640 W TOPCon solar panel with 156 cells. Voc 57.4 V · Isc 13.86 A · TcVoc -0.24%/°C.
Select the panel you want to replace
String Compatibility Calculator
Verify the replacement panel works with your inverter
Panel Matcher
Find all compatible panels for a specific inverter
Already have panels?
Find an inverter that fits your panel array with the right MPPT range and DC/AC ratio.
How the Algorithm Works
Learn how panels are scored and matched
Voc
57.4 V
Vmpp
48.22 V
Isc
13.86 A
Impp
13.28 A
TcVoc
-0.24 %/°C
TcPmax
-0.28 %/°C
Pmax
640 W
Cells
156
Bifaciality
80%
Length
2465 mm
Width
1134 mm
Thickness
30 mm
Weight
33.8 kg
The Tongwei TWMND-78HD640 is a 640 W solar panel. Finding a compatible replacement requires matching the original electrical characteristics — particularly Voc, Vmpp, Isc, and temperature coefficients — to ensure safe operation within the same string.
Use the form above to find panels that match these specifications. Then verify the replacement in the String Compatibility Calculator with your inverter.
| Model | Power | Voc | Isc |
|---|---|---|---|
| 625 W | 56.8 V | 13.74 A | |
| 630 W | 57 V | 13.78 A | |
| 635 W | 57.2 V | 13.82 A | |
| 645 W | 57.6 V | 14.05 A |
The most critical specs to match are: cell count (must be exactly 156), Voc close to 57.4 V (within ±5%), and temperature coefficient TcVoc close to -0.24%/°C. If Voc differs significantly, the string voltage at extreme temperatures may shift outside the inverter's MPPT range. The replacement finder above pre-screens all candidates by these criteria.
A higher wattage panel usually has a higher Vmpp or Isc, which can affect string voltage and current. Small increases (up to 10–15%) are typically safe if the other electrical specs align. The replacement finder shows a compatibility score — 'Exact match' means the specs align closely. Always verify the replacement in the String Compatibility Calculator with your inverter before installation.
If the replacement has a significantly different Voc or Vmpp, the string voltage may shift outside the inverter's MPPT range, reducing energy production or causing faults. This effect is amplified at temperature extremes: at low temperatures, voltage rises by the TcVoc coefficient. The replacement finder automatically accounts for this — it scores candidates by how closely the electrical specs match the original Tongwei TWMND-78HD640.