Abstract: An apparatus to monitor and optimise power output by one or more solar panels to which the apparatus is coupled comprises a processor configured to generate a periodic wave and apply the periodic wave to an output of the one or more solar panels. Analogue-to-digital voltage and current converters receive voltage and current signals respectively from the one or more solar panels and provide digital voltage and current signals to the processor. The processor is configured to: calculate a voltage amplitude and a direct current offset of the periodic wave applied to the output of the one or more solar panels; calculate a differential of a power and a voltage of the one or more solar panels based on the voltage amplitude and the direct current offset; and modify the voltage of the one or more solar panels such that the differential of the power and the voltage of the one or more solar panels is zero, or substantially zero.