Two quotes land on your desk: both say "620 W", both say "tier-1", and they differ by $0.012/W. The datasheet is where the real differences hide — in the second decimal of a temperature coefficient, a missing PID test, or a warranty curve that quietly gives up 3% more over 30 years. Here are the twelve specifications that actually separate modules, in the order a procurement engineer should check them.
The power block: specs 1–4
- 1. Pmax (rated power, W). Measured at STC: 1000 W/m², 25°C cell temperature, AM1.5 spectrum — lab conditions your site will rarely see. Check the power tolerance: 0/+5 W (positive-only) is standard for tier-1; a ±3% tolerance means you might be paying for watts you don't get.
- 2. Module efficiency (%). Power per unit area. Matters when roof space or land is the binding constraint; irrelevant if you have room to spare and $/W is lower on a bigger, less efficient module.
- 3. Voc — open-circuit voltage. Drives string sizing: Voc rises in cold weather, and the string's cold-morning Voc must never exceed the inverter's maximum DC input (1000 V or 1500 V). Always check Voc together with its temperature coefficient.
- 4. Isc — short-circuit current. Determines cable, fuse and connector sizing. Modern high-current modules (Isc > 18 A) may exceed older inverters' per-MPPT current limits — verify before mixing.
The performance block: specs 5–8
- 5. Temperature coefficient of Pmax. The hot-climate yield spec: −0.34%/°C (PERC) vs −0.29%/°C (TOPCon) vs −0.24%/°C (HJT). Our dedicated guide quantifies the revenue impact.
- 6. NMOT/NOCT power. Output at realistic operating conditions (~800 W/m², 20°C ambient). Two 620 W modules can differ by 8–10 W at NMOT — this figure is closer to what you'll actually harvest.
- 7. First-year + linear degradation. The warranty curve: e.g., ≤1% year one, ≤0.4%/yr thereafter, ending at 87.4% after 30 years. Compare the END value, not the marketing headline.
- 8. Bifaciality factor (bifacial modules). Rear-side output as a percentage of front-side: 70% (PERC) to 90%+ (HJT). Multiply by your site's albedo contribution to estimate real rear gain — see our bifacial gain article.
The reliability block: specs 9–12
- 9. PID resistance. Potential-induced degradation can silently eat 10%+ of output in humid, high-voltage systems. Look for IEC 62804 test results (96 h, 85°C/85% RH) — not just the word "anti-PID".
- 10. Salt mist & ammonia certification. IEC 61701 (coastal sites, <500 m from sea) and IEC 62716 (agricultural roofs). Skipping this voids many warranties in those environments.
- 11. Mechanical load rating. Front (snow) and rear (wind uplift) test loads — typically 5400/2400 Pa. Check against your site's design loads and the mounting layout used in the test (clamp positions matter).
- 12. Hail rating. IEC 61215 tests 25 mm hail at 23 m/s as standard; hail-prone regions (central US, northern Italy, Australia) should ask for 35 mm+ test reports.
Quick comparison checklist
| Check | Red flag | Tier-1 standard |
|---|---|---|
| Power tolerance | ±3% | 0/+5 W |
| Warranty end value (yr 25/30) | <84% | ≥87% |
| Temp. coefficient Pmax | worse than −0.35%/°C | −0.30%/°C or better |
| PID test | "anti-PID" claim only | IEC 62804 report available |
| Product warranty | 10 years | 12–15 years |
Econo Solar supplies full datasheets, IEC test reports and BOM-level warranty terms with every quote — request the datasheet pack for any module we stock.