PV*SOL 3D Solar Layout Design for UK Rooftop PV Systems

PV*SOL 3D Solar Layout Design for UK Rooftop PV Systems: What Every EPC Contractor Needs to Know

The UK solar market installed over 1.3 GW of new solar capacity in 2023 alone, with commercial rooftop installations accounting for a growing share of that figure. Yet despite the surge in demand, a significant number of EPC contractors are still submitting design packages that fail at the grid connection stage, underperform against yield projections, or require costly redesigns because the original PV*SOL 3D solar layout design for UK rooftop PV systems was configured incorrectly from the start. The gap between using PV*SOL and using it well is wider than most contractors realise, and the consequences of that gap are measured in kilowatt-hours, client relationships, and engineering hours lost.

This guide is written specifically for EPC contractors, design engineers, and project managers working on UK commercial and industrial rooftop solar projects. It covers how to build an accurate 3D model in PV*SOL, how to run shading simulations that hold up against independent verification, how to satisfy G98 and G99 requirements at the string configuration stage, and how to produce design outputs that slot cleanly into downstream AutoCAD workflows. Where relevant, it also addresses the most common errors we see in designs submitted to professional solar engineering support services and how they can be resolved before they cost you a project.

Importing Roof Geometry and Setting Tilt and Azimuth Angles in PV*SOL for UK Installations

One of the most instructive failure cases in commercial rooftop solar design UK involves a 480 kWp logistics centre project in the East Midlands. The EPC team had produced what appeared to be a polished PV*SOL output. The yield report looked reasonable. The shading simulation had been run. The problem emerged during site survey when the installer realised the design had been built using a single flat roof plane, when the actual structure had four pitches at varying inclinations between 8 and 22 degrees, two plant rooms breaking the southern elevation, and a sawtooth northern rooflight running the full length of the building. The 3D model bore almost no resemblance to the physical asset.

Accurate roof geometry is the foundation of every reliable 3D PV system design. PV*SOL Premium allows you to build multi-plane roof models by adding individual roof surfaces, each with its own tilt angle, azimuth orientation, and ridge height. For UK projects, the most reliable starting geometry comes from one of three sources: a measured building survey, an architect or structural drawing set with confirmed ridge and eaves levels, or an aerial survey produced via drone photogrammetry. Google Maps roof tracing within PV*SOL is useful for initial scoping only and should never be used as the geometric basis for a final design submission.

When setting azimuth in PV*SOL, remember that the software uses a meteorological convention where south is 0 degrees, east is negative 90, and west is positive 90. For UK rooftop installations, any roof surface deviating more than 45 degrees from true south will require a specific yield sensitivity analysis showing the client what they are losing relative to an optimal orientation. Multi-pitched roofs with east-west split arrays are increasingly common in the UK commercial sector because they reduce peak export to the grid, which is directly relevant for G99 applications where the DNO may impose export limitation as a condition of connection.

Handling Complex Multi-Pitched Roofs in the PV*SOL 3D Environment

PV*SOL’s roof surface editor allows you to define hip ends, dormers, and irregular polygonal planes, which is essential for the kind of older industrial stock that makes up a large portion of the UK commercial rooftop opportunity. The workflow for a complex multi-pitched roof follows a logical sequence. You begin by modelling each distinct plane as a separate surface object, assigning the correct pitch and orientation to each. You then define the building perimeter and any rooftop obstructions, including plant rooms, smoke vents, rooflights, and parapet walls, as 3D obstacle objects.

The critical step that is frequently skipped is setting the correct parapet height and standoff distances as physical objects rather than simply excluding those areas from the panel placement grid. When modelled as 3D objects, parapets cast accurate near-field shadows on adjacent panel rows, which materially affects the shading simulation output. When they are simply treated as exclusion zones, the shading loss from those objects disappears from the energy yield model entirely.

