presentational waves squeeze all bodies. how much more do we need to put a stop comp claim for help find beyond is getting smaller on dw science and take time to handle this city and sweden by look, i'm assuming that somebody below something truly extraordinary is hiding just insight in a secret location the local energy company built a giant underground furnace, and that was a long process. even the king swung by to check it out. these caves used to store a hidden oil stash during the time of the cold war. and now they flooded them with water and go to to near pointing point to build one of the largest p batteries of its kind. and we came here to tell you why we invested was a bit more than an hour drive from the capital stucco. it's a city of about a 160000 people. it's pretty cold about to minus 2 degrees

celsius. that's in the middle of winter. i can get much, much colder here, even below minus 20. so people here take the heating really seriously. pretty much old houses, the 98 percent of them are connected to pipes like be a huge network of 900 kilometers and just the city. and the main purpose is people will instead of having a small boiler in each home down several huge port less than the local power plants that heat the entire city through. pipes like these sweeten, has a proud history of building systems like this called district teaching. and even though the idea is fairly old, this is the big cold for keeping people warm in the future. but then in very little to no fossil fuels, that's because district teaching networks can be switched to renewable heat sources, for example, of biofuels like woods or heat from the us on the sun. or that can also tap into

heat that would otherwise go to waste, such as from the auto census. the system investor was one of the largest in sweden, has been run by the local energy company, rely in the heat since the 1950s. and that's what we have to say. hi, hi. this is these advanced and he'll be taking us on the ground. she's in charge of the company's heat and electricity strategy. so when's the last time you've done this? i've been the process of september when the king was here to do the honoring opening of the gate. it's a tough act to follow for me, i think a press office a and an engineer also coming with us to be able to fill in the caves. we have to agree to one thing that location has to remain secret. you won't find it on google maps, and yes, we've tried. so why come we tell anyone where exactly the case of

fish we in the energy production site? and so it's because of security reasons. okay, so we also can show the drive now. so we'll do a katia, and then we have the case for here you can see down where the average starts. and here is where we should get rough. let's go. we're heading down about 25 meters. so here's the rest of this. there is free. so if something goes wrong, we only have to climb up. well, what? so we want to be fit if you want to be these tunnels lead to 3 men made real case today is the solve the hot water tanks. but they have a turbulent and troubled history. they are in the united states and the soviet union stand on the verge of direct military confrontation. throughout the 19 sixties and seventies,

the cold war had the world and its grip. sweden had declared itself unusual and independence. it was essential to have enough fuel to keep the country running in case of full scale war broke out. so it started to stop pile. and that's why the case invested also what builds to store oil. the amount of organs used for whole year was kept in here, but after the cold war and not have any use for it. and it's been sitting here since then up until today, because it turned out these caves can fix a big problem that a lot of cities around the world have. this is the best of those, this power plant. it's a so called code generation plant, meaning it produces electricity and heat at the same time. so it's a very efficient way to use fuel normal power plants that just produces electricity . forensic fuel to create spe, this has been used to drive the turbine, but much of the heat that's generated in this process simply gets lost, cools away. only about 40 percent at best of the energy that's stored in the fuel

gets used. the rest is wasted. a combined heat and power plants like the one invest those uses up to 90 percent because it reuse us the otherwise loss pete's and turns it into hot water. this can get the feds into the district teaching system distributed via the pipes we saw earlier. so people can use the homes and half what was the powerful spirit night to 6 is 3 and what's going on or you think in the oil crisis and we convert that into cold. and then during those years since that we have been more and boilers and the generating thirst and now we use waste, household waste we use, we use what would that's been something and then also biofuel. and this power plant is the reason why that filled up the caves with water during the summer. we need to have the power plant running because everyone's best house hot shower, even on the warm summer days. but to keep the plan running needs to produce

a minimum amount of hot water, often more than can be used up in the summer. and in winter, it's sometimes con, produce enough heat, especially on really for us. the days when it gets colder, we need to fire up another power plant. so the idea was simple, but ingenious. why not dust off those big caves they had under the city and turned them into a giants heat battery that can store the extra heat from summer. so it can be used to keep houses warm in winter. but now it's getting really want. you can see those 95 degrees for just underneath us if the one of the cabins. ok. so that keeps coming. coming out from the ceilings from the mountains because it goes above it feels like outside to minus a degree. and now if this feels like you're in a summer holiday, that's what i can do like it. yeah, exactly. instead of oil the case and now storing heats when the power plant

