Entrenching failure – how absurd digging rules are holding back a solar revolution

13 November, 2023
CapX, by Ben Hopkinson

To deliver a fully decarbonised grid by 2035, the government is banking on a near fivefold increase in solar capacity. Can it be done? Yes, but it won’t be easy. And as it stands the biggest barrier to installing those panels in time is our slow-motion bureaucratic planning system.

To get permission to build a new solar farm, or for that matter to build anything, means jumping through all manner of hoops. Some obstacles, such as the need to carry out consultation after consultation, or to check for great crested newts, are well known.

Yet, there’s one hurdle that’s slipped under the radar. And it can double the cost of preparing a solar farm planning application, threatening the viability of the project at a time when we need more clean sources of energy than ever before. Let’s talk about trenching.

Before submitting a planning application, developers seeking to build a solar farm will have to conduct a ‘cultural heritage assessment’ which can involve digging trenches covering up to 4% of the site in the hopes of uncovering historical artefacts.

Nobody wants to see our cultural heritage threatened, but the status quo is completely disproportionate.

Let’s be clear, there’s a big difference between tarmacking over a field for a new road and installing a solar farm. To start with, roads are built to last. Solar panels by contrast typically have a lifespan of 25 years. Roads (and houses too) also disrupt what’s beneath the soil a lot more.

Yet, some planning authorities are treating solar farms, roads, and houses as if they were the same. This often means demanding extensive trenching even before planning permission is granted, and without any guarantee that it will be.

Trenching 4% of a site may not seem all that much, but in practice it is disruptive, expensive, and may do more harm than good to heritage artefacts.

A large-scale 480 megawatt solar farm, such as the proposed West Burton solar farm in Lincolnshire, will cover around 2,000 acres, or about two thirds of the size of the Royal Borough of Kensington and Chelsea. Trenching 4% of that would mean digging a hole the size of 40 football pitches.

Yet, it’s not just the 4% actually dug out that’s affected. All that soil you dig up has to go somewhere and the digging equipment takes up space too. All in all, 4% trenching can take around a fifth of a site out of action for months. The landowner must be compensated for any damage to the land, or loss of production.

If you were a farmer considering leasing your land to a solar farm, losing up to 20% of the land while the project is going through planning, at which point it may get rejected, is a massive deterrent. If the planning permission is turned down for any reason, the disruption is for nothing. As a result, securing land for clean solar energy is more expensive than it needs to be.

There is also uncertainty: what county archaeologists ask for is a bit of a lottery. One solar farm fell on the county boundary between Gloucestershire and Wiltshire, the Gloucestershire planning archaeologist was happy with 2% trenching, while the Wiltshire one arbitrarily wanted 2.5%.

Even within counties there’s a big variance in the amount of trenching required. Oxfordshire has required different solar farms to do targeted trenching, 1% trenching, 1.5% trenching, or 2% trenching.

All this digging ain’t cheap.

Mike Rutgers from solar developer Low Carbon says for a moderate sized solar farm, trenching can cost up to £500,000. For a larger solar farm, this can climb up to £1m-3m. In most cases, this is money spent before planning permission is even approved, which can scare off potential investors who are unwilling to risk significant sums on a project that may never materialise.

Potentially the most damaging issue with trenching is that it doesn’t do much to help preserve cultural heritage. As the current system adds burdens to building solar farms it means fewer farms are built. The government’s own draft National Policy Statement on renewable energy states that, ‘solar PV developments may have a positive effect, for example archaeological assets may be protected by a solar PV farm as the site is removed from regular ploughing and [mitigations are used]’. Intensely farming land is a bigger threat to any artefacts underneath than any solar farm.

There are two potential solutions to the challenges that trenching creates. If we are wedded to the idea that trenching is necessary, we should make trenching a planning condition, meaning trenching would happen after permission is granted, rather than before (whether or not it is granted). This would still add to the cost, but would reduce the uncertainty of large upfront expenditures on a project that may not receive planning permission.

A solar project should never be rejected at permission stage on the grounds of underground archaeology alone, because there are a number of mitigations that avoid harm to any cultural artefacts. Instead of burying the mounts of solar panels, they can be put on more expensive concrete shoes that rest on the ground, leaving any artefacts below ground undisturbed.

Even when there are large findings, the developers of solar farms can always just design and build around them, as it is highly unlikely that any find will stretch across more than 5% of the site.

However, what’s really needed is clear guidance for if and when trenching is necessary. Right now it’s a lottery. In almost all cases, instead of trenching, geophysical technology, which scans the ground for objects, should be used. Only if the geophys reveals something significant should trenching come into the process.

To deliver a fivefold increase in solar, the UK doesn’t need to follow America’s lead and embark on a massive multi-billion pound subsidy spree. We just need to stop throwing up unnecessary hurdles.

By updating the National Planning Policy Framework and National Policy Statement for renewables to offer clear guidance for when trenching is and isn’t necessary, the government could cut the cost of building new clean sources of power with the stroke of a pen. What are they waiting for?