Solar PV Sizing Tool
A guided 16-step engineering calculator for solar system design
A guided solar PV design application that walks the user through load auditing, inverter sizing, battery bank configuration, panel arrangement, protection, cable sizing, and a final market search — built for Nigeria and global standards.
What needed to change
Solar installers and DIY designers in Nigeria routinely size systems by gut feel or by copying specs from unrelated installations. The result is either undersized systems that fail under load, or oversized systems that waste money on unnecessary panels and batteries. There was no structured, auditable tool that walks a designer through every step from load audit to final bill of materials — one that respects Nigeria-specific conditions like high ambient temperature, cloudy regions, and local market pricing.
What made it hard
- Must work offline-first — Nigerian installers are often on site with poor internet.
- Must handle both 12V/24V small residential systems and 48V+ commercial systems with multiple MPPT trackers.
- Must validate MPPT voltage windows, not just power — many tools skip this and produce designs that trip inverters.
- Must produce a downloadable report the installer can hand to the customer.
- Must reflect Nigerian market pricing and locally available components.
How we built it
We built a 16-step wizard that mirrors the actual engineering workflow. Each step validates its inputs against the inverter's real specifications before allowing the user to continue. The calculation engine is split into 20+ pure functions (load audit, energy calculation, inverter sizing, battery sizing, panel arrangement, protection, cable sizing, validation) — each one independently tested with Vitest. The state lives in a single Zustand store, which makes 'go back and change something' work cleanly without stale values. The whole thing runs client-side, so it works with no backend and can be used offline after first load.
What it does
- 16-step guided workflow from load audit to final design
- Automatic component matching against a Nigerian market database
- Multiple MPPT tracker support for commercial inverters
- Series/parallel panel arrangement calculator with voltage-window validation
- Protection and cable sizing with ambient temperature derating
- Nigeria-specific defaults (peak sun hours, PR, market prices)
- PDF export of the complete bill of materials
- Shareable design summary
What changed
The tool is now live at /solar-sizing and is being used by our own installation team as a pre-audit step before site visits. It has reduced the time to produce a first-pass design from several hours of spreadsheet work to under 10 minutes. It also serves as a lead-generation asset — visitors who try the tool often contact us to discuss a real installation.
What I'd do differently
The hardest part wasn't the calculations — it was the UX for the panel arrangement step. Small residential systems (4–6 panels) and commercial systems (50+ panels) need completely different UIs, but we wanted one component that handles both. We solved it with a 'simplified view' for arrays above 40 panels, which shows the series/parallel structure without rendering hundreds of individual panel rectangles. In a future version, I would add a visual panel-layout designer that respects roof geometry.
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