JA Solar JAM78S30 590W vs LONGi Hi-MO 7 620W
The JA Solar JAM78S30 590W wins this comparison by a narrow margin. It offers better long-term durability with 15-year warranty. For most residential installations, the JA Solar JAM78S30 590W is the stronger choice.
Key Differences
- • JA Solar JAM78S30 590W is rated at 590W while LONGi Hi-MO 7 620W is rated at 620W, a 30W difference.
- • LONGi Hi-MO 7 620W achieves 23% efficiency vs 22.6% for the other, a 0.4 percentage point gap.
- • JA Solar JAM78S30 590W comes with a 15-year product warranty vs 12 years for the other.
- • JA Solar JAM78S30 590W uses TOPCon N-type cells while LONGi Hi-MO 7 620W uses HPBC (Back Contact N-type) cells, representing different technology generations.
Specifications Breakdown
Module Efficiency
The LONGi Hi-MO 7 620W achieves 23% module efficiency compared to JA Solar JAM78S30 590W's 22.6%, meaning LONGi Hi-MO 7 620W converts 0.4 percentage points more sunlight into electricity per square meter. In practical terms, the JA Solar JAM78S30 590W produces 218.2 watts per square meter of panel area while the LONGi Hi-MO 7 620W produces 229.3 W/m². For rooftop installations where space is limited, this efficiency gap determines how many kilowatts you can fit on your available roof area. Over a 25-year system life, even a small efficiency advantage compounds into meaningful additional energy production.
Power Output
The LONGi Hi-MO 7 620W delivers 620W per panel versus 590W for the JA Solar JAM78S30 590W, a 30W difference per module. To build an 8 kW residential system, you would need 14 JA Solar JAM78S30 590W panels or 13 LONGi Hi-MO 7 620W panels. Choosing the higher-wattage option saves 1 panel, reducing total racking hardware, wiring, and installation labor costs. Higher wattage per panel is particularly valuable for commercial-scale installations where panel count directly impacts balance-of-system costs.
Temperature Coefficient
Both panels share an identical temperature coefficient of -0.28%/°C, meaning they lose power at the same rate as cell temperature rises above the 25°C standard test baseline. At 65°C cell temperature, both retain 94.4% of rated power. Neither panel has a thermal performance advantage, which makes this specification a non-factor in the comparison.
Warranty Coverage
The JA Solar JAM78S30 590W is backed by a 15-year product warranty and 30-year performance guarantee, while the LONGi Hi-MO 7 620W offers 12-year product and 30-year performance coverage. The JA Solar JAM78S30 590W provides 3 additional years of defect protection, covering manufacturing issues, material failures, and premature performance loss. Based on their published degradation rates (1% first year then 0.4%/year for JA Solar JAM78S30 590W; 0.5% first year then 0.35%/year for LONGi Hi-MO 7 620W), after 25 years the JA Solar JAM78S30 590W should retain approximately 89.4% of original output versus 91.1% for the LONGi Hi-MO 7 620W. This 1.7 percentage point gap in end-of-life output meaningfully impacts lifetime energy economics.
Physical Dimensions & Weight
The JA Solar JAM78S30 590W measures 2384×1134×35mm and weighs 31 kg, while the LONGi Hi-MO 7 620W measures 2384×1134×35mm at 31 kg. 2.70 m² of panel area for the JA Solar JAM78S30 590W versus 2.70 m² for the LONGi Hi-MO 7 620W. Their weights are closely matched, so neither panel imposes a significantly different structural load on the mounting system. Similar footprints mean both panels fit comparably on standard residential rooftop configurations.
Specification Comparison
| Specification | JA Solar JAM78S30 590W | LONGi Hi-MO 7 620W |
|---|---|---|
| Power | 590W | 620W |
| Efficiency | 22.6% | 23% |
| Power Density | 20.3 W/sq ft | 21.3 W/sq ft |
| Cell Type | TOPCon N-type | HPBC (Back Contact N-type) |
| Bifacial | No | Yes |
| Weight | 31 kg | 31 kg |
| Temp Coefficient | -0.28%/°C | -0.28%/°C |
| Snow Load | 5400 Pa | 5400 Pa |
| Wind Load | 2400 Pa | 2400 Pa |
| Product Warranty | 15 years | 12 years |
| Performance Warranty | 30 years | 30 years |
| Degradation (Year 1) | 1% | 0.5% |
| Annual Degradation | 0.4% | 0.35% |
| Country | China | China |
5-Dimension Head-to-Head Analysis
1. Efficiency & Power Density
Winner: LONGi Hi-MO 7 620WThe LONGi Hi-MO 7 620W achieves 23% efficiency versus 22.6% — a 0.4 percentage point advantage. On a typical 30-panel residential roof, this translates to approximately 0.9 kW more total system capacity, or 5 kWh more annual production in an average US location.
2. Hot Climate Performance
Winner: TieBoth panels share a temperature coefficient of -0.28%/°C — identical heat tolerance.