PV*SOL Shading Analysis: How the 3D Simulation Engine Works and How It Compares to PVsyst

The PV*SOL shading analysis engine operates on a time-step simulation basis, calculating the irradiance incident on each defined roof surface at hourly intervals throughout the reference meteorological year. It does this by computing the sun’s position relative to the modelled scene geometry, identifying which panel strings are shaded by which objects at each time step, and then applying string-level electrical shading losses to the energy yield calculation.

Where PV*SOL and PVsyst diverge most significantly is in how they handle near-shading electrical effects. PVsyst uses a detailed module-by-module bypass diode model within its near-shading module, allowing the designer to specify whether individual strings or entire sub-arrays are affected by a shading event. PV*SOL’s approach is computationally lighter and uses a shading factor table approach, which can be faster to set up but requires the designer to carefully validate the electrical shading loss settings against the actual bypass diode topology of the chosen module.

In practice, for typical UK commercial rooftop projects with relatively straightforward rectangular arrays, the yield difference between a correctly configured PV*SOL model and an equivalent PVsyst model is usually within 1 to 2 percent. The divergence grows when you have complex shading patterns, non-standard string configurations, or bifacial modules, where PVsyst’s more granular approach tends to produce more defensible results. For solar layout optimisation on projects where the yield model is central to the financial model or a planning condition, having both tools cross-validate the output is worth the additional engineering time.

Running an Accurate Shading Simulation in PV*SOL: A Step-by-Step Approach

Start by confirming that the meteorological dataset loaded in PV*SOL matches the project location. PV*SOL draws from the Meteonorm dataset, and for UK sites you should verify that the loaded weather file corresponds to the correct grid cell rather than defaulting to the nearest major city. A project in Aberdeenshire using Edinburgh weather data will carry a meaningful irradiance error that compounds through every downstream yield calculation.

Once the weather file is confirmed, run the 3D shading scene calculation and review the annual shading loss value against your initial expectation. For a well-designed UK commercial rooftop with adequate row spacing and no significant near-field obstructions, annual shading losses below 3 percent are achievable. If your model is returning figures above 5 percent, investigate whether all roof obstacles have been correctly modelled in 3D before accepting that figure as accurate. A number of elevated shading loss values we have reviewed turned out to be caused by a single incorrectly placed obstacle object casting a shadow across the entire southern array face.

String Configuration and Inverter Matching in PV*SOL to Satisfy UK G99 and G98 Requirements

The string configuration stage is where a well-modelled 3D scene can still produce a non-compliant design. The solar panel layout tool within PV*SOL is sophisticated, but it does not automatically ensure that your inverter selection and string configuration meet the requirements of Engineering Recommendation G99 or G98. That validation step requires the designer to apply the rules manually and cross-reference the PV*SOL electrical output against DNO submission requirements.

G99 applies to generating units with a registered capacity above 50 kW connected at low voltage, or any installation connected at high voltage. G98 applies to units below 16 A per phase at low voltage. For the majority of commercial rooftop PV UK projects in the 50 to 500 kWp range, the relevant standard is G99, which requires a formal application to the Distribution Network Operator and compliance with specific protective relay settings, power quality requirements, and, increasingly, export limitation or active network management conditions.

How PV*SOL Supports G99-Compliant Inverter Selection

PV*SOL’s inverter database includes most of the major inverter brands active in the UK market, and the software’s inverter matching tool flags configurations where the DC voltage or current falls outside the inverter’s specified operating range. However, it does not automatically check whether the selected inverter model holds the relevant G99 type-tested approval under the MCS or equivalent certification framework. That check must be performed separately, typically by cross-referencing against the relevant inverter manufacturer’s UK G99 compliance documentation.

A scenario we see repeatedly in submitted designs involves a correctly sized PV*SOL output where the designer has selected an inverter variant for its favourable clipping ratio, without confirming that the specific firmware version installed on site is the same version covered by the G99 type test certificate. DNOs are increasingly rigorous about this, and a firmware mismatch discovered at the commissioning stage can delay an energisation date by weeks.

