The system is cleaned as and when required, upon arrangement with the operator (every three to five years, depending on the property). Regular cleaning guarantees that the photovoltaic system performs at its best and is therefore recommended. Soiling and debris may also have a negative impact on the performance of the system, thus reducing its economic efficiency. In order to ensure that the flat-rate fee can be honoured, a supply of water and electricity must be available on site at the time the cleaning needs to be performed.