--- title: "GCL GCL-M12/66GDF-660 Solar Panel: Specs & Datasheet | ComparePV" description: "GCL GCL-M12/66GDF-660 solar panel. Specs: 21.20% efficiency, Monocrystalline cells, dimensions, warranty and temperature coefficient." source: "https://comparepv.com/panel/gcl-gcl-m12-66gdf-660" image: "https://comparepv.com/og/panel/gcl-gcl-m12-66gdf-660.png" updated: 2026-09-11 --- # GCL GCL-M12/66GDF-660 Middle of its segment, weak in heat 320 panels in the segment PERC 650-700 W ## Identity - **Manufacturer:** GCL - **Model:** GCL-M12/66GDF-660 - **Series:** GCL-M12/66GDF - **Rated power:** 660 W - **Cell technology:** PERC - **Bifacial:** yes ## How it compares Compared against segment PERC 650-700 W (320 panels). | Measure | This panel | Segment median | Standing | Rank | | --- | --- | --- | --- | --- | | Power (Wp) | 660 W | 660 W | Typical | | | Module efficiency | 21.20% | 21.25% | Typical | 9,145 | | Power density | 212.5 | 212.5 | Typical | 9,028 | | Temperature coefficient | -0.350 | -0.340 | Weak - bottom 10% | 10,489 | | Weight (kg) | 38.5 kg | 34.5 kg | Weak - bottom 17% | | | Performance warranty | 30 yrs | 30 yrs | Typical | 21 | ### Full peer table | Measure | This panel | Segment median | Standing | Rank | | --- | --- | --- | --- | --- | | Module efficiency | 21.20% | 21.25% | Typical | 9,145 | | Power density | 212.5 | 212.5 | Typical | 9,028 | | Temperature coefficient | -0.350 | -0.340 | Weak - bottom 10% | 10,489 | | Weight per kWp | 58.3 | 52.3 | Weak - bottom 17% | 11,742 | | Performance warranty | 30 yrs | 30 yrs | Typical | 21 | ### Watch out for - **-0.350 %/°C temperature coefficient** - Bottom 10% of the PERC 650-700 W segment, against a median of -0.340. - **58.3 kg per kWp** - Bottom 17% of the PERC 650-700 W segment, against a median of 52.3. - **Best for:** Utility-scale, agrivoltaic and floating. - **Not ideal for:** Hot climates and weight-limited structures. ## Specification ### Electrical - **Rated power (Pmax):** 660 W - **Efficiency:** 21.20 % - **Voltage at Pmax (Vmp):** 38.00 V - **Current at Pmax (Imp):** 17.37 A - **Open-circuit voltage (Voc):** 45.80 V - **Short-circuit current (Isc):** 18.31 A - **Max system voltage:** 1500 V ### Temperature - **Temperature coefficient of Pmax:** -0.350 %/degC - **Temperature coefficient of Voc:** -0.280 %/degC - **Temperature coefficient of Isc:** 0.050 %/degC - **NOCT:** 45 degC ### Cell and construction - **Cell type:** Monocrystalline - **Cell technology:** PERC - **Cell count:** 132 - **Bifacial:** yes ### Physical - **Length:** 2384 mm - **Width:** 1303 mm - **Thickness:** 33 mm - **Weight:** 38.5 kg - **Area:** 3.11 m2 - **Power density:** 212.5 Wp/m2 ### Warranty and degradation - **Product warranty:** 12 years - **Performance warranty:** 30 years - **Output guaranteed at end of warranty:** 85.0 % - **First-year degradation:** 2.00 % - **Annual degradation:** 0.45 % - **Output after 30 years:** 561 W ## Rank in the whole catalogue | Measure | Position | | --- | --- | | Efficiency | 9145 of 14129 | | Power density | 9028 of 14129 | | Temperature coefficient | 10489 of 14129 | | Weight | 11742 of 14129 | | Warranty | 21 of 14129 | ## Pros - **Dual-Glass Construction - C&I-Grade Mechanical Strength** - The glass-glass encapsulation (2 mm + 2 mm tempered low-iron glass) delivers a snow load rating of up to 5,400 Pa and wind load resistance up to 2,400 Pa. It eliminates moisture-driven degradation risk by removing the rear-side EVA backsheet - a critical advantage in floating and agrivoltaic installations where exposure to condensation is continuous. - **Bifacial Design - Real-World Rear-Side Energy Harvest** - The bifacial architecture captures irradiance reflected from the ground surface, yielding an additional 5-25% in annual energy output compared to monofacial modules - depending on the albedo of the mounting surface (grassland ~20%; white roofing membrane ~60-80%). The gain is most significant in ground-mounted systems and agrivoltaic arrays with elevated mounting structures. - **30-Year Linear Power Warranty, Degradation ≤0.40%/yr** - The manufacturer guarantees 84.95% of nominal power output after 30 years of operation at an annual degradation rate of ≤0.40%. The peer-comparable Trina Solar Vertex TSM-DE21 675W carries an equivalent warranty