Can I overplant my solar farm?

The judgment in Ross v Secretary of State for Housing, Communities and Local Government and Renewable Energy Systems Ltd [2025] EWHC 1183 (Admin), was handed down on 19 May 2025 and provides a detailed and authoritative assessment of the practice known as “overplanting” in solar renewable energy schemes. 

Whilst the judgment deals with the policy context of the National Policy Statements in England, it provides useful guidance for projects in Wales and Scotland and will be of assistance to developers bringing forward schemes under each of the Town and Country Planning and Nationally Significant Infrastructure Planning regimes. 

Facts

The Longhedge Solar Farm, promoted by Renewable Energy Systems Limited (RES), comprised a total site area of 94 hectares, with a buildable area of 63.5 hectares.  The application was granted on appeal by the Planning Inspectorate and had a number of planning conditions attached, which controlled the physical extent of the development but not the specific panel numbers or their power rating.  A planning condition also limited power export to the grid to 49.9MWac. 

The DC capacity (circa 78.5MWdc) exceeded the AC export capacity by a ratio of 1.57, with the excess capacity serving three functions:

1. to offset panel degradation during operation;
2. to reflect that panels in normal operating conditions do not reach their laboratory condition rating; and
3. to maximise the time, the site could operate at its full AC export limit. 

Any possible exceedance of the 49.9MWac export limit was avoided by inverters being de-rated, otherwise known as “inverter clipping”.  The Claimant accepted that the planning condition limiting the AC export capacity of the scheme meant the application properly fell within the Town and Country Planning regime.

While not the primary policy for the application, the National Policy Statement EN-3 was a material consideration and paragraph 2.10.55 and footnote 92 were central to the main challenge, and read: 

2.10.55 The installed generating capacity of a solar farm will decline over time in correlation with the reduction in panel array efficiency. There is a range of sources of degradation that developers need to consider when deciding on a solar panel technology to be used. Applicants may account for this by overplanting solar panel arrays.⁹²

⁹²            “Overplanting” refers to the situation in which the installed generating capacity or nameplate capacity of the facility is larger than the generator’s grid connection. This allows developers to take account of degradation in panel array efficiency over time, thereby enabling the grid connection to be maximised across the lifetime of the site. Such reasonable overplanting should be considered acceptable in a planning context so long as it can be justified and the electricity export does not exceed the relevant NSIP installed capacity threshold throughout the operational lifetime of the site and the proposed development and its impacts are assessed through the planning process on the basis of its full extent, including any overplanting.

Throughout the appeal process and public inquiry, the Inspector took multiple opportunities to seek information from the Appellant (RES) on the installed capacity of the scheme and the environmental effects of overplanting. The Inquiry Rule 6 Party maintained that overplanting for any purpose other than panel degradation was contrary to National Policy Statement EN-3, and that reliance on inverter clipping meant wasted energy, and so would not represent the best use of the land. 

In allowing the appeal, the Inspector dealt directly with the level of overplanting, its purpose and its likely effects, concluding that these would not justify dismissing the appeal.

The Claimant’s challenge relied on an argument that the Inspector had failed to properly interpret and apply National Policy Statement EN-3 paragraph 2.10.55 and footnote 92 in the determination of the appeal. 

In his judgment, Mr Justice Eyre concluded that the Inspector had properly understood and applied policy in EN-3 in finding that overplanting for reasons other than panel degradation was not inconsistent with the policy wording and that overplanting for site maximisation and to allow for actual site conditions was quite consistent with the policy’s objective of maximising renewable energy generation.

The Court also endorsed the wording at paragraph 2.10.56 of NPS EN-3, “AC installed export capacity should not be seen as an appropriate tool to constrain the impacts of a solar farm”, rejecting the Claimant’s arguments that designing around a 49.9MWac export limit was artificially constraining the development.

The Court further rejected the position that there was a two-stage test in considering overplanting: that it is be justified, and then separately shown to be reasonable, and instead adopted the single stage consideration of the reasons for overplanting and their justification, which the Inspector had applied.

What this means for solar developers

The facts in relation to overplanting will be specific to each site and will have to be explained in terms of their consistency with national and local energy policy.  However, this judgment makes clear that maximising renewable energy generation while taking full account of the actual impacts of doing so lies at the heart of interpreting the Energy National Policy Statements.

As the case sat at the (current) threshold of the Town and Country Planning and Nationally Significant Infrastructure Planning regimes, it provides useful guidance on the factors considered material to determining solar schemes in both regimes, particularly development density and the efficient use of available grid export capacity.

Emily Kell-Rowan, Cathryn Tracey and Patrick Robinson were instructed by RES in the inquiry and subsequent legal challenge and Alex Minhinick leads on a number of Burges Salmon’s solar DCO instructions. 

If you would like to discuss the contents of this blog further or have queries on the judgment and how it might take effect in practice, please contact Patrick Robinson ([email protected]), Emily Kell-Rowan ([email protected]), Cathryn Tracey ([email protected]) or Alex Minhinick ([email protected]).