My Solar PV Battery app

Emoncms
32

Absolutely awesome @TrystanLea, thankyou.

For anyone not an expert (like me) who needs a simple and low effort way to get the Powerwall state-of-charge (SOC) into emonCMS - there are many, many other and more elegant ways, NodeRed, MQQT etc including those in @miker’s thread (see above) - but if you aren’t familiar with any of these and don’t want to learn right now because you just want to get it working, this might be just up your street.

You’ll need to know how to to ssh into your emonpi, and some Linux command line basics only.

SUMMARY

  1. Create a python script (8 lines, below) to execute on the emonpi, to fetch the Powerwall SOC and send it to emonCMS.
  2. Create a crontab entry to automatically run the script every minute.

DETAIL

  1. ssh in to emonpi as user pi. Create a python script using your favourite Linux editor (nano is easiest) called, say, getsoc.py in your home directory (/home/pi) with these contents <credit to @TrystanLea for this>:
import urllib2, json
# 1. Fetch data from API 1
response = urllib2.urlopen('http://URL_OF_YOUR_POWERWALL/api/system_status/soe')
jsonstr = response.read()
data = json.loads(jsonstr)
soc = data['percentage']
# 2. Post data onwards to API 2
response = urllib2.urlopen('http://URL_OF_YOUR_EMONPI/input/post?node=powerwall&data=soc:'+str(soc)+'&apikey=YOUR_API_KEY')

EmonCMS will automagically create a new feed powerwall:soc if it does not already exist (thanks @TrystanLea).

You should try running it from the shell:

pi@emonpi: python getsoc.py

but you may get an error, as I did, something like:

urllib2.URLError: <urlopen error [SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed (_ssl.c:727)>

To circumvent this problem (google it if you want to find out more…) use this command instead:

pi@emonpi: PYTHONHTTPSVERIFY=0 python getsoc.py

You should be able to see the Input and Feed refreshed in emonCMS. If so, move on. Otherwise you need to find out why it’s not working. You can add print statements to the python script e.g print “hello” or print soc to help.
3. Create a crontab entry to run this script every minute. If you need more info type man crontab and/or man 5 crontab to get more info, or google it.

pi@emonpi: crontab -e

It will take you into a nano edit of the crontab file, which has prefilled guide comments in it. Add the following lines to the end of the file:

MAILTO=""
* * * * * PYTHONHTTPSVERIFY=0 /usr/bin/python /home/pi/getsoc.py

Make sure there is a newline at the end of the file, else it will fail to work.
When you exit the editor it will automatically try to add your cron job and tell you if it succeeded. If it did, then that’s it, you’re done.
I hope.

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