KTH Energy Storage Research Infrastructure (KTH ESRI)


Thermal energy storage




Thermal energy storage


KTH Royal Institute of Technology

Contact Person 1:

Justin NingWei Chiu

Contact Person 2:

Saman Nimali Gunasekara



TRL Level:


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KTH Energy Storage Research Infrastructure (KTH ESRI)

KTH Energy Storage Research Infrastructure (KTH ESRI)

KTH ESRI on material, component and system levels offer research added merits through the whole value chain in an international context. Almost all the facilities lie within KTH and Stockholm University premises in Stockholm. KTH coming with a number of successful contributions in world-class infrastructure sharing BRISK2 EUHorizon2020 (https://brisk2.eu/). KTH has the capacity in taking the role as the Work Package leader for transnational access of the infrastructure, owing to our many years’ experience in three Research Infrastructure (RI) projects.

1. TES- Materials Characterization Infrastructure

The KTH materials characterization infrastructure collection in Stockholm, Sweden is a unique assortment of thermal physical characterization means at the same institute’s location (lab). The collection includes Phase Equilibrium evaluation of PCM Blends, characterization of sensible heat material, measurements of cp, enthalpy with μDSC as well as T-history setup; thermal conductivity with TPS instrument; dynamic viscosity with Brookfield rotational viscometer DV-II Pro; density measurement with pycnometer.


The unique selling points of the installations are bulk scale PCMs characterization of using temperature-history facility (-35 to 160 °C, with up to 0.1 k/min very slow rates and samples of ~10 ml), micro-Differential scanning calorimetry facility (micro-DSC, ~-40 to 120 °C, allowing large samples (1 ml) than in a normal DSC); thermal conductivity using transient plane-source facility (TPS for ~-30 to 90 °C with the capability to go beyond 140 °C); viscometer facility (for ~5 to 80 °C but with potential to upgrade to rather high temperatures too) and density measurement facility at fixed temperatures. All infrastructure are located within a single premises allowing full range of testing.

The operating cost of the characterization setup amounts to 800€/experimental day. Excluding maintenance and internal use time, the equipment is available for international use up to 6 months a year. We have typical 1-3 international users per year on material testing infrastructure, e.g. Hokkaido University, Japan, 2019; Clauger Co, France 2019; and for I-TES Co, Italy, 2019.

2. Component Testing Infrastructure

The energy technology lab (EGI) at KTH has a number of installations for thermal energy storage component testing. They include PCM, TCM and high-temperature sensible TES prototypes. Each of the installations is of high quality with unique design attributes that link research to pilot scale operations.

2.1 Plugin SHTES and LHTES Installation

The installations are thermal performance of plug-in SHTES and LHTES 10 to 30 kWhth, -10 ℃ to 90 ℃, 0.15 to 5.0 m3/h testing capability. This includes one 200 L and one 300 L storage test setups with 1 m³ of hot water source buffer and 1 m³ of cold water sink buffer. The heat pump runs on nominal electric power load of 10 kW and a 21 kW resistive heater is connected to the circulation loop. The 200 L storage setup is capable of accommodating packed bed encapsulated thermal energy storage and the 300 L setup can accommodate bulk PCM. The heat transfer is performed in direct contact fashion where spiral coil heat exchanger is placed in the 300 L test setup. With current water running as heat transfer fluid under 1 bar, the operating range for the current setup is from above 0 °C to below 100 °C. Modulated charge/discharge simulating ambient conditions and real user behaviors can be tested. (see Figure 2 a.).


2.2 Bench Scale Mobile LTES Installation

EGI has a bench-scale 60 L TES system (from the project Heat on Wheels) with certified 2 bar pressure resistance where the application conditions can be applied and characterized for various bulk PCMs and sensible heat storage mediums. The system is linked with 100L buffer bath controlled by duo vapor compression driven temperature bath 5.2 kW heating and 1.4 kW cooling for 5 °C temperature difference. The operating range lies in -50 °C to 200 °C depending on the heat transfer fluid. (see Figure 2 b.)


2.3 Bench Scale Ammonia-Metal Halide TCS Installation

We have a bench-scale TCS rig with 2 identical reactors (each of ~0.77 kWh storage capacity) simultaneously operated to respectively store and release heat, at 25-120 °C, 1-15 bar operation. The system is designed for reaction between metal halides and NH3. The metal halide can be impregnated into thermal conductivity enhancement matrices. The heat exchanger inside the reactor comprises perforated fins ad vertical tubes made of Al. (see Figure 2 c.)


