--- title: "Longi Solar LR8-66HYD-665M vs Longi Solar LR8-66HYD-660M - Solar Panel Comparison | ComparePV" description: "Compare Longi Solar LR8-66HYD-665M vs Longi Solar LR8-66HYD-660M side by side: what actually differs, output when it is hot, thirty-year production, and the full specification." source: "https://comparepv.com/compare/longi-lr8-66hyd-665m/longi-solar-lr8-66hyd-660m" updated: 2026-09-11 --- # Longi Solar LR8-66HYD-665M vs Longi Solar LR8-66HYD-660M 665M leads on the differences that matter The largest is module efficiency: 0.20 pp more efficient. 17 of 18 comparable parameters are identical, with 1 more left out because at least one datasheet does not publish it. ## The two panels | Attribute | A | B | | --- | --- | --- | | Panel | [Longi Solar LR8-66HYD-665M](https://comparepv.com/panel/longi-lr8-66hyd-665m) | [Longi Solar LR8-66HYD-660M](https://comparepv.com/panel/longi-solar-lr8-66hyd-660m) | | Manufacturer | Longi Solar | Longi Solar | | Power | 665 Wp | 660 Wp | | Efficiency | 24.60 % | 24.40 % | | Technology | Back Contact | Back Contact | ## Where they differ Ranked by how much the difference matters, not by datasheet order. | Parameter | 665M | 660M | Difference | | --- | --- | --- | --- | | Module efficiency | 24.60 % | 24.40 % | +0.20 pp for 665M | ## Every compared parameter | Parameter | 665M | 660M | | --- | --- | --- | | Rated power | 665 Wp | 660 Wp | | Module efficiency | 24.60 % | 24.40 % | | Power density | 246.2 Wp/m² | 244.3 Wp/m² | | Open-circuit voltage | 50.02 V | 50.21 V | | Voltage at max power | 41.28 V | 41.40 V | | Short-circuit current | 16.78 A | 16.65 A | | Current at max power | 16.11 A | 15.95 A | | Temperature coefficient | -0.260 %/°C | -0.260 %/°C | | Dimensions | 2382x1134x30 mm | 2382x1134x30 mm | | Module area | 2.701 m² | 2.701 m² | | Weight | 33.5 kg | 33.5 kg | | Weight per kWp | 50.4 kg/kWp | 50.8 kg/kWp | | Product warranty | 12 yrs | 12 yrs | | Performance warranty | 30 yrs | 30 yrs | | Annual degradation | - | 0.35 %/yr | | Cell technology | Back Contact | Back Contact | | Cell type | Monocrystalline | Monocrystalline | | Cell count | 132 | 132 | | Bifacial | Yes | Yes | ## Thirty-year yield A 1.0% first-year loss then 0.40% a year, assumed for both panels, at 1,200 kWh/kWp a year Same temp coeff. for both panels (-0.260 %/°C), so a warmer roof scales both curves by the same factor: the totals fall together and neither panel gains on the other. - **Cumulative output, 665M:** 22,312 kWh - **Cumulative output, 660M:** 22,144 kWh - **Gap:** 168 kWh ## Output when hot | Condition | Cell temperature | 665M | 660M | Retained | | --- | --- | --- | --- | --- | | Standard test conditions | 25 °C | 665 W | 660 W | 100.0% of rated power | | Cool, bright day | 40 °C | 639 W | 634 W | 96.1% of rated power | | Typical summer roof | 55 °C | 613 W | 609 W | 92.2% of rated power | | Hot roof | 70 °C | 587 W | 583 W | 88.3% of rated power | ## Against the whole database | Measure | 665M | 660M | Out of | Note | | --- | --- | --- | --- | --- | | Efficiency | #51 | #99 | 14,005 | 665M leads by 48 places | | Power density | #42 | #88 | 14,005 | 665M leads by 46 places | | Heat behaviour | #511 | #511 | 14,005 | Tied - the same position in the database | | Weight | #3,742 | #4,172 | 14,005 | 665M leads by 430 places | | Warranty | #21 | #21 | 14,005 | Tied - the same position in the database | | Overall | #643 | #817 | 14,005 | 665M leads by 174 places | ## Questions ### Which panel is better: Longi Solar LR8-66HYD-665M or Longi Solar LR8-66HYD-660M? According to our database: **Longi Solar LR8-66HYD-665M** has higher module efficiency (**24.60%** vs **24.40%**). See the full spec comparison and 30-year energy simulation above for a complete picture. ### What is the efficiency of Longi Solar LR8-66HYD-665M and Longi Solar LR8-66HYD-660M? **Longi Solar LR8-66HYD-665M** has a module efficiency of **24.60%**, while **Longi Solar LR8-66HYD-660M** is **24.40%**. Higher efficiency means more electricity from the same roof area - useful when space is limited. ### What cell technology does Longi Solar LR8-66HYD-665M use vs Longi Solar LR8-66HYD-660M? **Longi Solar LR8-66HYD-665M** uses **Back Contact** cells; **Longi Solar LR8-66HYD-660M** uses **Back Contact**. Modern **n-type** technologies (**TOPCon**, **HJT**, BC) typically deliver higher efficiency and lower degradation compared to older **PERC** (p-type) cells. ### What is the warranty on Longi Solar LR8-66HYD-665M and Longi Solar LR8-66HYD-660M? **Longi Solar LR8-66HYD-665M** has a **30 years** power warranty; **Longi Solar LR8-66HYD-660M** has a **30 years** power warranty. The power warranty guarantees a minimum percentage of rated output at the end of the warranty period (typically 80**-87%**). Product (materials) warranties are usually shorter. ### Are Longi Solar LR8-66HYD-665M and Longi Solar LR8-66HYD-660M bifacial panels? Both **Longi Solar LR8-66HYD-665M** and **Longi Solar LR8-66HYD-660M** are bifacial - they capture reflected light from the ground, which can add 5**-15%** more annual energy on ground-mount or elevated rooftop installations with a light surface beneath. ## Related comparisons - [Longi Solar LR8-66HYD-665M vs Longi Solar LR8-66HYD-670M](https://comparepv.com/compare/longi-lr8-66hyd-665m/longi-lr8-66hyd-670m) - One difference: module efficiency - [Longi Solar LR8-66HYD-665M vs Longi Solar LR7-72HYD-660M](https://comparepv.com/compare/longi-lr8-66hyd-665m/longi-lr7-72hyd-660m) - 7 differences, the largest is open-circuit voltage - [Longi Solar LR8-66HYD-665M vs Longi Solar LR8-66HYD-655M](https://comparepv.com/compare/longi-lr8-66hyd-665m/longi-solar-lr8-66hyd-655m) - 3 differences, the largest is module efficiency - [Longi Solar LR8-66HYD-665M vs Longi Solar LR7-72HYD-655M](https://comparepv.com/compare/longi-lr8-66hyd-665m/longi-lr7-72hyd-655m) - 9 differences, the largest is module efficiency - [Longi Solar LR8-66HYD-665M vs Longi Solar LR8-66HYD-650M](https://comparepv.com/compare/longi-lr8-66hyd-665m/longi-solar-lr8-66hyd-650m) - 3 differences, the largest is module efficiency - [Longi Solar LR8-66HYD-665M vs Longi Solar LR7-72HYD-650M](https://comparepv.com/compare/longi-lr8-66hyd-665m/longi-lr7-72hyd-650m) - 9 differences, the largest is module efficiency --- Source: https://comparepv.com/compare/longi-lr8-66hyd-665m/longi-solar-lr8-66hyd-660m Not in this file, on the page: the thirty-year yield curve year by year at a cell temperature you pick and a written summary generated on request.