We describe a photovoltaic power conditioning unit for delivering power from multiple photovoltaic panels to an ac mains power supply output, comprising: a dc input for receiving power from multiple photovoltaic panels; an ac output for delivering ac power to the ac supply; a bank of electrolytic energy storage capacitors for storing energy from the dc source for delivery to the ac supply; a dc-to-ac converter coupled to the ac output and having an input coupled to the bank for converting energy stored in the bank to ac power for the ac supply; and further comprising: a plurality of sense and control circuits, one for each capacitor in the bank, wherein each circuit is coupled in series with a capacitor, and is configured to disconnect the associated capacitor from the bank upon detection of a current flow thorough the associated capacitor of greater than a threshold current value.