The higher the temperature, the lower will be the power output. Adding more modules in series, and therefore increasing the string voltage, will eliminate this problem. Also, make sure that there’s sufficient air circulation beneath the panels and that this open space is not blocked in any way.
Conducting a bi-annual survey of the installation site is a good idea. If shading is not an issue, most likely it will be the higher than normal operating temperature of the solar panels. It has been scientifically proven that the voltage drop rises with the rise in temperature. The higher the temperature, the lower will be the power output.
The factors that could contribute to a low power problem are: This is possibly the most common cause of low voltage. Ensure that there are no trees around and that the solar panels are not blocked by shadow at any time during the day. Keep in mind that a solar systems lasts for more than 25 years and trees grow over time.
Having faulty wiring can lead to all sorts of problems, and this could also be a reason why your solar panel voltage is low. Imagine having a loose wire, not only could it start a fire, but it can also disrupt how much voltage your system makes.
If your solar panel or array drops volts when under a load, the problem may be any number of issues. The best place to start is as follows: Start with your testing equipment. Make sure it is working correctly and that the connections during testing are good.
Two common reasons for a solar panel to register no voltage are a faulty inverter or charge controller. Other possible causes include a damaged PV module, poor wiring, shading, and temperatures higher than the ideal operating range.