Assessing the Value of Coupling Thermal Energy Storage with Air-Source Heat Pumps for Residential Space Heating in U.S. Cities

TL;DR

This study evaluates the economic and energy benefits of integrating salt hydrate thermal energy storage with air-source heat pumps for residential heating in U.S. cities, identifying SrBr2 as the most promising material.

Contribution

It provides the first techno-economic analysis of salt hydrate TES materials coupled with ASHPs for residential heating, using a novel modeling approach across multiple U.S. cities.

Findings

Salt hydrate TES can reduce household electricity costs by up to 8%.

SrBr2 is identified as the most promising salt hydrate due to high energy density.

Break-even costs for SrBr2 TES are within DOE targets.

Abstract

Widespread air source heat pump (ASHP) adoption faces several challenges that on-site thermal energy storage (TES), particularly thermochemical salt hydrate TES, can mitigate. No techno-economic analyses for salt-hydrate-based TES in residential applications exist. We quantify the residential space heating value of four salt hydrate TES materials - MgSO4, MgCl2, K2CO3, and SrBr2 - coupled with ASHPs across 4,800 representative households in 12 U.S. cities by embedding salt-hydrate-specific Ragone plots into a techno-economic model of coupled ASHP-TES operations. In Detroit, salt hydrate TES is projected to reduce household annual electricity costs by up to $\$$241 (8$\%$). Cost savings from TES can differ by over an order of magnitude between households and salt hydrates. We identify the most promising salt in this study, SrBr2, due to its high energy density and low humidification parasitic load. Break-even capital costs of SrBr2-based TES range from $\$$13/kWh to $\$$17/kWh, making it the only salt hydrate studied to reach and exceed the U.S. Department of Energy's $\$$15/kWh TES cost target. Sensitivities highlight the importance of variable TES sizing and efficiency losses in the value of TES.