This case produced some important conclusions on how to approach overplanting in solar farm proposals. Of the six grounds of challenge, this article focuses primarily on Grounds 1 to 3 and identifies some key takeaways from the judgement for solar farm developers and other parties to an appeal, especially when dealing with issues of overplanting and the number of panels proposed.

The Proposal

The claim was based on a solar farm proposal with a maximum energy generating capacity of 49.9MW. The Proposal included overplanting of solar panels for three reasons:

  1. To address degradation over time of the solar panels’ ability to generate energy
  2. To account for the difference in maximum solar panel capacity that is calculated in laboratory conditions (“the STC Rating”) as opposed to conditions on the ground (the latter resulting is lower capacities)
  3. To ensure that the site production is maximized, when taking account for configurations and the varying levels of sunlight during the day, so an export capacity of 49.9MW can be ensured for a greater part of the day.

The Proposal was granted permission by the Inspector and the Claimant challenged the approval.

Although this Proposal was under the 50MW threshold required to be an NSIP, the Inspector nevertheless had regard to NPSs due to the proximity of the maximum generating capacity of the site to the threshold limit.

Takeaway 1: This is a reminder that even if a solar farm proposal is below the 50MW threshold*, it would be prudent to have regard to policies in the NPSs in designing the Proposal, especially when the maximum generating capacity is close to the threshold, as the NPS still be a material consideration for decision-making.

As to the Claimant’s concerns that the Proposal was deliberately designed to remain below the 50MW threshold, Mr Justice Eyre remarked:

“15. It was clear that the Second Defendant saw a benefit in keeping the Solar Farm’s capacity below the NSIP threshold and that the export capacity was deliberately limited so as to achieve that. There was no impropriety in that course. If there are two potential statutory regimes governing developments of different kinds there is nothing improper in an applicant so arranging matters as to ensure that a proposed development does not cross the threshold which would bring it under one of those regimes. In practice here it cannot be said that there was any material difference in the rigour of the approach taken in considering the application. The Decision was taken by the Inspector after extensive submissions and having regard to the NPS’s which would have been applicable if the Solar Farm had been a NSIP.”

Grounds

There were 6 grounds of challenge against the Inspector’s decision:

  1. The Inspector misinterpreted NPS EN-3 on the circumstances when overplanting is permissible, namely that overplanting is permissible for reasons 2 and 3 (given above) not just reason 1.
  2. The Inspector was required to have regard to the “reasonableness of overplanting” prior to, and separate from, the planning balance exercise. Alternatively, the Inspector should have had regard explicitly to the reasonableness of overplanting as an obviously material consideration.
  3. The Inspector failed to control the density of the solar panels or to assess the application on a proper worst-case basis.
  4. The Inspector failed to have regard to the energy loss from “clipping” and the environmental consequences.
  5. The EIA screening opinion was flawed since the author could not have rationally been satisfied that he was approaching the issue on a worst-case basis.
  6. The Inspector failed to address the impact on Skylarks and Yellowhammers.

Arguments under all six grounds were heard by the High Court, but the claim was ultimately dismissed.

Background

The key parts of the NPS EN-3 policies are as follows:

“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.(fn 92)”

“Fn 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.”

Interestingly, in this case, the Claimant’s planning consultant had written to the Secretary of State for further clarity on the EN-3 policies (April 2024) and in response the Secretary of State said (May 2024):

“In the Energy Policy Statement EN-3 guidance, overplanting is countenanced where reasonable, to address panel degradation. Unreasonable overplanting, or overplanting for any other reason, would not be supported. It will be a matter of planning judgement for the decision maker in any case to decide what the purpose of the overplanting is and whether it is reasonable.

Due to the variable nature of solar projects, it would be difficult to determine a single overplanting measurement that would be appropriate in all circumstances which is why it is for decision makers to take into account the specifics of each project.”

The Court reminded the parties that the interpretation of policy is an objective exercise to be conducted by the Court and that the “subjective views of the author of the document as to what it means is irrelevant” to that exercise (referencing Lewison LJ in R (TW Logistics Ltd) v Tendring DC [2013] EWCA Civ 9, [2013] P & C.R 9). The only extent to which such views can be of assistance in the interpretation exercise is if “it provides a reasoned analysis which is persuasive on its own merits” ([30]). The Court was not of the view that such analysis was provided in the above response, and the final section of the response suggests that a flexible approach is appropriate.

The exact number of panels which would form the Proposal was not determined, but an indicative number of 128,752 610w solar panels was provided to the Inspector and the farm was to cover an area of 94.24 ha with the built area being 63.5 ha.

Ground 1

The Court upheld the Inspector’s interpretation of EN-3 policies on overplanting, namely that nothing in the wording of the policies renders overplanting for the purposes of tackling differences in STC ratings to actual estimated capacity and for the purposes of site maximisation. Just because there is a policy statement which expressed one form of development is acceptable it does not always necessarily mean that all other forms will be unacceptable. Such an implication in this case would be neither natural nor necessary ([76]). As always, the Court reiterated the importance of reading policies as a whole and having in mind the objectives of policies which seek to support renewable energy production (especially when the need to maximise each location is recognised in the policy).  The focus of the policy is also on the impacts of a proposal rather than its capacity – see paragraph 2.10.56 of NPS EN-3 ([84]).  For those reasons, the Court concluded that it was not impermissible in policy to allow for overplanting to account for STC ratings vs actual estimated capacity of panels and for site maximisation.

Takeaway 2: The policies in NPS EN-3 do not restrict overplanting only to the extent that they may be required to address degradation of the panels over time. Overplanting for other appropriate purposes can also be permissible under the national policy.

