--- title: "Longi Solar LR8-66HVD-640M 640W Solar Panel - Specs & Review | ComparePV" description: "Longi Solar LR8-66HVD-640M 640W solar panel. Specs: 23.69% efficiency, Monocrystalline cells, dimensions, warranty and temperature coefficient." source: "https://comparepv.com/panel/longi-lr8-66hvd-640m" updated: 2026-09-11 --- # Longi Solar LR8-66HVD-640M Middle of its segment, heavy for its output 72 panels in the segment Back Contact 600-650 W ## Identity - **Manufacturer:** Longi Solar - **Model:** LR8-66HVD-640M - **Series:** Hi-MO X10 Scientist / LR8-66HVD 640~665M - **Rated power:** 640 W - **Cell technology:** Back Contact - **Bifacial:** yes ## How it compares Compared against segment Back Contact 600-650 W (72 panels). | Measure | This panel | Segment median | Standing | Rank | | --- | --- | --- | --- | --- | | Power (Wp) | 640 W | 635 W | Typical | | | Module efficiency | 23.69% | 23.70% | Typical | 580 | | Power density | 236.9 | 236.9 | Typical | 521 | | Temperature coefficient | -0.260 | -0.260 | Typical | 511 | | Weight (kg) | 33.5 kg | 32.3 kg | Weak - bottom 21% | | | Performance warranty | 30 yrs | 30 yrs | Typical | 21 | ### Full peer table | Measure | This panel | Segment median | Standing | Rank | | --- | --- | --- | --- | --- | | Module efficiency | 23.69% | 23.70% | Typical | 580 | | Power density | 236.9 | 236.9 | Typical | 521 | | Temperature coefficient | -0.260 | -0.260 | Typical | 511 | | Weight per kWp | 52.3 | 50.4 | Weak - bottom 21% | 5,829 | | Performance warranty | 30 yrs | 30 yrs | Typical | 21 | ### Watch out for - **52.3 kg per kWp** - Bottom 21% of the Back Contact 600-650 W segment, against a median of 50.4. - **Best for:** Residential, commercial, utility-scale, shaded-installations and hot-climate. - **Not ideal for:** Weight-limited structures. ## Specification ### Electrical - **Rated power (Pmax):** 640 W - **Efficiency:** 23.69 % - **Voltage at Pmax (Vmp):** 40.78 V - **Current at Pmax (Imp):** 15.69 A - **Open-circuit voltage (Voc):** 49.52 V - **Short-circuit current (Isc):** 16.38 A - **Max system voltage:** 1500 V ### Temperature - **Temperature coefficient of Pmax:** -0.260 %/degC - **Temperature coefficient of Voc:** -0.200 %/degC - **Temperature coefficient of Isc:** 0.050 %/degC - **NOCT:** 45 degC ### Cell and construction - **Cell type:** Monocrystalline - **Cell technology:** Back Contact - **Cell count:** 132 - **Bifacial:** yes ### Physical - **Length:** 2382 mm - **Width:** 1134 mm - **Thickness:** 30 mm - **Weight:** 33.5 kg - **Area:** 2.70 m2 - **Power density:** 236.9 Wp/m2 ### Warranty and degradation - **Product warranty:** 15 years - **Performance warranty:** 30 years - **Output guaranteed at end of warranty:** 88.8 % - **First-year degradation:** 1.00 % - **Annual degradation:** 0.35 % - **Output after 30 years:** 569 W ## Rank in the whole catalogue | Measure | Position | | --- | --- | | Efficiency | 580 of 14005 | | Power density | 521 of 14005 | | Temperature coefficient | 511 of 14005 | | Weight | 5829 of 14005 | | Warranty | 21 of 14005 | ## Pros - **24.62% efficiency, top of segment** - Maximum module efficiency of 24.62% matches Sunpro Power SPDG-BC132R12 (24.62%) and Talesun CIPRO-TM9C72M (24.6%), and clearly outperforms Waaree ARKA (21.29%). This is enabled by N-TaiRay cell technology and HPBC 2.0 architecture. - **No front busbars (HPBC 2.0)** - The back-contact architecture eliminates visible front-side gridlines, reducing busbar shading losses and improving module aesthetics - a key advantage for premium projects where visual appearance matters. - **Low temperature coefficient of -0.26%/°C** - This coefficient is roughly 0.03 pp better than typical TOPCon modules, translating into smaller power losses at high panel temperatures and higher real-world summer yield. - **Two-sided