Monitoring Performance Of Large-Scale Heat Storages For District Heating In Denmark.pdf

These storages, two pit thermal energy storages (PTES) and one pilot borehole thermal energy storage (BTES), allow for high solar fractions by storing solar heat from summer for use during winter heating seasons.

Key Findings:

High Solar Fraction: The 75,000 m³ PTES in Marstal achieved a calculated solar fraction of 41%.
Seasonal Operation: All three storages exhibit clear seasonal charging (summer) and discharging (winter) patterns.
Efficient Performance:
The Marstal PTES demonstrated a storage efficiency of 62% in 2015, slightly exceeding design specifications.
Storage cycle numbers ranged from 0.8 to 1, indicating efficient use of the heat capacity.
Temperature Stratification: Significant thermal stratification (temperature differences between top and bottom) was observed during spring and autumn, reaching up to 30 K.

Monitoring Data Analysis:

The paper provides detailed analysis for the Marstal PTES, including:

Energy Balance: 7813 MWh of solar heat were charged into the storage in 2015, with 5435 MWh discharged to the district heating network.
Thermal Losses: Total thermal losses amounted to 2946 MWh in 2015, primarily transferred to the surrounding ground and ambient air.
Temperature Development: Temperature sensors placed throughout the storage volume and surrounding ground documented seasonal temperature fluctuations, with minimum temperatures around 20°C and maximum temperatures exceeding 80°C.

Long-Term Observations:

85 temperature sensors installed inside and around the storages allow for ongoing monitoring of:

Long-term temperature trends in the storage volume itself.
Heat transfer to and from the surrounding ground.
The impact of seasonal variations on thermal performance.

This comprehensive analysis provides valuable insights into the performance, efficiency, and potential of large-scale UTES for sustainable district heating systems.