1. A power supply system configured to be capable of feeding supply electric power, which is supplied to a building including a wiring and an electric load connected to the wiring by a power system of a power supplier based on a power supply contract, into the electric load, the power supply system comprising: a solar power generating device configured to generate solar electric power by solar light; an electricity storing device connected to the wiring and configured to be capable of storing solar electric power generated by the solar power generating device and supply electric power supplied by the power system and to be capable of discharging the stored electric power into the wiring; a consumption controlling means for controlling consumption of supply electric power supplied by the power system and for controlling consumption of solar electric power through consumption by storage in the electricity storing device and through consumption by the electric load; a predicted amount calculating means for calculating a predicted amount of electric power used on a following day by the electric load based on a use record of the electric load, and a predicted amount of electric power generated on the following day by the solar power generating device based on a weather prediction; a shortage amount calculating means for calculating a shortage amount of electric power, which is a difference between the predicted amount of electric power used and the predicted amount of electric power generated, when the predicted amount of electric power used is larger than the predicted amount of electric power generated; and a storage amount setting means for setting the shortage amount at a predicted storage amount, which is an amount of electric power stored by the electricity storing device after completion of storage of electric power by the electricity storing device, when a limit storage amount, which is an upper limit amount of electric power stored by the electricity storing device, is equal to or higher than the shortage amount, and for setting the limit storage amount at the predicted storage amount when the limit storage amount is smaller than the shortage amount, wherein: in a specified time slot determined based on the power supply contract, during which cost of electric power is lower than in other time slots than the specified time slot, the consumption controlling means carries out control such that the electricity storing device stores supply electric power until an amount of electric power stored by the electricity storing device reaches the predicted storage amount; and in the other time slots, when an amount of solar electric power generated is larger than an amount of electric power consumed by the electric load, the consumption controlling means carries out control such that the electricity storing device stores a surplus of solar electric power.