Within PV*SOL, the string configuration tool allows you to define maximum string lengths, minimum operating temperatures, and cable resistance parameters. For UK projects, always set the minimum temperature to minus 10 degrees Celsius for open-field-equivalent rooftop conditions, particularly for exposed industrial roofs in northern England and Scotland. This directly affects the maximum open-circuit voltage calculation and therefore the number of modules you can safely connect in series without exceeding the inverter’s DC input voltage limit.

Exporting PV*SOL Design Outputs to Support AutoCAD Electrical Schematic Workflows

One of the most underused capabilities of PV*SOL Premium in the UK EPC market is its design export functionality. The software can produce scaled layout drawings, shadow diagrams, detailed yield reports, and system summary sheets that, when correctly configured, significantly reduce the time required to produce a full design package for planning, building warrant, or DNO submission.

The standard export workflow for a UK commercial rooftop project typically involves producing a DXF or DWG file of the 3D roof layout from PV*SOL, importing that file into AutoCAD or AutoCAD Electrical as a base layer, and then overlaying the electrical schematic elements: DC string wiring, combiner box locations, cable routes, AC distribution board connections, and metering arrangements. The PV*SOL DXF export preserves the scaled panel positions and roof geometry, which means your AutoCAD draughtsperson is working from a geometrically accurate base rather than redrawing the layout from scratch.

Configuring PV*SOL Outputs for Planning and DNO Submission

For planning applications, particularly where a commercial rooftop installation requires prior approval or full planning permission under Permitted Development thresholds, the shadow diagram output from PV*SOL is directly usable as a supporting document. The diagram shows the annual shading pattern cast by the array onto the roof surface and surrounding context, which addresses the most common concern raised by planning officers regarding visual impact and overshadowing.

For G99 DNO submissions, the PV*SOL simulation output provides the generation forecast data required by the DNO to assess the impact of the proposed installation on the local network. The key figures required are peak AC output, annual energy generation, and, where applicable, the export limitation setpoint confirmed by the inverter control system. PV*SOL’s report export function produces a PDF summary that includes all of these values in a standardised format.

Before you finalise any export, work through the solar design preparation checklist to confirm that every required element is present and correctly formatted. Missing or incorrectly labelled outputs are among the most common reasons for DNO submission rejections and planning application deferrals in the UK market.

Common Errors EPC Contractors Make When Using PV*SOL for UK Commercial Rooftop Projects

Having reviewed hundreds of PV*SOL design packages for UK commercial projects, the errors that recur most frequently are not the result of unfamiliarity with the software. They are the result of process gaps: points in the design workflow where a critical decision is made without the right information, or where a default setting is accepted without being verified against the specific project conditions.

Using Default Performance Ratio Values Without Site-Specific Justification

PV*SOL applies individual loss parameters rather than a blanket performance ratio, which is one of its strengths compared to simpler yield tools. However, when designers leave soiling loss, cable loss, and transformer loss parameters at their factory defaults without adjusting for the specific site conditions, the resulting yield figure can be meaningfully optimistic. A rooftop in a high-traffic industrial area near a motorway junction will carry a soiling loss significantly higher than the default value, particularly if the roof pitch is shallow and there is no regular maintenance programme in place. Documenting the basis for each loss parameter in the design report is both good engineering practice and increasingly expected by technical due diligence reviewers on financed projects.

Incorrect Module Orientation and Row Spacing on Low-Pitch Roofs

On flat or near-flat roofs, which account for a large proportion of the UK commercial rooftop opportunity, the inter-row spacing required to limit mutual shading losses to an acceptable level is one of the most consequential design decisions made in PV*SOL. The correct row spacing depends on the module tilt, the latitude of the site, and the minimum solar elevation angle at which you are willing to accept unobstructed irradiance. For UK sites at latitudes between 51 and 57 degrees north, a common design target is to achieve zero row-to-row shading for solar elevation angles above 10 degrees, which typically corresponds to a pitch-to-height ratio of around 3.5 to 4 for a 10-degree tilt.

