Add support for protocol v3.15 and multiple units

[lampra1]

Hi,
Thank you for this software. I use it for some weeks now and works fine.

1. The growatt protocol has been updated to v3.15 and now supports string voltage & current (registers 70-88) for newer inverters. This should be rather easy to implement in growatt.py but it also needs grafana dashbord update.
2. Could you add support for multiple inverters (i.e. unit 1, unit 2 etc)?

[ZeroErrors]

1. The growatt protocol has been updated to v3.15 and now supports string voltage & current (registers 70-88) for newer inverters. This should be rather easy to implement in growatt.py but it also needs grafana dashbord update.

If you have access to a newer inverter to test changes on I could try and add in support for these values. To make a dashboard it would be easiest if I had some data to work with.
I just added the ability to read the modbus version from unit so that it can be made to only read data from a register when it is supported.

2. Could you add support for multiple inverters (i.e. unit 1, unit 2 etc)?

I added support for units based on the code in https://github.com/jrbenito/canadianSolar-pvoutput/blob/dev/canadian_reads.py however I have no way to test if this works correctly with multiple units so if you are able to do so please let me know.
You will need to update the config files since I have changed the format a little to make it work better with multiple units.

[lampra1]

Hi,
I do have access to a newer model. Let me know how to provide the data and I will send it to you. I could also provide live data if you have an accessible influx db.
Though I am not sure if the modbus version on the inverter is correct. Reading holding register 73 returns [305] but it is definitely newer version as the unit reports also values per string (not the case for ver 3.05).
I will test the multi unit version and I will let you know.

[lampra1]

I started testing the multi unit version today and so far everything went smooth.
Sidenote: Unit numbering needs to be in ascending order in the .cfg file
Now an aggregated grafana dashboard (of all units) for power and production would look nice!
Regarding modbus version of my units, here are the readings:
root@OpenWrt:~/multi/solarmon# ./solarmonmulti.sh Setup InfluxDB Client... Done! Setup Serial Connection... Dome! Loading inverters... Growatt: Name: main Unit: 1 Modbus Version: 305 Growatt: Name: unit2 Unit: 2 Modbus Version: 304 Growatt: Name: unit3 Unit: 3 Modbus Version: 304 Dome!

[ZeroErrors]

@lampra1 This PR #30 adds the ability to change the inverter type so if you have a working version of growatt.py that needs modifications to work with v3.15 I'm happy to accept a PR that adds it as another inverter_type.

[lampra1]

@ZeroErrors Thank you for the update.
I do have a working version of growatt.py but it relies on a previous (2.3) version of pymodbus.
I will try to test with newer pymodbus versions within the next few weeks.