Thermo-physical Characterisation of Solid Media and Insulation for Solid-Media Thermal Energy Storage (SMTES) for GeoSUSTAIN project

Background

The GeoSUSTAIN project (Sustainable Medium-Depth Geothermal Solutions with Solid Media Thermal Energy Storage for H/C) develops an underground solid-media thermal energy storage (SMTES) concept, where excavation materials or drill cuttings act as the storage medium, combined with high-temperature insulation. SMTES is intended to store heat at around 80–110 °C for industrial and district energy use. The performance and design of such systems depend critically on the thermo-physical properties of the solid media and surrounding insulation (thermal conductivity, heat capacity, density, and their dependence on temperature, moisture and compaction). At present, data for real excavation and insulation materials under these conditions are scarce. Underground TES is well established in the forms of borehole, aquifer and water-filled pit/tank storage, with documented performance at low–medium temperatures for district heating and building applications. In contrast, high-temperature solid-media TES is less mature but attractive due to potentially higher energy density, low material cost, and the possibility to use waste or recycled granular materials. Experimental and modelling studies show that heat exchanger design (e.g. tube layouts, air vs. liquid heat transfer fluids, flow regime, and charging/discharging strategies) strongly influences charge/discharge rates and thermal stratification in solid beds. A key challenge for scaling up SMTES from lab to pilot and full-scale is to preserve good heat transfer while controlling thermal losses and mechanical stability; this requires reliable thermo-physical property data as input to design and upscaling models.

Aim

The aim of the thesis is to experimentally characterise the thermo-physical properties of selected solid storage materials and insulation candidates for SMTES and to provide property data for GeoSUSTAIN modelling and design, including upscaling studies.

Research Questions

How do thermal conductivity, volumetric heat capacity and other properties of excavation materials and drill cuttings vary with temperature (20–110 °C), moisture content and compaction?

How do glass foam aggregate and at least one alternative insulation perform thermally under SMTES-relevant temperatures and mechanical loading?

What storage energy density (kWh/m³) and indicative material rankings follow from the measurements, and how can these support heat-exchanger design and scaling-up of SMTES?

Methodology

A first task is a focused literature review on (i) underground TES concepts and performance, (ii) heat-exchanger design for solid-media TES/SMTES, and (iii) methodologies for scaling up TES from lab to pilot and full scale. Laboratory tests will then be carried out on representative solid media (e.g. excavation sand, drill cuttings) and insulation materials (e.g. glass foam aggregate) using the developed test rig. Basic physical properties (density, porosity, moisture content) will be measured, followed by thermal conductivity and heat capacity tests over the relevant temperature range, including limited thermal cycling. Results will be analysed to derive simple correlations and energy-density estimates and will be delivered in formats suitable for use in GeoSUSTAIN numerical simulations of SMTES heat-exchanger design and scale-up.

Expected Outcomes

• Experimental setup and methodology

• Thermo-physical property datasets and correlations

• Material benchmarking and ranking

• SMTES heat-exchanger design inputs

• Property inputs for scale-up models

• MSc thesis report + presentation

• Contribution of findings to the GeoSUSTAIN project and potential scientific publications

Duration

The project should start in Jan-Feb 2026 at the latest, with a duration of up to 6 months.

Location

KTH, Department of Energy Technology, Heat and Power Division.

Main Supervisor

Examiner