scope, confirming that the GCL-M12/66GDF aligns with the top-tier standard for utility-scale modules. - **Tier-1 Bankable Manufacturer Since 1990** - GCL System Integration Technology (GCL-SI) appears on the Bloomberg NEF Tier 1 module manufacturer list, satisfying the rigorous bankability criterion of non-recourse financing for ≥6 projects of ≥10 MW each, backed by ≥6 different lenders. This status directly streamlines project finance for PV plants built on this series. - **21.1-21.7% Efficiency - On Par with Leading Peers** - The peak module efficiency of 21.7% matches the Trina Solar Vertex TSM-DE21 675W (21.7%) and trails the BYD AURO MSTK-33 and Neo Solar Power NESE 655-675-66MHT-G12 (both 21.73%) by only 0.03 percentage points. The gap is below the threshold of practical significance for C&I and utility-scale project design. ## Cons - **P-Type PERC - Previous-Generation Cell Technology** - P-type PERC cells carry a higher temperature coefficient of Pmax (-0.35%/°C) compared to N-type TOPCon (~-0.29%/°C) and greater susceptibility to LID (Light-Induced Degradation). GCL itself already offers a successor product - the GCL-NT12/66GDF (N-type TOPCon, 700 W, 22.53% efficiency) - indicating that the M12/66GDF series represents technology the market is progressively phasing out; TOPCon is projected to reach approximately 60% share of global module production by 2030. ## About this series Series GCL GCL-M12/66GDF are modules designed for maximum yield in installations where every meter counts, and reliable performance in challenging conditions. The application of a **bifacial** structure allows for the actual use of reflected light from the ground, which is particularly beneficial on light surfaces, ground-mounted installations, and where you design higher mounting frames. The key advantage of this series is its **dual glass** construction - glass-glass - which supports durability, minimizes the risk of degradation related to moisture, and enhances resistance to typical operational issues. The GCL-M12/66GDF targets safe and predictable yields in projects where the schedule and maintenance are costly: PV farms, **agrivoltaics**, and \ installations. Thanks to refined production processes, the series is focused on minimizing phenomena such as PID and microcracking, translating to smoother operation and fewer surprises over the long term. In practice, it stands out from the competition by combining high bifacial energy potential with the durability of the glass-glass construction - without compromising on professional applications. ## Notable figures - Efficiency of 21.2% matches the \*\*PERC 650-700W\*\* median - At 212.5 W/m² power density, roof space requirements are typical for \*\*PERC 650-700W\*\* panels - At -0.35%/°C, hot weather performance is typical for \*\*PERC 650-700W\*\* panels - Weight of 38.5 kg is 4.0 kg above \*\*PERC 650-700W\*\* median (34.5 kg) - verify structural support - Bifaciality factor of 70% can add 4-10% extra yield with reflective mounting surface ## Questions ### What warranty does the GCL-M12/66GDF series carry and what does it cover? The GCL-M12/66GDF series comes with a 12-year product warranty covering physical defects and workmanship, along with a 30-year linear power output warranty. The manufacturer guarantees that after 30 years the panel will retain at least 84.95% of its nominal power output. This is one of the longer power warranty standards available in this product class, which is particularly significant for utility-scale PV farm projects where the investment horizon extends to 25-30 years. ### Are the GCL-M12/66GDF panels suitable for agrivoltaic and floating PV installations? Yes, the GCL-M12/66GDF series was specifically designed with these applications in mind. The dual glass (glass-glass) construction provides high resistance to moisture and vapor ingress, which is critical for installations over water bodies and in agricultural environments. An additional advantage is the bifacial technology - in installations on elevated mounting structures or over water (where the bright surface reflects sunlight), the module can deliver a measurable increase in energy yield. ### What does bifacial technology offer in the GCL-M12/66GDF panels - how much additional energy can be harvested? Bifacial