How to use a multimeter to test solar panels?
Measuring the full power output of a solar cell module requires a load. However, as a first step, we can use a simple multimeter to make measurements without a load to get the open circuit current voltage (VOC) and short circuit current (ISC).
For large outdoor solar panels, any multimeter with 10A (amps) and 50V (volts) current scales can be used.Regarding the requirements for small solar charging panels, a thermal gun for measuring the temperature of solar panels is useful on particularly hot days. Choose a sunny day and point the solar panel at the sun. Make sure that none of the components are shaded in one place. Shading even part of the corners of a solar power panel can cause a dramatic drop in output.
In a typical multimeter, the negative terminal is the black wire labeled COM. insert the red wire into the V terminal for voltage measurements and 10A for high current measurements. A temperature gun is only really needed on very hot days. The temperature should be measured on the back side of the solar panel (monocrystalline, polycrystalline, Sunpower) as the reflection of the sun off the module will distort the reading. The emissivity of the material will also affect the reading, so pointing the sensor at a metal surface will give a different reading than the back panel, even if they are the same temperature. In most cases, the gun can be pointed anywhere on the backsheet and give a reliable reading. However, a piece of black tape on the solar PV module can also be used to give a more reliable reading.
Measuring Voltage (Voc)
For Voc, set the multimeter to a DC voltage scale that is greater than the expected solar PV module voltage. If unsure, use a scale setting of 200V. Connect the leads of the multimeter to the solar panel leads (power to power, ground to ground) and record the voltage. VOC readings will decrease as the module is heated.
Measure the current Isc
Disconnect the multimeter from the solar panel before changing settings. For Isc, set the multimeter to a DC current scale that is greater than the expected solar panel current. If you are unsure, use the 10A scale setting. Replace the power (red) lead to a 10 A outlet to prevent blowing the fuse in the multimeter while making measurements. Connect the multimeter leads to the solar panel leads and record the voltage.
Conclusion:
Multiplying VOC and ISC gives an approximate power estimate. As an example, Voc equals 35.8 V, current equals 10.07, and the product is 363.5 W. However, we must also take into account the fill factor. The equation for maximum power (Pmax, or sometimes written as MPP) is
Pmax=Voc*Isc*FF
By determining the panel's actual Voc, Isc and estimated Pmax and comparing them to the solar power panel's rating, we can quickly assess whether the panel's performance is close to optimal. If the panel's Voc and Isc are quite similar to those determined in these measurements, the solar panel is therefore likely to perform well.
