There is a version of commercial solar that treats design as an afterthought. A quick panel layout generated by software, dropped into a proposal, and handed over. The problems that approach creates then appear during installation, during maintenance, and in the gap between what a system was projected to produce and what it does. In this article, Tom Mayers, Solar PV Design Engineer at Lynx Sustainable Solutions, explains what good design involves.
I sometimes joke that my job is putting squares on a roof. From the outside, that is what it can look like. But there is a significant amount of work that goes into those squares before they go anywhere near a roof.
Good design starts with how a building uses energy, not how big its roof is
The first thing we ask for when a client comes to us is their half-hourly energy consumption data. That matters because a solar PV system should be built around a building’s energy use, and a large warehouse with a huge roof might have relatively modest energy consumption. Fill that roof with panels, and a significant proportion of the output goes straight back to the grid, which is not worthless, but it does raise the question of whether the capital expenditure was justified. If you are exporting half of what you generate, it is worth asking whether the system was sized with your consumption in mind.
A well-designed system matches generation to consumption as closely as possible. That means the starting point is always the load profile, not the roof space.
Every commercial roof presents a different challenge
Once we understand the energy picture, we start looking at the roof itself.
No two commercial roofs present the same design challenge. The structural capacity of the roof, what shades it and from where, which direction it faces, its profile, and what the grid connection allows all shape what is possible and where. Get any one of those wrong, and you are either redesigning on-site or leaving performance on the table for the life of the system.
All of that must be understood before a design can be finalised. Some of it can be established remotely. We use Google Earth 3D models, shading simulation software, and consumption data to build an initial picture, but remote analysis only gets you so far.
What a site survey changes
The initial proposal is always produced with the caveat that a physical survey is needed before anything is finalised.
When we go on site, we can see what a satellite image cannot: the exact condition of the roof, what is already on the roof and where, what the electrical infrastructure looks like inside the building, and where cables can and cannot be run safely. The electrical side is particularly important. Until we have eyes on the distribution board and the incoming supply, we are making educated guesses about the connection design.
After the survey, a detailed report is produced covering everything found on site. That feeds back into the design, which is then reviewed before anything is issued. On a standard warehouse project, we typically go through six to eight design iterations before we reach a contract pack. On more complex projects, it can be significantly more. Not because things keep going wrong, but because the design evolves as we get more information and as the client’s requirements develop.
What it looks like when someone puts squares on a roof
We have worked on projects where the initial design was produced by someone without a background in solar. The results were instructive.
On one tender, we were handed designs that had clearly been put together without solar-specific expertise. Unfortunately, most of the roofs we had to work with faced north, which isn’t great for PV generation in the UK. There were no thermal gaps between panels, which are essential because metal components expand and contract with temperature changes and without them, you risk structural problems over time. Panels were specified right up to the roof edges with no maintenance access. In some sections, they were within 100 millimetres of the roof lights, whereas the minimum compliant clearance is 500 millimetres. The designs did not even meet the specifications set out for the same tender.
The installers were being asked to work on a roof with no safe way to operate. Getting it to a workable state required significant redesign. That work could have happened at the start, at no cost to anyone, with the right expertise involved from the beginning.
What to look for when a solar design lands on your desk
If you are evaluating solar proposals, a few things are worth checking before you go any further.
Look at the generation report. It should show projected output and how that maps to your energy consumption. If the system is projected to export a large share of its output, ask why it was sized to do so. It may be intentional. It may not be.
Look at the quality of the drawings. A properly designed system will be presented in detailed CAD drawings, including notes, dimensions, revision history, and clear annotations of components and cable runs. If what you have been sent appears to have been auto-generated with panels dropped onto a roof image, that is worth paying attention to. The quality of the drawings reflects the quality of the thinking behind them.
And ask whether the due diligence has been done. Is there a shading analysis? Has a structural assessment been carried out? Is there a clear electrical design? The documentation that supports a design tells you a great deal about the process that produced it.
The design process is where a project is either set up well or not. By the time anyone sets foot on site, most of the decisions that determine how a system performs over the next 25 years have already been made. A system that has not been designed properly will not perform as projected, will not be straightforward to maintain, and will not deliver on the goals it was installed to meet. That is why we put so much stock in getting the design right and implementing the quality controls that produce results for our clients.
If you are considering solar as part of your estate’s decarbonisation strategy, please get in touch.