means the module harvests energy from both the front side and the rear side by capturing light reflected from the ground surface. The actual gain depends on the albedo of the surface beneath the array: with bright gravel, concrete, or snow, you can expect an additional 5-15% in energy production compared to a standard monofacial module of the same nominal power rating. In ground-mounted installations with an appropriately selected mounting height, the bifacial gain is most reliably measurable. ### How much does the GCL-M12/66GDF panel weigh, and is it difficult to install on a rooftop? The GCL-M12/66GDF module weighs 38.5 kg and measures 2384 × 1303 × 33 mm. These are dimensions typical of large 675 W modules - decidedly above average for a rooftop installation. The series is intended primarily for ground-mounted applications, utility-scale PV farms, agrivoltaic systems, and floating PV, rather than conventional residential rooftops. Rooftop installation requires at least a two-person crew and a suitably engineered mounting structure. ### How do the GCL-M12/66GDF panels perform in high temperatures and on overcast days? The temperature coefficient of power (Pmax) is -0.35%/°C, which is a strong result for PERC technology - it means that when the panel heats up to 65 °C (typical summer operating conditions) you lose approximately 14% of nominal power output, less than older polycrystalline modules. The half-cut cell technology additionally reduces losses under partial shading and diffuse light conditions, improving production on overcast days. ### Is GCL a Tier 1 manufacturer and can they be trusted for large-scale projects? Yes, GCL System Integration (GCLSI) is classified as a Tier 1 manufacturer by independent industry agencies, which establishes bankability - banks and financial institutions funding PV farms accept these modules when structuring project financing. The company is part of the GCL Group, one of the world's largest producers of solar cells and silicon wafers. For large-scale projects, this translates into supply chain reliability, manufacturing stability, and the ability to enforce warranty claims. ## Datasheet [Manufacturer datasheet (PDF)](https://comparepv.com/datasheets/721941406890bafba8917-57c37b1be549.pdf) ## Alternatives | Panel | Power | How it differs | | --- | --- | --- | | [AIKO AIKO-A650-MAE72Mw](https://comparepv.com/panel/aiko-aiko-a650-mae72mw) | 650 W | Cooler, lighter, +4.0 pp | | [AIKO AIKO-A680-MDE72Mw](https://comparepv.com/panel/aiko-aiko-a680-mde72mw) | 680 W | Cooler, lighter, +4.0 pp | | [AIKO AIKO-A675-MDE72Mw](https://comparepv.com/panel/aiko-aiko-a675-mde72mw) | 675 W | Cooler, lighter, +3.8 pp | | [AIKO AIKO-A645-MAE72Mw](https://comparepv.com/panel/aiko-aiko-a645-mae72mw) | 645 W | Cooler, lighter, +3.8 pp | | [AIKO AIKO-A700-MAE78Dw](https://comparepv.com/panel/aiko-aiko-a700-mae78dw) | 700 W | +40 W, cooler, +3.8 pp | | [WINAICO WST-675BKX72-A2](https://comparepv.com/panel/winaico-wst-675bkx72-a2) | 675 W | Cooler, lighter, +3.8 pp | | [AIKO AIKO-A695-MAE78Dw](https://comparepv.com/panel/aiko-aiko-a695-mae78dw) | 695 W | Cooler, lighter, +3.7 pp | | [AIKO AIKO-G670-MCH72Mw](https://comparepv.com/panel/aiko-aiko-g670-mch72mw) | 670 W | Cooler, lighter, +3.6 pp | | [GCL GCL-M12/66GDF-655W](https://comparepv.com/panel/gcl-gcl-m12-66gdf-655w) | 655 W | Very close match | | [GCL GCL-M12/66H-665W](https://comparepv.com/panel/gcl-gcl-m12-66h-665w) | 665 W | Lighter, -5 yr warranty | | [AIKO AIKO-A805-GRH78Dw](https://comparepv.com/panel/aiko-aiko-a805-grh78dw) | 805 W | +145 W, cooler, +3.9 pp | | [AIKO AIKO-A800-GRH78Dw](https://comparepv.com/panel/aiko-aiko-a800-grh78dw) | 800 W | +140 W, cooler, +3.7 pp | | [AIKO AIKO-A795-GRH78Dw](https://comparepv.com/panel/aiko-aiko-a795-grh78dw) | 795 W | +135 W, cooler, +3.6 pp | | [AIKO AIKO-A790-GRH78Dw](https://comparepv.com/panel/aiko-aiko-a790-grh78dw) | 790 W | +130 W, cooler, +3.4 pp | | [Trina Solar TSM-NEG21C.20Q-760](https://comparepv.com/panel/trina-solar-tsm-neg21c-20q-760) | 760 W | +100 W, cooler, +3.3 pp | | [AIKO AIKO-A785-GRH78Dw](https://comparepv.com/panel/aiko-aiko-a785-grh78dw) | 785 W | +125 W, cooler, +3.2 pp | --- Source: https://comparepv.com/panel/gcl-gcl-m12-66gdf-660 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.