How to Read Solar Panel Specifications [Use To Size Your System]

If you are new to solar panels, you may want to learn how to read the specs to understand exactly what you're doing with your setup.

In this guide, we show you how to read solar panel specifications and how to make sense of the number when you buy or design your solar system.

Most Important Specs To Pay Attention To

Short Circuit Current (ISC)

Short circuit current is amp rating that flows out of the panel when the positive and negative leads are shorted together. This is the highest current a solar panel can produce under standard test conditions.

This spec rating can help you size your fuse for over current protection & solar charge controller

Fuse Size – ISC (amp) X 1.56

Solar charge controller size - ISC + 20% is recommended

Open Circuit Current (VOC)

Open circuit current is the max voltage a solar panel can produce without any load.

This spec rating can help you determine the maximum voltage permitted by the solar charge controller for safety measure.

Solar charge controller size - VOC + 3.5% is recommended

Max Voltage Power

When solar panels are connected to MPPT controller under standard test condition, the max voltage power rating is the voltage when the power output is the greatest.

The actual Vmp will vary due to time of day, shading, temperature and solar panel surface condition.

Max Current Power

Max current power (IMP) is current when the power output is the highest. This is relative to the max voltage power rating (VMP) that we mentioned above. The actual current rating due to due to time of day, shading, temperature, and solar panel surface condition.

Max Power Point (Pmax)

The max power point is the sweet spot between the highest voltage and amps to produce the highest wattage (Volts X Amps = Watts)

This spec rating is monitored and adjusted by a MPPT controller to balance the volts and amps to maximize power output.

The wattage a solar panel is listed as Pmax (Pmax = Vmp X Imp)

Good To Know

Normal Operating Cell Temperature (NOCT)

NOCT is the temperature rating reached by open circuit cells in a module with these standard perimeter:

  • 800 W/m2 (sunlight intensity)
  • 20 degree celsius
  • 1 m/s wind speed
  • 45 degree tilt angle

We use this spec to estimate power loss.

Assume the following:

  • Solar panel with NOCT of 40 degree C
  • -0.5% / C max power temperature coefficient

Estimated power loss on temperature = (0.05 X (40 - 25)) = 7.5%

Standard Test Condition (STC)

The performance of all panels are specified against a set of conditions used industry-wide called Standard Test Conditions. These conditions are extremely unlikely to occur in real life. 

  • 25 degree celsius
  • 1000 W/m2

Read More: Learn How To Size Solar Inverter

Ying Xu

Graduated from the University of Kansas with an Aerospace Engineering degree & served 4 years as an US Air Force officer. Experienced with basic survival skills, weapon system security,  technical disaster recovery, and system troubleshooting

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