I don't think powerwall has that functionality. At least original powerwalls only provided backup power. From a C&I perspective this is one of the sources of revenue for batteries - however there are many different ways for electricity charges to be passed on to customers. It isn't only kWh.
"When originally announced in 2015, two models of Powerwall were planned: 10 kWh capacity for backup applications and 7 kWh capacity for daily cycle applications"
