Solar system design covers everything before installation: array sizing, 3D layout, SAP/HEM compliance modelling, inverter and battery specification, and the Building Control compliance pack. We deliver it as a single Stage 2-4 architect-coordinated package or as a standalone design-only commission.
What our design service includes
- 1Plot or scheme assessment. Drawings review (DWG, PDF, SKP), ground floor area calculation, roof orientation analysis, shading study using satellite imagery and adjacent building data.
- 2Array sizing. FHS 40% rule minimum plus a recommended over-size (typically 15-30% above minimum) based on household demand profile, EV expectation and battery plan.
- 33D solar PV design. Panel placement on the roof model, annual generation analysis using PVsyst, monthly generation profile, sun-path overlay, shading impact at solstices.
- 4SAP 10.3 and HEM modelling. Dual-route Part L 2026 compliance modelling. DER vs TER calculation, EPC band projection, recommendations to improve fabric performance where the headroom is marginal.
- 5Inverter and battery specification. Hybrid inverter sized to the array and future battery; battery capacity recommendation aligned to household load profile and tariff plan; ASHP electrical loading coordination.
- 6Building Control compliance pack. Submission-ready documentation for the Approved Inspector or LABC route. Includes SAP/HEM file, panel and inverter data sheets, BBA certificate references, mounting hardware specification.
RIBA stages and the right engagement point
When you engage us during your build project materially affects what we can do for you:
| RIBA Stage | Decisions still open | What we can do |
|---|---|---|
| 2 — Concept Design | Roof geometry, glazing ratio, plot orientation | Influence architectural decisions for optimal PV |
| 3 — Spatial Coordination | M&E layout, inverter location, service routing | Coordinate PV with the rest of building services |
| 4 — Technical Design | Panel make and model, mounting hardware spec | Specify the system within the existing design |
| 5 — Manufacturing | Installation programme only | Limited optimisation — system must fit what's already designed |
For self-builders we recommend engaging at Stage 2 if possible — the cost of design coordination is no different but the optimisation upside is meaningfully larger.
Custom solar systems for non-standard projects
Standard 3-bed semis with south-facing pitched roofs are straightforward — but most architect-led projects aren\'t standard. We have designed solar systems for: contemporary flat-roof self-builds with ballasted arrays; AONB replacement dwellings using BIPV slate; modular off-site MMC homes with factory pre-fit; passive house specifications above FHS minimum; mixed-use developments with shared communal arrays; and Conservation Area listed-curtilage infill plots. The methodology is the same — the constraints are different.
For volume housebuilders, our house-type design service is amortised across plot count. We design the system once for each house type in your portfolio; you build to the same specification across hundreds or thousands of plots. Per-plot design cost falls from £450 on a 50-plot first installation to ~£180 on a 500-plot framework.
Tools and outputs
Our design package uses industry-standard tools: PVsyst for production modelling and shading analysis; OpenSolar for fast 3D plot-level design; SketchUp for architectural visualisation handed back to your architect; Elmhurst Design SAP and the BRE HEM engine for compliance modelling. Outputs to clients: PDF design report, 3D model in SKP and DWG, PVsyst report, SAP/HEM models, complete Building Control submission pack.
To book a design consultation, request a free 30-minute call. For an initial cost estimate sized to your plot, use the FHS PV calculator.