Longi Solar LR8-66HVD-660M vs Longi Solar LR8-66HVD-640M
VS
The verdict
660M leads on the differences that matter
The largest is module efficiency: 0.74 pp more efficient. 16 of 19 comparable parameters are identical.
See all 3 differencesHow alike are they
16
of 19 comparable
parameters are identical
parameters are identical
identical
differs
01
3 of 19 parameters
What actually differs
Parameter
660M
640M
Difference
Module efficiency
24.43 %
23.69 %
0.74 pp more efficient
Power density
244.3 Wp/m²
236.9 Wp/m²
7.4 Wp/m² higher
Rated power
660 Wp
640 Wp
20 W more power
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.
660M
22,317 kWh
640M
21,640 kWh
Lifetime gap
677 kWh
Output when it is hot
Rated power carried across the range a module actually sees
Scenario
660M
640M
Standard test conditions
25 °C
100.0% of rated power
660 W
640 W
Cool, bright day
40 °C
96.1% of rated power
634 W
615 W
Typical summer roof
55 °C
92.2% of rated power
609 W
590 W
Hot roof
70 °C
88.3% of rated power
583 W
565 W
03
Full specification
Parameter
660M
640M
Difference
Power and efficiency
Rated power
660 Wp
640 Wp
+20 W for 660M
Module efficiency
24.43 %
23.69 %
+0.74 pp for 660M
Power density
244.3 Wp/m²
236.9 Wp/m²
+7.4 Wp/m² for 660M
Open-circuit voltage
49.92 V
49.52 V
Effectively the same
Voltage at max power
41.18 V
40.78 V
Effectively the same
Short-circuit current
16.70 A
16.38 A
Effectively the same
Current at max power
16.03 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
50.8 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
#87
vs
#580
660M leads by 493 places
Power density
#88
vs
#521
660M leads by 433 places
Heat behaviour
#511
vs
#511
Tied - the same position in the database
Weight
#4,172
vs
#5,829
660M leads by 1,657 places
Warranty
#21
vs
#21
Tied - the same position in the database
Overall
#559
vs
#1,271
660M leads by 712 places
05
Open the full database
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06
Written summary
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07
Questions about this pairing
Which panel is better: Longi Solar LR8-66HVD-660M or Longi Solar LR8-66HVD-640M?
According to our database: Longi Solar LR8-66HVD-660M has higher module efficiency (24.43% 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-660M and Longi Solar LR8-66HVD-640M?
Longi Solar LR8-66HVD-660M has a module efficiency of 24.43%, 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-660M use vs Longi Solar LR8-66HVD-640M?
Longi Solar LR8-66HVD-660M 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-660M and Longi Solar LR8-66HVD-640M?
Longi Solar LR8-66HVD-660M 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-660M and Longi Solar LR8-66HVD-640M bifacial panels?
Both Longi Solar LR8-66HVD-660M 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.