High Court considers role of National Policy Statement in ‘overplanted’ solar farm development with capacity under 50MW

A recent High Court judgment confirmed that a solar farm development with a transmission capacity below the threshold for consenting under the Nationally Significant Infrastructure Project (“NSIP”) regime with appropriately justified ‘overplanting’ of panels is not in principle inconsistent with the National Policy Statement for Renewable Energy Infrastructure (“EN-3”).

The local planning authority can properly evaluate a planning application in such a case under the Town and Country Planning Act 1990 (the “1990 Act”) by considering the reasonableness of any overplanting among the development’s other benefits and harms when determining the planning balance in the usual way.

Factual background

Rushcliffe Borough Council initially refused the developer’s application for planning permission for the Longhedge Solar Farm (the “solar farm”), but the developer successfully appealed and a planning inspector granted planning permission in October 2024.

The claimant in Ross v Secretary of State for Housing, Communities and Local Government challenged the planning inspector’s grant of permission on grounds relating mainly to the interpretation and application of EN-3 provisions about ‘overplanting’ solar panels (ie., installing more panels than would be needed for a solar development to transmit a certain amount of energy to the grid).

Here, the solar farm’s indicative layout was expected to generate 78.54MW of DC electricity, although its transmission capacity would on any final design be limited to 49.9MW of AC electricity. That transmission capacity falls below the current 50MW NSIP threshold for development consent under the Planning Act 2008 (the “2008 Act”) regime, so the application was determined under the 1990 Act regime.

The developer had justified the extent of the anticipated overplanting as reasonable on the basis that solar panels degrade over time and do not operate to their full lab-tested capacity in real-world conditions. The solar farm’s capacity would not therefore be maximised throughout its lifespan without the overplanting. The claimant argued that only the first of these justifications aligned with national policy so the extent of the overplanting was unjustified and the inspector should not have granted planning permission for the solar farm as proposed as it should have been an NSIP.

The decision

Mr Justice Eyre dismissed the claimant’s appeal mainly because he considered that the inspector had correctly interpreted and applied the relevant EN-3 sections in the context of the whole policy, as well as the “nature, purpose, and effect of the overplanting” on the solar farm. Overplanting the solar farm would be reasonable to address panel degradation over time, provided the overplanting could be justified; the NSIP threshold would not be exceeded; and the solar farm’s full impacts were evaluated by the decision-maker, including the overplanting.

Although the claimant argued that overplanting was only permissible for the only reason specifically addressed by EN-3, namely to account for solar panel degradation over time, Mr Justice Eyre agreed with the inspector that the additional factors cited by the developer – overplanting to account for real-world conditions and to maximise the site’s capacity throughout its life – would not necessarily be inconsistent with the policy and would be reasonable if the three above-noted conditions are met.

After concluding that the overplanting of the solar farm aligned with national policy and was reasonable, Mr Justice Eyre rejected the claimant’s arguments that a more restrictive reading of EN-3 was necessary to ensure the solar farm as proposed would not have undue adverse impacts ‘on the ground’. The inspector had rightly acknowledged that any adverse impacts would factor in the planning balance, weighing against the benefits of the solar farm as proposed, but there was no need to consider as separate factors the reasonableness of the extent of the overplanting, the possibility of building the solar farm on a physically smaller site with a different arrangement of panels, or potential implied waste arising from limiting the panels’ operation to keep the solar farm’s transmission capacity below 50MW. The inspector was justified in granting planning permission after due consideration of the planning balance for the solar farm – a highly fact-sensitive exercise where principles cannot readily be drawn from prior case law.

TLT comment

This case generally confirms that in relation to planning applications for solar developments under the 1990 Act regime, a favourable planning balance must be made out in the usual way for permission to be granted. National policy that is ordinarily applicable to NSIPs to be consented under the 2008 Act may also be considered as part of this balancing exercise, particularly if a development’s AC transmission capacity is near the NSIP threshold.

EN-3 supports reasonable overplanting to account for solar panel degradation over time. Reasonableness requires that the overplanting can be justified; a development’s transmission capacity does not exceed the NSIP capacity threshold; and a development’s full impacts are assessed, including any overplanting.

Overplanting can be justified for reasons other than to account narrowly for the degradation of solar panels over time, but applicants should ensure their justifications and plans align with national policy aims to help avoid legal challenges under either the 1990 Act or the 2008 Act (as relevant).

The NSIP threshold relates to export capacity (in AC), and the court in this case saw nothing improper in the developer limiting the solar farm’s transmission capacity to 49.9MW to avoid NSIP status. Developers with commercial or operational reasons for preferring to pursue consent for a scheme under either the 1990 Act or the 2008 Act regime should be confident using either.

EN-3 also anticipates that a solar project’s full details may not be known at the time of application, particularly as solar technology is rapidly evolving. Some degree of design flexibility should therefore be acceptable in an application, particularly in relation to project sizing and siting, although developers should bear in mind the indicative range of figures cited by the policy and be prepared to provide evidence justifying significant departures from those.

Katherine Evans said “this decision provides some welcome clarity over the issue of “overplanting”.  Local planning authorities have often declined to deal with planning applications where they believe that there is a possibility of generating electricity over the 50MW limit set out in the Planning Act 2008 despite there being other factors that would ensure that the limit was not exceeded.  With changes to the limit to 100MW from the end of 2025, this may not be as much of an issue as it has been previously but with improvements to technology, limits are often pushed sooner than ever anticipated at the outset.”

TLT’s Future Energy Planning and Environment team has expertise with both the 2008 Act and the 1990 Act consenting routes and can advise clients wishing to proceed with an application under either regime.

This publication is intended for general guidance and represents our understanding of the relevant law and practice as at May 2025. Specific advice should be sought for specific cases. For more information see our terms & conditions.