--- title: "Fellow Energy FE66-18X 500W Solar Panel - Specs & Review | ComparePV" description: "Fellow Energy FE66-18X 500W solar panel. Specs: 21.10% efficiency, Monocrystalline cells, dimensions, warranty and temperature coefficient." source: "https://comparepv.com/panel/fellow-energy-fe66-18x" updated: 2026-09-11 --- # Fellow Energy FE66-18X Light for its output, short guarantee 706 panels in the segment PERC 500-550 W ## Identity - **Manufacturer:** Fellow Energy - **Model:** FE66-18X - **Series:** FE66-18X - **Rated power:** 500 W - **Cell technology:** PERC - **Bifacial:** yes ## How it compares Compared against segment PERC 500-550 W (706 panels). | Measure | This panel | Segment median | Standing | Rank | | --- | --- | --- | --- | --- | | Power (Wp) | 500 W | 535 W | Weak - bottom 4% | | | Module efficiency | 21.10% | 20.90% | Strong - top 20% | 9,297 | | Power density | 210.6 | 209.0 | Typical | 9,583 | | Temperature coefficient | -0.350 | -0.350 | Typical | 10,419 | | Weight (kg) | 25.0 kg | 28.4 kg | Strong - top 16% | | | Performance warranty | 25 yrs | 30 yrs | Weak - bottom 23% | 9,798 | ### Full peer table | Measure | This panel | Segment median | Standing | Rank | | --- | --- | --- | --- | --- | | Module efficiency | 21.10% | 20.90% | Strong - top 20% | 9,297 | | Power density | 210.6 | 209.0 | Typical | 9,583 | | Temperature coefficient | -0.350 | -0.350 | Typical | 10,419 | | Weight per kWp | 50.0 | 53.0 | Strong - top 16% | 3,317 | | Performance warranty | 25 yrs | 30 yrs | Weak - bottom 23% | 9,798 | ### Strengths - **50.0 kg per kWp** - Top 16% of the PERC 500-550 W segment, against a median of 53.0. - **21.10% module efficiency** - Top 20% of the PERC 500-550 W segment, against a median of 20.90%. ### Watch out for - **25 year performance warranty** - Bottom 23% of the PERC 500-550 W segment, against a median of 30 yrs. - **Best for:** Residential, commercial and shaded-installations. - **Not ideal for:** Owners who want a long output guarantee. ## Specification ### Electrical - **Rated power (Pmax):** 500 W - **Efficiency:** 21.10 % - **Voltage at Pmax (Vmp):** 38.37 V - **Current at Pmax (Imp):** 13.04 A - **Open-circuit voltage (Voc):** 45.55 V - **Short-circuit current (Isc):** 13.93 A - **Max system voltage:** 1500 V ### Temperature - **Temperature coefficient of Pmax:** -0.350 %/degC - **Temperature coefficient of Voc:** -0.275 %/degC - **Temperature coefficient of Isc:** 0.045 %/degC ### Cell and construction - **Cell type:** Monocrystalline - **Cell technology:** PERC - **Cell count:** 132 - **Bifacial:** yes ### Physical - **Length:** 2094 mm - **Width:** 1134 mm - **Thickness:** 35 mm - **Weight:** 25.0 kg - **Area:** 2.37 m2 - **Power density:** 210.6 Wp/m2 ### Warranty and degradation - **Product warranty:** 12 years - **Performance warranty:** 25 years - **Output guaranteed at end of warranty:** 83.1 % - **First-year degradation:** 2.50 % - **Annual degradation:** 0.60 % - **Output after 30 years:** 401 W ## Rank in the whole catalogue | Measure | Position | | --- | --- | | Efficiency | 9297 of 14005 | | Power density | 9583 of 14005 | | Temperature coefficient | 10419 of 14005 | | Weight | 3317 of 14005 | | Warranty | 9798 of 14005 | ## Pros - **Bifacial design with active rear side** - The dual-glass bifacial construction captures albedo-reflected irradiance from the ground surface (light membrane, gravel, concrete), delivering an additional 5–15% energy yield compared to a monofacial module of the same nameplate power under typical mounting conditions. - **10BB half-cut PERC – reduced hotspot risk** - Ten busbars combined with half-cut cells reduce internal module resistance and limit mismatch losses under partial shading. The hotspot risk is significantly lower than in legacy 5–6 BB full-cell modules, contributing to longer laminate service life. - **1500 VDC system voltage compatibility** - Support for 1500 VDC systems allows strings of ~24–26 modules, reducing the number of MPPT inputs and overall BoS costs (cabling, connectors, protective devices) by