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420-BG vs 640 XL 4 of 19 identical Swap Change panels

Silfab SIL-420-BG vs Silfab SIL-640 XL

Silfab
SIL-420-BG
420 Wp 21.90 % PERC
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: 1.02 pp more efficient. 4 of 19 comparable parameters are identical.

See all 15 differences
How alike are they
4 of 19 comparable
parameters are identical
identical differs
01

What actually differs

15 of 19 parameters
Parameter 420-BG 640 XL Difference
Module efficiency 21.90 % 22.92 % 1.02 pp more efficient
Temperature coefficient -0.377 %/°C -0.290 %/°C 0.087 %/°C better in heat
Rated power 420 Wp 640 Wp 220 W more power
Power density 219.0 Wp/m² 229.2 Wp/m² 10.2 Wp/m² higher
Weight 20.8 kg 29.5 kg 8.7 kg lighter
Open-circuit voltage 46.36 V 57.76 V 11.40 V apart
Short-circuit current 11.40 A 13.76 A 2.36 A apart
Module area 1.918 m² 2.793 m² 0.875 m² apart
Weight per kWp 49.5 kg/kWp 46.1 kg/kWp 3.4 kg/kWp lighter
Cell technology PERC N-type PERC vs N-type
Voltage at max power 38.51 V 48.78 V 10.27 V apart
Current at max power 10.91 A 13.12 A 2.21 A apart
Cell count 66 156 90 cells apart
Bifacial No Yes No vs Yes
Dimensions 1864x1029x35 mm 2465x1133x35 mm 1864x1029x35 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
420-BG
14,160 kWh
640 XL
21,577 kWh
Lifetime gap
7,417 kWh
Output when it is hot
Rated power carried across the range a module actually sees
Scenario 420-BG 640 XL
Standard test conditions 25 °C 100.0% of rated power 420 W 640 W
Cool, bright day 40 °C 94.3% of rated power 396 W 612 W
Typical summer roof 55 °C 88.7% of rated power 372 W 584 W
Hot roof 70 °C 83.0% of rated power 349 W 556 W
03

Full specification

Parameter 420-BG 640 XL Difference
Power and efficiency
Rated power 420 Wp 640 Wp +220 W for 640 XL
Module efficiency 21.90 % 22.92 % +1.02 pp for 640 XL
Power density 219.0 Wp/m² 229.2 Wp/m² +10.2 Wp/m² for 640 XL
Open-circuit voltage 46.36 V 57.76 V 11.40 V apart
Voltage at max power 38.51 V 48.78 V 10.27 V apart
Short-circuit current 11.40 A 13.76 A 2.36 A apart
Current at max power 10.91 A 13.12 A 2.21 A apart
Temperature
Temperature coefficient -0.377 %/°C -0.290 %/°C +0.087 %/°C for 640 XL
Mechanical
Dimensions 1864x1029x35 mm 2465x1133x35 mm 1864x1029x35 mm vs 2465x1133x35 mm
Module area 1.918 m² 2.793 m² 0.875 m² apart
Weight 20.8 kg 29.5 kg -8.7 kg for 420-BG
Weight per kWp 49.5 kg/kWp 46.1 kg/kWp -3.4 kg/kWp for 640 XL
Warranty and degradation
Product warranty 25 yrs 25 yrs Same
Performance warranty 30 yrs 30 yrs Same
Annual degradation 0.30 %/yr 0.30 %/yr Same
Technology
Cell technology PERC N-type PERC vs N-type
Cell type Monocrystalline Monocrystalline Same
Cell count 66 156 90 cells apart
Bifacial No Yes No vs Yes
04

Against the whole database

14,129 panels
Efficiency
#6,847 vs #2,403
640 XL leads by 4,444 places
Power density
#6,850 vs #2,433
640 XL leads by 4,417 places
Heat behaviour
#13,470 vs #2,220
640 XL leads by 11,250 places
Weight
#3,065 vs #1,004
640 XL leads by 2,061 places
Warranty
#21 vs #21
Tied - the same position in the database
Overall
#8,049 vs #661
640 XL leads by 7,388 places
05

More useful comparisons

Open the full database
Same series, other bin
Silfab
Silfab SIL-420-BG vs Silfab SIL-430 BG+
9 differences, the largest is module efficiency
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Silfab
Silfab SIL-420-BG vs Silfab SIL-410-BG
3 differences, the largest is module efficiency
Same series, other bin
Silfab
Silfab SIL-420-BG vs Silfab SIL-380 BK
10 differences, the largest is rated power
Same series, other bin
Silfab
Silfab SIL-420-BG vs Silfab SIL-370 BK
10 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
Silfab
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-BG or Silfab SIL-640 XL?
According to our database: Silfab SIL-640 XL has higher module efficiency (22.92% vs 21.90%); Silfab SIL-640 XL tolerates heat better (temp coeff -0.290%/°C vs -0.377%/°C). See the full spec comparison and 30-year energy simulation above for a complete picture.
What is the efficiency of Silfab SIL-420-BG and Silfab SIL-640 XL?
Silfab SIL-420-BG has a module efficiency of 21.90%, 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-BG use vs Silfab SIL-640 XL?
Silfab SIL-420-BG uses PERC 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-BG and Silfab SIL-640 XL?
Silfab SIL-420-BG 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-BG and Silfab SIL-640 XL bifacial panels?
Silfab SIL-640 XL is bifacial (captures light from both faces); Silfab SIL-420-BG 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.