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Green Energy Intl and Consulting
Posted 2 months ago

KNOW YOUR SOLAR PANEL SPECIFICATIONS AND HOW THEY AFFECT YOUR SYSTEM.



Ever asked yourself what the specification at the back plate or spec sheet of your panel mean? Or what impact do they have in sizing your off grid, on grid or grid-tied system? And what makes technicians prefer a certain solar panel for a specific job than the other?

Essentially the back plate/ spec sheet of your panel summarizes the product specification of that panel. In this post we take an example of Jinko panel (Not for marketing purposes but decision making) to understand the mystery behind each spec ;





1. Maximum Power (Pmax)

The Pmax is the solar panel power output, where the combination of the volts and amps measured gives the highest wattage (volts x amps = watts).

Smart MPPT charge controller like Victron periodically measures the panel voltage under varying loads and then adjusts the solar input circuit to balance the volts and amps and maximize the power output during bulk-charge mode. A reason they are better than PWM charge controllers. The wattage that a solar panel is listed as is the Pmax where Pmax = Vmp x Imp at standard test conditions.





2.Power measurement tolerance

This is directly related to your system’s Pmax. It is the amount of energy your system can produce above or below the rated maximum (Pmax). It can either be listed in watts, or as a percentage of the total output. So a panel rated at 200 watts with a power tolerance of +/- 3 can produce between 194-206 watts.





3. Maximum power voltage Vmp

The voltage at maximum power is the voltage when the power output is the greatest. It is the voltage seen when the panel is connected to the MPPT controller under standard test conditions. The Vmp normally varies during the day and with temperature, shading, soiling of the panel surface, etc. You can measure this voltage with a multimeter at the solar input terminals of an MPPT controller during bulk-charge mode.





4.Open-Circuit Voltage (Voc)

This tells us the maximum voltage that the solar panel can produce with no load on it (i.e. measured with a multimeter across the open ends of the wires attached to the panel). If two or more panels are wired in series it will be Voc of panel 1 + Voc of panel 2, etc. The voltage is generally highest mid-morning as the sun rises rapidly and the panel temperature is still quite low.



The Voc + approx 3.5 per cent must be less than the maximum solar voltage permitted by the solar-charge controller. Some controllers shut down if it’s exceeded, while some may continue to operate but the lifespan of the controller could be compromised.





Short Circuit Current (Isc)

This is the current obtained when the positive and negative terminals of the panel are connected to each other through an ammeter in series. Is the highest current the solar panel cell can deliver without any damage. Isc is used to determine how many amps a panel can handle when connected to a device like a solar charge controller or an inverter circuit.

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