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Mind the Temperature Gap: The Role of Pit Thermal Energy Storage in a Sector-Coupled Energy System with High-Temperature District Heating

Caspar Schauß, Amos Schledorn, Tom Kähler, Kristina Schumacher, Mathias Ammon, Tom Brown

TL;DR

PTES offers large-scale thermal flexibility for district heating, but prior large-scale models often ignore the temperature gap between storage and the network. Using PyPSA-DE with explicit forward/return temperatures and temperature-dependent boosting, the study analyzes a net-zero 2045 German scenario, comparing PTES with and without temperature constraints and boosting. The results show PTES reduces annual system costs by $135$–$345$ million and lowers district heating prices by up to $4$ per MWh, with gains depending on network temperatures and boosting technology; idealized, temperature-agnostic cases overstate benefits. The findings highlight PTES as a valuable tool for leveraging low-price electricity, while underscoring the need to account for temperature constraints in planning and policy to maximize sector coupling benefits.

Abstract

Pit thermal energy storage (PTES) provides large-scale thermal storage capacity in district heating systems, supporting flexibility on both daily and seasonal scales. Most existing large-scale energy system studies on PTES do not account for temperature differences between storage and the network. Neglecting these temperature differences can result in less efficient PTES integration, since they affect usable energy capacity and introduce additional costs for discharge requiring temperature boosting. To explore how temperature constraints shape the system-level value of PTES, we use PyPSA-DE, an open-source sector-coupled capacity expansion model of Germany and neighboring countries in a scenario with net zero carbon emissions for 2045. To isolate PTES effects, we examine counterfactual scenarios: systems without PTES, idealized systems with PTES but without temperature constraints, and feasible systems with boosting. We find that PTES reduces German annual system costs by 135-345 M EUR per year relative to systems relying solely on tank storage. Lowering maximum forward temperatures from 124 degrees C to 95 degrees C decreases district heating costs by 7.6 percent without PTES and 10 percent with PTES. Idealized scenarios without temperature constraints yield district heating cost savings of up to 15 percent, indicating that temperature-agnostic modeling overestimates PTES benefits. PTES provides economic value even under current high temperatures, though temperature misalignment limits its contribution during peak demand due to the need for boosting. The findings highlight the role of PTES in leveraging low-price electricity through electrified heating while emphasizing the importance of explicitly accounting for temperature constraints.

Mind the Temperature Gap: The Role of Pit Thermal Energy Storage in a Sector-Coupled Energy System with High-Temperature District Heating

TL;DR

PTES offers large-scale thermal flexibility for district heating, but prior large-scale models often ignore the temperature gap between storage and the network. Using PyPSA-DE with explicit forward/return temperatures and temperature-dependent boosting, the study analyzes a net-zero 2045 German scenario, comparing PTES with and without temperature constraints and boosting. The results show PTES reduces annual system costs by – million and lowers district heating prices by up to per MWh, with gains depending on network temperatures and boosting technology; idealized, temperature-agnostic cases overstate benefits. The findings highlight PTES as a valuable tool for leveraging low-price electricity, while underscoring the need to account for temperature constraints in planning and policy to maximize sector coupling benefits.

Abstract

Pit thermal energy storage (PTES) provides large-scale thermal storage capacity in district heating systems, supporting flexibility on both daily and seasonal scales. Most existing large-scale energy system studies on PTES do not account for temperature differences between storage and the network. Neglecting these temperature differences can result in less efficient PTES integration, since they affect usable energy capacity and introduce additional costs for discharge requiring temperature boosting. To explore how temperature constraints shape the system-level value of PTES, we use PyPSA-DE, an open-source sector-coupled capacity expansion model of Germany and neighboring countries in a scenario with net zero carbon emissions for 2045. To isolate PTES effects, we examine counterfactual scenarios: systems without PTES, idealized systems with PTES but without temperature constraints, and feasible systems with boosting. We find that PTES reduces German annual system costs by 135-345 M EUR per year relative to systems relying solely on tank storage. Lowering maximum forward temperatures from 124 degrees C to 95 degrees C decreases district heating costs by 7.6 percent without PTES and 10 percent with PTES. Idealized scenarios without temperature constraints yield district heating cost savings of up to 15 percent, indicating that temperature-agnostic modeling overestimates PTES benefits. PTES provides economic value even under current high temperatures, though temperature misalignment limits its contribution during peak demand due to the need for boosting. The findings highlight the role of PTES in leveraging low-price electricity through electrified heating while emphasizing the importance of explicitly accounting for temperature constraints.
Paper Structure (26 sections, 6 equations, 14 figures, 1 table)

This paper contains 26 sections, 6 equations, 14 figures, 1 table.

Table of Contents

  1. Introduction
  2. Methods
  3. PyPSA-DE
  4. District heating in PyPSA-DE
  5. Spatial resolution
  6. District heat demand
  7. District heat supply
  8. Large thermal energy storage
  9. Temperature modelling
  10. PTES model
  11. Energetic storage capacity
  12. Boosting via resistive heaters
  13. Boosting via heat pumps
  14. Scenarios
  15. Results
  16. ...and 11 more sections

Figures (14)

  • Figure S1: Common network temperatures in largest German district heating systems pelda_district_2021 and typical PTES temperature ranges danishenergyagencyTechnologyDataEnergy2025 at implemented Danish sites. The temperature gaps indicate the need for temperature boosting when discharging PTES into legacy networks and considering network return temperatures for an accurate estimation of usable energy capacity.
  • Figure S2: Schematic integration of PTES into district heating systems with (a) resistive booster and (b) booster heat pump. Potential mass flows (arrows) and corresponding temperatures (color-coded) are shown for a state where $T^{\text{fwd}}_t > T^{\text{top}}$.
  • Figure S3: District heating network temperatures, heat pump COPs and boosting ratios for resistive heaters and heat pumps exemplarily in the district heating system of Rostock for MidST temperature levels, i.e. 108.8/52.7° C.
  • Figure S4: Spatially aggregated district heating balances in Germany for two example weeks in January and July 2045 at MidST . The top panel shows results without PTES, the middle panel with PTES and free boosting (unphysical scenario for reference), and the bottom panel with PTES and resistive boosting. The secondary y-axis shows the average electricity price and the color of the price curve the corresponding average forward temperature in district heating networks.
  • Figure S5: Temporally aggregated district heating balances in Germany for 40 largest systems at MidST in 2045. The left panel shows results without PTES and the right panel with PTES boosted by resistive heaters. The secondary x-axes show the system-specific and average annual district heating demands (left) and the system-specific and average savings in district heating prices (right). On the bottom the aggregated supply mix is shown including the base regions.
  • ...and 9 more figures