Overplanting solar farms: A legal win for flexibility in renewable energy

On 23 May 2025, the High Court handed down judgment in Ross v Secretary of State for Housing, Communities and Local Government and Renewable Energy Systems Ltd 2025 EWHC 1183 (Admin).  

The main issue considered by the Court was the interpretation of the provisions of the National Policy Statement for Renewable Energy Infrastructure EN-3 (EN-3) in relation to “overplanting” of solar panels, and how many you can install on a site that’s technically capped at 49.9MW of export capacity (being below the capacity threshold for a solar farm to be a National Significant Infrastructure Project, which is 50MW).

Overplanting

In solar terms, overplanting means installing more generating capacity (in DC terms) than the site is allowed to export to the grid (in AC terms) (or more simply, installing more solar panels than is actually required). 
This makes sense. Panels degrade over time, weather conditions vary, and solar farms don’t always hit their peak output. So, by installing more panels than strictly necessary, they can make sure they’re hitting the 49.9MW export limit more consistently.

Overplanting was sought in this case to address three factors:

1. Solar panel degradation over time.
   
   
2. The maximum output of a solar panel is determined in laboratory conditions, but the actual output of any solar panel in a field will be less than in laboratory conditions.
   
   
3. The combined effect of the configuration of the site and of fluctuations in the level of sunlight throughout the day/year.

The legal question: Is that allowed?

The claimant in this case argued no. Or at least, not unless it’s just to make up for panel degradation. The claimant pointed to EN-3 and argued that overplanting should only be used to offset the natural decline in panel performance over time.

This wasn’t accepted by the Court. Mr Justice Eyre held that overplanting for reasons beyond that necessary to address panel degradation was not inconsistent with EN-3.

Mr Justice Eyre also considered the claimant’s argument in relation to footnote 92 of EN-3, being that overplanting must be reasonable. Footnote 92 reads:

“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.”

Mr Justice Eyre held that footnote 92 does not impose a separate requirement that overplanting must be reasonable. Footnote 92 is clear that overplanting should be considered acceptable in planning terms if:

1. It can be justified.
   
   
2. The export does not exceed the NSIP threshold (i.e. it must be below 50MW).
   
   
3. The impacts of the development are assessed on the basis of its full extent (including the overplanting).

What does this all mean?

In short: we now have clearer legal backing to overplant solar farms below 50MW, as long as they stay within the export cap (ie, 49.9MW) and the impacts of the development are assessed on the basis of its full extent.

This case is a reminder that planning law is rarely black and white. Policies are interpreted, not just applied, and sometimes, what seems like a technical detail like how many panels you can squeeze into a field can end up shaping the future of the energy grid.

Please click here to read the full judgment. 

Our content explained