AC whole house battery charging based on grid-tied solar output and mains load

[dlarue]

Our solar PV system is soon to be switched to NEM 3.0( So CA ) in Jan 2025 and I'll be building 1 or 2 15 kWh LFP packs to get us through the 4p-9a no/low solar periods.  I'm looking for a programmable 48V charge controller which would only charge the battery packs from AC power when the solar/micro-inverters are producing and programatically limit backfeeding.

With the charge controller programmable for something like setting the AC charge controller to limit the grid to seeing a 10W backfeed with the rest charging batteries. Like a zero export inverter but for battery charging.

Also would need a whole house inverter(3 kW) which would then take over the household load as the solar PV generation waned but allowing for the grid seeing a load of only 10-100 W through the evening, night and early morning no/low solar periods.

From what I've seen, solar PV charge controllers want direct DC solar input. Am AC based charge controller system which monitors only solar inverter AC power flow and the mains panel lines while having the ability to adjust the battery charging according according to solar PV output and household loading could bolt onto any existing home grid-tied system. And do so without going onto or touching the thousands of existing grid-tied solar installations.

The clock is ticking so looking for solutions since the CPUC and the CA IOUs own us otherwise.

[dlarue]

It's looking like nobody makes a zero export based solar battery charger. At least not a battery charger which is based on AC power input and uses monitoring of AC power from solar PV inverters and house load(mains) monitoring to regulate battery charge rates.

My next step is to look for an AC based battery charger with an open control API so I can do my own solar PV output and house load monitoring and command the charger appropriately.

[NiHaoMike]

How about an Open Energy Monitor ( https://openenergymonitor.org ) along with hacking some surplus "telecom rectifiers" with ESP32 or similar to allow them to limit output current? Note that unlike a zero export inverter, it doesn't actually need to prevent export and therefore a response time of a few seconds would be acceptable. (In practice, it would not be hard at all to get the response time to a few 10s of milliseconds.)

[rteodor]

Not sure I fully understand, but since you need an inverter anyway why not get one with charger included ? Victron Multiplus or the like.

[dlarue]

Not sure I fully understand, but since you need an inverter anyway why not get one with charger included ? Victron Multiplus or the like.

I've not yet looked at inverters yet but since they expect DC connections to the solar PV modules I figured they would not work limiting backfeeding of the grid by the AC connected inverters.
I'll look at inverters to see if any have power flow sensing for battery charge control. Thanks for the feedback.

[dlarue]

Not sure I fully understand, but since you need an inverter anyway why not get one with charger included ? Victron Multiplus or the like.

If the inverters also mentioned don't do line sensing battery charge control I would have to start doing my own sensing and control. I was thinking of first looking for chargers with communications control(RS485, other). I hadn't thought about doing PWM on the charger out. Thanks for the feedback.

I went looking through Victron's site and documentation and finding this video shows that they have a sensor module which feeds to their Multi unit to do what I want. It was 2016 so I'll look to see what their current configurations look like.  https://youtu.be/tbpQzEZTElI?t=168

[Marco]

Deye also has a zero export hybrid inverter, I'm sure there are more.

As for the simmer load, just add some lights after the CT.

[darkspr1te]

This is more or less the setup I have.
I use a victron MPPT solar charge controller connected to 5kv battery system and thats connected  to a victron multiplus gx.
The victron is programmed only to charge the battery from ac 'if' it gets below 30% battery, i can choose feedback or not but I dont use it so it's turned off.
The victron automatically takes power from battery/solar first and AC second and only uses AC to 'fill in' larges loads if you wish or not, the ESS "energy storage system' can be setup in many ways but for me AC is only a backup if i have battery/solar issues on my setup with no grid feedback.
the system uses ve.direct (serial Tll) and ve.can for battery management comms and is quite easy to setup once you watched a few videos.
for a idea of how it's done you should watch offgridgarage on youtube , he does all sorts of hacks but essentially he's totally offgrid with only a AC grid source as fail over.


darkspr1te

[rteodor]

This is more or less the setup I have.
I use a victron MPPT solar charge controller connected to 5kv battery system and thats connected  to a victron multiplus gx.
The victron is programmed only to charge the battery from ac 'if' it gets below 30% battery, i can choose feedback or not but I dont use it so it's turned off.
The victron automatically takes power from battery/solar first and AC second and only uses AC to 'fill in' larges loads if you wish or not, the ESS "energy storage system' can be setup in many ways but for me AC is only a backup if i have battery/solar issues on my setup with no grid feedback.
the system uses ve.direct (serial Tll) and ve.can for battery management comms and is quite easy to setup once you watched a few videos.
for a idea of how it's done you should watch offgridgarage on youtube , he does all sorts of hacks but essentially he's totally offgrid with only a AC grid source as fail over.


darkspr1te

Yeah, but the OP said he has AC micro-inverters and I do not know how they can be controlled for zero export.
Victron ecosystem has most of their interfaces open so many things are possible. I imagine some some AC sensor would be needed but how to tell to micro-inverters to wind down their output when the battery is full  and there is not enough load is unknown to me.

For off-grid systems Victron has this solved: the inverter will increase the AC frequency and micro-inverters will ramp down or turn off completely at some set frequency. Andy from Off Grid Garage demonstrated this in one or two videos. But how to do this control in a grid connected system ? I do not know.

[dlarue]

The Victrons would have done the job but they don't have all the required certifications for my State in order to be connected to the grid.
I looked at Sol-Ark but they would have been many thousands more than the Victrons(2 of them) and with the EG4 18K(really 20K) having a 2nd AC input(Generator) which is AC coupled and can take grid-tied inverter circuits as input that's the route I'm taking. i had brushed them aside in my investigations from comments about them being a Chinese company but found out they are an American company, out of Texas, who's designs are manufactured in China. The inverters have similar feature sets, support diverse energy inputs for ESS charging and CTs for zero export adjustments.  And to control the power output of the grid-tied inverters they, like others, use phase shifting of the base AC signal to 'throttle' input power when storage is at capacity and settings are for zero export.

[tszaboo]

I've been also searching for AC coupled batteries. I there are some inverters that will do it without panels, only with a battery connected. My plan is to connect to the so-called P1 port on the electricity meter. It's region specific, I don't think I've seen this outside the Benelux countries. So this reports every 10 second my usage/generation. Then use the info from this to control the battery inverter through ethernet, modbus or RS485 or whatever its supporting.
There is no need for current clamps or whatever. My solar inverter is from Solaredge, doesn't support batteries.
But that's OK, because most inverters are only going to support very specific battery brands, and they are not very good in price/capacity. So that's why I think a second inverter for a battery makes sense.