approximately 5–10% compared to 1000 VDC designs. - **21.1% efficiency – leading edge of the 500 Wp PERC segment** - At 500 Wp and 21.1% efficiency, the module outperforms direct peers: Emmvee GRAPHITE Monoperc Black (21.03%) and Lina Energy LEPV 132 HC ICON PLUS (21.06%), delivering higher power density and requiring less roof area per installed kWp. - **Full Black variant – residential aesthetics** - The Full Black option (black frame, black backsheet) positions the series competitively in the residential rooftop segment, where uniform appearance influences purchasing decisions and can support a higher installation price point. ## Cons - **Discontinued series – limited serviceability** - The FE66-18X line is officially discontinued, meaning no new modules are available for system expansion, warranty replacement stock is constrained, and long-term service continuity is at risk. The manufacturer – Jiangsu Xiehang Energy Technology (founded 2020) – has a short market track record, further amplifying service continuity risk. - **PERC technology – superseded by N-type TOPCon** - By 2024, TOPCon exceeded 66% of global production capacity, displacing PERC (down to ~35–40% share). TOPCon modules deliver a temperature coefficient of approx. -0.29%/°C versus -0.35%/°C for the FE66-18X, translating to approximately 1.5–2.5% higher annual yield at the same nameplate power — a measurable LCOE disadvantage versus current-generation modules. - **Power warranty at 83.1% after 25 years – below premium standard** - The manufacturer guarantees ≥83.1% of rated power after 25 years, while leading Tier-1 brands (Jinko, LONGi, JA Solar) guarantee 84.8–87.4% over the same period. The 1.3–4.3 percentage-point gap translates into measurably lower cumulative energy yield over the module's full service life. - **Significant efficiency gap vs. peer Gokin GK-3-54HGF** - At the same 500 Wp nameplate, the Gokin GK-3-54HGF achieves 24.5% efficiency versus 21.1% for the FE66-18X — a 3.4 pp difference (~16% higher power density). For area-constrained residential rooftops, this directly caps the maximum installable system power. ## About this series The **Fellow Energy FE66-18X** series consists of monocrystalline panels based on **half-cut PERC** technology, which effectively minimize energy losses caused by shading and light-induced degradation (LID). The use of half-cut cells reduces the module's internal resistance, resulting in improved energy yield even under challenging conditions - cloud cover or elevated temperatures. Thanks to the **10-busbar design**, the cells operate more efficiently, and the risk of hot spot formation is significantly reduced. The panels are available in various aesthetic variants, including a **Full Black** version, making them an attractive choice for residential rooftop installations where aesthetics matter. Compatibility with a **1500 VDC** system voltage allows for the design of longer strings and reduces installation costs on the BOS side. The FE66-18X series performs well both in prosumer installations and in commercial projects requiring proven modules with high power density. It is a solid choice for installers seeking a balance between build quality, durability, and price. ## Notable figures - Efficiency of 21.1% matches the \*\*PERC 500-550W\*\* median - Power density of 210.6 W/m² matches the \*\*PERC 500-550W\*\* median - Temperature coefficient of -0.35%/°C matches the \*\*PERC 500-550W\*\* median - Weight of 25.0 kg (3.4 kg below \*\*PERC 500-550W\*\* median of 28.4 kg) allows easier transport and roof mounting - Ranked #9297 out of 14005 panels for efficiency in the database ## Questions ### What warranty does the Fellow Energy FE66-18X series come with? The FE66-18X series includes a 12-year product warranty covering manufacturing defects and materials, plus a 25-year linear power output warranty. After 25 years, the module is guaranteed to produce at least the stated minimum percentage of its rated power. Fellow Energy is a Tier 1 manufacturer, which adds credibility to these