During the Cold War, the vast caverns beneath the Swedish city of Västerås housed an oil reserve of 300,000 cubic meters.
The oil was there in case World War III broke out and Sweden found itself cut off from international energy markets.
In 1985, as geopolitical tensions began to subside, the caverns emptied and have remained so until now, BBC Technology correspondent Chris Baraniuk explained.
The Swedish energy company Mälarenergi has embarked on a project to decontaminate the facility and fill it with hot water at temperatures up to 95 degrees Celsius.
In essence, it is building a giant underground thermos, which the firm says will be the largest of its kind in Europe.
“It’s quite wet,” Lisa Granström, acting head of the company’s Heat and Power business unit, told the BBC’s technology correspondent, describing her latest visit to the tunnels, which are at an undisclosed location.
“[Las cavernas son] much warmer than you might expect. They still smell a bit of oil,” he explained.
The caves have the capacity to store approximately the equivalent of 120 Olympic swimming pools and are 11 times larger than the largest surface hot water tank Mälarenergi has near the area, Granström added to Chris Baraniuk.
plan details
This type of thermal storage is one of several ways to store heat in the ground for later use.
With the rise of renewable energy and concerns about energy security in Europe following the Russian invasion of Ukraine, some experts argue that more use should be made of underground heat storage systems. Baraniuk indicated.
In the case of Västerås, the heat from the caverns will be sent through pipes to a district heating network, which supplies 98% of the homes in the city of 130,000 inhabitants.
Mälarenergi intends to start filling the caverns with water at the end of the year. The facility will offer 500MW of district heating power, the BBC journalist said.
But where does the heat come from? To burn things The company has a nearby power plant with furnaces for the combustion of waste or biomass, which generate electrical or thermal energy.
Granström told Baraniuk that carbon capture technology, which would reduce harmful emissions from the plant, is not yet in place, but his company is considering installing it.
The hot water reservoir will allow Mälarenergi to continue heating homes on cold winter days when demand is high, without reducing electricity production at the power plant.
A great natural thermos
Storing heat underground tends to work well because it’s very difficult for heat to escape: the ground itself acts as a great insulator.
Granström explained to the BBC that the Mälarenergi caverns will retain heat for several weeks and that the system should be particularly stable once a few years pass and the temperature of the adjacent ground rises.
“Once it heats up, the loss is not that great, because you have already heated the rocks around it,” he said.
This may draw the attention of the inhabitants of cities like London, who must endure high temperatures while traveling on the tube to or from work.
For decades, the heat from people and trains has been raising the temperature of the clay surrounding the British capital’s subway tunnels. So much so, that this clay now has an ambient temperature of between 20 and 25 degrees Celsius, which makes it very difficult to cool the wagons and platforms of the network.
The project in Västerås is not the first of its kind.
In Finland, the energy company Helen began filling a slightly smaller cavern system on the island of Mustikkamaa with hot water in 2021.
The facility is now operational and supplies heat to 25,000 one-bedroom apartments year-round, the company said.
“These solutions are great,” Fleur Loveridge of the University of Leeds (UK) told Baraniuk.
to take into account
According to the UK Coal Authority, a quarter of the British population lives on abandoned coal mines.
A significant number of these mines are flooded and naturally maintain relatively warm temperatures, around 15ºC.
This water from the mines could be further heated, perhaps by a heat pump system, before being piped to nearby houses, where it would heat radiators or provide hot water.
Such a system could use heat exchangers to heat a closed water loop, so that potential contaminants from the mine water do not enter the domestic supply.
Professor Loveridge pointed out that heating accounts for about a quarter of UK carbon emissions and decarbonising heating is quite difficult.
Millions of homes still rely on fossil fuel boilers, for example.
“We should, as a country, use all the sources to produce and store thermal energy that we have,” he said.
But there is an alternative to giant underground thermoses: what about hot rock sponges? Matthew Jackson, from Imperial College London, explained to the BBC that aquifers, porous underground bodies of rock that naturally retain water, could be used in the UK.
It is possible to pump heat, or cold, into large areas of these “sponges” and then draw the heat or cold back through a fluid when needed, to heat or cool homes.
Such a system could be even more efficient than hot water tanks in caverns, Jackson said.
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BBC-NEWS-SRC: https://www.bbc.com/mundo/noticias-65276827, IMPORTING DATE: 2023-04-20 03:50:06
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