Open-circuit voltage is the difference of electrical potential between two terminals of a device when there is no external load

External electric load

If an electric circuit has a well-defined output terminal, the circuit connected to this terminal is the load....

 connected, i.e. the circuit

Electrical network

An electrical network is an interconnection of electrical elements such as resistors, inductors, capacitors, transmission lines, voltage sources, current sources and switches. An electrical circuit is a special type of network, one that has a closed loop giving a return path for the current...

 is broken or open. Under these conditions there is no external electric current

Electric current

Electric current is a flow of electric charge through a medium.This charge is typically carried by moving electrons in a conductor such as wire...

 between the terminals, even though there may be current internally (e.g. self-discharge

Self-discharge

Self-discharge is a phenomenon in batteries in which internal chemical reactions reduce the stored charge of the battery without any connection between the electrodes...

 currents in batteries). It is sometimes given the symbol V_oc.

The open-circuit voltage

Voltage

Voltage, otherwise known as electrical potential difference or electric tension is the difference in electric potential between two points — or the difference in electric potential energy per unit charge between two points...

s of batteries and solar cell

Solar cell

A solar cell is a solid state electrical device that converts the energy of light directly into electricity by the photovoltaic effect....

s are often quoted under particular conditions (state-of-charge, illumination, temperature, etc.).