Frankly, the actual control mechanism we landed on is pretty simply in the end - thanks to some sterling work by Switchin on their control device.
Each battery system runs independently, if not being directly told otherwise.
The ZCell+SP PRO simply charges when there is surplus energy trying to export past it, and discharges when there is net positive demand trying to import through it.
Downstream of that pairing, the Solar Edge unit attached to solar plus a Lithium battery tries to add in energy whenever it can.
The control strategy we landed on is this simple: Maximise the use of the ZCell.
In detail that means:
- Charge the ZCell first (suppress charging of the Li battery until the Zcell is full)
- Discharge the ZCell first (suppress discharging of the Li battery until the ZCell is empty)
This control is implemented entirely with some control command sent to the Solar Edge unit - the SP PRO + ZCell is just 'doing its thing' (being monitored, but not actively controlled beyond just doing what it does anyway).
That's kinda 'it' - and this plays to the strengths of both technologies. Jeff tells me that the Li battery, which has been in for a while, is already losing peak capacity with age (as Li batteries do, when you actually exercise them hard).
Now, with the ZCell there, the Li battery will have a far longer life, as its only called on for overnight demand over 10kWh, and otherwise it just sits there, topped up and on standby.
On the other hand, the ZCell loves hard work, so its being worked as hard as possible (by being used in preference).
The end to end outcome is actually a win-win - and its been a fascinating first look at how such a hybridisation can be made to work. I see potential for us to learn a lot from this (including for higher scale work in the future and/or work with other sorts of hybrid in the future).
Kudos to Jeff for knowing what he wanted - he wanted to prove it could all be made to operate well, and his resolute insistence that the vendors concerned help him to do that... worked out
(20min delay)