Several points to consider.  ...

Several points to consider.  It would probably be best to size the generator on the daily demand rather than the chlorinator capacity and aim to generate in a few hours less than 24. That way you can ensure enough hypochlorite even when the cell performance starts to degrade.

In the past some used to size generators to produce the days supply in a few hours to use off peak electricity. However unless there is a supply of really cheap off peak electric this is unlikely to be commercially viable.

I would not have a standby cell as long as it is possible to get a drum of commercial hypochlorite to site in a day, which should be the capacity of the hypochlorite storage. Instead rely on diluting the commercial hypochlorite to the 1% approx. of the normal generation. If getting the supply there is tricky you could have a few drums on site but make sure to use them to turn over stock in a month. 

Also it all depends on the softener actually being effective.