Design and engineering

MCS is the domestic scheme. On a commercial array it is not the thing that protects your capital, and we do not present it as one. What protects your capital is a design that meets named engineering standards, a contract that holds the parties to them, and a sign-off discipline that does not let the installer mark his own work.

The drawings, the load model and the specification are the asset you are actually buying. Everything the system earns over its design life is set on paper before a single fixing goes onto the roof. This page sets out the standards the design is held to and the discipline that signs it off.

A commercial design is assured by a stack of named standards rather than a single badge. Each one governs a different part of the work, and together they are how a system over 50 kWp is signed off without MCS.

• BS 7671 governs the electrical installation: the wiring, the earthing and the protection.
• IEC 62446-1 governs commissioning and inspection: the documentation and tests a PV system is handed over against.
• A G99 connection agrees with your Distribution Network Operator how the array connects and exports safely.
• CDM 2015 governs how the project is planned and built so the work is safe and properly co-ordinated.
• A JCT or NEC contract holds the parties to all of the above, with a defects period that survives switch-on.

Standards only matter if they reach the parts that fail first. The detail that decides whether a system runs for its design life is in the joints, the protection and the cable, so we hold a fixed specification at component level.

Every joint we make on site uses a sealed connector rather than a taped or improvised one, because a wet or corroded DC joint is a common cause of underperformance and fire risk on older arrays. Earthing and surge protection are specified to BS 7671, so the array is protected against faults and transients rather than left exposed. Cable is sized and rated for the design life of the system rather than the minimum that passes on the day, so it is not carrying avoidable losses or running hot later in its design life.

The discipline that matters most is the one that stops a job marking its own homework. On every install, our Qualifying Supervisor reviews the install report before the work is signed off. The Qualifying Supervisor is a fully AM2-trained electrician, the practical assessment that confirms an electrician can install and test to the standard, so the review is a competent second set of eyes rather than a rubber stamp.

The point is simple. The installer never signs himself off. The engineer who built the job and the engineer who approves it are not the same person, which is how a defect gets caught on paper before it becomes a fault on the array.

We describe the design in terms of the standards it meets and the discipline that signs it off rather than a headline number we cannot stand behind. There is no fabricated uptime figure or service-level promise here, because an honest engineering claim is one you can name the standard for.

That engineer-led approach runs across the group of three companies. Alectrona installs to this design standard, Sentinel is a free independent monitoring app so you can see the asset for yourself, and Solar Tech Support is the independent brand-agnostic diagnostics and repair arm for when something does need a hands-on fix.

The design does not start at a desk with a satellite photo. It starts with a measured survey of your actual roof, and on a commercial array that survey is flown rather than walked. Our pilot holds an in-house A2 Certificate of Competency and a General Visual Line of Sight operational authorisation, and the drone work is fully insured, so we capture the roof without standing a team on a fragile or live surface to do it. That matters to the design because the model is only as honest as the data it is built on.

The flight produces three things the engineering depends on. A measured layout of the usable roof area, so the panel count and array geometry are drawn against real dimensions rather than an estimate. A shading read across the day, so strings are arranged to keep a shaded module from dragging its neighbours down. And, where a thermal pass is flown, a heat picture that surfaces a delaminating membrane or an existing hot joint before anything new is fixed to it. The same thermographic discipline underpins the IEC 62446-1 commissioning inspection later, so the array is checked the way it was designed. The full method is set out on the 3D drone survey page.

An array over 50 kWp cannot simply be switched on and left to export. It connects under a G99 agreement with the Distribution Network Operator, which across Yorkshire and northern Lincolnshire is Northern Powergrid and across Greater Manchester and Lancashire is SP Electricity North West, formerly Electricity North West. The G99 application tells the network operator how much the system will generate and export, and the operator returns a connection offer that may set an export limit, ask for additional protection, or in some cases require reinforcement before the full capacity is allowed onto the local network.

This is why the engineering design and the connection are worked in step rather than one after the other. The export limit the operator agrees feeds straight back into the inverter configuration and the array sizing, so we hold the design open until the G99 position is clear instead of installing capacity the network will not accept. It is also a real part of the programme: the turnaround belongs to the network operator rather than to us, so we lodge the application early. How that timeline runs alongside survey, design and install is covered on the how we quote page, and the export side connects to the wider economic picture set out across the commercial finance pages.

A rooftop install over 50 kWp is construction work, and it falls under the Construction (Design and Management) Regulations 2015. CDM is not paperwork bolted on at the end. It assigns clear duties from the design stage, names who plans the work and who controls the site, and requires that the way the system will be built and later maintained is thought through before anyone goes up. For a finance or facilities director that is the difference between a co-ordinated project and an uninsured liability on your roof.

