With over 160 projects, updates and reports on heat pumps so far, it is fair to say at Nesta we talk about heat pumps a fair bit.

Heat pumps are a proven technology that produce heat at more than three times the efficiency of a gas boiler. As such, they are an important part of the movement towards net zero. However, they are not the only heat technology available.

There are 29 million homes in the UK, ranging from small modern flats to ageing terraced houses. This diversity means we need a range of solutions to suit different spaces and price points in order to stop using fossil fuels to heat our homes.

We’ve profiled some of the emerging technologies that could join heat pumps as part of a low-carbon heating revolution, now or in the very near future.

Heat batteries or thermal storage products can be “charged” with heat. The heat is stored efficiently to minimise heat loss and is then “discharged” later. The advantage of storing heat is that battery devices can be charged during times of surplus energy (from home solar or wind) or low-cost energy (such as flexible tariffs) and used when needed.

Domestic hot water tanks still exist in around 9m UK homes, but the 15m homes with a ‘combi’ boiler may have either never had one or since had it removed. The Mixergy smart hot water tank takes hot water from a heat pump or solar thermal system directly into the tank and uses either home solar or off-peak grid electricity to heat via their internal immersion heater. They use the natural stratification of water to keep the top of the tank hot while the rest of the tank remains cool, meaning that it can heat what is needed without having to charge the whole tank.

Tepeo’s solid state thermal store zero-emission boiler consists of a solid, heavy core (think a lump of concrete) that is heated up to 800°C by an electric element. As it is super-insulated, it remains hot throughout the day and can discharge heat into water for space heating and domestic uses. It is used in conjunction with a water tank as the transfer of heat from the core to water is not immediate. The advantage of this type of heat storage is that it can offer flexibility by smoothing demand and not overloading the electricity grid during peak times.

Sunamp’s Thermino is a phase change heat battery. A phase change material is one that changes state between a solid, liquid or gas through the operation of its use. In doing so it holds and then discharges more heat than a substance that remains in the same phase (or a steady state) during the process.

The internal substance holds around four times the amount of energy as water can hold at the same temperature which makes it an effective heat storage material. When the heat is needed, it is discharged into water through a heat exchanger, causing the substance to cool and return to a solid state.

Infrared heating emits a wave that heats the objects it collides with, similar to feeling the direct heat from the sun. The benefits of infrared heating are that heating panels are quite small and can be installed individually on most walls or even ceilings and there is no need to plumb in radiators. They are well suited to replace old electric systems or in new-build properties that are not connected to the gas grid.

Ambion’s infrared panels are always on, but pulsing, so they gradually heat the fabric of the property itself which then emits warmth back into the room. Early trial data of their first 1,000 installations shows a spread of performance ratios that averages at 2.69 but varies depending on house types (with flats having a higher ratio; and detached properties a bit lower). Due to their relatively cheap and easy installation they are emerging as an extremely flexible heating option well suited to smaller properties and flats.

Solar thermal systems have been around for a while but have needed to be used in conjunction with another heating system (such as electric immersion heating or even gas) to reach a high enough temperature for effective and safe domestic use.

Naked Energy’s evacuated solar tubes can provide the level of heat we would expect to be used in a domestic setting, and alongside a hot water storage tank, can be used to heat a home using direct solar energy at essentially no cost.

Naked Energy arranges solar tubes in a modular array, allowing them to be installed in a low profile onto flat or angled roofs or even vertical walls. The solar collectors are housed inside sealed tubes that are ‘evacuated’ of air and moisture, minimising thermal losses and concentrating the sun’s energy into water at around 80°C, up to as high as 120°C. These are high-end solar thermal products and are well suited to properties with limited space.

Microwave boilers might sound like something from a sci-fi novel but Heat Wayv has been producing microwave products for military use for over a decade. Heat Wayv is prototyping a domestic microwave boiler which they are looking to launch in the UK from 2023.

The Heat Wayv boiler does not heat water directly but uses microwaves to heat an alternative fluid up to ten times faster than water can be. The heat is then rapidly transferred into water as a secondary step through a heat exchanger. The aim is to get near to the experience of a combi boiler in providing direct hot water to the user in around 10-20 seconds from turning on the tap.

The Heat Wayv boiler is also small enough to replace a combi boiler like-for-like on your wall. However, the efficiency of the system and how much energy it uses in comparison to a heat pump is currently unknown.

While heat pumps are very much the benchmark for low-carbon heating, a future where we no longer use fossil fuels to heat our homes will include a mix of technologies for different locations, properties, users and circumstances. These products will likely make up this mix, as will improved and optimised versions that are yet to come, and even products not currently available.