2.4 High Temperature STES Installation

Ceramic or rock packed bed high-temperature TES testing rig are used for testing the performances of various solid thermal storage mediums, such as rock, concrete, ceramics. Potential application could be concentrating solar power, industrial heat recovery and Carnot battery. The radial flow packed bed design has the unique advantage of

  • Limited thermal losses

  • Limited pressure drop

  • Lower thermomechanical stresses

2.5 Additional Heat Transfer Testing Installations

Additional installations for component testing include heat transfer aspects in encased storage with fins, with mini channel heat exchanger, packed bed cold thermal storage and submerged finned pipe heat exchanger.

2.6 Operation and Transnational Visits

The operating cost of the infrastructure amounts to an average 800€/experimental day. Excluding maintenance and internal use time, the equipment is available for international use up to 6 months a year. We have typical 3 international users per year on component testing infrastructure. Eg. DTU, Denmark, 2020. UNIGE, Italy, 2020. Ansaldo Eneriga, Italy, 2020.

3. Application Scale System Infrastructure

KTH EGI is enlisted with a number of TES systems testing infrastructure. These infrastructure accommodate testing in real applications with high technology readiness level (TRL) with eminent visits from Swedish Ministry of Higher Education and his Majesty the King of Sweden.

3.1 Concentrating Solar Power (CSP) Installation with TES

Concentrating Solar Power (CSP) pilot testing setup with

  • Fresnel lens based high flux solar simulator

  • Micro gas turbine system

  • Stirling engine

  • Packed bed high-temperature thermal storage system (as listed in component infrastructure)

  • Jet impingement heat transfer rig

The available instruments are DIAS PYROVIEW 512N short wavelength Infrared camera, which can measure temperature in the range of 600-1500 ºC, FLIR SC5000 middle wavelength Infrared camera; High-speed data acquisition systems for transient measurements (pressure, strain, among others); Optris Pyrometers, which can measure the temperature up to1600 ºC. A large variety of aerodynamic probes; Gas sampling probes rated for temperatures up to 1250 ºC; Gas analyzing systems; Multi-directional hot wire anemometer; Hot film equipment; Multi-channel high precision pressure and temperature measurement systems; QNix 8500 high precision coating thickness meter; Sunstone Orion 100c micro-welder.

3.2 Solar PV/Thermal Hybrid with Heat Pump and ES Facility

EGI is building energy storage testing with solar PV/thermal hybrid with heat pump (see Figure 7). The two primary functions are thermal characterization of PV/thermal (PVT) collectors and system performance of a PVT-sourced heat pump. The installations included in this infrastructure are:

a Davis weather station; PVT arrays equipment for 14 modules; thermal storage of 300L with two independent heat exchangers; the PVT circuits are commissioned with a water/propylene glycol mix (40/60) and the tanks have fresh water; the hot water tank of 200L in size; the heat pump, inverter controlled model from Thermia capable of generating 10 kW of heat.

Recent scientific achievements encompass:

  • N. Sommerfeldt and H. Madani Larijani, "In-depth techno-economic analysis of PV/Thermal plus ground source heat pump systems for multi-family houses in a heating dominated climate," Solar Energy, vol. 190, s. 44-62, 2019.

3.3 Climatic Chambers Facility

KTH EGI is also equipped with climate chambers. They are four full room sized climatic chambers and one 1 m³ chamber for various thermal and ambient testing. Three allow -35 °C to +40 °C testing and one is capable of -40°C to +180°C. These chambers are being upgraded to use low GWP refrigerants.

3.4 Full Scale UTES (ATES and BTES) Facility

KTH EGI has since several years been responsible for monitoring a borehole underground energy storage (BTES) at Stockholm University The system consists of 130 boreholes, 230 m deep with 2.5 MW cooling capacity and 1.4 MW heating capacity (see Figure 5) Distributed temperature sensing using Laser and optical fibers (Raman-based, uncertainty, calibration) is installed in several boreholes allowing detailed monitoring of the system.

The same type of distributed temperature sensor system is installed in an aquifer TES (ATES) connected to two office buildings. The ATES is located in an esker in the north part of Stockholm.

Akademiska Hus BTES at Stockholm

3.5 Full Scale Live-in Lab Facility

KTH Live-in-Lab (LiL) is a student dormitory with Full scale testbeds, including everything from systems (BMS, heat pumps, boreholes, waste heat exchangers, PVs etc.) to building operators (13 boreholes) and users (310 students). The installations include building automation and ventilation to user experience and physical layout of co-living units. 4 students dormitory rooms are under voluntary anonymous monitoring year round with worldwide students.