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Module Measurement without Load

Simple Module Measurement without load using a Multimeter

A load is needed to measure the full power output of a solar module. Yet, a simple multimeter can be used first for module measurement without Load  , so as to know the VOC (open current voltage), and ISC (short circuit current). For the large outdoor modules, any multimeter with a current scale up to 10 amps and 50 Volts will work.  A thermal gun is useful for measuring the panel’s temperature on hot days. For measuring, try to choose a sunny day and direct the module so that it faces the sun and try to ensure no part of the module is shaded. Even a slight shading of a part of the corner of the module will cause a dramatic loss in output. In a normal multimeter, the negative terminal is the black lead and is  labeled COM. Plug the red lead into the V terminal for measuring voltage and the 10 A for measuring large currents. A temperature gun  is only really required on hot days. Generally, the gun is pointed anywhere on the back sheet and a reliable reading is given. However, placing a piece of black tape onto the module can be used as well to give a more reliable reading.

Measuring Voc

For  measuring VOC:
  1. Set the multimeter to a DC voltage scale that is greater than the expected module voltage. If unsure use the 200 V scale setting.
  2. Connect multimeter leads to the solar panel leads (connect power to power and ground to ground)
  3. Record the measured voltage. The VOCreadings will typically decrease as the module heats up and this variation will be accounted for below.
Record the temperature of the surface of the panel and the time of day in which your measurements were taken.

Measuring Isc

Before changing the setting disconnect the multimeter from the module. For ISC:
  1. Set the multimeter to a DC current scale that is greater than the expected module current. If unsure use the 10 A scale setting.
  2. Change the red “power” lead to the 10 A socket, so as to prevent blowing the fuse in the multimeter while taking the measurements.
  3. Connect the multimeter leads to the leads of the solar panel and record the voltage.


By multiplying the VOC and ISC together we can get a rough estimate of the power. Yet, we must also take into account the fill factor. The equation for maximum power (PMAX, or MPP) is: PMAX =VOC × ISC × FF   We cannot measure the fill factor without a load but typically the fill factor is around 0.7. By measuring the actual VOC, ISC, and estimating the PMAX of the panel and comparing it to the rating of the module, we can quickly evaluate the performance and determine if the panel is performing near optimal point. Safety precautions should be strictly followed when working with solar modules, as they can represent a hazard due to the generation and presence of live electrical current which can cause shocks and serious damage if not handled adequately.  
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