--- title: "Just Solar JST405M(120) 405W Solar Panel - Specs & Review | ComparePV" description: "Just Solar JST405M(120) 405W solar panel. Specs: 21.10% efficiency, Monocrystalline cells, dimensions, warranty and temperature coefficient." source: "https://comparepv.com/panel/just-solar-jst405m-120" updated: 2026-09-11 --- # Just Solar JST405M(120) Middle of its segment, modest efficiency 52 panels in the segment Back Contact 400-450 W ## Identity - **Manufacturer:** Just Solar - **Model:** JST405M(120) - **Series:** JST390-410W(120) - **Rated power:** 405 W - **Cell technology:** Back Contact ## How it compares Compared against segment Back Contact 400-450 W (52 panels). | Measure | This panel | Segment median | Standing | Rank | | --- | --- | --- | --- | --- | | Power (Wp) | 405 W | 435 W | Weak - bottom 9% | | | Module efficiency | 21.10% | 22.30% | Weak - bottom 3% | 9,297 | | Power density | 210.7 | 222.7 | Weak - bottom 3% | 9,565 | | Temperature coefficient | -0.340 | -0.290 | Weak - bottom 3% | 8,778 | | Weight (kg) | 21.0 kg | 20.8 kg | Weak - bottom 5% | | | Performance warranty | 25 yrs | 25 yrs | Typical | 9,798 | ### Full peer table | Measure | This panel | Segment median | Standing | Rank | | --- | --- | --- | --- | --- | | Module efficiency | 21.10% | 22.30% | Weak - bottom 3% | 9,297 | | Power density | 210.7 | 222.7 | Weak - bottom 3% | 9,565 | | Temperature coefficient | -0.340 | -0.290 | Weak - bottom 3% | 8,778 | | Weight per kWp | 51.9 | 48.2 | Weak - bottom 5% | 5,230 | | Performance warranty | 25 yrs | 25 yrs | Typical | 9,798 | ### Watch out for - **21.10% module efficiency** - Bottom 3% of the Back Contact 400-450 W segment, against a median of 22.30%. Ranked 9,297th in the whole database. - **-0.340 %/°C temperature coefficient** - Bottom 3% of the Back Contact 400-450 W segment, against a median of -0.290. Ranked 8,778th in the whole database. - **210.7 watts per square metre** - Bottom 3% of the Back Contact 400-450 W segment, against a median of 222.7. Ranked 9,565th in the whole database. - **Best for:** Residential, commercial and shaded-installations. - **Not ideal for:** Tight roof space, hot climates and roofs where every square metre has to count. ## Specification ### Electrical - **Rated power (Pmax):** 405 W - **Efficiency:** 21.10 % - **Voltage at Pmax (Vmp):** 34.64 V - **Current at Pmax (Imp):** 11.70 A - **Open-circuit voltage (Voc):** 41.60 V - **Short-circuit current (Isc):** 12.40 A - **Max system voltage:** 1500 V ### Temperature - **Temperature coefficient of Pmax:** -0.340 %/degC - **Temperature coefficient of Voc:** -0.250 %/degC - **Temperature coefficient of Isc:** 0.040 %/degC - **NOCT:** 44 degC ### Cell and construction - **Cell type:** Monocrystalline - **Cell technology:** Back Contact - **Cell count:** 120 ### Physical - **Length:** 1754 mm - **Width:** 1096 mm - **Thickness:** 30 mm - **Weight:** 21.0 kg - **Area:** 1.92 m2 - **Power density:** 210.7 Wp/m2 ### Warranty and degradation - **Product warranty:** 10 years - **Performance warranty:** 25 years - **Output guaranteed at end of warranty:** 81.4 % - **First-year degradation:** 3.00 % - **Annual degradation:** 0.65 % - **Output after 30 years:** 317 W ## Rank in the whole catalogue | Measure | Position | | --- | --- | | Efficiency | 9297 of 14005 | | Power density | 9565 of 14005 | | Temperature coefficient | 8778 of 14005 | | Weight | 5230 of 14005 | | Warranty | 9798 of 14005 | ## Pros - **Back Contact technology – no front-side shading** - 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. - **Up to 21.3% efficiency – competitive within peer group** - 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. - **Favorable temperature coefficient: -0.34%/°C** - 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. - **Standard form factor – easy installation, low weight** - 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. ## Cons - **Not on BNEF Tier-1 bankable list** - 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. - **10-year product warranty – below market standard** - 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. - **Monofacial only – missed bifacial yield potential** - 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. ## About this series 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. ## Notable figures - Efficiency of 21.1% is 1.2pp below the \*\*Back Contact 400-450W\*\* median (22.3%) - 210.7 W/m² power density is 12.0 W/m² below \*\*Back Contact 400-450W\*\* median (222.7 W/m²) - requires larger installation area - At -0.34%/°C, loses 0.05pp more power per degree than \*\*Back Contact 400-450W\*\* median (-0.29%/°C) - Ranked #9297 out of 14005 panels for efficiency in the database ## Questions ### What is Back Contact technology in the Just Solar JST390-410W(120) series and what does it mean in practice? In Back Contact modules, all