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

TL;DR

This study evaluates how pit thermal energy storage (PTES) can enhance sector-coupled energy systems with high-temperature district heating, emphasizing the importance of temperature constraints for accurate system modeling and economic assessment.

Contribution

It introduces a detailed modeling approach that incorporates temperature differences in PTES, revealing their impact on system costs and the underestimated benefits of PTES.

Findings

PTES reduces system costs by up to 345 million EUR annually.

Lowering maximum temperatures decreases district heating costs significantly.

Ignoring temperature constraints overestimates PTES 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.