jules43

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A couple of weeks on, and I'm reporting on my findings to date.  There appear to be three options
1. query locally via direct cable - reports of the software for this as sketchy at best.
2. set up a man-in-the-middle - capture the data for local processing and then forward to server.growatt.com.
3. query the growatt hosted server.growatt.com
 
I have not tried #1. I don't plan to as I can't see a current use case (for me)
I'm about to try #2.  All my home automation 'operations' do not rely on the internet (it's all locally hosted on a mac with indigo software with zwave (rather than wifi) communication protocols).  This has been super solid for 10+ years. The use case for #2 is if Growatt shut up shop , or start to charge for the service etc.. - again something I don't want to do.  I'm going to try running this in a docker container on an always-on mac.  Also, I believe it is possible to increase the frequency of data - from the standard 5 minutes to 1 minute.  This will be great to see.  This amount of data locally is not a big deal.
I have had success with #3.  There are a lot of API calls that can be invoked - including getting the 5 minute 'chart data' that you are after.  It provides the data in json, so you'll need to do some parsing / processing to get it into Excel friendly format.  To date, I have got the json being returned, and am about to work out exactly which is the key data I want.  I'm thinking I am going to call all the key APIs every day (for the previous full day as well as intra-day).  I will dump these to local files.  I plan to import into my influx db and/or create csv for that Excel friendly format.
 
Hope this is of use and/or interest.  Let me know if a further update would be useful, or any questions on the above.
 
Full disclosure, I'm based in the UK but , as with most things internet / tech, this does not seem to be a major issue.  Just wish I had more Sun hitting the panels.

Follow up for others who may see this.
I believe the issue was that the CT clamp (placed between power company’s meter and the consumer unit) was faulty / inaccurate. Installers actually cut away some of the insulation, pls a “turn it off, turn it back on” strategy and all appears to be reporting the right data and no more charging battery from the grid.