Next generation thermal energy storage for low carbon heating and reduced fuel poverty

In brief:

• The Pulham group’s salt hydrate phase-change materials (PCMs) are the first to retain their high energy density and stability over more than 40,000 cycles, making commercial use possible.

• Development of the PCMs drew on the group’s decades of expertise in understanding crystallisation behaviour, and use of in situ X-ray powder diffraction experiments at the Diamond Light Source to interrogate, in real time, the structural and chemical behaviour of the new PCM formulations during repeated heating and cooling cycles.

• Sunamp’s Thermino heat batteries, with PCMs developed by the Pulham group at their core, provide high efficiency heat storage and maximise use of locally generated renewable energy and off-peak electricity, therefore reducing carbon emissions. 

• In partnership with social housing providers across the UK, Sunamp heat batteries have increased comfort and saved residents money, demonstrating a genuine solution to help combat fuel poverty.

• Ongoing close collaboration with Sunamp is extending the technology into industry and automotive applications, and provides valuable opportunities for School of Chemistry students at both undergraduate and postgraduate levels.

Read more below.

The challenge: Heat storage for net zero

Globally, heat accounts for nearly half of all energy consumption and 40% of energy-related carbon dioxide emissions. In order to make better use of renewable energy in this crucial sector, improved thermal energy storage is key. Traditional heat-storage materials which have been in use for centuries, such as hot bricks and water, lose huge amounts of heat and take up lots of space. Phase-change materials (PCMs) which absorb heat on melting and release it on freezing can provide a chemistry-based solution.

Powerful partnership: School of Chemistry collaboration with Sunamp Ltd

Sunamp Ltd set out to develop heat battery technology that could store energy from any source as heat and release it on demand to provide space heating and hot water in homes. However, the company quickly found that available salt hydrate PCMs, which they hoped would form the basis of heat storage in their technology, failed after only a few heating and cooling cycles. Seeking research input to tackle this problem, Sunamp was introduced via Interface to Professor Colin Pulham, who brought years of expertise in crystallisation science. 

The chemistry solution: New phase-change materials for reliable and long-lasting heat storage

Research by Prof Pulham and his group developed polymer-based additives that act as crystal-habit modifiers to prevent incongruent melting – the phenomenon that was causing the existing phase change material to degrade instead of reproducibly changing phase. The team also made use of longstanding links to access use of in situ X-ray powder diffraction experiments at the Diamond Light Source. There, they were able to interrogate, in real time, the structural and chemical behaviour of their new PCM formulations during repeated temperature cycling. The observations confirmed complete inhibition of incongruent melting over a wide range of conditions.

The new PCM formulations retain their high energy density and stability over more than 40,000 cycles and have set the international standard for cycling stability through the RAL Quality Mark, gaining the first and only A Grade RAL Certification for stability over 10,000 cycles.

Real-world impact: Sunamp success, carbon savings and reduced fuel poverty

With these new PCM formulations at their core, Sunamp have brought to market the world’s first commercially viable residential thermal energy storage systems. Their Thermino range of heat batteries are highly efficient and maximise use of locally generated renewable energy and off-peak electricity, thereby reducing use of fossil energy sources and resulting carbon emissions. Simply by reducing heat loss compared to traditional hot water cylinders, Sunamp heat batteries installed by 2021 had reduced CO₂ emissions by 4.6 kilotonnes. Heat batteries also save households money, with proven savings of up to 75% on utility bills.

Installations in social housing across central Scotland have confirmed the financial savings and increase in comfort for residents and demonstrated the impact that heat batteries can have in tackling fuel poverty. Resident testimony confirms the improvement to their quality of life:

"It saves a lot of money, put it that way. You’re getting your hot water for free. Before that, this house was a really cold, cold house…It makes a lovely difference.”

Sunamp is going from strength to strength as heat battery sales ramp up across the UK and beyond. Their technology, supported by new PCM formulations developed by the Pulham group, is quickly being extended into new applications to provide emissions savings and environmental benefits – in the automotive, commercial and industrial sectors, and for domestic cooling.

Continuing collaboration: New chemistry solutions for Sunamp challenges

Other School of Chemistry colleagues are now bringing their capabilities and expertise to tackle Sunamp’s challenges. This includes: ongoing computational research targeting increased understanding of nucleation processes and the development of new nucleators (Morrison group); development of new high-temperature, solid-solid PCMs (Kirk group); and research into barocaloric materials that could potentially replace hydrofluorocarbons as refrigerants in cooling systems (Hobday group). 

Related outputs

1. D.E. Oliver, A.J. Bissell, X. Liu, C.C. Tang and C.R. Pulham, “Crystallisation studies of sodium acetate trihydrate – suppression of incongruent melting and sub-cooling to produce a reliable, high-performance phase-change material”, CrystEngComm, 2021, 23, 700-706. DOI: 10.1039/D0CE01454K.
2. A.J. Bissell, D. Oliver, C.R. Pulham, E.J. Goddard, G. Odling and K. Fisher, “Metal Nitrate Based Compositions For Use as Phase Change Materials”, Granted patent WO 2020/074883 A1, 2020.

Find out more

Sunamp website