--- title: "Silfab SIL-420 QD vs Silfab SIL-640 XL - Solar Panel Comparison | ComparePV" description: "Compare Silfab SIL-420 QD vs Silfab SIL-640 XL side by side: what actually differs, output when it is hot, thirty-year production, and the full specification." source: "https://comparepv.com/compare/silfab-sil-420-qd/silfab-sil-640-xl" updated: 2026-09-11 --- # Silfab SIL-420 QD vs Silfab SIL-640 XL 640 XL leads on the differences that matter The largest is module efficiency: 1.42 pp more efficient. 7 of 19 comparable parameters are identical. ## The two panels | Attribute | A | B | | --- | --- | --- | | Panel | [Silfab SIL-420 QD](https://comparepv.com/panel/silfab-sil-420-qd) | [Silfab SIL-640 XL](https://comparepv.com/panel/silfab-sil-640-xl) | | Manufacturer | Silfab | Silfab | | Power | 420 Wp | 640 Wp | | Efficiency | 21.50 % | 22.92 % | | Technology | N-type | N-type | ## Where they differ Ranked by how much the difference matters, not by datasheet order. | Parameter | 420 QD | 640 XL | Difference | | --- | --- | --- | --- | | Module efficiency | 21.50 % | 22.92 % | +1.42 pp for 640 XL | | Rated power | 420 Wp | 640 Wp | +220 W for 640 XL | | Power density | 215.4 Wp/m² | 229.2 Wp/m² | +13.8 Wp/m² for 640 XL | | Weight | 21.0 kg | 29.5 kg | -8.5 kg for 420 QD | | Annual degradation | 0.40 %/yr | 0.30 %/yr | -0.10 %/yr for 640 XL | | Open-circuit voltage | 38.84 V | 57.76 V | 18.92 V apart | | Module area | 1.950 m² | 2.793 m² | 0.843 m² apart | | Weight per kWp | 50.0 kg/kWp | 46.1 kg/kWp | -3.9 kg/kWp for 640 XL | | Voltage at max power | 33.08 V | 48.78 V | 15.70 V apart | | Cell count | 108 | 156 | 48 cells apart | | Bifacial | No | Yes | No vs Yes | | Dimensions | 1721x1133x35 mm | 2465x1133x35 mm | 1721x1133x35 mm vs 2465x1133x35 mm | ## Every compared parameter | Parameter | 420 QD | 640 XL | | --- | --- | --- | | Rated power | 420 Wp | 640 Wp | | Module efficiency | 21.50 % | 22.92 % | | Power density | 215.4 Wp/m² | 229.2 Wp/m² | | Open-circuit voltage | 38.84 V | 57.76 V | | Voltage at max power | 33.08 V | 48.78 V | | Short-circuit current | 13.50 A | 13.76 A | | Current at max power | 12.70 A | 13.12 A | | Temperature coefficient | -0.290 %/°C | -0.290 %/°C | | Dimensions | 1721x1133x35 mm | 2465x1133x35 mm | | Module area | 1.950 m² | 2.793 m² | | Weight | 21.0 kg | 29.5 kg | | Weight per kWp | 50.0 kg/kWp | 46.1 kg/kWp | | Product warranty | 25 yrs | 25 yrs | | Performance warranty | 30 yrs | 30 yrs | | Annual degradation | 0.40 %/yr | 0.30 %/yr | | Cell technology | N-type | N-type | | Cell type | Monocrystalline | Monocrystalline | | Cell count | 108 | 156 | | Bifacial | No | Yes | ## Thirty-year yield Each panel's own declared degradation curve, at 1,200 kWh/kWp a year Same temp coeff. for both panels (-0.290 %/°C), so a warmer roof scales both curves by the same factor: the totals fall together and neither panel gains on the other. - **Cumulative output, 420 QD:** 13,941 kWh - **Cumulative output, 640 XL:** 21,577 kWh - **Gap:** 7,636 kWh ## Output when hot | Condition | Cell temperature | 420 QD | 640 XL | Retained | | --- | --- | --- | --- | --- | | Standard test conditions | 25 °C | 420 W | 640 W | 100.0% of rated power | | Cool, bright day | 40 °C | 402 W | 612 W | 95.7% of rated power | | Typical summer roof | 55 °C | 383 W | 584 W | 91.3% of rated power | | Hot