Longi Solar LR8-66HVD-645M vs Longi Solar LR8-66HVD-640M
VS
The verdict
Identical on every published parameter
All 19 comparable parameters agree. Two records this alike are usually one panel sold under two names, or two bins of the same production line - decide on price and on who you would rather buy from.
How alike are they
19
of 19 comparable
parameters are identical
parameters are identical
identical
differs
01
0 of 19 parameters
What actually differs
Every comparable parameter agrees. The full specification is below.
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 (-0.260 %/°C), so a warmer roof scales both curves by the same factor: the totals fall together and neither panel gains on the other.
645M
21,809 kWh
640M
21,640 kWh
Lifetime gap
169 kWh
Output when it is hot
Rated power carried across the range a module actually sees
Scenario
645M
640M
Standard test conditions
25 °C
100.0% of rated power
645 W
640 W
Cool, bright day
40 °C
96.1% of rated power
620 W
615 W
Typical summer roof
55 °C
92.2% of rated power
595 W
590 W
Hot roof
70 °C
88.3% of rated power
570 W
565 W
03
Full specification
Parameter
645M
640M
Difference
Power and efficiency
Rated power
645 Wp
640 Wp
Effectively the same
Module efficiency
23.88 %
23.69 %
Effectively the same
Power density
238.8 Wp/m²
236.9 Wp/m²
Effectively the same
Open-circuit voltage
49.62 V
49.52 V
Effectively the same
Voltage at max power
40.88 V
40.78 V
Effectively the same
Short-circuit current
16.46 A
16.38 A
Effectively the same
Current at max power
15.78 A
15.69 A
Effectively the same
Temperature
Temperature coefficient
-0.260 %/°C
-0.260 %/°C
Same
Mechanical
Dimensions
2382x1134x30 mm
2382x1134x30 mm
Same
Module area
2.701 m²
2.701 m²
Same
Weight
33.5 kg
33.5 kg
Same
Weight per kWp
51.9 kg/kWp
52.3 kg/kWp
Effectively the same
Warranty and degradation
Product warranty
15 yrs
15 yrs
Same
Performance warranty
30 yrs
30 yrs
Same
Annual degradation
0.35 %/yr
0.35 %/yr
Same
Technology
Cell technology
Back Contact
Back Contact
Same
Cell type
Monocrystalline
Monocrystalline
Same
Cell count
132
132
Same
Bifacial
Yes
Yes
Same
04
14,005 panels
Against the whole database
Efficiency
#394
vs
#580
645M leads by 186 places
Power density
#356
vs
#521
645M leads by 165 places
Heat behaviour
#511
vs
#511
Tied - the same position in the database
Weight
#5,361
vs
#5,829
645M leads by 468 places
Warranty
#21
vs
#21
Tied - the same position in the database
Overall
#1,084
vs
#1,271
645M leads by 187 places
05
Open the full database
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The same specification on paper
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06
Written summary
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07
Questions about this pairing
Which panel is better: Longi Solar LR8-66HVD-645M or Longi Solar LR8-66HVD-640M?
According to our database: Longi Solar LR8-66HVD-645M has higher module efficiency (23.88% vs 23.69%). See the full spec comparison and 30-year energy simulation above for a complete picture.
What is the efficiency of Longi Solar LR8-66HVD-645M and Longi Solar LR8-66HVD-640M?
Longi Solar LR8-66HVD-645M has a module efficiency of 23.88%, while Longi Solar LR8-66HVD-640M is 23.69%. Higher efficiency means more electricity from the same roof area - useful when space is limited.
What cell technology does Longi Solar LR8-66HVD-645M use vs Longi Solar LR8-66HVD-640M?
Longi Solar LR8-66HVD-645M uses Back Contact cells; Longi Solar LR8-66HVD-640M uses Back Contact. 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 Longi Solar LR8-66HVD-645M and Longi Solar LR8-66HVD-640M?
Longi Solar LR8-66HVD-645M has a 30 years power warranty; Longi Solar LR8-66HVD-640M 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 Longi Solar LR8-66HVD-645M and Longi Solar LR8-66HVD-640M bifacial panels?
Both Longi Solar LR8-66HVD-645M and Longi Solar LR8-66HVD-640M are bifacial - they capture reflected light from the ground, which can add 5-15% more annual energy on ground-mount or elevated rooftop installations with a light surface beneath.
Shop prices: See 174 Longi Solar offers
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.