Understanding Open-Circuit Voltage (Voc) & Short-Circuit Current (Isc) in Solar Panels
Updated: Jun 23
When purchasing or installing a solar module, or solar panel, there are various key specifications you must look at. Two such key specifications are Open-Circuit Voltage and Short-Circuit Current.
What is open-circuit voltage?
It is the voltage the solar panel outputs when there is no load connected to it. The open-circuit voltage (Voc) can be obtained by simply measuring the voltage across the positive and negative terminals of the panel using a voltmeter.
It’s important to remember that Voc represents the maximum voltage a solar panel can produce under standard test conditions. These conditions include a cell temperature of 25°C, a light intensity of 1000W/m2, and an atmospheric density of 1.5.
Why is measuring Voc important?
When multiple solar panels are connected in series, their open-circuit voltages are added. The Voc plays a crucial role when determining the maximum number of solar panels that can be connected to your inverter or charge controller without overloading them. Exceeding the voltage limit may cause immediate failure of the inverter or charge controller, or it may compromise their lifespan.
The best time to measure Voc is usually in the morning, when the sun's rays first start to strike your panel. At this time, the solar panel is at its coolest, and the Voc is at its highest.
What is short-circuit current?
It is the current the solar panel produces when no load is connected to it. Short-circuit current (Isc) can be measured by connecting the positive and negative terminals of the panel to each other through an ammeter in series. While measuring Isc on your own is usually safe and does not harm the panel, care must be taken to avoid arcing.
It’s important to keep in mind that Isc represents the highest current the solar panel can produce under standard test conditions.
Why is measuring Isc important?
The Isc value is used to determine the maximum current that the solar panel can handle when connected to devices like inverters or charge controllers.
A short circuit poses a hazardous situation that can potentially occur even in a fully functional system equipped with a battery and other devices. Knowing the short-circuit rating of your solar panel allows you to install appropriate safeguards such as fuses or circuit breakers that can withstand the occurrence of a short circuit.
Typically, the panel produces significantly higher current at midday during the summer when tilted towards the sun, presenting an ideal opportunity to measure Isc accurately.
Watch this video to learn how to measure Voc and Isc of your solar panel: