How to read a solar panel datasheet
The handful of datasheet numbers that matter, explained with a real panel.
A panel datasheet looks dense, but a handful of numbers tell you most of what matters. As an example we use the JA Solar DeepBlue 4.0 Pro 600 W from the directory.
Power and efficiency
Pmax 600 W at STC. STC (standard test conditions) is a lab setting: 1000 W of sunlight per square metre at a cell temperature of 25 °C. Real panels rarely see that, so treat Pmax as a label for comparison, not as what you'll get on the roof. Efficiency 23.2% is how much of the sunlight that lands on the panel becomes electricity; higher means more power from the same roof space.
Heat loss: the temperature coefficient
-0.29% per °C means the panel loses that share of its power for every degree its cells are above 25 °C. On a hot roof cells can reach 65 °C, 40 degrees above the test, so this panel would give about 88% of its rated power. Closer to zero is better, which counts in South Africa.
NOCT
NOCT 45 °C is the cell temperature in a milder, more realistic test (800 W/m², 20 °C air, a light breeze). Some datasheets give the power at NOCT too, which is closer to everyday output.
Voltage and current
Voc (52.79 V) is the voltage with nothing connected and Isc (14.04 A) the current when shorted, both at STC. They are not hard maximums: the installer adds margins because the voltage rises on cold mornings and the current rises in strong sun and, on a bifacial panel like this one, with light reflected onto the back. The installer uses them to keep a string of panels within the inverter's limits.
Warranty: two different promises
The product warranty (12 years) covers defects in the panel. The power warranty (30 years) promises a minimum output over time: here a 1% drop in the first year, then 0.4% a year, ending at about 87.4% after 30 years.
Coast and salt
Near the sea, look for a salt-mist test (IEC 61701) on the datasheet or a certificate. Each panel page in the directory says whether it is stated. Also read the maker's installation manual: it may set a minimum distance from the sea and extra corrosion protection for the warranty to hold. JA Solar's manual, for example, allows installs 50 m to 500 m from the sea only with corrosion protection.
Written by the Halvora Directory team and checked against public sources (7 Nov 2026). General information, not advice for your installation.