Panel Technology for Estimators — Mono PERC, TOPCon, Bifacial
You do not need to be a cell physicist to estimate solar. You need to read four numbers off the datasheet and know what they do to the design.
The technologies
| Type | Module efficiency | Temp coeff (Pmax) | Note |
|---|---|---|---|
| Mono PERC | 20–21% | ~−0.35%/°C | Mature, lowest cost/W |
| TOPCon | 21.5–23% | ~−0.30%/°C | Now mainstream, better hot-climate yield |
| HJT | 22–24% | ~−0.24%/°C | Best temperature behaviour, premium price |
What each number does
- Efficiency → watts per m² → how much roof you need for a target kWp. Higher efficiency = fewer panels, less racking, less labour.
- Temperature coefficient → in a 65 °C cell, a −0.30%/°C panel loses ~12% vs a −0.35%/°C panel losing ~14%. Matters a lot in the tropics.
- First-year degradation (1–2%) and annual degradation (0.4–0.55%) → feed the 25-year yield and warranty.
Bifacial
Bifacial modules capture reflected light on the back. Rear gain is 5–10% on a light-coloured flat roof or ground mount with high albedo, near zero flush-mounted on a dark roof. Only model bifacial gain when the install actually supports it — and note bifacial modules need a slightly higher DC current rating in the cable and MPPT check.
Estimating takeaway
For a fixed roof area, higher-efficiency modules raise the achievable kWp and lower balance-of-system cost per watt, partly offsetting their price premium. Run the BOM both ways when the roof is the constraint.
EngEst Pro’s Solar PV Calculator uses the panel’s efficiency, temperature coefficient, and degradation from your selected module to size the array, project 25-year yield, and build the BOM — swap the panel and everything updates.
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