Harnessing Underground Heat: Sweden's Innovative Heating Solution

In the depths beneath the city of Vasteras, Sweden, a remarkable heating solution is taking shape in the form of a vast underground cavern system. Originally constructed during the Cold War era to store oil, these man-made caverns have been repurposed to serve as a reservoir for hot water, providing an innovative approach to heating urban areas.

As winter temperatures in Vasteras can plummet to as low as -20 degrees Celsius, the need for effective heating solutions is critical for the city's 160,000 residents. The region utilizes a district heating system where multiple homes are connected to a centralized power plant, rather than relying on individual boilers. This setup is particularly advantageous as it allows for efficient energy use by burning household waste and wood to generate both electricity and heat.

Lisa Granstrom, the head of heat and electricity strategy at Malarenergi, the municipal energy company, emphasizes the efficiency of co-generation plants like the one in Vasteras. Unlike conventional power stations that waste heat generated from steam production, the co-generation facility captures this heat and channels it into a sprawling network of 900 kilometers of pipes, ensuring that residents enjoy warm homes year-round.

Even during the summer months, when hot showers are still in high demand, the power plant must remain operational. The system boasts an energy efficiency that is nearly double that of traditional power plants, utilizing up to 90% of the energy input.

However, the winter months can present challenges, with the power plant sometimes struggling to meet the increased demand for heating. This shortfall can necessitate the use of additional fossil fuel-powered boilers, resulting in carbon emissions. To address this issue, Malarenergi identified the potential of the underground caverns as a heat storage solution.

These caverns, once used for oil storage, were decommissioned in 1985. After years of inactivity, the energy company began a project in 2019 to clean and retrofit the cavern system for its new purpose. This involved removing residual oil and installing piping to facilitate the storage of hot water, a process that took five months and cost approximately $15.5 million.

Once operational, the caverns can hold an impressive volume of water, equivalent to 100 Olympic-sized swimming pools. The insulated nature of the bedrock ensures that heat loss is minimal, allowing the stored water to retain its temperature efficiently, much like a thermos keeps coffee warm.

During summer, excess heat generated can be stored in the caverns, which can then be utilized during the colder months, potentially providing heat to the city for up to two weeks, depending on external temperatures. This innovative approach not only conserves energy but also significantly reduces carbon emissions by about 1,600 tons annually, equivalent to the emissions produced by approximately 460 individuals.

The success of this project has sparked interest in similar initiatives across other regions. While not all cities may have access to abandoned oil storage facilities, other methods for creating heat storage systems exist. For instance, the Varanto project in Finland aims to develop a cavern system capable of storing even larger volumes of heated water.

In Nordic countries like Sweden, Finland, and Norway, the geological conditions are favorable for constructing such cavernous storage systems. However, alternative approaches may be necessary in areas with less stable bedrock. Techniques such as drilling wells to heat natural underground layers or constructing large pits lined with waterproof materials to store hot water are being explored in various locations, including Denmark and the Netherlands.

Ultimately, the Vasteras project exemplifies a forward-thinking approach to urban heating, demonstrating how repurposing existing infrastructure can lead to sustainable energy solutions. As cities worldwide grapple with the challenges of climate change and energy efficiency, the lessons learned from this innovative underground heating system may inspire similar efforts elsewhere.