Ground-Mounted Solar Installation

When the ground beats the roof

Some roofs cannot take an array. They face north, they are overshadowed by a mature oak, they are listed, they are Cornish slate at the end of its life, or the rafters are undersized and strengthening them costs more than the panels.

Where there is usable land, a ground mount removes all of those constraints at once. It also removes scaffolding, gives you free choice of orientation and tilt, and puts every component within reach of someone standing on grass.

What it adds is groundwork, a cable run, and a planning question.

Choosing the position

The position is a compromise between four things.

• Shading. Ground level sees more obstruction than roof level. Hedges grow, neighbouring boundaries have fences, and a low winter sun is blocked by things that are irrelevant in June. We assess shading across the whole year, not on the day of the survey.
• Distance. Every metre is trench, duct and cable. It is rarely a technical problem and always a cost.
• What the trench crosses. A run across lawn is simple. A run under a gravel drive, a patio, a mature root protection area or an existing service is not.
• What you want to look at. Arrays are large and dark and they do not disappear into a garden. Where it goes matters as much for living with it as for generation.

Foundations

The frame has to resist both the weight of the array and the wind trying to lift it, and that resistance comes from the ground.

Screw piles are the usual answer. Helical steel piles wound into the soil, with no concrete, no spoil to dispose of, and immediate load-bearing capacity. They suit most reasonable soil, they can be adjusted for level, and they can be removed if the array is ever taken away.

Concrete pads or ballast take over where screw piles cannot get purchase — shallow soil over rock, heavily made-up ground, or sites where digging is restricted. They are heavier, slower and more disruptive, but they work where nothing else will.

Ground conditions decide this, which is why a proper look at the site precedes any quotation.

The cable run

Running DC from the array to an inverter near the house is generally more efficient than converting at the array and running AC, because the higher string voltage means lower current and lower losses for the same power.

Whichever approach is used, the cable is sized for the run, not chosen from habit. Voltage drop over eighty metres at the wrong cable size quietly costs generation for the life of the system. Cable goes in duct or as armoured cable, at a proper depth, with marker tape above it so the next person with a spade knows it is there.

Planning

This is the part that most often changes the plan. Permitted development rights for a standalone array at a house exist but are narrow — limited in footprint and height, normally one installation per property, and restricted close to boundaries and in designated areas. Listed buildings and conservation areas bring further constraints.

We check the position before design work starts. Where an application is needed we will tell you what is likely to matter to the case officer — visibility from public vantage points, the relationship to boundaries, and screening — but the application itself is yours to make or to appoint someone for.

Living with it

Ground arrays need a little more attention than roof arrays. Grass grows and shades the lower row. Mud splashes onto the bottom edge of the panels in winter. Livestock lean on frames, and rabbits find cables interesting. None of these are difficult problems, but they are why we specify frames with adequate clearance and route cable where nothing can chew it.