02 March 2026
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Christian Engelke, Owner and Consultant at EngC Consulting, explores how ice energy storage works and why it offers a compelling alternative to boreholes and ground collectors.
Ground Source Heat Pumps (GSHPs) have long been celebrated for their efficiency and ability to deliver both heating and passive/ active cooling. Yet in the UK, installations have slowed in recent years - with 2025 f igures suggesting fewer than 800 registered systems under 45 kW, the lowest since 2010. High upfront costs, drilling requirements, and lengthy planning processes have all contributed to this slowdown.
But innovation is on the horizon. Ice energy storage offers a fresh approach that could make GSHPs more accessible, quicker to install, and easier to integrate into both residential and commercial projects. By harnessing the latent heat released when water freezes, this technology provides a compact, sustainable alternative to boreholes and ground collectors - and could help reposition GSHPs as a competitive choice in the UK’s energy transition.
Key benefits of ice energy storage
- No drilling required – avoids costly boreholes and ground collectors
- Compact installation – prefabricated tanks fit into limited land space
- Fast setup – installation time reduced by up to 50%
- Dual function – provides heating and passive cooling without compressor use
- High efficiency – annual performance factors (SCOP) between 4 and 5
- Sustainable – uses free environmental energy, reducing CO₂ emissions
- Durable – actively regenerated, maintaining performance for decades
- Applications – suitable for single-family homes, schools, offices, logistics halls, and data centres
The principle of ice energy storage
An ice energy storage system is a sustainable and economical solution for supplying heating and cooling to buildings. It stores environmental energy at a low temperature level without loss and makes it usable for a heat pump at any time.
Why low temperatures are ideal?
In the ground, temperatures in the UK are between about 10 and 12 °C all year round – regardless of the season. This geothermal heat flows into the uninsulated ice storage tank and either brings in additional energy or cools the storage tank in summer. 10 to 12 °C are ideal conditions for heating with a heat pump as well as for cooling buildings.
How the ice storage system works?
The ice storage tank is a large water tank that is installed in the ground. It can be made of plastic (for volumes up to approx. 20,000 litres) or concrete structures (for larger systems of up to 1000m3). The heat pump extracts energy from the water in the storage tank via heat exchangers until it gradually freezes. This creates a special effect: crystallisation heat.
What is heat of crystallisation?
Heat of crystallisation is the energy released when water freezes. The special feature is that this energy is contained in the phase transition – i.e. exactly at the moment when water becomes solid (ice) from 0 °C to liquid 0 °C. This releases as much heat as would be necessary to heat water from 0 °C to about 80 °C. This large amount of energy is available to the heat pump without the need for additional environmental heat. The resulting ice is therefore a thermal waste product that is extremely valuable for heating operations.
Direct use or storage?
If energy is available in the environment – for example through air, sun, roof or façade collectors, waste heat or rainwater – it is either fed directly to the heat pump or stored in the ice storage tank.
Regeneration – recharge several times a year
An ice storage tank is regenerated several times over the course of the year, i.e. recharged with heat. Various environmental energy sources are used for this purpose:
1. Solar air absorbers that absorb solar heat directly from the ambient air
2. Energy fences that harness wind and solar energy on fence surfaces
3. Active roofs that combine rainwater retention, greening and energy generation
These sources provide heat even on cold winter days or in the transitional period and ensure that the storage system retains its full capacity for decades.
High efficiency – more free energy than electricity
A properly designed ice energy storage system achieves annual performance factors between 4 and 5. This means that for one kilowatt hour of electrical energy, the heat pump supplies an additional more than 4 kWh of free environmental heat. This ensures low operating costs and a very good climate balance.
Advantages over geothermal probes or horizontal collectors
Geothermal boreholes continuously extract heat from a limited volume of earth. Over time, the surrounding soil can cool down, reducing efficiency. An ice reservoir, by contrast, is actively regenerated and maintains full performance for decades – independent of geological conditions or permits for deep drilling.
Another advantage is the significantly smaller footprint required. A 10 kW GSHP system typically needs around 120 m² for boreholes, 300 m² for a horizontal collector loop, but only 19 m² if an ice store is used. This is less than a tenth of the space required compared to traditional ground extract solutions.
For larger commercial systems, the difference is even more striking. A 400 kW installation would require approximately 3,500 m² for boreholes (depending on ground conditions), 12,000 m² for a horizontal collector loop, yet just 320 m² for a single 500 m³ ice energy store.
Sustainable and economical
A properly designed ice energy storage system has a payback period of less than ten years. It uses free environmental energy, significantly reduces operating costs and avoids fossil fuels. The technology is durable and can be used for both heating and cooling.
The heart of the system: control and efficiency
The key components are the control technology. It ensures that the cheapest energy source is always used and that regeneration takes place optimally. With system efficiency monitoring, the system is permanently monitored, the operation is analysed and adapted to the actual consumption. This means that the system works with maximum efficiency at all times.
Future outlook
In Germany, companies such as Solar Eis and Kraftwerk Solutions have pioneered ice energy storage systems, providing valuable experience and technical input that can inform future UK projects. More than 1,000 systems are already in use in single-family homes. There are now more than 500 systems in commercial buildings – such as schools, office and administration buildings, logistics halls or data centres.
In the UK two residential systems have been realised over the last 7 years and the potential is there. For the residential market the key benefit is that it is simple to install. Premanufactured tank and other accessories make the installation quick and cost effective. Especially for new build or complete building renovations GSHP with ice energy store could be a real winner.
For commercial systems using a 400kW GSHP the installation of the ice energy storage from planning to commissioning takes only three months.
Conclusion
Ice energy storage combines a simple physical principle with modern system design to deliver reliable heating and cooling. By regenerating itself through environmental sources, it avoids the long term efficiency losses of conventional ground probes, while offering installers and building owners a faster, more flexible solution. With hundreds of systems already operating across Europe - from single family homes to schools and logistics centres - the technology has proven its durability and efficiency. For the UK, the opportunity is clear: ice energy storage could help overcome barriers to GSHP adoption, reduce costs, and support the drive toward lowcarbon heating. The time is right to explore this innovation more widely and bring its benefits to both residential and commercial markets.
www.engcconsulting.co.uk
Source
Images and input for the article have been provided by Solar Eis www.solareis.com and Kraftwerk Solutions www.kraftwerkernergiezukunft.de. Both companies have pioneered innovative ice energy storage systems in Europe, and their expertise is helping to shape future projects and applications in the UK.
