrock of the city of Helsinki, to a civil defense shelter that can house 6,000 people in the event of the worst happening. It's an expansive facility. It stretches out some 17,000 square meters under the Finnish capital. 

‌Most of the Shelters, which were started at the height of the Cold War and are designed to protect citizens in the event of a nuclear conflict, have a dual purpose; some are sports centers like this one, others are storage facilities, and some are car parks. 

‌While those behind the new plans for heat storage are still awaiting permission to go ahead, their hope is to tie it into the Finnish capital's ambitious 2030 carbon neutrality target.

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