TERMISK ENERGILAGRING I LÅGTEMPERERADE FJÄRRVÄRMESYSTEM : Jämförelse av olika värmelagringslösningar för lågtempererade fjärrvärme i Sverige

Sammanfattning

Purpose: The purpose of this study was to compare different thermal energy storage technologies for low-temperature district heating systems under Swedish conditions. The study focused on three storage technologies accumulator tanks, phase change materials (PCM), and borehole thermal energy storage (BTES). The comparison was based on storage capacity, heat losses, efficiency, storage volume, and economic performance. Method: The study was carried out using theoretical calculations and comparative analysis based on literature data and thermodynamic equations. All storage systems were dimensioned for the same storage capacity of 100 MWh and evaluated with a storage period of one month in order to create comparable conditions. Heat losses, efficiency, storage volume, investment costs, operation and maintenance costs, and costs related to energy losses were calculated and compared. Results: The results showed that BTES had the lowest heat losses and the highest efficiency, with approximately 95.92% remaining energy after one month of storage. PCM systems showed relatively low heat losses and high energy density, making them suitable for compact and temperature-stable energy storage. Accumulator tanks had the lowest investment cost and the simplest technical design but also the highest heat losses during long-term storage. The economic analysis showed that PCM systems had the highest investment and maintenance costs, while BTES systems required high initial investments but lower long-term energy loss costs. Conclusions: The study concludes that no thermal energy storage technology is optimal for all district heating systems. Accumulator tanks are more suitable for short-term storage and operational balancing, PCM systems are suitable for compact and temperature-stable storage, and BTES systems are the more suitable for long- term and large-scale seasonal storage under Swedish conditions. Thermal energy storage can contribute to improved energy efficiency, increased flexibility, and better integration of renewable energy sources in future district heating systems.