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Soaring demand for the installation of photovoltaic (PV) panels on existing buildings is leading to uncertainties in planning, with very little precedent set for what is and isn’t allowed when it comes to the impact on neighbouring properties. It is clear, though, that developers and contractors must start factoring such considerations into their plans.

Demand for the retrofitting of PV panels is driven primarily by the commercial need to meet impending EPC targets, though factors such as spiralling energy costs are also coming into play. There have been a few high-profile instances, over the past few years, where planning laws and procedures have been called into question over the presence of solar panels on neighbouring properties.

A High Court ruling in 2019, in the planning dispute between William Ellis McLennan and Medway Council, confirmed that the impact of a development on a neighbour’s solar panels was capable of being a material consideration in the determination of a planning application. The council’s failure to take account of this meant its decision to grant planning consent was unlawful, and the High Court overturned the decision.

It is common practice to use complex modelling to simulate the likely impact of a proposed design on its neighbours. We need to start factoring PV panels into this process

However, what constitutes a material planning consideration can be problematic when it comes to planning law, because a consideration is just that; something to be considered or taken into account. It isn’t a strict condition that must be factored into initial plans, and the importance given to each material consideration depends on the circumstances of the case and on the planning judgment of the decision-maker. This ambiguity also means that different local authorities may take different views on the weight to be attributed to different material planning considerations when making decisions.

The 2022 revision of the BRE 209 good practice guidance on site layout planning for daylight and sunlight makes specific reference to considerations that must be taken into account on solar panels and their rights to light. The focus here is on the impact that any overshadowing will have on the energy consumption of the affected building and its carbon emission levels. This is a good practice guide and not a regulation. It does, however, offer an idea of what factors will be considered when assessing a planning submission.

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As an industry we are not yet at the tipping point when it comes to PV panels affecting planning consents, but this is likely to come in the next few years.

Developers like to have certainty. So too do their surveyors and lawyers: uncertainty creates risk, and our job is to help avoid and mitigate those risks. We need to see local authorities put in place clear policies so that developers and their contractors can see the restrictions up front. This will ensure that decisions are fair and consistent and will remove the risk factor. However, it will take a long time until all authorities have adopted relevant policies, and there may still be inconsistency between areas, unless national guidance is issued.

Software is available that will not only assess the shadowing levels but can go one step further and test the impact on the panels’ effectiveness

A point to note in the McLennan vs Medway ruling was that the decision hinged on the developer having made no effort to consider the impact of the project on its neighbour’s solar panels. On this basis, for the time being at least, it is going to be important for the construction industry to factor these considerations into the planning stage.

On rights to light, it is common practice to use complex modelling to simulate the likely impact of a proposed design on its neighbours. As an industry, we need to start factoring PV panels into this process. Software is available that will not only assess the shadowing levels but can go one step further and test the impact on the panels’ effectiveness, even putting a value on any loss of efficiency.

This data can be used to demonstrate that specific consideration has been made and can provide a readymade case against any potential objections. Beyond that, though, with input from a PV specialist surveyor, it can be used to guide design decisions that could mitigate the impact on the panels themselves, which would reduce the risk of having to go back to the design stage to amend plans should a successful appeal be lodged.

These models can also be used when negotiating with building owners on neighbourly matters by providing them with suggested solutions for mitigating any potential impact. For example, specific ways could be proposed to optimise individual panels to make best use of sunlight or use reflected light to maximise exposure.

This same modelling approach could prove valuable to those considering the installation of solar panels on their own projects too, especially in areas where future construction of taller buildings in the vicinity is likely. By modelling different scenarios, contractors can future-proof the panels’ efficiency by establishing the best positioning for installation. It is also good practice to engage with the local planning authority to check the solar scheme is compliant, helping both to de-risk the project and to gain necessary assurances prior to progression.

Solar power is going to play a big part in the UK achieving its carbon reduction targets. This is undoubtedly going to lead to PV panels being cited in more neighbourly matter planning disputes in urban construction. It is unlikely to be long before more precedent is set.

Stuart Patience is head of solar PV at building consultant Hollis and Tim Brown is a senior associate in the planning team at Trowers & Hamlins