electrical connections are routed to the rear side of the panel, leaving the entire front surface active — no busbars shadow the cells. In the JST390-410W(120) series, this results in higher cell efficiency at the same module footprint. For the end user it means more energy harvested from a limited roof area without adding extra panels. ### What warranties come with the Just Solar JST390-410W(120) panels? Just Solar provides a 10-year product warranty covering material and workmanship defects, plus a 25-year linear power output warranty guaranteeing performance stays above the declared degradation schedule. Keep your purchase invoice and installation documentation, as they are typically required when filing a warranty claim. ### How does the JST390-410W(120) series handle partial shading — for example from a chimney or dormer window? The 120-cell half-cut layout divides the module into two independent electrical strings, so shade falling on one portion of the panel does not shut down the entire module. On residential rooftops with chimneys, dormers, or antennas — common in Central Europe — this results in more stable and predictable daily energy production compared to conventional full-cell modules. ### How do the Just Solar JST390-410W(120) panels perform in overcast or low-light conditions? The JST390-410W(120) series is engineered for strong Low Irradiance performance, which matters in climates with frequent morning fog, heavy cloud cover, or diffuse autumn light. The modules maintain high efficiency at reduced irradiance levels, which has a meaningful impact on annual energy yield in regions with moderate solar resources. ### Do the JST390-410W(120) panels need frequent cleaning? What does the self-cleaning coating actually do? The anti-soiling coating on the front glass reduces adhesion of dust, pollen, and particulate matter, allowing rain to wash away most deposits without manual intervention. This translates to less frequent professional cleaning and lower O&M costs — a notable advantage near busy roads, agricultural fields, or industrial emission zones. ### How much does the Just Solar JST390-410W(120) panel weigh, and will it fit a standard roof mounting system? The module weighs approximately 21 kg with dimensions around 1754×1096×30 mm, which is compatible with standard aluminum racking systems commonly used in residential and small commercial installations. Two installers can handle transport and placement without specialized lifting equipment. Always verify roof load capacity with a structural engineer before installing on older timber-frame roofs. ## Datasheet [Manufacturer datasheet (PDF)](https://comparepv.com/datasheets/JST390-410M-120-80bd28bc3d30.pdf) ## Alternatives | Panel | Power | How it differs | | --- | --- | --- | | [AIKO AIKO-455-MAH54Db](https://comparepv.com/panel/aiko-aiko-455-mah54db) | 455 W | +50 W, cooler, +2.2 pp | | [Longi Solar LR5-54HTH-455M](https://comparepv.com/panel/longi-lr5-54hth-455m) | 455 W | +50 W, cooler, +2.2 pp | | [Yingli YL455CF54 e/2](https://comparepv.com/panel/yingli-yl455cf54-e-2) | 455 W | +50 W, cooler, +2.2 pp | | [Einnova Solarline ESM-455T](https://comparepv.com/panel/einnova-solarline-esm-455t) | 455 W | +50 W, +2.2 pp, +5 yr warranty | | [SunEvo Solar SE5-54HBC-455W](https://comparepv.com/panel/sunevo-solar-se5-54hbc-455w) | 455 W | +50 W, cooler, +2.2 pp | | [Just Solar JST-EDMH-(445-465)W-TD (455W class)](https://comparepv.com/panel/just-solar-jst-edmh-445-465-w-td-455w-class) | 455 W | +50 W, +2.2 pp, +5 yr warranty | | [Luxor Solar LX-455M/182R-96+ GG](https://comparepv.com/panel/luxor-lx-455m-182r-96-gg) | 455 W | +50 W, cooler, +2.2 pp | | [Just Solar JST390M(120)](https://comparepv.com/panel/just-solar-jst390m-120) | 390 W | -15 W, -0.8 pp | | [Just Solar JST395M(120)](https://comparepv.com/panel/just-solar-jst395m-120) | 395 W | -10 W, -0.6 pp | | [Just Solar JST400M(120)](https://comparepv.com/panel/just-solar-jst400m-120) | 400 W | -0.3 pp | | [Just Solar JST410M(120)](https://comparepv.com/panel/just-solar-jst410m-120) | 410 W | Very close match | | [Longi Solar LR7-54HJD-510M](https://comparepv.com/panel/longi-lr7-54hjd-510m) | 510 W | +105 W, cooler, +3.9 pp | | [AIKO AIKO-A495-MCE54Mw](https://comparepv.com/panel/aiko-aiko-a495-mce54mw) | 495 W | +90 W, cooler, +3.7 pp | | [Longi Solar LR7-54HJD-505M](https://comparepv.com/panel/longi-lr7-54hjd-505m) | 505 W | +100 W, cooler, +3.6 pp | | [AIKO AIKO-A490-MCE54Mw](https://comparepv.com/panel/aiko-aiko-a490-mce54mw) | 490 W | +85 W, cooler, +3.4 pp | | [Longi Solar LR7-54HJD-500M](https://comparepv.com/panel/longi-lr7-54hjd-500m) | 500 W | +95 W, cooler, +3.4 pp | --- Source: https://comparepv.com/panel/just-solar-jst405m-120 Not in this file, on the page: a thirty-year output simulator and alternatives filtered by how closely they match these dimensions.