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7.3 Economic efficiency by energy saving with Best Mix power supply

<< How much energy can be saved in one-day running of Best Mix power supply? >>

To begin with general AC to DC converter, based on the condition of 3-phase input, 24V/3kW of output, and 75% of efficiency;

Power in a day is 72kW」・(=3kW times 24 hours).
Taking into account efficiency, 96kWh (=72/0.75) is required.  

With the condition that midnight range is 11:00 to 7:00, charge per 1kWh is 7.15 yen, and 25 yen per 1kWh for other than that,

Total one-day charge is 1,828.8 yen (=1/3×7.15+2/3×25).

In the case that Best Mix power supply (existing system) is used, providing that solar battery can supply all load for 6 hours per day as an average, and the battery discharges for one hour and a half with conversion efficiency of 80%, charge/discharge efficiency of 75% , and the battery is charged during midnight,

Total charge in all day long is 1150.3 yen.
The difference between those is 678.5 yen per day (=1828.8-1150.3)
Breakdown is as follows,
600 yen for energy cost from solar battery, 78.5 yen for decline in midnight charging cost.
Provided that solar battery costs 3M yen, it would take you 13 years and 8 months to pay back but, the difference should be considered significantly in terms of clean energy.
Also, the midnight charge of 78.5 yen is valuable in terms of no blackout operation although it is less than the battery cost (136 yen as average per day based on lifetime expectancy).