A stand-alone PV system is the only energy source available for its users: it must therefore provide enough power to all the connected appliances without any failure. The major issues arising during its sizing is that:

• One side, the demand is not constant all over the day and all over the seasons

• And on the on the other side, the energy available from the PV array changes all along the day and is not constant over the seasons

The periods of low energy yield, rainy season, and overcast for example might correspond to periods of high demand with as an example, an increased need of lighting due to overcast.

When irradiation for a particular location is known, then the equivalent sun hours can be calculated. Irradiation is defined as the amount of energy delivered by the sun per unit of surface. Sizing of standalone PV systems should be undertaken based on the lowest equivalent sun hours. In north hemisphere, this corresponds to winter months values.

Off grid PV systems are sized in four major steps:

• Determination of energy needs to be covered

• Sizing the PV array

• Sizing the battery bank

• Selecting the balance of system