Comment: With many homes still reliant on fossil fuel heating systems, Johan du Plessis, CEO of Tepeo, a British clean tech company, looks at how smart heat batteries will help accelerate the transition to low-carbon heat while keeping the electricity grid in balance.
According to a report published by the National Audit Office earlier this year, heating the UK’s 28 million homes accounted for 18% of all UK greenhouse gas emissions in 2021.
The main source of these emissions is from burning natural gas to heat homes. A low-carbon alternative to home heating presents itself in the form of domestic thermal energy storage (TES) or heat batteries.
Electric storage heating technology such as night storage heaters, which store heat during off-peak hours and then release it gradually during peak hours the following day, isn’t a new concept.
Yet, despite having been around since the early 1960s, it’s yet to become mainstream.
A primary limitation of night storage heaters is that they aren’t installed with wet heating systems (radiators or underfloor heating), which are currently used in approximately 23 million UK homes.
Switching to this type of storage heating would entail replacing all wet radiators with night storage heaters, which would have a huge carbon footprint – not to mention the cost and disruption for homeowners.
From storage heaters to heat batteries
Research and development have more recently focused on optimising storage materials and product design while integrating smart capabilities. The outcome of this effort has been the modern heat battery boiler.
Heat batteries and night storage heaters are based on similar principles. The main difference is that heat batteries are specifically designed to integrate into existing wet heating systems. With this technology, households can eliminate their gas boilers – and the associated greenhouse gas emissions – without replacing radiators.
As mains gas is the only heating source for over two-thirds of UK households, switching to heat batteries can be transformational.
However, not all heat batteries are created equal. While some are predominantly aimed at water heating, others are specifically designed for space heating.
Different materials, different applications
Some heat batteries use phase-change materials to store thermal energy. These materials have minimal heat loss and are typically used in hot water production to replace traditional domestic water cylinders. Due to their lower energy density, they are typically unsuitable for space heating.
By contrast, magnetite materials display two to three times the energy density of phase-change materials. These heat batteries can reach temperatures as high as 800 degrees while being fully insulated and enclosed for complete user safety. Reducing size and footprint is essential to making TES suitable for homes where space comes at a premium.
How can heat batteries complement heat pumps?
Heat pumps have established themselves as the go-to low-carbon heating technology, thanks to government subsidies. Widespread adoption of these heating systems remains critical to achieving net zero. However, there are limitations to how many heat pumps can be installed.
Firstly, not all UK homes can be fitted with heat pumps. Around 20% of the housing stock, including millions of traditional terraced houses, is unsuitable for a heat pump due to insufficient outdoor space, but this percentage may be even higher.
A 2024 study from the University of Warwick found that, although around half of UK homes were “eligible” for heat pump installation subsidies, only 11% of homes were likely to be “heat pump-ready”.
Costs to upgrade pipework and radiators, lengthy installations and planning permissions are other barriers to adoption.
Secondly, the International Energy Agency warns that “without improving efficiency in parallel” heat pumps can nearly triple their peak demand during winter. Therefore, building retrofits, combined with “careful grid planning and demand‐side management”, will be critical to mitigating this surge in demand.
Highly flexible technologies such as heat batteries can complement heat pumps in two ways. They can be deployed in houses unsuitable for heat pumps, making decarbonised heating accessible to all, and they can ease pressure on the grid by shifting energy demand away from peak times.
