High-Density, Low-Hysteresis Thermal Storage Using Hydrated Salts in Surface-Functionalized Hydrogels

Lead Performer: University of Illinois at Urbana-Champaign – Champaign, IL
Partner: AO Smith – Milwaukee, WI
DOE Total Funding: $1,889,905
DOE Funding: $1,511,924
Cost Share: $377,981
Project Term: October 1, 2021 – September 30, 2023
Funding Type: BENEFIT 2020 Funding Opportunity Announcement

Project Objective

Thermal storage can potentially enable grid-integrated peak load shaving by utilizing energy production in off-peak hours. Several scenarios for using thermal storage in building applications are under investigation but are primarily restricted to water/ice as the storage material in the near-term. Beyond water/ice, a candidate material for cost-effective storage that combines higher storage density with high thermal conductivity, low hysteresis loss and low corrosion potential is still unclear. Nearly 70 years ago, Glauber’s salt (Na2SO4·10H2O) was identified as a leading phase change material (PCM) in terms of its heat storage density (~2x paraffin), thermal conductivity (~1W/m·K), safety, availability and cost (~$100/ton). However, the complex issues of supercooling and incongruent melting due to phase separation have prevented realization of the promise. The addition of thickeners and nucleating agents such as borax solve these issues but only over few cycles.

The goal of the project is to (a) resolve the above long-standing challenges with the salt through a unique materials approach, (b) evaluate the system performance in a water heater test bed, in collaboration with AO Smith, and (c) explore its commercial potential in water heater and other energy applications. In the proposed work, a multidisciplinary team from UIUC and AO Smith will design and synthesize the material, characterize and model phase change and transport phenomena, and finally optimize and evaluate the material for the systems level. The project team combines expertise in thermal transport, materials chemistry, with performance evaluation and optimization of thermal energy systems.

AO Smith, the largest manufacturer of water heaters and boilers in North America, is highly interested in the Glauber’s salt PCM technology being developed in this project. Connected or smart water heaters, paired with low-cost thermal storage technologies like this PCM, will be essential for utilities, aggregators, and the nation, to get the most out of grid flexibility. This technology, with its high storage density and low cost, could be especially impactful in the retrofit market by reducing cost and space barriers to thermal storage adoption. AO Smith will assist with technology demonstration and provide guidance on market implementation.

Project Impact

The development of cost-effective and resilient thermal energy storage is critical for decarbonization of the building stock and the energy system. Based on U.S. building energy consumption, building equipment responsible for air heating/cooling and water heating will require 4.9 and 1.6 Quads respectively, combining the residential and commercial sector. Considering a third as peak load of which half can be shifted, about 1 Quad of energy can be shifted. With average electricity prices at roughly 15 cents per kWh-8 hours for peak load and 5 cents per kWh-16 hours for off peak – and assuming that around 50% energy is used by above-mentioned applications, the payback period for the TES on average is then around 2.25 years for residential and 3.75-4.5 years for the commercial sector.

Contacts

DOE Technology Manager: Sven Mumme
Lead Performer: Sanjiv Sinha, University of Illinois

Related Publications

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