Patent ID: 8773156

Claim:
A method for measuring insulation resistance in a photovoltaic (PV) array comprising: selecting a group of PV panels in the PV array for a measurement of insulation resistance; setting a bypass selector for each PV panel in the selected group to a non-bypassed switch state; setting a bypass selector for each PV panel not included in the selected group to a bypassed switch state; measuring a value of insulation resistance for the selected group of PV panels; saving previously measured values of insulation resistance for a selected PV array component in a historical record; calculating a rate of change in the insulation resistance value for the selected PV array component by comparing measurements from historical records with current measurements; projecting a time duration for the insulation resistance value to fall below a specified threshold value of insulation resistance, at the calculated rate of change; and performing preventive maintenance on the selected PV array component before the expiration of the projected time duration.