Denmark digs 70,000 m³ trenches — to reduce electricity prices

When completed, these ditches are filled with water and then covered. This liquid allows the storage of surplus energy from the country’s renewable sources.

Denmark came up with a surprising but very effective solution to contain the price of electricity: large underground cavities capable of storing up to 70,000 m³ of hot water, the equivalent of 70 million liters.

The idea goes through transform surpluses of renewable energy into heat and reserve them for times when electricity is more expensive.

The system, called Pit Thermal Energy Storage (PTES) and developed by , is already in operation in Høje Taastrupin the east of the country, and operates as a large thermal battery connected to the district heating network.

So, when there is excess electricity generated from renewable sources, this energy is used to produce heatinstead of getting lost. Later, this heat is used when demand increases and costs rise.

The technical basis is simple: water is heated to temperatures between 80 and 90°C and stored in huge underground warehouses. Instead of storing electricity, as a conventional battery would, these infrastructures conserve useful heat, which can then be injected into the urban system when necessary.

The installation reaches a capacity of approx. 3.300 MWha value that shows the true project size. Furthermore, its flexibility allows it to integrate different energy sources, from wind and solar surpluses to industrial waste heat, all within the same thermal infrastructure, says .

One of the most relevant changes compared to other thermal storage models is that this system was no longer designed just to store heat from one season to the next: it can complete up to 30 cycles of loading and unloading per year, which multiplies its practical and improves your profitability.

This more frequent use also reduces thermal lossessince the heat is not trapped for such long periods. In this way, the installation gains dynamism and works almost in real timeadapting to fluctuations in the energy market and helping to mitigate spikes in electricity prices.

O system performance depends, to a large extent, on its coverage, conceived as a technical element of great importance. This is not a simple closure, but rather a insulation solution that limits heat lossallows the release of steam and prevents the entry of rain or snow — decisive factors in maintaining its efficiency.