produces more than the safety needs, the water inside the caves gets heated up to 95 degrees celsius. the bedrock make sure only little of that heat escapes. it will say like a service like the coffee and the service order will also stay home and that one cold days when the city needs more heat than the power of time can provide the heat, stored in the case can be used to keep people want. i don't need to start up another boy in there. eh, an indian, those foreigners are reserve boilers for those really, really cold days. are sid wrong on fossil fuels and without heating to heat, so soft for make them start. we can reduce our c, o 2 emissions. all 3 caves together can store enough heat to keep the city warm for up to 2 weeks depending on the outside temperature. and that's what they're doing right now. that's all the noise working now, it's taking the water from the top of the cavern and taking it to the usage

stranger. this transfers the heat from the watson, the caves to the water that's running through the district teaching network. now unfortunately, this is as close as we can get to the case. that's because the fields and thankfully, so on the other side of the field. and you have the concrete, the concrete because on the other side there, there's a 100000 cubic meter of 95 degrees health walker. so if it's not our company, we own the cooking. we were as you can imagine converting an old oil deposit into a heat storage cave was a big undertaking. or yeah, the 1st we would have to do was to open it up because they've been close down for over 50 years. and then when we're opening up, we have to clean them from all the oil that was in there. and that was a long and sticky process. but then after that, we need to do all the pricing said needed to be inside the case because now we

can't reach them anymore. so after that was done, you see lives up again and started to fill up with water that's allowed to move in 5 months, as the case holds as much water as almost a 100 with olympic sized swimming pools. the whole project cost $15.00 and a half a 1000000 us dollars and investment. the company, which is owned by the city, hopes to recruit within 5 to 10 years. because every time they using the heat stored in the caves, the savings and fuel, we use it almost every day in some capacity and sometimes we are filling up would be your own cold days. we are using it to the distribution. of course, the company says the cabinets can save $1600.00 tons of c o 2 emissions per year, about as much as $460.00 people in sweden limits. in the grand scheme of things. this might not sound like that much. but if that were most orange capes like it's, it could make a difference. so it's great to, to lower stories. this is implemented and we get the more experienced it from it.

this a spend and a retired professor who sweetens go to guy on district teaching. to people to try to avoid risk and don't have to take risk. so if somebody has taken the risk and it's been successful, then you have thoughts. of course not every place has abandoned oil storage slides just sitting around. but it's also possible to build caves from scratch, like this project from finland, just doing expense will be 3 times bigger than the one invest that was scheduled to start operating in 2028. the notary countries have huge potential to the lot small capes storage. we have a crystalline bedrock and it's ideal to, to, to make larger cabins and these can, to uphold with better x. so the conditions floor is kendall. so as you have seen, how car superior can in sweet and then filled up and also involving. and it's also called all the places that take those boxes, like parts of canada in the us could explode rock, kevin storage as well. places with less the bedrooms have to store heat different

things. you can also heat up natural underground layers of friction, rock, sand, or gravel, that whole ground floor top which you access by drilling wells. that's being done in many places in the netherlands and also in germany. actually it's problem and building a seat at this way. and speaking of drilling, another technique is to make bull holds up to several 100 me to sleep through which a hot fluid is circulated. the seats up the surrounding rock solid and the clay that then supports the heat. or it's possible to biggest huge pits line it with water proof material and use it to store hot water like here in denmark for smaller amounts of feats. lots of things like this one investor was, can do the trick as well. it's 11 times smaller than the underground case, and the list goes on. district heat is very local. you have to have the local solution to your local studies the underground, so i'm as invested will spruce that storing heat in the cave as possible on a large scale. and it can become a role model for other places looking to level of the heat that we'd like to hear

from you. do you have district teaching where you live and are there any storage projects like this one that is known the comments and don't forget to hit subscribed for more videos like this one. the we are all set. we are watching close to the,

to bring you the story behind the new, the will on about. i'm biased information for free might say, due to me in your state innovation green, the green revolution global. so listen to a whole lot of crime. it's probably up to speed if the care of subscribe to those channels every friday, subscribe to plan. it's a the the.