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420 QD vs 640 XL 7 of 19 identical Swap Change panels

Silfab SIL-420 QD vs Silfab SIL-640 XL

Silfab SIL-420 QD
Silfab
SIL-420 QD
420 Wp 21.50 % N-type
Open panel page Datasheet PDF
VS
Silfab
SIL-640 XL
640 Wp 22.92 % N-type Bifacial
Open panel page Datasheet PDF
The verdict

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.

See all 12 differences
How alike are they
7 of 19 comparable
parameters are identical
identical differs
01

What actually differs

12 of 19 parameters
Parameter 420 QD 640 XL Difference
Module efficiency 21.50 % 22.92 % 1.42 pp more efficient
Rated power 420 Wp 640 Wp 220 W more power
Power density 215.4 Wp/m² 229.2 Wp/m² 13.8 Wp/m² higher
Weight 21.0 kg 29.5 kg 8.5 kg lighter
Annual degradation 0.40 %/yr 0.30 %/yr 0.10 %/yr slower
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 lighter
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
02

What it means on a roof

Thirty years of production
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.
420 QD
13,941 kWh
640 XL
21,577 kWh
Lifetime gap
7,636 kWh
Output when it is hot
Rated power carried across the range a module actually sees
Scenario 420 QD 640 XL
Standard test conditions 25 °C 100.0% of rated power 420 W 640 W
Cool, bright day 40 °C 95.7% of rated power 402 W 612 W
Typical summer roof 55 °C 91.3% of rated power 383 W 584 W
Hot roof 70 °C 87.0% of rated power 365 W 556 W
03

Full specification

Parameter 420 QD 640 XL Difference
Power and efficiency
Rated power 420 Wp 640 Wp +220 W for 640 XL
Module efficiency 21.50 % 22.92 % +1.42 pp for 640 XL
Power density 215.4 Wp/m² 229.2 Wp/m² +13.8 Wp/m² for 640 XL
Open-circuit voltage 38.84 V 57.76 V 18.92 V apart
Voltage at max power 33.08 V 48.78 V 15.70 V apart
Short-circuit current 13.50 A 13.76 A Effectively the same
Current at max power 12.70 A 13.12 A Effectively the same
Temperature
Temperature coefficient -0.290 %/°C -0.290 %/°C Same
Mechanical
Dimensions 1721x1133x35 mm 2465x1133x35 mm 1721x1133x35 mm vs 2465x1133x35 mm
Module area 1.950 m² 2.793 m² 0.843 m² apart
Weight 21.0 kg 29.5 kg -8.5 kg for 420 QD
Weight per kWp 50.0 kg/kWp 46.1 kg/kWp -3.9 kg/kWp for 640 XL
Warranty and degradation
Product warranty 25 yrs 25 yrs Same
Performance warranty 30 yrs 30 yrs Same
Annual degradation 0.40 %/yr 0.30 %/yr -0.10 %/yr for 640 XL
Technology
Cell technology N-type N-type Same
Cell type Monocrystalline Monocrystalline Same
Cell count 108 156 48 cells apart
Bifacial No Yes No vs Yes
04

Against the whole database

14,005 panels
Efficiency
#7,958 vs #2,350
640 XL leads by 5,608 places
Power density
#7,783 vs #2,379
640 XL leads by 5,404 places
Heat behaviour
#2,165 vs #2,165
Tied - the same position in the database
Weight
#3,317 vs #1,004
640 XL leads by 2,313 places
Warranty
#21 vs #21
Tied - the same position in the database
Overall
#8,547 vs #650
640 XL leads by 7,897 places
05

More useful comparisons

Open the full database
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Silfab SIL-420 QD vs Silfab SIL-440 QD
6 differences, the largest is module efficiency
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Silfab SIL-420 QD vs Silfab SIL-430 QD
4 differences, the largest is module efficiency
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Silfab SIL-420 QD vs Silfab SIL-430-QD
4 differences, the largest is module efficiency
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Silfab SIL-420 QD vs Silfab SIL-370 NT mono PERC
14 differences, the largest is module efficiency
Same series, other bin
Silfab
Silfab SIL-640 XL vs Silfab SIL-630 XL
3 differences, the largest is module efficiency
Same series, other bin
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Silfab SIL-640 XL vs Silfab SIL-620 XL
3 differences, the largest is module efficiency
06

Written summary

07

Questions about this pairing

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.

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Every figure here is from the manufacturers' own datasheets - a dash means the value is not published, never an estimate. The thirty-year projection and the temperature scenarios are calculations from those figures, and each states its assumption above.