Solar PV systems generally require minimal maintenance. Periodic cleaning of the panels to remove dirt or debris will boost their efficiency and power production. Dirty panels could cause some cells to become faulty due to reverse polarity if a cell is covered by dirt while the rest of the panel is producing normally. The time between cleaning depends on the environment where the panels are installed. An environment like a farm may cause panels to become dirty much faster due to dirt roads and diesel vehicles operating in the area. Urban environments cause panels to become dirty less quickly but monthly checks will give an indication of visible dirt on the panel surfaces. An efficiency check on the inverter by a professional may also indicate lower-than-normal power production due to dirty panels. Annual system checks are also required to ensure the system operates normally. Fans and filters on the inverters must be cleaned to prevent heat buildup. Wiring and connectors are also checked while DC combiners have fuses that could protect the system and panels from overloads.