Monday, 2 January 2017

Emailing you a daily solar performance update

The ability to see the live data, and view a performance graph is great, but sometimes you'll be away from home and be wondering how your system is doing.

You could spend some time configuring your network to allow remote connections by changing some firewall rules and adding some authentication, or vpn if your router supported it - that would work well, and would mean that you had all the abilities that you have when you're at home.

However there is an alternative method, in reality it's probably sufficient for you to get a daily email of the performance data sent from your Raspberry Pi - that would have the advantage that since that traffic is outbound, it would require no firewall changes, and you could pick up your email anywhere - so that's the method I'm going to describe now.

These instructions presume you've already got a Raspberry Pi or similar making periodic connections to your charge controller and you can read the data on demand.

All that's needed in addition to that is -

  • Some software to send emails (smtp client)
  • A couple of cron jobs to send the emails and tidy up old data
  • A gmail account

Create a Gmail account 
You could use an existing one, though for security you may just make a new one, as you may have to configure it to use less secure authentication and the username and password are stored in plain text on the Pi, which, depending on your setup, may be in an relatively insecure location, e.g. garden shed.

Test the Gmail account to make sure you can send an email and have the email address and password to hand.

Install an smtp client for php 
Full instructions for this are given at

If you're on Raspbian or similar follow the Debian/Ubuntu instructions.

Make some cron jobs
I send my daily email at 9am - I chose this time as at most times of the year there's light at that time of day, and I've found that to be necessary in order to be able to get the kWh data from the charge controller reliably with my setup.

I have the following root cronjobs

* * * * * /var/www/html/epsolar/getsolarstats.php

This harvests performance data every minute and stores it in a database - this is for the dashboard.

50 8 * * * truncate -s 0 /home/pi/report.txt

At 08:50 each day I delete the contents of the previous days email.

 0 9 * * * (sleep 30; /var/www/html/epsolar/example_cli.php >> /home/pi/report.txt)

At 09:00 I run the command line solar data harvesting script and save it to a text file (report.txt).  If this were done exactly at 09:00 then it would clash with the script that runs every minute to do similar things, and would end up not getting data.  Cronjobs have a resolution of 1 minute, so without a little trick there would always be a clash whatever time I chose to do this.

The trick to avoid the clash is to trigger the cron job, but to include a sleep 30 command which makes the command wait for 30 seconds then do it's data gathering - in this way the clash is avoided and both scripts get their data.

As the Pi user I have the following cron job

1 9 * * * cat /home/pi/report.txt | msmtp -a gmail targetemailaddress

Send the email at 09:01

Script modifications
I modified /var/www/html/epsolar/example_cli.php to include


as the first line and

$tracer = new PhpEpsolarTracer('/dev/ttyUSB21');

contains the device connection parameters (yours will differ).

The original comes from

I further modified it to order the data into the desired sequence, and I removed some sections that I didn't need.

That's it - I now get a daily email so I can keep an eye on my voltages and power generation when away from home.

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