generation despite BC design** - A bifaciality factor of around 75% is a notable achievement, since back-contact modules traditionally struggle with efficient rear-side generation - the series won the pv magazine Award 2025 for bifacial back-contact innovation. - **Enhanced mechanical durability via N-TaiRay** - The N-TaiRay wafer offers a 16% higher fracture resistance and fewer impurities, which combined with the A+ Anti-Shading feature reduces the risk of microcracks and local hotspots under partial shading. ## Cons - **Shorter 15-year product warranty** - The product warranty is 15 years, below the 25-year standard now offered by many tier-1 manufacturers for premium n-type modules. The 30-year linear power warranty remains competitive with peers. - **Limited field track record for BC technology** - The Hi-MO X10 series with HPBC 2.0 architecture launched in 2024, so it lacks the long-term field track record that mature TOPCon and PERC technologies have accumulated over more than a decade. ## About this series This Longi Solar Hi-MO X10 Scientist LR8-66HVD 640-665M series is designed for investors seeking maximum energy production from limited roof space and reliable performance in real-world conditions. The application of **N-TaiRay cells** and **HPBC 2.0 architecture** enables better light utilization and minimizes typical losses associated with conventional modules featuring visible front grids. The result is not only high efficiency but also more predictable energy generation under variable sunlight conditions. A practical advantage of this series is **A+ Anti-Shading** - a solution that supports energy gains when the module is partially shaded by a chimney, tree, or structural elements. Furthermore, the construction is engineered for **safety** by reducing the risk of hotspots and offering lower susceptibility to micro-cracks. This is an excellent choice for modern residential installations and premium projects where yield, aesthetics (lack of visible front gridlines), and durability are prioritized over the compromises typical of less expensive solutions. ## Notable figures - Efficiency of 23.7% matches the \*\*Back Contact 600-650W\*\* median - At 236.9 W/m² power density, roof space requirements are typical for \*\*Back Contact 600-650W\*\* panels - At -0.26%/°C, hot weather performance is typical for \*\*Back Contact 600-650W\*\* panels - At 33.5 kg (1.2 kg above \*\*Back Contact 600-650W\*\* median of 32.3 kg), requires checking roof load capacity - 75% bifaciality enables rear-side power generation, boosting yield by 4-11% on reflective surfaces ## Questions ### What is HPBC 2.0 technology in the LONGi Hi-MO X10 Scientist and how does it compare to standard TOPCon? HPBC 2.0 (Hybrid Passivated Back Contact) is a back-contact cell architecture built on LONGi's proprietary n-type N-TaiRay wafer. All electrical contacts sit on the rear of the cell, eliminating front-side busbar shading and pushing module efficiency up to 24.62% on the 665M variant. Typical TOPCon modules top out at 22–23%, making HPBC 2.0 a meaningful advantage on rooftops where usable area is limited. ### What warranties come with the LONGi Hi-MO X10 Scientist LR8-66HVD solar panels? LONGi provides a 15-year product warranty covering manufacturing and material defects, plus a 30-year linear power output warranty. After 30 years, modules are guaranteed to retain at least 88.85% of rated power. This is among the longest power warranty terms on the market today and significantly reduces investment risk over the system's lifetime. ### How does the LONGi Hi-MO X10 Scientist handle partial shading from a chimney or nearby trees? The Hi-MO X10 series includes LONGi's A+ Anti-Shading technology, which the manufacturer claims reduces power losses from partial shading by