In practice it means the access, the fall protection, the isolation procedure and the sequence of work are designed alongside the electrical system rather than improvised on the day, and that the project hands over a health and safety file the building keeps. That file tells whoever maintains the array in five years' time how it was built and how to work on it safely, which is the same continuity the operations and maintenance service relies on. CDM, the named standards and the JCT or NEC contract are the three things that together stand in for MCS at this scale.

Before you commit to anything, the survey and the model are already done and the outputs are yours: the drone survey report and the 3D roof model, the PV*SOL yield and self-consumption model built against your own half-hourly data, a single-line electrical diagram, the array layout on your roof, an itemised specification naming the actual modules, inverters and mounting system, and a programme. The figure attached to that is calculated from your building. We publish no price per kWp and no from-price, because neither can be honest before the roof has been surveyed.

At handover you receive the full document pack: BS 7671 electrical certification, IEC 62446-1 commissioning and test data, the G99 connection paperwork and any G100 export-limitation evidence, as-built drawings, the operations and maintenance manual, the warranty schedule for every component with its start dates, and the handover of monitoring so you can see the system yourself from day one. The install report is reviewed and signed off by the Qualifying Supervisor, and the electrical work is carried out by an AM2-trained electrician, before anything is energised.

After handover there is a defined defects rectification period, and ongoing operations and maintenance if you want it. The group is built so that the people who monitor the system and the people who diagnose and repair it are the same engineering business that installed it, rather than a subcontractor you have never met. Any saving or payback figure for your site comes out of your survey and your PV*SOL model. It is indicative general information about energy performance rather than financial or tax advice, and the tax treatment of any funding route belongs with your accountant.

This is a worked example rather than a delivered project. Alectrona publishes no completed installs and no client references, so the building, its load and its grid position are illustrative and deliberately kept qualitative. The modelling, the named standards and the survey method are exactly how we would design and build a system of this kind, and there is no generation, saving or payback figure here because we hold no metered record we could stand behind.

A distribution centre on a single-span flat roof carries a firmly daytime load. Forklift and materials-handling charging, conveyor and sortation plant, lighting and the building services all draw hardest across the working shift, which is the same window the roof generates in. Two constraints shape the work from the start. A roof of this kind is large but often lightly loaded structurally, so the mounting system has to stay inside what the deck and frame can safely carry, checked for wind loading to BS EN 1991-1-4 for the building height and exposure. And where the local network has limited headroom, an unconstrained full-export connection risks a slow and expensive path through the network operator's assessment.

The starting point is the half-hourly meter data, modelled against generation in PV*SOL, because that is what shows how much of each generated unit is used on site rather than exported. The array is sized to that shift pattern so it tracks the load rather than overshooting into low-value export. The roof is captured by an in-house drone survey and processed into a 3D model that fixes the usable area once the firefighter access set-backs, the plant, the rooflights and the penetrations are taken out. With self-consumption high, an export-limited design is the natural fit: the connection is constrained under G100 so the system asks little or nothing of the network on the export side, which can avoid triggering reinforcement and shorten the path to a G99 connection agreement. What the method produces is an array where most of what the roof makes offsets an imported unit directly, on a capital case resting on the building's own consumption rather than a generic headline figure.

The same method meets a harder modelling problem on a stadium stand roof, and this too is a worked example rather than a delivered project. For most of the week a ground draws a modest baseload from offices, hospitality kitchens, ground maintenance and the club shop. On a match day that profile changes completely, with floodlights, catering and crowd facilities running at once, often into the evening when a rooftop array is producing little or nothing. The work also cannot interfere with fixtures, safety certification or the day-to-day running of the ground.

So the load leads, not the roof. We model consumption across a typical week in PV*SOL and size the array to the daytime baseload it can genuinely offset rather than to the headline area of the roof. That is also where a battery earns its place or fails to, because shifting midday generation into an evening peak is exactly the job storage does, and the model shows whether the arithmetic works before anyone specifies one. A stand roof is a more demanding structural read than a warehouse deck, and wind loading to BS EN 1991-1-4 matters more on an exposed, high roof, so mounting is specified to suit the construction with a non-penetrative, weather-tight approach wherever the structure allows. The connection goes through the formal G99 process, the array is certified to BS 7671 and inspected to IEC 62446-1, and CDM 2015 does more work than usual on a site with its own safety certification and a public crowd to think about. We describe the outcome qualitatively and quote no generation, saving or payback number, because none exists that we could evidence.