Zappi and home battery

a303

Hello,

I'm planning to have solar installed at home shortly, and I'm considering whether to also opt for a Zappi and/or a home battery to help make the use of the energy generated.

However, I really can't understand how a Zappi would interact with a home battery if I opted to have both installed.

For example:
- it's a lovely sunny day.  The solar panels have filled the battery, and started exporting to the grid.  The Zappi has spotted this and is putting the surplus into the car instead.  However, it clouds over, and solar generation drops off to nil.

What I want to happen in this scenario is for the Zappi to switch off, and the home battery to start powering the house.
What I'm concerned might happen is the battery reacts quicker than the Zappi, and tries to power the Zappi and the house whilst the Zappi merrily keeps going.

Can anyone help me out (please!) by explaining:
1 - what would happen in this scenario
2 - how it would happen?  (i.e. what each of the current sensors see to drive the outcome)

Does it make a difference if the battery is DC-linked through a hybrid inverter vs AC-linked through it's own inverter?

Thanks in advance to anyone who can help me understand this!
Kevin

QrizB

This isn't the most helpful answer, but with a clever enough system you can set these priorities and the kit will follow your instructions.

Someone else will probably be along shortly with examples of what a "clever enough system" looks like in practice, and costs.

Love the user name, by the way; I've spent far too much of my holidays stuck in traffic on the A303!

Reed_Richards

What you fear is indeed a real problem, although perhaps not quite in the way you imagine.  If I boil a kettle my battery (or the inverter controlling it) cannot respond quickly when the kettle switches off so it will send power to the gird as it ramps down its output.  Anything monitoring just export to the grid could see this as excess solar power, switch something on and drain the battery.  I know nothing of the specifics of the Zappi but anything with only a single monitor is unlikely to work reliably.  You need to monitor both what power is being exported to the grid and what power the battery is providing (or alternatively what power the solar panels are providing).

EVandPV

The zappi can monitor an ac coupled battery with a ct sensor which in turn enables priority settings that can be set to charge the battery first from surplus pv.
There's also an 'avoid drain' option to prevent the zappi using power from the battery.

I think this pretty much covers what your looking for.

EVandPV

Here's the part in the manual that covers this ......

a303

Thanks everybody for taking the time to reply.

I see how this can work if the Zappi can monitor current out of the battery.  Presumably that's only for an AC coupled battery?

Is there an equivalent for a DC battery (& hybrid inverter)?

EVandPV

The manual says this about dc batteries .....

Reed_Richards

It is perfectly feasible to monitor the link between the inverter and a DC battery to find out what the battery is up to but you need a sensor that can detect a DC current and a CT sensor works on AC.

Heedtheadvice

? Not quite. Some ct sensors work on both ac and dc but yes in the domestic solar world often just ac and what the sensing circuit copes with is important.

It is not imposdible to measure the current and direction with a contactless sensor and associated circuit. Indeed many a clamp meter (or accessory) is commonly used for that purpose (without affecting the charge discharge capability), from small currents to very large currents (thousands of amps).

Not suggesting these are used for any of the equipment mentioned earlier in posts but just as an example for what is possible see https://www.isotel.eu/dc-ct/index.html

Petriix

The export setting should work, as long as the battery monitors the export, it will see the 100W going to the grid and reduce its power output accordingly. The Zappi will then see the output from the solar/battery drop and reduce its use. They will feed back in this loop until the battery output is just covering the house load and the Zappi is no longer charging.

a303

Thank you all so much for your answers - very helpful!