Decarbonisation of heat: advanced systems with heat pumps

Since our last update the policy landscape has changed; BEIS has announced their consultation on the Future Support for Low Carbon Heat and the Domestic Renewable Heat Incentive (RHI) is to be extended for a year until the end of March 2022, after which the Government plans to replace it with the Clean Heat Grant scheme. The proposal is to support the installation of air, ground, or water source heat pumps (but not hybrid heat pumps), through a grant of £4,000. The consultation on the proposals closes on 7th July 2020, and NEA will be responding to it in due course.

In this blog (our third on this topic) we wanted to talk you through some examples of ‘advanced systems’ which combine heat pumps with other technologies to reduce running costs. One of the simplest additions to a heat pump system is to combine it with solar PV to reduce running costs. During one of our Technical Innovation trials in Wakefield we found this to be an effective method for reducing heating costs whilst improving comfort levels and heating controllability.

The graph below shows the electricity generated from one of the PV systems in Wakefield compared to the electricity consumed by the heat pump. A PV system will have greatest generation during in summer months, which of course is when you tend not to need to have your heating on. By combining the heat pump with the PV system, the cost of running the heat pump between those months can be substantially reduced, which can allow residents to build up credit on their electricity account, and so spreads the heating costs over the year, making the winter heating more affordable. As heat pumps are typically operated for longer periods over the day compared to traditional heating systems, there is an opportunity to utilise the electricity generated by the PV system to operate the heat pump.

An alternative technology combines solar PV with solar thermal panels in what is called PV-T.

This technology can work alongside ASHPs to reduce household energy costs even further. We trialled this technology in Kent and East Sussex[1] and once again noted positive outcomes for residents. The photovoltaic panel runs more efficiently because it is cooled by water running through the panel, which in turn heats the domestic hot water without the need for the heat pump to do so. It is important to note that a solar PV-T system costs around the same as separate solar PV and solar thermal systems. The properties which benefited from this advanced system were previously heated by solid fuel, storage heaters or electric boilers. Residents were typically dissatisfied with the cost of running their heating system before the system was fitted and either satisfied or very satisfied afterwards. One householder told us that her energy supplier had asked to come and inspect the meter because the family’s electricity use had dropped to half their previous use!


A further combination is to utilise energy storage alongside a heat pump to capitalise on cheaper electricity costs available through some suppliers. Most heat pumps will run on a single rate electricity tariff and produce between 2.5 and 4 units of heat for each unit of electricity consumed. The cost of space heating with a heat pump is lower than for electric panel heaters and storage heaters, but costs can be further reduced by running it on off-peak electricity through a time of use tariff – utilising stored electricity or heat from an off-peak period, for use later in the day during more expensive periods. This practice is likely to become more common in the future but can be done right now with widely available technologies.

An example of this is where an ASHP is combined with a heat battery which can “charge up” during off-peak electricity periods and supply heat during the peak rate period. There are several types of heat batteries available, some using dense ceramic cores, some large water tanks, and others utilising phase change materials. Heat batteries are generally more efficient and sometimes smaller than traditional hot water cylinders.


A Daikin high-temperature heat pump (left) and the Sunamp heat battery and hydrobox (right)

NEA worked with Ongo Homes in North Lincolnshire to install ASHPs and heat batteries in homes that were off the gas grid[2]. 11kW Daikin high-temperature heat pumps were installed alongside SunAmp Heat Stack batteries with a 40kWh storage capacity. Households were encouraged to switch to Economy 10 (the trial took place before the inception of more flexible TOU tariffs), to allow the heat pump to operate and heat battery charge primarily during the cheaper off-peak periods. There were some challenges accessing E10 tariffs, nevertheless, the combination of ASHP and heat battery proved popular with residents and led to a significant shift of the electricity consumption to off-peak periods. Running costs were lower compared to the original heating system.

Thanks to the Energy Savings Trusts Redress Scheme, NEA is excited to be working with our partners at North Devon Homes to trial the Boxergy[3] system, which combines battery storage, a heat battery and a high-temperature ASHP. The system will use a time of use tariff and will maximise the use of off-peak electricity by charging the heat and electrical batteries off-peak for later use when tariffs are higher. The heat battery will provide domestic hot water throughout the day, with the option of supplementing the space heating energy requirement if necessary. The system is ideal for off-gas properties, with Boxergy claiming that running costs are lower than for gas central heated properties. Savings can be achieved with Economy 7, but they are greatest when using an advanced time of use tariff like Octopus Go or Octopus Agile, which have particularly low off-peak charges. Results are anticipated in early 2022.

Find out more about NEA’s technical team and the services we offer. If you would like us to evaluate the performance of a new heating system or provide extra support to residents during a heating upgrade programme, please contact us on 0191 269 2904 or

Our next Blog will be on smart heating controls, for heating just where and when you need it!

[1] CP752 – Air-source heat pumps with solar PV-T panels, Optivo,

[2] CP780 – Various heating solutions for social housing in North Lincolnshire, Ongo Homes,



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