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The future of residential heat decarbonisation

15 March 2021:

Grant Feasey, AES Solar

Decarbonising heat is the next great energy challenge for the UK – Solar Energy can play a key role.

In 2019 – 91% of heat energy was sourced from fossil fuels. Heating and hot water in domestic buildings account for around 10% of all greenhouse gas emissions in the UK [1]. A lot of progress is required – and fast – to meet our climate obligations.

Gas grid dominance

Around 85% of homes are connected to the gas grid with the remainder often dependent on oil, LPG, solid fuel boilers or expensive electricity [2]. Gas is cheap, and all these sources are convenient and reliable – for now at least.

The solutions will need to be many to suit the variety of technical challenges, house types, budgets and personal preferences to be catered for.

Solar with everything

Solar can complement any other heat source to provide most of the domestic hot water requirement in summer months and reduce the energy required from other sources for domestic hot water and space heating during the rest of the year. It provides a significant portion of the heat energy requirement, emissions-free and zero cost at source.

It is already a standard option to include a solar coil or electric immersion heater on any hot water cylinder or thermal store. This allows solar thermal, solar PV or solar PVT to used to input heat in combination with any other heat source.

Solar Thermal usually only requires a couple of panels on a roof. Modern options are pleasing to the eye and can blend in much like a Velux window.

Solar PV is an obvious choice to provide the low carbon and cost-effective electricity needed to drive heat pumps. It can also be fed directly into the cylinder via an immersion heater. If roof space is limited then solar thermal can be a more space efficient choice.

Electricity demand is increasingly coming from other loads within the house or electric vehicles. Therefore, it makes perfect sense to include both solar thermal and PV, or good quality PVT, to efficiently generate heat directly and free up the available electricity for other things.  This may be particularly true where grid capacity is limited and therefore curtails the amount of PV that can be connected.

Alongside Oil, LPG and biomass, Solar thermal provides a viable option for homeowners to take a chunk off their carbon emissions and energy costs, all at a lower capital outlay than replacing a perfectly good boiler.

Utility-scale solar for domestic heat

Heat networks present a proven option to provide low carbon heat to a large number of buildings without putting the burden of upfront cost and decision making on the individual. And guess what? Solar works great with those too! The economics and technical feasibility have been proven for decades in other countries such as Denmark, Austria and Germany[3].

Hydrogen is a much talked about option to reduce reliance on methane gas. Solar PV could generate a significant share of electricity required to produce that hydrogen.

Turning up the solar heat

There are many talented organisations and individuals in solar heat, both in the private sector and in academic institutions involved in solar heat throughout the UK. They offer proven technology, innovative solutions and a strong skills base. A combination of progressive regulation, consistent and well-structured incentives and strong public awareness can build on that strong foundation. In turn, this can develop and grow the supply chain, reduce costs and establish a path to a sustainable, subsidy free contribution to low carbon heat and the economy.

The outgoing Renewable Heat Incentive has had an underwhelming impact – perhaps due to lack of awareness and the low attraction of drip-fed of money over several years. The Green Homes Grant in England – covering 66% of a system upfront costs (100% in some cases) – held much promise as a forebearer to a more longer term and punchy upfront grant scheme. Unfortunately, poor administration and badly calibrated policing have created something of a false start – the impact has been muted and the overall spend will be no more than 20% of the original proposed budget. Strong uptake by installers is still vitally important to demonstrate the demand and the potential.

Lessons must be learned and acted on to give the mechanism a fair chance to prove itself. The teething problems of the current scheme must not be allowed to be used as evidence against future incentives.

Similar initiatives can and do work. In Scotland, the similar ‘75% cashback’ scheme has been bolted onto the long running and very successful interest free loan offer. This means the administration and quality checking is managed by a proven and experienced entity using an established system. The impact has been far more noticeable, and anecdotally the experience of installers and end-users has been overwhelmingly positive. In Germany, the requirement for every part funded heating system to include solar has resulted in a 26% increase in deployment in 2020[4].

For new build, the future is regulation – specifically, the (very) long awaited Future Homes Standard [5] and building regulation updates now due to be fully implemented by 2025 including the mooted ban on gas boilers in new homes [6].

In Scotland it is estimated up to 90% of new homes now include solar thanks to progressive building regulation [7]. Industry and stakeholder engagement in the ongoing government consultations are vital to push for the adoption of the innovative policy details that could establish solar as a key part of the domestic heat puzzle UK wide. Solar is more cost effective to incorporate at build stage and it would mean a portion of the heat energy requirement is zero carbon for the lifetime of the building.

There is no one size fits all solution for low or zero carbon domestic heat. In every case, solar heat could – and should – be part of the future home.