3. Durability & Warranty
Winner: JA Solar JAM78S30 590WJA Solar JAM78S30 590W leads with a 15-year product warranty versus 12 years. LONGi Hi-MO 7 620W degrades more slowly at 0.35% per year versus 0.4%. After 25 years, expect 89.4% vs 91.1% of original output for JA Solar JAM78S30 590W and LONGi Hi-MO 7 620W respectively.
4. Power Output
Winner: LONGi Hi-MO 7 620WThe LONGi Hi-MO 7 620W delivers 620W versus 590W per panel — 30W more. For an 8 kW system, you need 13 panels with the higher-wattage option versus 14 panels, saving 1 panels and the associated racking and labor costs.
5. Cell Technology
Winner: LONGi Hi-MO 7 620WThe JA Solar JAM78S30 590W uses TOPCon N-type: TOPCon (Tunnel Oxide Passivated Contact) adds a thin tunnel oxide layer to reduce recombination losses, achieving higher efficiency than PERC while being manufacturable on existing production lines. The LONGi Hi-MO 7 620W uses HPBC (Back Contact N-type): HPBC (Hybrid Passivated Back Contact) is a proprietary LONGi architecture combining back-contact design with advanced passivation for both high efficiency and aesthetic uniformity. HPBC (Back Contact N-type) represents a newer generation technology with a longer performance runway as manufacturing matures.
JA Solar JAM78S30 590W
JA Solar's JAM78S30 is a high-wattage N-type TOPCon module achieving 22.6% efficiency for large-scale installations.
Pros
- + Very high 590W output
- + Excellent efficiency
- + Low temperature coefficient
- + Bifacial design
Cons
- - Very large and heavy
- - Requires heavy-duty mounting
- - Not for small roofs
LONGi Hi-MO 7 620W
The Hi-MO 7 620W is LONGi's highest-output panel using proprietary HPBC (Hybrid Passivated Back Contact) technology for exceptional efficiency. Newer LR7/LR8 variants support 620W+ output.
Pros
- + Highest LONGi output
- + HPBC cutting-edge back-contact technology
- + 23.0% efficiency
- + Excellent degradation profile
Cons
- - Very large form factor
- - Premium pricing
- - New technology
Choose JA Solar JAM78S30 590W If...
- ✓ Long-term warranty protection is a top priority and you plan to stay in your home for 15+ years
- ✓ You prefer newer cell technology with a longer performance improvement runway
- ✓ Large commercial or ground-mount systems requiring maximum output.
Choose LONGi Hi-MO 7 620W If...
- ✓ Your roof space is limited and you need maximum power per panel
- ✓ You want fewer panels to reach your target system size, reducing racking and labor costs
- ✓ You want maximum output retention over the system's 25-30 year lifespan
- ✓ Large installations wanting LONGi's most advanced HPBC technology.
Our Recommendation
Both the JA Solar JAM78S30 590W and LONGi Hi-MO 7 620W are excellent solar panel options, and the margin between them is narrow. The JA Solar JAM78S30 590W wins 1 of 5 comparison dimensions by a slim margin. Your decision may come down to local pricing, installer availability, and which specific performance metrics matter most for your project. Either product is a solid investment.
Frequently Asked Questions
Which is better, JA Solar JAM78S30 590W or LONGi Hi-MO 7 620W?
The JA Solar JAM78S30 590W wins this comparison by a narrow margin. It offers better long-term durability with 15-year warranty. For most residential installations, the JA Solar JAM78S30 590W is the stronger choice.
Which panel is more efficient, JA Solar JAM78S30 590W or LONGi Hi-MO 7 620W?
The LONGi Hi-MO 7 620W at 23% module efficiency. Higher efficiency means more watts per square foot of roof space, which is critical for space-constrained installations. The difference of 0.4 percentage points translates to approximately 30W per panel under standard test conditions.
Which has a better warranty, JA Solar JAM78S30 590W or LONGi Hi-MO 7 620W?
The JA Solar JAM78S30 590W comes with a 15-year product warranty and 30-year performance guarantee. The LONGi Hi-MO 7 620W offers 12-year product and 30-year performance warranties. JA Solar JAM78S30 590W provides 3 additional years of product coverage.
Which panel performs better in hot weather?
The JA Solar JAM78S30 590W has a temperature coefficient of -0.28%/°C and the LONGi Hi-MO 7 620W is -0.28%/°C. Both handle heat equally. A lower (less negative) temperature coefficient is better.
How many JA Solar JAM78S30 590W vs LONGi Hi-MO 7 620W panels do I need for an 8 kW system?
For an 8 kW system: you need 14 JA Solar JAM78S30 590W panels (590W each) or 13 LONGi Hi-MO 7 620W panels (620W each). The LONGi Hi-MO 7 620W requires fewer panels, saving on racking hardware and installation labor.
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Last updated: February 2026