approximately 70% compared to TOPCon modules. This is a practical advantage for urban rooftops surrounded by vegetation or architectural elements. The 132-cell layout further limits the impact of localized shading on the full string output. ### How do the LONGi Hi-MO X10 Scientist LR8-66HVD panels perform in high summer temperatures? The power temperature coefficient is -0.26%/°C, one of the lowest among silicon-based modules. When a panel heats up to 70°C on a dark roof in summer, it loses less output than a standard TOPCon module rated at -0.29 to -0.35%/°C. For a 10 kWp system, this translates into a measurable gain in annual energy yield. ### Is the LONGi Hi-MO X10 Scientist LR8-66HVD bifacial, and does that matter for a pitched roof installation? Yes, the LR8-66HVD series is bifacial — it captures light from both sides of the module. On a pitched roof where the panel sits close to the roof surface, the bifacial gain is limited because very little reflected irradiance reaches the rear glass. The benefit is marginal on sloped rooftops but real on ground-mount or flat-roof systems with a reflective surface such as a white membrane or gravel. ### How much does the LONGi Hi-MO X10 Scientist panel weigh, and can a standard roof structure support it? The module weighs approximately 33.5 kg and measures 2382×1134×30 mm. The higher weight results from its dual-glass construction. Before installation — particularly on older roof structures — a structural assessment is recommended to verify load capacity for combined snow, wind, and panel weight. The mounting system including rails and clamps must be rated for this module class. ## Datasheet [Manufacturer datasheet (PDF)](https://comparepv.com/datasheets/lr-8-66-hvd-640-665-m-30-30-and-15-frame-scientist-bgv-01-20-2b55af0fbbce.pdf) ## Alternatives | Panel | Power | How it differs | | --- | --- | --- | | [AIKO AIKO-A650-MAE72Mw](https://comparepv.com/panel/aiko-aiko-a650-mae72mw) | 650 W | +10 W, lighter, +1.5 pp | | [AIKO AIKO-A680-MDE72Mw](https://comparepv.com/panel/aiko-aiko-a680-mde72mw) | 680 W | +40 W, lighter, +1.5 pp | | [AIKO AIKO-A675-MDE72Mw](https://comparepv.com/panel/aiko-aiko-a675-mde72mw) | 675 W | +35 W, lighter, +1.3 pp | | [AIKO AIKO-A645-MAE72Mw](https://comparepv.com/panel/aiko-aiko-a645-mae72mw) | 645 W | Lighter, +1.3 pp | | [AIKO AIKO-G670-MCH72Mw](https://comparepv.com/panel/aiko-aiko-g670-mch72mw) | 670 W | +30 W, lighter, +1.1 pp | | [Longi Solar LR7-72HVHF-670M](https://comparepv.com/panel/longi-lr7-72hvhf-670m) | 670 W | +30 W, lighter, +1.1 pp | | [AIKO AIKO-A640-MAE72Mw](https://comparepv.com/panel/aiko-aiko-a640-mae72mw) | 640 W | Lighter, +1.1 pp | | [Longi Solar LR8-66HGD-595M](https://comparepv.com/panel/longi-lr8-66hgd-595m) | 595 W | -45 W, hotter, -1.7 pp | | [Longi Solar LR7-72HGD-600M](https://comparepv.com/panel/longi-lr7-72hgd-600m) | 600 W | -40 W, hotter, -1.5 pp | | [Longi Solar 600M](https://comparepv.com/panel/longi-600m) | 600 W | -40 W, -1.3 pp, -5 yr warranty | | [Longi Solar LR7-72HTH-605M](https://comparepv.com/panel/longi-lr7-72hth-605m) | 605 W | Lighter, -1.3 pp, -5 yr warranty | | [AIKO AIKO-A700-MAE78Dw](https://comparepv.com/panel/aiko-aiko-a700-mae78dw) | 700 W | +60 W, heavier, +1.3 pp | | [AIKO AIKO-A695-MAE78Dw](https://comparepv.com/panel/aiko-aiko-a695-mae78dw) | 695 W | +55 W, heavier, +1.2 pp | | [Jinko Solar JKM650-670N-66QL6-BDV (670W class)](https://comparepv.com/panel/jinko-solar-jkm650-670n-66ql6-bdv-670w-class) | 670 W | +30 W, lighter, +1.1 pp | --- Source: https://comparepv.com/panel/longi-lr8-66hvd-640m Not in this file, on the page: the I-V and temperature curves lifted from the manufacturer's datasheet, a thirty-year output simulator, a bifacial gain calculator and alternatives filtered by how closely they match these dimensions.