roof | 70 °C | 365 W | 556 W | 87.0% of rated power | ## Against the whole database | Measure | 420 QD | 640 XL | Out of | Note | | --- | --- | --- | --- | --- | | Efficiency | #7,958 | #2,350 | 14,005 | 640 XL leads by 5,608 places | | Power density | #7,783 | #2,379 | 14,005 | 640 XL leads by 5,404 places | | Heat behaviour | #2,165 | #2,165 | 14,005 | Tied - the same position in the database | | Weight | #3,317 | #1,004 | 14,005 | 640 XL leads by 2,313 places | | Warranty | #21 | #21 | 14,005 | Tied - the same position in the database | | Overall | #8,547 | #650 | 14,005 | 640 XL leads by 7,897 places | ## Questions ### Which panel is better: Silfab SIL-420 QD or Silfab SIL-640 XL? According to our database: **Silfab SIL-640 XL** has higher module efficiency (**22.92%** vs **21.50%**). See the full spec comparison and 30-year energy simulation above for a complete picture. ### What is the efficiency of Silfab SIL-420 QD and Silfab SIL-640 XL? **Silfab SIL-420 QD** has a module efficiency of **21.50%**, while **Silfab SIL-640 XL** is **22.92%**. Higher efficiency means more electricity from the same roof area - useful when space is limited. ### What cell technology does Silfab SIL-420 QD use vs Silfab SIL-640 XL? **Silfab SIL-420 QD** uses **N-type** cells; **Silfab SIL-640 XL** uses **N-type**. Modern **n-type** technologies (**TOPCon**, **HJT**, BC) typically deliver higher efficiency and lower degradation compared to older **PERC** (p-type) cells. ### What is the warranty on Silfab SIL-420 QD and Silfab SIL-640 XL? **Silfab SIL-420 QD** has a **30 years** power warranty; **Silfab SIL-640 XL** has a **30 years** power warranty. The power warranty guarantees a minimum percentage of rated output at the end of the warranty period (typically 80**-87%**). Product (materials) warranties are usually shorter. ### Are Silfab SIL-420 QD and Silfab SIL-640 XL bifacial panels? **Silfab SIL-640 XL** is bifacial (captures light from both faces); **Silfab SIL-420 QD** is monofacial. Bifacial panels work best on ground mounts or raised structures with a light-coloured surface underneath. ## Related comparisons - [Silfab SIL-420 QD vs Silfab SIL-440 QD](https://comparepv.com/compare/silfab-sil-420-qd/silfab-solar-inc-sil-440-qd) - 6 differences, the largest is module efficiency - [Silfab SIL-420 QD vs Silfab SIL-430 QD](https://comparepv.com/compare/silfab-sil-420-qd/silfab-sil-430-qd) - 4 differences, the largest is module efficiency - [Silfab SIL-420 QD vs Silfab SIL-430-QD](https://comparepv.com/compare/silfab-sil-420-qd/silfab-sil-430-qd-1) - 4 differences, the largest is module efficiency - [Silfab SIL-420 QD vs Silfab SIL-370 NT mono PERC](https://comparepv.com/compare/silfab-sil-420-qd/silfab-sil-370-nt-mono-perc) - 14 differences, the largest is module efficiency - [Silfab SIL-640 XL vs Silfab SIL-630 XL](https://comparepv.com/compare/silfab-sil-640-xl/silfab-sil-630-xl) - 3 differences, the largest is module efficiency - [Silfab SIL-640 XL vs Silfab SIL-620 XL](https://comparepv.com/compare/silfab-sil-640-xl/silfab-sil-620-xl) - 3 differences, the largest is module efficiency --- Source: https://comparepv.com/compare/silfab-sil-420-qd/silfab-sil-640-xl Not in this file, on the page: the thirty-year yield curve year by year at a cell temperature you pick and a written summary generated on request.