--- title: "Suntech STP-NT11/66QGDF-645 vs Suntech STP-NT11/66QGDF-665 - Solar Panel Comparison | ComparePV" description: "Compare Suntech STP-NT11/66QGDF-645 vs Suntech STP-NT11/66QGDF-665 side by side: what actually differs, output when it is hot, thirty-year production, and the full specification." source: "https://comparepv.com/compare/suntech-stp-nt11-66qgdf-645/suntech-stp-nt11-66qgdf-665" updated: 2026-09-11 --- # Suntech STP-NT11/66QGDF-645 vs Suntech STP-NT11/66QGDF-665 665 leads on the differences that matter The largest is module efficiency: 0.70 pp more efficient. 16 of 19 comparable parameters are identical. ## The two panels | Attribute | A | B | | --- | --- | --- | | Panel | [Suntech STP-NT11/66QGDF-645](https://comparepv.com/panel/suntech-stp-nt11-66qgdf-645) | [Suntech STP-NT11/66QGDF-665](https://comparepv.com/panel/suntech-stp-nt11-66qgdf-665) | | Manufacturer | Suntech | Suntech | | Power | 645 Wp | 665 Wp | | Efficiency | 23.90 % | 24.60 % | | Technology | TOPCon | TOPCon | ## Where they differ Ranked by how much the difference matters, not by datasheet order. | Parameter | 645 | 665 | Difference | | --- | --- | --- | --- | | Module efficiency | 23.90 % | 24.60 % | +0.70 pp for 665 | | Power density | 238.8 Wp/m² | 246.2 Wp/m² | +7.4 Wp/m² for 665 | | Rated power | 645 Wp | 665 Wp | +20 W for 665 | ## Every compared parameter | Parameter | 645 | 665 | | --- | --- | --- | | Rated power | 645 Wp | 665 Wp | | Module efficiency | 23.90 % | 24.60 % | | Power density | 238.8 Wp/m² | 246.2 Wp/m² | | Open-circuit voltage | 49.85 V | 50.45 V | | Voltage at max power | 41.62 V | 42.21 V | | Short-circuit current | 16.29 A | 16.57 A | | Current at max power | 15.50 A | 15.76 A | | Temperature coefficient | -0.260 %/°C | -0.260 %/°C | | Dimensions | 2382x1134x30 mm | 2382x1134x30 mm | | Module area | 2.701 m² | 2.701 m² | | Weight | 33.1 kg | 33.1 kg | | Weight per kWp | 51.3 kg/kWp | 49.8 kg/kWp | | Product warranty | 15 yrs | 15 yrs | | Performance warranty | 30 yrs | 30 yrs | | Annual degradation | 0.35 %/yr | 0.35 %/yr | | Cell technology | TOPCon | TOPCon | | Cell type | Monocrystalline | Monocrystalline | | Cell count | 264 | 264 | | Bifacial | Yes | Yes | ## Thirty-year yield Each panel's own declared degradation curve, 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, 645:** 21,809 kWh - **Cumulative output, 665:** 22,486 kWh - **Gap:** 677 kWh ## Output when hot | Condition | Cell temperature | 645 | 665 | Retained | | --- | --- | --- | --- | --- | | Standard test conditions | 25 °C | 645 W | 665 W | 100.0% of rated power | | Cool, bright day | 40 °C | 620 W | 639 W | 96.1% of rated power | | Typical summer roof | 55 °C | 595 W | 613 W | 92.2% of rated power | | Hot roof | 70 °C | 570 W | 587 W | 88.3% of rated power | ## Against the whole database | Measure | 645 | 665 | Out of | Note | | --- | --- | --- | --- | --- | | Efficiency | #351 | #51 | 14,005 | 665 leads by 300 places | | Power density | #356 | #42 | 14,005 | 665 leads by 314 places | | Heat behaviour | #511 | #511 | 14,005 | Tied - the same position in the database | | Weight | #4,693 | #3,223 | 14,005 | 665 leads by 1,470 places | | Warranty | #21 | #21 | 14,005 | Tied - the same position in the database | | Overall | #1,084 | #414 | 14,005 | 665 leads by 670 places | ## Questions ### Which panel is better: Suntech STP-NT11/66QGDF-645 or Suntech STP-NT11/66QGDF-665? According to our database: **Suntech STP-NT11/66QGDF-665** has higher module efficiency (**24.60%** vs **23.90%**). See the full spec comparison and 30-year energy simulation above for a complete picture. ### What is the efficiency of Suntech STP-NT11/66QGDF-645 and Suntech STP-NT11/66QGDF-665? **Suntech STP-NT11/66QGDF-645** has a module efficiency of **23.90%**, while **Suntech STP-NT11/66QGDF-665** is **24.60%**. Higher efficiency means more electricity from the same roof area - useful when space is limited. ### What cell technology does Suntech STP-NT11/66QGDF-645 use vs Suntech STP-NT11/66QGDF-665? **Suntech STP-NT11/66QGDF-645** uses **TOPCon** cells; **Suntech STP-NT11/66QGDF-665** uses **TOPCon**. 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 Suntech STP-NT11/66QGDF-645 and Suntech STP-NT11/66QGDF-665? **Suntech STP-NT11/66QGDF-645** has a **30 years** power warranty; **Suntech STP-NT11/66QGDF-665** 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 Suntech STP-NT11/66QGDF-645 and Suntech STP-NT11/66QGDF-665 bifacial panels? Both **Suntech STP-NT11/66QGDF-645** and **Suntech STP-NT11/66QGDF-665** 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 - [Suntech STP-NT11/66QGDF-645 vs Suntech STP730S-D66-Nsh+](https://comparepv.com/compare/suntech-stp-nt11-66qgdf-645/suntech-stp730s-d66-nsh) - 11 differences, the largest is rated power - [Suntech STP-NT11/66QGDF-645 vs Suntech STP-NT11/66QGDF-670](https://comparepv.com/compare/suntech-stp-nt11-66qgdf-645/suntech-stp-nt11-66qgdf-670) - 3 differences, the largest is module efficiency - [Suntech STP-NT11/66QGDF-645 vs Suntech STP-NT11/66QGDF-660](https://comparepv.com/compare/suntech-stp-nt11-66qgdf-645/suntech-stp-nt11-66qgdf-660) - 3 differences, the largest is module efficiency - [Suntech STP-NT11/66QGDF-645 vs Suntech STP-NT11/66QGDF-655](https://comparepv.com/compare/suntech-stp-nt11-66qgdf-645/suntech-stp-nt11-66qgdf-655) - 3 differences, the largest is module efficiency - [Suntech STP-NT11/66QGDF-645 vs Suntech STP-NT11/66QGDF-650](https://comparepv.com/compare/suntech-stp-nt11-66qgdf-645/suntech-stp-nt11-66qgdf-650) - One difference: module efficiency - [Suntech STP-NT11/66QGDF-645 vs Suntech STP-NT11/66QGDF-640](https://comparepv.com/compare/suntech-stp-nt11-66qgdf-645/suntech-stp-nt11-66qgdf-640) - One difference: module efficiency --- Source: https://comparepv.com/compare/suntech-stp-nt11-66qgdf-645/suntech-stp-nt11-66qgdf-665 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.