QUICK SELF-CHECK
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PANELS • SPECS • DEGRADATION
Panels: what specs actually mean
Panel shopping is mostly spec literacy. A few numbers tell you how a module behaves on a hot roof over 25+ years.
Key specs
| Spec | Why it matters | Watch for |
|---|---|---|
| Power (watts) at STC | Lab rating; used for system nameplate. | Compare same panel size; don’t overpay for tiny % gains. |
| Efficiency (%) | Power per area; matters if roof space is limited. | Higher efficiency often costs more; return on investment depends on space constraint. |
| Temp coefficient | Hot roofs reduce output; lower magnitude is better. | Look for around −0.29%/°C to −0.35%/°C. |
| Degradation | Output declines slowly each year. | Typical warranties target ~80–88% at year 25. |
What “tier” and “bankability” really imply
Bankability is about manufacturer stability, warranty backing, and supply chain reliability—not just today’s efficiency number.
- Warranty terms: product vs performance (they’re different).
- Failure modes: microcracks, PID, delamination, hotspots.
- Installer matters: mounting, flashing, cable management.
Actionable questions to ask
- What is the exact module model number?
- Is it N‑type (often better temp behavior) or P‑type?
- How is roof penetration sealed and warranted?
- What monitoring granularity do I get (panel-level vs system-level)?