---
title: "JA Solar JAM66D46-740/LB vs JA Solar JAM78D40-625/MB/1500V - Solar Panel Comparison | ComparePV"
description: "Compare JA Solar JAM66D46-740/LB vs JA Solar JAM78D40-625/MB/1500V side by side: what actually differs, output when it is hot, thirty-year production, and the full specification."
source: "https://comparepv.com/compare/ja-solar-jam66d46-740-lb/ja-solar-jam78d40-625-mb-1500v"
updated: 2026-09-11
---

# JA Solar JAM66D46-740/LB vs JA Solar JAM78D40-625/MB/1500V

JAM66D46-740/LB leads on the differences that matter

The largest is module efficiency: 1.40 pp more efficient. 5 of 19 comparable parameters are identical.


## The two panels


| Attribute | A | B |
| --- | --- | --- |
| Panel | [JA Solar JAM66D46-740/LB](https://comparepv.com/panel/ja-solar-jam66d46-740-lb) | [JA Solar JAM78D40-625/MB/1500V](https://comparepv.com/panel/ja-solar-jam78d40-625-mb-1500v) |
| Manufacturer | JA Solar | JA Solar |
| Power | 740 Wp | 625 Wp |
| Efficiency | 23.80 % | 22.40 % |
| Technology | TOPCon | N-type |


## Where they differ

Ranked by how much the difference matters, not by datasheet order.


| Parameter | JAM66D46-740/LB | JAM78D40-625/MB/1500V | Difference |
| --- | --- | --- | --- |
| Module efficiency | 23.80 % | 22.40 % | +1.40 pp for JAM66D46-740/LB |
| Rated power | 740 Wp | 625 Wp | +115 W for JAM66D46-740/LB |
| Power density | 238.2 Wp/m² | 223.6 Wp/m² | +14.6 Wp/m² for JAM66D46-740/LB |
| Weight | 38.2 kg | 34.6 kg | -3.6 kg for JAM78D40-625/MB/1500V |
| Open-circuit voltage | 49.80 V | 55.49 V | 5.69 V apart |
| Short-circuit current | 18.73 A | 14.36 A | 4.37 A apart |
| Module area | 3.106 m² | 2.795 m² | 0.311 m² apart |
| Weight per kWp | 51.6 kg/kWp | 55.4 kg/kWp | -3.7 kg/kWp for JAM66D46-740/LB |
| Temperature coefficient | -0.290 %/°C | -0.300 %/°C | +0.010 %/°C for JAM66D46-740/LB |
| Cell technology | TOPCon | N-type | TOPCon vs N-type |
| Voltage at max power | 41.96 V | 46.37 V | 4.41 V apart |
| Current at max power | 17.64 A | 13.48 A | 4.16 A apart |
| Cell count | 132 | 156 | 24 cells apart |
| Dimensions | 2384x1303x33 mm | 2465x1134x35 mm | 2384x1303x33 mm vs 2465x1134x35 mm |


## Every compared parameter


| Parameter | JAM66D46-740/LB | JAM78D40-625/MB/1500V |
| --- | --- | --- |
| Rated power | 740 Wp | 625 Wp |
| Module efficiency | 23.80 % | 22.40 % |
| Power density | 238.2 Wp/m² | 223.6 Wp/m² |
| Open-circuit voltage | 49.80 V | 55.49 V |
| Voltage at max power | 41.96 V | 46.37 V |
| Short-circuit current | 18.73 A | 14.36 A |
| Current at max power | 17.64 A | 13.48 A |
| Temperature coefficient | -0.290 %/°C | -0.300 %/°C |
| Dimensions | 2384x1303x33 mm | 2465x1134x35 mm |
| Module area | 3.106 m² | 2.795 m² |
| Weight | 38.2 kg | 34.6 kg |
| Weight per kWp | 51.6 kg/kWp | 55.4 kg/kWp |
| Product warranty | 12 yrs | 12 yrs |
| Performance warranty | 30 yrs | 30 yrs |
| Annual degradation | 0.40 %/yr | 0.40 %/yr |
| Cell technology | TOPCon | N-type |
| Cell type | Monocrystalline | Monocrystalline |
| Cell count | 132 | 156 |
| Bifacial | Yes | Yes |


## Thirty-year yield

Each panel's own declared degradation curve, at 1,200 kWh/kWp a year

- **Cumulative output, JAM66D46-740/LB:** 24,828 kWh
- **Cumulative output, JAM78D40-625/MB/1500V:** 20,970 kWh
- **Gap:** 3,858 kWh


## Output when hot


| Condition | Cell temperature | JAM66D46-740/LB | JAM78D40-625/MB/1500V | Retained |
| --- | --- | --- | --- | --- |
| Standard test conditions | 25 °C | 740 W | 625 W | 100.0% of rated power |
| Cool, bright day | 40 °C | 708 W | 597 W | 95.5% of rated power |
| Typical summer roof | 55 °C | 676 W | 569 W | 91.0% of rated power |
| Hot roof | 70 °C | 643 W | 541 W | 86.5% of rated power |


## Against the whole database


| Measure | JAM66D46-740/LB | JAM78D40-625/MB/1500V | Out of | Note |
| --- | --- | --- | --- | --- |
| Efficiency | #433 | #4,774 | 14,005 | JAM66D46-740/LB leads by 4,341 places |
| Power density | #431 | #4,955 | 14,005 | JAM66D46-740/LB leads by 4,524 places |
| Heat behaviour | #2,165 | #6,093 | 14,005 | JAM66D46-740/LB leads by 3,928 places |
| Weight | #4,997 | #9,802 | 14,005 | JAM66D46-740/LB leads by 4,805 places |
| Warranty | #21 | #21 | 14,005 | Tied - the same position in the database |
| Overall | #185 | #3,028 | 14,005 | JAM66D46-740/LB leads by 2,843 places |


## Questions


### Which panel is better: JA Solar JAM66D46-740/LB or JA Solar JAM78D40-625/MB/1500V?

According to our database: **JA Solar JAM66D46-740/LB** has higher module efficiency (**23.80%** vs **22.40%**); **JA Solar JAM66D46-740/LB** tolerates heat better (temp coeff **-0.290%/°C** vs **-0.300%/°C**). See the full spec comparison and 30-year energy simulation above for a complete picture.


### What is the efficiency of JA Solar JAM66D46-740/LB and JA Solar JAM78D40-625/MB/1500V?

**JA Solar JAM66D46-740/LB** has a module efficiency of **23.80%**, while **JA Solar JAM78D40-625/MB/1500V** is **22.40%**. Higher efficiency means more electricity from the same roof area - useful when space is limited.


### What cell technology does JA Solar JAM66D46-740/LB use vs JA Solar JAM78D40-625/MB/1500V?

**JA Solar JAM66D46-740/LB** uses **TOPCon** cells; **JA Solar JAM78D40-625/MB/1500V** 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 JA Solar JAM66D46-740/LB and JA Solar JAM78D40-625/MB/1500V?

**JA Solar JAM66D46-740/LB** has a **30 years** power warranty; **JA Solar JAM78D40-625/MB/1500V** 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 JA Solar JAM66D46-740/LB and JA Solar JAM78D40-625/MB/1500V bifacial panels?

Both **JA Solar JAM66D46-740/LB** and **JA Solar JAM78D40-625/MB/1500V** 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.


## Related comparisons

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Source: https://comparepv.com/compare/ja-solar-jam66d46-740-lb/ja-solar-jam78d40-625-mb-1500v

Not in this file, on the page: the thirty-year yield curve year by year at a cell temperature you pick and a written summary generated on request.