Basics Modules IV Curves
IV Curves
IV curves are plots of the current versus voltage for solar cells, solar modules, solar panels, or solar arrays. The IV curve can tell a lot about how the system is operating. Where the voltage is zero, the current is called short circuit current (Isc). This is the current you get if you short the wires together. Where the current is zero, the voltage is called open circuit voltage (Voc). This is the voltage when the wires are not connected to any load. Between these two points is the maximum power point (Pmp). The current and voltage at the maximum power point are called the peak power current (Ipp) and the peak power voltage (Vpp).
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If the system is health, the IV curve has a nice flat top and is squared off with a rounded corner, as shown in the figure. If there is a problem with the system the IV curve sides are more sloped. The measure of this effect is called the fill factor (Ff). It is calculated using the formula (Ipp X Vpp) / (Isc X Voc). If the fill factor is low (70% or so depending on the type of cells) there can be sick modules or loose wires. If there is no current then there is an open circuit. If the IV curve has a double hump, one or more cells or modules are sick or have a shadow on them.
More information about IV curves is in the Solar Basics and Solar Design books.