Designers using the automatic panel placement function in PV*SOL sometimes accept the default row spacing without checking whether it meets this criterion for the specific latitude of their project. The automatic placement tool optimises for maximum panel count within the available roof area, not for minimum shading loss, and on a large flat roof the difference in annual yield between an optimised and a default spacing can represent tens of thousands of kilowatt-hours over the system lifetime.

Omitting Horizon Shading for Rural and Peri-Urban Sites

For commercial rooftop projects in rural locations, particularly sites in valley positions or with elevated terrain to the south, the horizon shading profile can reduce annual yield by 1 to 3 percent even when there are no near-field obstacles. PV*SOL allows you to import a horizon profile directly from the Meteonorm dataset or enter it manually based on a surveyed horizon angle at each azimuth direction. This step is routinely omitted from designs submitted for commercial projects outside urban areas, producing yield figures that are not achievable at the actual site.

How Lion Solar Solutions Supports EPC Contractors Through These Challenges

Lion Solar Solutions provides specialist PV*SOL EPC contractor support services for UK commercial and industrial projects, including independent design review, full PV*SOL design production, and technical due diligence for investor and lender reporting. For contractors who need a robust, submission-ready design package without the internal resource to produce it, our engineering team works to the same standard regardless of project scale. You can learn more about how the design process is structured in our guide on how a PV solar system is designed.

Solar Layout Optimisation Strategies for Maximum Commercial Rooftop Yield in the UK

Beyond avoiding errors, the most commercially valuable use of PV*SOL for UK rooftop projects is as an iterative optimisation tool. Running multiple design scenarios within a single project file allows the designer to quantify the yield and cost trade-offs between different layout strategies before a single panel is ordered.

A practical example from a 350 kWp distribution centre project in Yorkshire illustrates this well. The initial design used a uniform 10-degree east-west split layout across the full roof area, producing a peak export of 180 kW and an annual yield of approximately 310,000 kWh. The DNO’s indicative G99 offer came back with a 150 kW export limitation condition, which would have required an active export limitation system and associated capital cost. By running three alternative layout scenarios in PV*SOL, the design team identified that reconfiguring the southern section of the array to a higher-pitch south-facing arrangement, while reducing the total panel count by 8 percent, shifted the daily generation profile and reduced the peak export to 148 kW without the export limitation system, satisfying the DNO condition and avoiding approximately 12,000 GBP in additional hardware cost.

This kind of iterative scenario analysis is only possible when the solar roof planning UK process includes adequate time for design iteration before the G99 application is submitted. Rushing the design stage to meet a procurement deadline is consistently one of the most expensive decisions an EPC contractor can make on a commercial rooftop project.

Frequently Asked Questions About PV*SOL 3D Solar Layout Design for UK Rooftop PV Systems

The following questions address the most frequent queries we receive from EPC contractors and design engineers working with PV*SOL on UK commercial rooftop solar projects.

Conclusion: Getting More From PV*SOL on Every UK Rooftop Solar Project

PV*SOL is one of the most capable tools available for rooftop solar design UK professionals, but its value is entirely dependent on the rigour with which it is applied. The contractors who consistently produce accurate, submission-ready designs with PV*SOL are not necessarily those with the longest experience of the software. They are the ones who treat every input parameter as a decision that requires justification, who model the physical reality of the site rather than an idealised version of it, and who use the iterative scenario capability of the tool to genuinely optimise the design rather than simply produce a single output for documentation purposes.

The areas where UK EPC contractors most frequently lose value through PV*SOL are predictable and preventable: incomplete roof geometry, default meteorological data, unvalidated loss parameters, and string configurations that have not been cross-checked against current G99 documentation. Addressing each of these systematically produces designs that are more accurate, more defensible, and more likely to deliver the yield and financial returns that clients are counting on.

For contractors who need additional resource or a second set of expert eyes on a complex design, specialist engineering support can make the difference between a project that progresses smoothly through DNO application and planning, and one that requires expensive rework at a late stage. Whether you are working on your first large commercial rooftop project or your fiftieth, the underlying discipline of thorough, site-specific PV*SOL simulation is what separates reliable design from optimistic paperwork.

Heval Arcan