To equalize a level of power load and prevent reverse power transmission of the power stored in a storage battery to a power company by promotion of use of midnight electrical power and shift of peak power generated in the day time to midnight.

A home power supply system combined with solar power generation and midnight power storage is provided. The storage battery is charged, as a rule, in the midnight period using the midnight power via an inverter which also operates as an automatic charger, and the commercial power supply is used for household consumption. In the solar power generation period in the day time, when the electrical power generated with the solar system is higher than the preset value, an extra power is sold to the power company via the inverter/ automatic charger. In the intermediate time period between the midnight period and solar power generation period in the day time, the power stored in the storage battery is supplied for household consumption, and storage, if it is generated, is compensated by the commercial electrical power of the power company. In the case where the power stored in the storage battery is supplied for household consumption, a reverse transmission preventing circuit consisting of parallel connection of a forward thyristor and a backward thyristor is provided between the storage battery and the commercial power supply and a control circuit for preventing reverse transmission of power to the power company is also provided. As a result, the reverse transmission of the power stored in the storage battery to the power company is forcibly prevented.