Biodiversity net gain on solar farms

A ground-mounted solar scheme on arable land usually clears the 10 per cent biodiversity net gain requirement several times over, and the reason is arithmetic rather than ambition. Arable land scores low in the statutory metric, grassland in reasonable condition scores considerably higher, and almost all of the site area between and beneath the panels can carry that grassland. The difficulty is not generating units. It is demonstrating that the grassland will actually reach and hold the condition claimed for 30 years, on a site whose operational life and decommissioning conditions may run to a different timetable.

Biodiversity net gain under Schedule 7A to the Town and Country Planning Act 1990 expects the statutory metric to be completed by a competent person and the biodiversity gain plan to be approved by the local planning authority. A draft is a starting point for that person, not a substitute.

Why solar schemes usually exceed the requirement

The baseline does the work. Intensive arable and improved grassland carry low distinctiveness scores, so the pre-development unit total on a typical solar site is small relative to its area.

Post-development, the metric records the habitat actually proposed. A species-rich or species-poor neutral grassland, managed by grazing or cutting, scores higher, and the gain across tens of hectares is large even after the metric's multipliers are applied.

Those multipliers matter and are the part that gets overlooked. The metric applies a time to target condition, which discounts units for habitat that takes years to establish, and a difficulty multiplier reflecting how hard the habitat is to create. Grassland created from an arable baseline is not instant, and claiming good condition at year one will not survive review.

A biodiversity net gain assessment carries the calculation, and the version of the statutory metric in force at the time of the application is the one to use.

Habitat under and between panels

The practical questions are about shading, access and mowing, and they are answered on the layout drawing rather than in the ecology chapter.

Panel geometry sets the light regime. Wider row spacing, higher panel clearance above ground and a shallower tilt all increase light reaching the ground and improve what can establish under the arrays. Those choices trade against generation capacity, so the ecological and electrical designs need to be developed together rather than sequentially.

Three areas on a solar site behave quite differently:

• Under the arrays, where shading is partial and seasonal and the seed mix has to tolerate it
• Between the rows, where light is close to open conditions and the richest grassland can establish
• Margins, buffers and the field boundaries, where hedgerows, scrub and tussocky grassland deliver most of the structural diversity

Treat them as separate habitat parcels in the metric where the condition differs in practice, and be prepared to justify the split. Recording a single uniform grassland across the whole site is simpler, and it is also what an ecology consultee will question first.

Condition assessment of managed grassland

Condition is assessed against published criteria, and for grassland those criteria cover species richness, the proportion of undesirable and injurious species, sward structure and the extent of bare ground and physical damage.

Two things determine whether the grassland hits moderate or good condition. The seed mix, which has to be a genuine grassland mix of local provenance rather than an amenity mix with a few wildflowers added, and the management, which has to produce a varied sward structure rather than a uniform cut.

Be realistic in the submission. A scheme that claims good condition from year five on a site with heavy historic fertiliser inputs and high residual soil phosphorus is claiming something the soil will not deliver. Soil nutrient status is worth testing, and where phosphorus is high, say so and target moderate condition, or plan for a cutting regime that removes material and reduces fertility over time. The mechanics of establishing habitat on disturbed ground are covered in soil translocation and habitat creation on stripped ground.

Grazing, cutting and the management plan

The habitat management and monitoring plan is the document that makes the units real. It needs to be specific enough that a different contractor could pick it up in year 18 and do the right thing.

1. The grazing regime, with stock type, approximate stocking density, timing and the reasons for each
2. The cutting regime where grazing is not practical, including cut heights, timing and removal of cuttings
3. Infrastructure the regime depends on, such as stock fencing, water supply and handling areas, shown on a plan
4. Scrub and hedgerow management on a defined cycle rather than as required
5. Monitoring, with the reporting years stated, the condition criteria to be assessed and the surveyor competence required
6. Remedial action triggers, saying what happens if condition falls short, and who pays

Sheep grazing is the usual answer on solar sites, and it keeps an agricultural use running alongside generation. It also constrains the design: cable routes, inverter compounds, fencing and gates all have to work with stock movement, and panel clearance has to be high enough that sheep can get under the arrays without damaging equipment.

Interaction with land classification evidence

Policy pushes solar towards poorer quality land, and the best and most versatile categories of agricultural land, meaning grades 1, 2 and 3a, attract protection. An agricultural land classification survey by a soil scientist establishes which grades are present, and the survey is done by auger and pit inspection rather than from published mapping, because the published mapping is too coarse for a site decision.

The two pieces of evidence interact in a way that is easy to present badly. A biodiversity gain case built on converting arable land to grassland sits awkwardly alongside an argument that the land is poor quality, so the submission should be consistent: the land classification evidence addresses soil capability for crop production, and the biodiversity evidence addresses current habitat value. Those are different measures and both can be low.

Where the scheme does take higher grade land, the planning case has to deal with it directly, and the soil handling and reinstatement proposals become part of the answer.

Decommissioning and the 30 year period

This is the real tension on a solar scheme. The biodiversity gain condition requires habitat to be maintained for at least 30 years from completion of development, secured by a planning obligation or a conservation covenant. A temporary permission for the solar use may run for a shorter or different period, with a condition requiring removal of the equipment and restoration of the land.

Restoration to arable would destroy the habitat the gain plan secures. So the two sets of obligations have to be drafted to work together, and the point to settle before determination is what happens to the land at the end of generation.

Three workable positions exist. Align the obligation period with the full 30 years and accept that the land stays as grassland after decommissioning. Draft the restoration condition to require reinstatement to grassland rather than arable. Or deliver part of the gain off site through a secured habitat unit arrangement with its own 30 year management, leaving the on-site grassland as a shorter commitment.

Whichever route is chosen, say so explicitly in the gain plan. A plan that is silent about decommissioning invites a condition that contradicts it.

Evidence the authority tests

Expect scrutiny of the baseline survey, the metric version and inputs, the condition assessments, the management plan and the securing mechanism. A preliminary ecological appraisal establishes the baseline habitats, and the habitat mapping should be dated and tied to the survey visit rather than to a desk exercise.

The weakest point in most solar submissions is the condition claim. The second weakest is hedgerow units, which are counted separately from area habitats and are governed by their own module in the metric, as explained in hedgerow units and the Hedgerows Regulations overlap.

Get the metric and the management plan drafted by the same team that will monitor the site. It shows in the document.

This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval. For specialist technical reports, qualified professional input may be required, and the statutory biodiversity metric and biodiversity gain plan require a competent person.