The answer to your question is "it depends"
This is a battery based Grid tie system, hopefully you purchase a battery based system on the advice if you lost power you would at least have backup when the grid was down. If that is the case, the problem with battery based Grid Tie is it's only as efficient as the battery bank will allow.
The problem with this is the larger the battery bank or the age of the battery bank can severally affect sell back efficiency. My guess depending on the size of the battery bank, you will see 75-90% of the Pv power being sold back into the grid.
Technical Services Director- Surrette Battery Company