long-term warranty commitments. ### Are the FE66-18X panels bifacial, and does that matter for a typical pitched roof installation? Yes, the FE66-18X series features bifacial cells that generate power from both sides of the module. On a pitched roof with a light-colored underlayer or high-reflectance membrane, you can expect an additional yield of 5–15% compared to standard monofacial modules. The bifacial gain is greatest in ground-mounted systems with a white or highly reflective surface beneath the panels. ### What is half-cut PERC technology and why does the FE66-18X series use it? Half-cut PERC is a technology where solar cells are laser-cut in half, reducing internal resistance and limiting losses from partial shading caused by chimneys or antennas. The PERC passivation layer increases electron recovery and improves efficiency, especially under diffuse light. The FE66-18X also uses a 10-busbar design, which further reduces the risk of hot spots forming on the module. ### Is the Fellow Energy FE66-18X available in a Full Black version, and is it suitable for residential rooftops? Yes, the FE66-18X series is available in a Full Black variant with a black frame and black backsheet, making it an aesthetically pleasing choice for residential rooftop installations. It is ideal for homeowners who want a discreet, uniform look. With up to 500 Wp per module, the series delivers high power density, so fewer panels are needed to reach the target system output. ### Can an FE66-18X installation operate at a 1500 V system voltage? Yes, the Fellow Energy FE66-18X modules are rated for a 1500 VDC system voltage. This allows longer string configurations with more modules in series, reducing the number of DC cables and inverters needed and lowering overall BoS costs. This is especially beneficial in large commercial or industrial PV projects where minimizing balance-of-system expenses significantly impacts LCOE. ### How do the FE66-18X panels perform in high temperatures or on overcast days? The half-cut PERC technology in the FE66-18X series reduces internal resistance, which limits thermal losses at elevated cell temperatures. The cell design also minimizes light-induced degradation (LID). On overcast days, the modules make better use of diffuse irradiance compared to older monocrystalline technologies, resulting in higher annual energy yields in climates with frequent cloud cover. ## Datasheet [Manufacturer datasheet (PDF)](https://comparepv.com/datasheets/1682581296565912-3f1c9c45ba30.pdf) ## Alternatives | Panel | Power | How it differs | | --- | --- | --- | | [Longi Solar LR7-54HJD-510M](https://comparepv.com/panel/longi-lr7-54hjd-510m) | 510 W | Cooler, +3.9 pp, +5 yr warranty | | [AIKO AIKO-A495-MCE54Mw](https://comparepv.com/panel/aiko-aiko-a495-mce54mw) | 495 W | Cooler, +3.7 pp, +5 yr warranty | | [Longi Solar LR7-54HJD-505M](https://comparepv.com/panel/longi-lr7-54hjd-505m) | 505 W | Cooler, +3.6 pp, +5 yr warranty | | [AIKO AIKO-A490-MCE54Mw](https://comparepv.com/panel/aiko-aiko-a490-mce54mw) | 490 W | Cooler, +3.4 pp, +5 yr warranty | | [Longi Solar LR7-54HJD-500M](https://comparepv.com/panel/longi-lr7-54hjd-500m) | 500 W | Cooler, +3.4 pp, +5 yr warranty | | [Talesun CIPRO-TN9C54M-500W](https://comparepv.com/panel/talesun-cipro-tn9c54m-500w) | 500 W | Cooler, +3.4 pp, +5 yr warranty | | [Gamko New Energy GKA120N-PRO-590W](https://comparepv.com/panel/gamko-new-energy-gka120n-pro-590w) | 590 W | +90 W, +2.7 pp, +5 yr warranty | | [Gamko New Energy GKA120N-PRO-585W](https://comparepv.com/panel/gamko-new-energy-gka120n-pro-585w) | 585 W | +85 W, +2.5 pp, +5 yr warranty | | [Bisol BGO 580](https://comparepv.com/panel/bisol-bgo-580) | 580 W | +80 W, cooler, +2.4 pp | | [Gamko New Energy GKA120N-PRO-580W](https://comparepv.com/panel/gamko-new-energy-gka120n-pro-580w) | 580 W | +80 W, +2.3 pp, +5 yr warranty | --- Source: https://comparepv.com/panel/fellow-energy-fe66-18x Not in this file, on the page: a thirty-year output simulator and alternatives filtered by how closely they match these dimensions.