A load is required to measure the total power output of the solar cell module. However, as the first step, we can use a simple multimeter to measure without load to obtain open circuit current voltage (VOC) and short circuit current (ISC). For large outdoor solar panels, any multimeter with 10A (ampere) and 50V (volt) current scales can be used. With regard to the requirements for small solar charging panels, the thermal gun used to measure the temperature of solar panels is very useful on very hot days. Choose a sunny day and aim the solar panel at the sun. Make sure that no part of the component is obscured. Even if some corners of the solar panel are covered, the output will drop sharply.
In a typical multimeter, the negative pole is a black wire marked COM. Insert the red wire into the V terminal to measure the voltage and 10A to measure the large current. Only in very hot days do you really need a temperature gun. The temperature should be measured on the back of the solar panel (single crystal, polycrystalline, Sunpower), because the sun’s reflection from the module will distort the reading. The emissivity of the material will also affect the reading, so pointing the sensor at the metal surface will give a different reading from the backplane even if their temperatures are the same. In most cases, the gun can point anywhere on the backplane and give a reliable reading. However, a piece of black tape on the solar PV module can also be used to provide 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 you are not sure, use a 200V scale setting. Connect the lead of the multimeter to the lead of the solar panel (power to power, ground to ground), and record the voltage. VOC readings will decrease as the components are heated.
Measuring current Isc
Before changing the settings, disconnect the multimeter from the solar panel. For Isc, set the multimeter to a DC current scale that is greater than the expected solar panel current. If you are not sure, use the 10A scale setting. Replace the power supply (red) lead to the 10 A socket to prevent the fuse in the multimeter from being burnt out during the measurement. Connect the lead of the multimeter to the lead of the solar panel and record the voltage.
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A rough power estimate can be obtained by multiplying VOC and ISC. For example, Voc equals 35.8V, current equals 10.07, and the product is 363.5W. However, we must also consider the fill factor. The equation for maximum power (Pmax, or sometimes written as MPP) is:
Pmax=Voc*Isc*FF
By determining the actual Voc, Isc and estimated Pmax of the panel and comparing them with the rated value of the solar panel, we can quickly assess whether the performance of the panel is close to optimal. If the Voc and Isc of the solar panel are quite similar to those determined in these measurements, the solar panel is likely to perform well.
If you want to know more about solar panels, please contact our Shenzhen Solar Panel Manufacturer Huanqi Technology (Shenzhen) Co., Ltd.