Capacity Utilization Factor (CUF) is the ratio of actual energy generated by rooftop solar plant over the year to the equivalent energy output at its rated capacity.
CUF % = annual energy generation from the plant in kWh x 100 / (installed plant capacity in kW x 365 x 24)
Minimum CUF is either defined by the state nodal agencies in their tender documents or the installer of the plant or the contractor for operation & maintenance can evaluate the minimum CUF based on the components deployed & local site & environment conditions.