Middle of its segment, modest efficiency
The Just Solar JST390-410W(120) series is designed to maximize energy generation from typical rooftops and ground-mounted structures without the need for oversized modules. The use of monocrystalline solar cells and a half-cut design promotes stable operation even with partial shading - which is important on roofs with chimneys, skylights, or installations near trees. In practice, this means more predictable production and easier adaptation to limited space.
The positive power tolerance is also noteworthy, which reduces the risk of disappointment after installation, as well as good performance in low light - in the mornings with fog and cloud cover, which is common in Poland. The manufacturer also highlights the self-cleaning coating, which reduces performance losses due to dirt and lowers maintenance costs.
This solution is ideal for installers and investors looking for modules for homes, small businesses, and farms, where repeatability of parameters, reliability, and quick installation are key.
Ranking
Signals from the data
Residential, commercial and shaded-installations.
Tight roof space, roofs where every square metre has to count and hot climates.
Bottom 1% of the Back Contact 290-490 W segment, against a median of 23.27%. Ranked 11,769th in the whole database.
Bottom 1% of the Back Contact 290-490 W segment, against a median of 232.7. Ranked 11,787th in the whole database.
Bottom 1% of the Back Contact 290-490 W segment, against a median of -0.260. Ranked 8,778th in the whole database.
The Back Contact architecture moves all electrical contacts to the rear of the cell, eliminating busbar shading losses present in conventional front-contact PERC designs. Industry data indicates a 5–7% relative gain in light absorption vs. standard front-contact cells. Combined with the half-cut configuration (120 cells = 60 half-cut pairs), the series also benefits from reduced resistive losses and improved partial-shading response.
Peak module efficiency of 21.3% matches the Luxor Solar Eco Line N-type TOPCon Glass-Glass Bifacial M108 (21.33%) and outperforms both VDS-S144/FNH (20.4%) and Sunket SKT410~430M10-108D4 (21.0%). Achieving this efficiency in a monofacial Back Contact module at 410 Wp max output demonstrates a well-optimized optical cell design.
The manufacturer-specified temperature coefficient of Pmax = -0.34%/°C outperforms typical standard PERC cells (-0.35 to -0.45%/°C) and is on par with many TOPCon modules. In practice, at a module temperature of 65°C, power loss is approximately 8.5%, compared to 10–12% for panels with weaker temperature coefficients, translating to measurably higher summer energy yield.
Dimensions of 1754×1096×30 mm and a module weight of 21 kg fit within the widely adopted residential format, compatible with common racking systems (Schletter, K2, Esdec). No specialized lifting equipment or reinforced substructures are required, reducing installation time and overall BoS costs.
Just Solar does not appear on the BloombergNEF Tier-1 bankable manufacturers list (Q1 2026 edition). For commercial projects and solar farms financed through non-recourse debt, lenders typically require modules from Tier-1 manufacturers. This limits the series to prosumer and self-financed installations and may complicate insurance underwriting for larger systems.
Just Solar offers only a 10-year product warranty (covering manufacturing defects, seals, and frame), whereas Tier-1 manufacturers such as JA Solar, Jinko Solar, and Luxor Solar now provide 15–25-year product warranties as standard. Any physical damage or delamination occurring after the 10-year window falls entirely on the system owner, increasing long-term LCOE risk over a 25-year project horizon.
The JST390-410W(120) series is available only in a monofacial configuration, while the direct peer Luxor Solar Eco Line TOPCon Glass-Glass Bifacial M108 410–430W (21.33%) offers a bifacial variant capable of generating an additional 5–30% energy from reflected irradiance in typical ground-mount installations. Selecting this series for ground arrays or installations over high-albedo surfaces means forgoing measurable annual energy gains.
- At 20.3% efficiency, this panel is 0.9pp below the Back Contact 0-400W median of 21.2%
- 202.9 W/m² power density is 9.2 W/m² below Back Contact 0-400W median (212.1 W/m²) - requires larger installation area
- -0.34%/°C temperature coefficient - 0.07pp worse than Back Contact 0-400W median (-0.27%/°C), expect higher hot weather losses
- At 21.0 kg (2.0 kg above Back Contact 0-400W median of 19.0 kg), requires checking roof load capacity
- Ranked #11769 out of 14005 panels for efficiency in the database
Specifications
Simulations
Degradation from this panel's own datasheet figures. No inverter, soiling or shading losses.
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