A monitoring system is an essential part of a PV plant. A monitoring system allows the yield of the plant to be monitored and compared with theoretical calculations and raise warnings on a daily basis if there is a performance shortfall. Faults can therefore be detected and rectified before they have an appreciable effect on production. Without a reliable monitoring system it can take many months for a poorly performing plant to be identified. This can lead to unnecessary revenue loss. The key to a reliable monitoring and fault detection methodology is to have good simultaneous measurements of the environmental conditions and plant power output.