Jurgens

Hi @LionKing
if sending electricity back to the grid is prohibited and you want to blend PV power with the grid power at the same time, then there's only one correct way to do it:
It's AC-DC-AC conversion, namely Axpert King, aka PIP-5048MK. Just like @Coulomb suggested. A quite affordable unit, that can handle up to 5kVA loads where for example 3kVA are comming from PV, while 2kVA are being pulled from the grid. If 5kVA unit is not enough for the house, this model allows you to parallel more units into a single powerfull system.

Specsheet: http://www.mppsolar.com/v3/catalogs/PIP-MK.pdf
User manual: http://www.mppsolar.com/manual/PIP-MK (PF1.0)/PIP-MK manual-20181106.pdf
 
A solution using On-Grid, Grid-Tie or Hybrid inverter is also possible, but it WILL send a small amount of electricity back to the grid every day. By design, there's no way how to prevent this behavior. No matter what brand of Inverter you use, no matter what additional electronics you will add. Sooner or later, the electric company will find-out.
In my country, some guys tried even super-expensive Studer Hybrid Inverter (Switzerland based company) which cost up to 5000 EUR a piece. And even these machines are sending a few watts back to the grid every day. Some added the intelligent dump load controllers, which are consuming excess spikes of PV power, but it's not perfect either. Luckily, local electric company is not issuing penalties....yet.

I've recently purchased and installed the following:
1 x Growatt SPF 5000TL HVM 5kVA/5kW Hybrid Inverter.
2 x Pylontech US3000 batteries.
1 x Pylontech cable kit with RJ45 BMS comms cable included.
I've just spent 5 days communicating with Growatt in China to figure out why I could not get the inverter to communicate with the BMS on the master battery properly.
After many, many emails back and forward, and far too many hours of research online, I finally got it right today and I think it is worth sharing this information here, in case anybody else needs it, because I couldn't find the right information anywhere on the internet, all in one place, explained properly.
It turns out that the Growatt SPF5000 has to be connected to the Pylontech batteries differently to the way Axpert inverters are connected to Pylontech batteries.
Everything I was reading online was saying that you need to plug the RJ45 comms cable into the CAN port on the master battery and then into the BMS port on the inverter, and then you need to set the battery type to Li (setting 05 on Axpert and Growatt inverters) and then choose Li profile L02 (also apparently the same for Axpert and Growatt inverters).
It turns out, the Growatt does NOT communicate via the CAN port. It communicates via the RS485 port that is positioned below the CAN port on the master battery.
And in addition to that, it requires a 9600 baud rate, which you can set using the 4 small white dipswitches on the master battery.
For the Growatt you must set those dipswitches to:  1 0 0 0 (ON OFF OFF OFF)
When connected to the CAN port and put into Li (L02) mode, the Growatt inverter faults and gives an error 20 and an error 04 constantly.
When connected to the RS485 port with the dipswitches set to 1000, comms is immediately established and it works as intended.
I also installed 2 firmware updates on the inverter, that were sent to me by Growatt in China (who were very helpful through this entire process despite not actually giving me the information I actually needed to solve this), but in retrospect I actually wonder if those firmware updates even made a difference because I was able to put the inverter into Li (L02) mode before applying those firmware updates anyway, I just didn't know about the RS485 port and the dipswitches.
Recommended configuration process
1. Turn inverter on but run off battery only. Disable A/C input and  A/C output (use isolator switches if you have them).
2. Go to setting 5 and select battery type = Li. Then select profile L02 (This is specifically for Pylontech batteries). Push ESC to return to home screen. Go back to setting 5 and verify that it was saved as Li.
3. Now shutdown the inverter and batteries completely. Turn the batteries off using the on/off flip switch, not just the red button on the master battery.
4. Now make sure that the end of the comms cable on the battery side (it will probably have a little sticker on it that says BAT) is plugged into the RJ45 port labelled RS485 that is below the CAN port. And also make sure that the other end is plugged into the RJ45 port labelled BMS on the inverter and NOT into the other RJ45 port that is labelled RS485 (Yes, I know, it's weird, just go with it).
5. Now set the 4 little white dipswitches to: ON OFF OFF OFF (1000).
6. Now turn the batteries back on and then turn the inverter back on.
You should no longer see any fault codes or the red fault light.
How to tell that the inverter really is communicating with the BMS properly
1. You should now see a little Li symbol next to the battery icon on the home screen of the inverter, and that Li symbol should NOT be flashing. When it's not flashing and is solid it means comms is working.
2. If you go and look at most of the battery values on the status screens or in settings related to battery level (SOC) you should now see percentage values where there were voltage values before. Setting 21 is a good example of that.
I hope this helps somebody else because the information available online with regards to the Growatt routers is of no help in this regard and most of the information available relates to Axpert inverters, which appear to be very similar to the Growatt at face value, but communicate with the Pylontech batteries differently from what I can see.