SunShift has two main goals:

To protect your solar investment your system must be operating correctly which includes equalising your batteries  once every three days as a minimum. This means the batteries need to reach 100% SOC at least once every three days. Therefore, if continuous overcast days stop the batteries from reaching 100% through your solar production then the grid will be used to charge the batteries. 

To increase your electricity savings SunShift will not charge your batteries from the grid unless required as explained above. Furthermore, if you have load shedding approaching and your don't have enough solar power to survive the outage, SunShift will charge your batteries, but thanks to the intelligent load and solar predictions it will not charge more from the grid than necessary to last the outage. This increases savings by not charging more from than the grid than required.