What is Open Circuit Voltage (VOC)

Open Circuit Voltage is crucial when looking at solar panels and solar controllers but what is it, and why are there two voltage measurements on solar panels?

Open Circuit Voltage or VOC is shown in the panel specifications and is the voltage available from the solar panel when there is no load attached and the circuit is incomplete, so no current is flowing, hence the name Open-Circuit. When a load is attached to the circuit it becomes complete and current flows. This flow of current induces a voltage drop so the voltage produced by the panel in a closed circuit will never exceed the Max-Power Voltage shown in the panel specifications.

So why is it important? Well MPPT & PWM solar controllers are designed to be able to handle a maximum voltage (this will vary from model to model), so you must check that the controller can handle the VOC level without being damaged. Combined charging units like our CTEK D250SE & Sterling BB1230S often have lower voltage limits than stand-alone solar controllers, so you should check whether the VOC of the panel you intend to use is below the maximum that the charging unit can tolerate. If you try to use a panel with a VOC higher than the charging unit can safely handle, the charger is very likely to suffer permanent damage.

The VOC can be found either on the panel itself on a label on the back or on the panel specifications which the retailer or manufacturer should be able to provide.  We hope you have found this helpful but for more information check out our Solar Power Guide.