How to Read a Solar Panel Datasheet — Every Spec Explained

Why Datasheets Matter

A solar panel datasheet is the manufacturer's official specification document. It contains every electrical, mechanical, and performance parameter you need to design a system, compare panels, and verify warranty claims. Understanding datasheets is essential for installers, engineers, and informed buyers.

Electrical Specifications at STC

Standard Test Conditions (STC) are 1,000 W/m² irradiance, 25°C cell temperature, and AM1.5 spectrum. Key parameters:

Parameter	Symbol	What It Means	LONGi Hi-MO 7 Example
Maximum Power	Pmax	Peak wattage output at STC	590 W
Open-Circuit Voltage	Voc	Voltage when no current flows (for string sizing)	51.7 V
Short-Circuit Current	Isc	Current when voltage is zero	14.50 A
Voltage at Pmax	Vmpp	Operating voltage at peak power	43.5 V
Current at Pmax	Impp	Operating current at peak power	13.56 A
Module Efficiency	η	Percentage of sunlight converted to electricity	22.8%

NOCT Specifications

Nominal Operating Cell Temperature (NOCT) conditions (800 W/m², 20°C ambient, 1 m/s wind) are closer to real-world performance. NOCT values are typically 25–30% lower than STC values. A typical NOCT for LONGi panels is 43±2°C.

Temperature Coefficients

Three temperature coefficients appear on every datasheet:

• Pmax coefficient (γ): Power loss per °C above 25°C. LONGi Hi-MO 7: −0.29%/°C. This is the most important for energy yield calculations.
• Voc coefficient (β): Voltage change per °C. Used for string sizing at cold temperatures. Typically −0.25 to −0.30%/°C.
• Isc coefficient (α): Current change per °C. Typically +0.04 to +0.06%/°C (current increases slightly with temperature).

Mechanical Specifications

• Dimensions (L × W × H): For mounting layout design. Hi-MO 7: 2,278 × 1,134 × 30 mm.
• Weight: For structural load calculations. Hi-MO 7: ~32 kg.
• Cell type and count: 144 half-cut N-type TOPCon monocrystalline.
• Glass: 3.2mm tempered, anti-reflective coated.
• Frame: Anodised aluminium alloy.
• Junction box: IP68 rated with bypass diodes.
• Connectors: MC4 compatible.

Ratings and Certifications

• IEC 61215: Design qualification — the panel passed rigorous testing for reliability
• IEC 61730: Safety — electrical insulation and fire safety standards
• Wind load: Typically 2,400 Pa (equivalent to ~170 km/h winds)
• Snow load: Typically 5,400 Pa
• Hail resistance: 25mm hailstones at 23 m/s

Warranty Information

Datasheets typically include warranty terms:

• Product warranty: Coverage against defects (25 years for LONGi Hi-MO 7)
• Performance warranty: Guaranteed minimum output over time (87.4% at year 30)
• First-year degradation: Maximum 1% (LONGi Hi-MO 7)
• Annual degradation: Maximum 0.4%/year (LONGi Hi-MO 7)

Frequently Asked Questions

What is the most important spec on a solar datasheet?

For energy yield: module efficiency (η) and temperature coefficient of Pmax (γ). For system design: Voc and Isc for inverter and string sizing.

What does NOCT mean?

NOCT (Nominal Operating Cell Temperature) is the cell temperature under realistic conditions (800 W/m², 20°C ambient). It indicates real-world operating temperature. Lower NOCT means better heat dissipation.

How do I use Voc for string sizing?

Multiply Voc by the number of panels in series, then adjust for the coldest expected temperature using the Voc temperature coefficient. The result must not exceed your inverter's maximum input voltage.