Photovoltaic cells are usually reliable, so its rare to hear of a faulty PV module. However, it is important to note that issues can occur especially if the installation was not done as required. A competent solar expert can perform PV diagnosis to identify the root cause of the problem and can also carry out effective repairs. A common issue is a burned out solar charge controller, which may not be allowing energy from the solar panels to reach the battery. Another issue is a faulty diode on the PV module itself. Loose electrical connections are also known to cause issues.
All these issues, and many others can be easily fixed when you hire a competent solar contractor. Only licensed contractors with a lot of experience in the industry and a great reputation should be accorded special consideration. You will also need to compare service charges to ensure you hire an affordable contractor.