The Second Defendant argued that even if the Claimant was right in their interpretation of the policy, permission would nevertheless have been granted. Mr Justice Eyre considered this argument only briefly since he did not find for the Claimant on policy interpretation. However, he remarked that had he found for the Claimant on this, the Second Defendant’s argument would not have succeeded since policy conflict with NPS EN-3 would have been a material consideration of substantial weight which would have weighed against permitting the Proposal. Therefore, it cannot be said that the Inspector’s conclusion would have necessarily been the same ([87]).

Ground 2

The Court held that EN-3 does not require a separate standalone assessment of the reasonableness of overplanting prior to the consideration of the planning balance. One of the matters which the Inspector does need to assess is whether there is “justification” for the overplanting proposed as per Footnote 92 of EN-3.

Alternatively, the Claimant argued that the extent of overplanting and whether the same export capacity can be achieved without any, or with less, overplanting was an obviously material consideration which the Inspector failed to have regard to and, in support of this position, they relied on the case of R (Galloway) v Durham CC [2024] EWHC 367 (Admin). The Court distinguished the case of Galloway from the present claim since the conclusions in Galloway were reached on a number of particular factors that were unique to that case. In Galloway, Mr Justice Fordham had found the Inspector’s decision to grant permission unlawful due to a failure to consider whether the permission was approving more panels over a larger area than were required for a 50 MW farm. This was because in that case the spacing between solar panels were reduced from 6.3m to 2.4m and this was a significant change which, Mr Justice Fordham found, was never addressed by the Inspector. Also, it was found that, properly measured, the capacity of the farm was 50% over the 50MW threshold and this surplus was also found to have not been explored. However, these factors were unique to Galloway and did not apply in the current case. In this appeal, the Inspector had properly probed into the DC/MEC ratio and sought an explanation for the overplanting which was provided with some detail to the Inspector via a technical note, where the extent of overplanting was explained by percentage and how it met the stated objectives.

Therefore, the Inspector had probed whether there was sufficient justification for the overplanting, that it was aimed at the appropriate objectives, and the overplanting was sufficient to the extent that it was required to meet those objectives.

Takeaway 3: If you are proposing overplanting as part of your solar farm proposal, it would help to produce a technical note which explains the reasons for overplanting and how the objectives are met, and to what extent, by the overplanting. This will aid in allowing the decision-maker to properly consider the justification for overplanting.

Under the same ground, Mr Justice Eyre remarked that, despite this being a rapidly changing industry with advances in technology, change of circumstances since the adoption of an NPS does not automatically require that less weight should be given to the policies. Moreover, the technical report provided here calculated the indicative number of panels having regard to the foreseen improvements in solar panel efficiency.

Takeaway 4: when calculating solar panel capacity and densities, it would be good for technical reports to take account of likely future improvements in technology.

Ground 3

The alleged error under this ground was that the Inspector had not properly sought to control the density of panels or assessed the Proposal on a worst-case basis. A challenge under this ground would only have been successful had it been demonstrated that the Inspector was irrational in his conclusion that he had sufficient information to decide the Proposal on a worst-case basis. The Claimant was not able to demonstrate this and, in coming to this conclusion, the Court had specific regard to the numerous steps the Inspector had taken to obtain further information on the Proposal. The Court also emphasised that, although the policies note the need for flexibility, as not all information may be available when a decision is made, this cannot be an excuse to not provide information that can be obtained. In the current case, although only indicative figures for the number of solar panels were provided, the Court found that this does not mean that the spacing and number of panels were not controlled since there were a number of controls (both physical and by way of conditions) which constrain these factors. For example, via conditions, the maximum height and ground clearance were controlled, along with provisions for a landscape scheme and management plans for biodiversity, landscape and ecology. As for physical constraints, issues such as shadowing and maintenance naturally restrict the practical limits of what densities can be achieved and this was considered in a technical report, which explained what was the minimum spacing required.

Takeaway 5: this again demonstrates how the details in technical reports can and should be used to demonstrate how the Proposal has been designed. In this case, the report had explained why it would not be possible to achieve the same power generation in a materially smaller area by increasing the density of panels. This, Mr Justice Eyre found, was an indication as to why, practically, solar farm operators are unlikely to install panels at higher densities.

Ground 4

Mr Justice Eyre found that the Inspector had taken account of the potential loss of energy as a result of clipping in the Decision and it had been an integral part of the consideration on overplanting ([125] – [132]).

Ground 5

The Court held that it was rationally open for the relevant officer to conclude that the Proposal was not an EIA development. The fact that he did not know of the exact number of panels that would be installed, nor their precise locations, does not mean that he did not have sufficient information (having regard to other details that were taken into account in his opinion) ([133] – [137]).

Ground 6

The Claimant argued that the Inspector had failed to consider the impact of the Proposal on Skylarks and Yellowhammers. The Court concluded that this was not a “principal controversial issue” by the time the Inspector came to make his decision, therefore, there is to be no criticism of his failure to mention this in his Decision. It was also noted that risks to bats and otters were addressed in the Statement of Case and in Closing Submissions by HTAG (the Rule 6 party to the appeal and the organisation which the Claimant is a member of) and therefore this was addressed in the Decision;  failure to do the same for Skylarks and Yellowhammers meant that the Inspector cannot now be criticised for not addressing these impacts in his Decision ([138] – [144]).

Takeaway 6: this is a reminder for all parties to an appeal that if they want a matter considered then this should be made clear to the Inspector (e.g. raised as an issue in the Statements of Case and addressed in closing submissions). The Inspector is required to consider the “principal controversial issues” in the case and not any potential effect on the protected species in the absence of an actual dispute about the impact at the time of the Decision.  

*Please note that the threshold is set to change from 50MW to a 100MW from 31 December 2025.