The best-defended solar site in Britain is behind an airport fence.

An airport operator is a steward before it is an energy buyer. It holds a piece of national infrastructure, a large part of a local economy, and a boundary that most of its neighbours will never cross. Very little of what happens inside that boundary is optional, which is exactly why the things that are optional deserve attention.

Electricity is one of them. An airport buys a great deal of it, continuously, at commercial retail prices, and it does so on a site that already has more of the ingredients of a microgrid than almost any farm or factory we work on: a single freeholder, a private distribution network behind one or two grid connections, standby generation, and an engineering team whose instinct is redundancy rather than novelty.

The arithmetic that governs everything else is the one we set out in use them where you make your own electrons. A unit made and used inside the fence displaces the full delivered price of electricity. The same unit exported earns a wholesale-linked rate, often three or four times less. An airport has the rare luxury of a load big enough to swallow almost everything it can make.

The land nobody can use

Walk the boundary of any regional airport and count the ground that is maintained but not used: the grass between taxiways, the strip inside the perimeter road, the noise bunds, the long car parks, the land under the approach that will never carry a building. It is mown at a cost every year and earns nothing.

This is the same argument we make about a capped landfill: the best solar site is usually the one with no competing use and a load nearby. An airfield has both, plus a security fence, a manned gate and CCTV already paid for. It is the best-defended solar site in the country and it is being cut with a tractor.

Why the panels stand up

The obvious answer, a field of tilted rows, is usually the wrong one airside. Flat, mown, drivable ground has operational value in itself, and anything that sits in the middle of it becomes a wildlife habitat, a snow trap and an obstruction argument.

A vertical bifacial fence line avoids most of that. Modules stood upright, glass on both faces, in a line along a boundary or between car park bays. The footprint is measured in centimetres. The mowing line stays clear. Snow does not sit on it. Sheep and machinery pass either side. And because it faces east and west rather than up, its output has two peaks, one in the morning and one in the late afternoon, instead of a single spike at noon.

That shape is worth money, for the reason set out in East-West arrays: every south-facing array in the country peaks at the same hour, and the market has responded by making that hour the least valuable one in the day. Airports are busiest at the shoulders, early departures and evening arrivals. Generation that arrives at the same time as the load is worth more than generation that arrives in a heap at midday and has nowhere to go.

The precedent is not theoretical. A major continental hub has run vertical bifacial fencing alongside its airfield infrastructure, on ground that had to stay clear, and it is producing. What that installation demonstrates is not a technology but a permission: an aerodrome safety case can be written for panels stood on end near operational surfaces.

Safeguarding comes first, not last

On any other site, planning is the gate. On an airfield, safeguarding is, and it should be engaged before a single layout is drawn. In practice that means four conversations.

None of these are reasons not to build. They are reasons to have the safeguarding manager in the room on day one rather than month nine, and to accept that the layout will be decided by the airfield rather than by the yield model. We would rather lose ten per cent of the generation and keep the scheme.

Foundations matter here too. Safeguarded land is land you may want back, and driven or wound-in ground screws can be unwound and the ground handed over as it was, which is a much easier conversation with an operations director than a line of concrete pads across the grass.

Where the electricity should go

In order, best first, because the order is the whole business case.

The terminal. Lighting, baggage systems, air handling, jet bridges, catering, IT rooms. A continuous base load, on the same site, at retail prices. Every unit that goes here is worth the most.

Ground support equipment and vehicles. Tugs, belt loaders, steps, buses and airside vans are electrifying, and the charging profile is dominated by turnaround gaps and overnight. Airports that electrify without generating simply move a fuel bill into an electricity bill and add a peak charge on top.

Passenger and staff charging. A car park is already a captive dwell of two hours to two weeks. Charging that is fed partly from the fence line beside it is both the cheapest kilowatt and the most visible one.

Batteries, for resilience as much as arbitrage. Peak shaving on the capacity charge, a smoother ride through the shoulders, and a genuine improvement to resilience that sits alongside standby generation rather than replacing it.

Then the neighbours. Cargo sheds, hotels, the maintenance apron, the business park at the gate. These buy at retail from a supplier today and sit within a few hundred metres of the generation, which is the private wire case in its simplest form. Export is what is left after all of that, not the plan.

The connection itself is usually the pinch point, and it is worth knowing early whether you are adding load, adding export, or both. That is a DNO conversation best had with a complete application rather than an optimistic one, and you can check the network at your postcode before spending anything.

The honest objections

Airside works are slow and expensive. Escorts, permits, night possessions, foreign object debris discipline. A cable run that costs a pound a metre on a farm does not cost a pound a metre across an operational apron. Price the access, not just the kit.

Airfield grassland is managed for bird hazard, not for wildflowers, so the biodiversity net gain story that works on a farm has to be rewritten here. The uplift is real but it has to be designed with the hazard management plan, not against it, and it may belong on the landside estate.

And solar does not touch the aircraft. It is worth saying plainly, because a scheme sold as decarbonising aviation will be judged against a standard it cannot meet. This decarbonises the airport as a building and a vehicle fleet, and it hedges a large operating cost for twenty-five years. That is enough.

An airport already owns the land, the load and the fence. All that is missing is the line along it.

We design and install for the people stewarding Britain's landscape and built environment, and an airfield is one of the largest single pieces of both that anyone is asked to look after. If you hold one, the first conversation is short: how long is your boundary, what does your half-hourly load look like, and who inside the organisation says yes to safeguarding.