As described in some detail in my last post, we have a single 10kWh Redflow ZCell zinc bromine flow battery hooked up to our solar PV via Victron inverter/chargers. This gives us the ability to:

• Store almost all the excess energy we generate locally for later use.
• When the sun isn’t shining, grid charge the battery at off-peak times then draw it down at peak times to save on our electricity bill (peak grid power is slightly more than twice as expensive as off-peak grid power).
• Opportunistically survive grid outages, provided they don’t happen at the wrong time (i.e. when the sun is down and the battery is at 0% state of charge).

By their nature, ZCell flow batteries needs to undergo a maintenance cycle at least every three days, where they are discharged completely for a few hours. That’s why the last point above reads “opportunistically survive grid outages”. With a single ZCell, we can’t use the “minimum state of charge” feature of the Victron kit to always keep some charge in the battery in case of outages, because doing so conflicts with the ZCell maintenance cycles. Once we eventually get a second battery, this problem will go away because the maintenance cycles automatically interleave. In the meantime though, as my project for Hack Week 21, I decided to see if I could somehow automate the Victron scheduled charge configuration based on the ZCell maintenance cycle timing, to always keep the battery as full as possible for as long as possible.