2 PV systems - one acting as grid

[swissco]

Really wondering
a) has somebody built something similar and can provide details?
b) will the Schneider inverters AC outputs (acting as grid and connected to the home panels) of the existing system be able to handle it when connecting the SolArk grid in/out port connected in parallel to the home panels?


Details:
I have an off-grid PV system (s1) with the panels mounted on a ground rack.
The rest of the equipment (inverters, charge controllers, battery) is located in building 1 (b1).
The s1 load out feeds the home panel of b1 and can deliver up to 12kW.

Building 2 (b2) is about 200ft away and its home panel is also connected to the s1 load out.

The system works great and has enough power and battery storage to satisfy the energy needs of both b1 and b2.
Matter of fact, the battery is filled up early in the morning and I am wasting all the PV production I could harvest the rest of the day.

To make better use of the excess PV production, I'm planning to get an EV that will be charged in b2.
The excess production of s1 is not enough for the EV, So I plan on adding another PV system s2.
For s2, I will add PV panels (8-12kW) on the roof of b2. These panels will feed a new charge controller and inverter at b2.

The EV charging will real-time adapt to the excess PV production available so it is not depleting the home battery.
Monitoring the charge level of the home battery, the active home load and the PV production output will be necessary to adapt the level 2 charger current output for EV charging.
Most likely using OpenEVSE hardware to implement this - see https://docs.openenergymonitor.org/a.../solar-pv.html.

I only plan to charge the EV during the day with excess PV production.
If no EV is connected to s2, I would like the s2 PV production to help with the home loads and charging of the s1 battery.
If an EV is charging, I would like all of the excess PV production from both s1 and s2 to help charge the car at maximum power available.

I'm considering that s1 grid input needs to be connected to the home panels - i.e. the s1 load out and home panels are treated as grid.

Has anybody done something like that and should I be worried about the s2 load out being connected this way?


S1:
(24) 370W PV panels (8.88kW) configured as 2 strings (12) panels each
(2) Charge Controllers(s) - SCHNEIDER ELECTRIC XW-MPPT 100-600, each connected to a string
(2) parallel connected Inverter(s): SCHNEIDER ELECTRIC Conext XW+ 6848, 6.8 KW 120/240 INVERTER/CHARGER
(1) lithium battery bank 28kWh/48V

S2:
(18-30) 400W PV panels
considering SolArk or EG4

 

[sunshine_eggo]

Trying to simplify...

S1 output connected to grid input of S2?

As long as the S2 inverter can operate battery-less, set preferential source as solar and fall back to "grid" when PV is insufficient, sounds very workable.

You're just trying to avoid batteries for S2?

 

[swissco]

to: sunshine_eggo
yes, trying to avoid batteries for S2 and also have nothing connected to load out of S2.
in other words S2 has PV input and only feeds the pseudo-grid (connected to home panel which also feeds the EV charger)

here are some example scenarios, that I'm not sure will function as I'm hoping - especially c) I'm worried about!

a) PV on S2 is at full exposure and could deliver ~10kW of power. Same for PV on S1 could output peak 8.8kW. Battery on S1 is in bulk mode and an EV is connected. Expecting battery should charge per charge curve and excess power from both S1 and S2 will go to home demand and EV charging.

b) PV on S2 is at full exposure and could deliver ~10kW of power. Same for PV on S1 could output peak 8.8kW. Battery on S1 is in float mode and EV connected. Expecting power from both S1 and S2 will go to home demand and EV charging. If EV charging is set to peak 50A, then only using a fraction of the available PV power (i.e. 18kW could deliver 75A (240V)).

c) PV on S2 is at full exposure and could deliver ~10kW of power. Same for PV on S1 could output peak 8.8kW. Battery on S1 is in float mode and EV is not connected. I'm assuming S2 is trying to feed the full 10kW back into the pseudo-grid by slightly raising the voltage on the home panel bus. I assume S1 is not sinking any current with the battery fully charged (besides some for home loads) so not sure how S2 reacts - for example, when there is no current flowing back into the pseudo-grid is it further increasing the voltage to the point where it causes an issue on the S1 load out?

 

[sunshine_eggo]

Okay, so S2 is purely "grid tie"? Why not just get a cheap GT inverter or microinverters?

There's some stuff at play here that makes it a bit tricky.

First, the "grid" inverter (S1) must be able to handle 1.0-1.2X the grid tie power, i.e., S2 @ no more than 8.88kW

a) that sounds like it should work, except S2 PV must meet the restrictions of the S1 inverter (typically 1.0-1.2X power). If battery hits absorption, S1 will frequency shift away to disconnect S2.

b) No. S1 inverter will shift frequency to disconnect S2. Charger must typically be in bulk mode to retain S2.

c) No. See b.

Basically, most AC coupled grid forming inverters use absorption voltage as a trigger for frequency shifting.

Your b and c scenarios will work AFTER the battery has been drawn down and bulk charging starts.

 

[swissco]

The devil is in the detail and I'm not sure how this new AC coupled S2 inverter should be connected to the existing system.
I found this generic setup in the Schneider Conext-XW-Multi-Cluster guide and the system appears to be what I need.


The problem is they are not specific where exactly the connections go on the Schneider inverters.
I found a more detailed setup example in the Schneider XW-Pro-Multi-Unit-Guide but this is using a BCS and connects the main panel to AC1


Below is my current setup showing S1 in Building 1 and the new system for Building 2. I'm currently connecting the house panel to AC out of the S1 Schneider inverter - so not sure if I need to modify and connect to AC1 when adding the system extension. The only thing connecting the 2 buildings is the underground feed - i.e. both home panels in each building are currently directly connected to AC out of S1.