zerofeed

Zerofeed solar power control shell script for OpenDTU / Tasmota / OpenWrt

• https://github.com/tbnobody/OpenDTU
• https://github.com/tasmota
• https://openwrt.org/

About

Zero feed script to make sure the solar modules are reducing their output to (ideally) not push any energy into the public network.

Inspired by https://github.com/tbnobody/OpenDTU/blob/master/docs/Web-API.md

Needs OpenDTU and the Tasmota smart meter IoT devices in your WLAN and is intended to be executed on an OpenWrt router (install curl & jq packages).

USE AT YOUR OWN RISK! Especially I don't know if the inverter is fit for this purpose as all this functionality was reverse engineered by the fabulous OpenDTU developers. I simply rely on their amazing work here.

Code

The script zerofeed-dbg.sh contains extensive debug output which was used during the development. The script zerofeed.sh should be completely silent to not bloat any logfiles. zerofeed-dbg.sh is the main source code.

Create the 'release' script file without debug output with:

grep -v echo zerofeed-dbg.sh > zerofeed.sh

Configuration

The script has several options to be adapted to your environment:

• SmartMeter IP (Tasmota) (update for your local network setup)
  SMIP=192.168.60.7

• DTU IP (OpenDTU) (update for your local network setup)
  DTUIP=192.168.60.5

• DTU default admin user access (from OpenDTU installation)
  DTUUSER="admin:openDTU42"

• DTU serial number (insert your inverter SN's here)
  DTUSN=(116190745467 116180400144 116190745954)

• DTU power limits to override the detected inverter limits (in Watt) (0 = disabled)
  DTULIM=(0 0 0) or DTULIM=(600 800 1000)

Of course the script can also handle single inverters, e.g. DTUSN=(116190745467) and DTULIM=(0). The array sizes of DTUMAXP, DTUMINP and DTULASTSOLPWR have to be adapted according to the number of interters too. Please check the script for that.

• SmartMeter type adaption:

The code is tested with a Logarex LK13BE (SML) smart meter
https://tasmota.github.io/docs/Smart-Meter-Interface/#logarex-lk13be-sml-eg-lk13be6067x9
which provides the current house/flat power consumption (in Watt) with a LK13BE specific Web-API answer that has to be adapted in the getSMPWR() function when a different smart meter is used!

Then the jq command with '.StatusSNS.LK13BE.Power_curr' has to be changed.

In the current LK13BE environment the full jq output looks like this:

$ curl -s http://192.168.60.7/cm?cmnd=status%208 | jq
{
  "StatusSNS": {
    "Time": "2022-12-19T08:56:05",
    "LK13BE": {
      "Power_total_in": 1914.7,
      "Power_total_out": 0.6,
      "Power_curr": 509,
      "Power_L1_curr": 69,
      "Power_L2_curr": 77,
      "Power_L3_curr": 362,
      "Volt_L1_curr": 226.5,
      "Volt_L2_curr": 226.3,
      "Volt_L3_curr": 225.6,
      "Amperage_L1_curr": 0.6,
      "Amperage_L2_curr": 0.77,
      "Amperage_L3_curr": 2.06,
      "HZ": 50,
      "phase_angle_p1": 304.1,
      "phase_angle_p2": 298.5,
      "phase_angle_p3": 327.3,
      "phase_angle_l2_l1": 239.8,
      "phase_angle_l3_l1": 120.2
    }
  }
}

Which makes the code in getSMPWR() produce the power consumption value:

$ curl -s http://192.168.60.7/cm?cmnd=status%208 | jq '.StatusSNS.LK13BE.Power_curr'
509

Please check your smart meter with the full jq output and find the needed power consumption in the JSON tree to get the correct string for your smart meter for the power value (analogue to the '.StatusSNS.LK13BE.Power_curr' example) - and update this string in getSMPWR() for your local setup.

Installation

The script can be executed without any installation on any Linux system, e.g. a Linux laptop, Raspberry Pi, OpenWrt or even on WSL2. It might also run on Windows (when bash, curl and jq are installed), but this was never tested. To reduce the power consumption and hardware effort the script is intended to run on an OpenWrt router, which is powered anyway and can handle this task easily.

To run and automatically start the zerofeed.sh script on your OpenWrt router a start/stop script zerofeed for OpenWrt 22.03 has been created which can be found in the openwrt directory of this repository.

The installation process:

1. Copy the zerofeed script to /etc/init.d/zerofeed on the router
2. Make sure the script is executable: chmod 755 /etc/init.d/zerofeed
3. Copy zerofeed.sh script to /usr/bin/zerofeed.sh on the router
4. Make sure the script is executable: chmod 755 /usr/bin/zerofeed.sh
5. Enable the script with: /etc/init.d/zerofeed enable

If you want to see the latest state in /var/run/zerofeed.state rename the two '#cho' statements in the zerofeed.sh script to 'echo'.

E.g. with

sed -i 's/\#cho/echo/g' /usr/bin/zerofeed.sh

To check if everything works as expected start the zerofeed process with

/etc/init.d/zerofeed start

Check with ps whether the script is running:

root@OpenWrt:~# ps | grep zerofeed
 5175 root      1324 S    {zerofeed.sh} /bin/sh /usr/bin/zerofeed.sh
 5410 root      1308 S    grep zerofeed

The process id and the latest state can be seen in /var/run:

root@OpenWrt:~# ls -l /var/run/zerofeed.*
-rw-r--r--    1 root  root       5 Nov 29 22:41 /var/run/zerofeed.pid
-rw-r--r--    1 root  root      35 Nov 30 08:20 /var/run/zerofeed.state
root@OpenWrt:~# cat /var/run/zerofeed.pid
5175
root@OpenWrt:~# cat /var/run/zerofeed.state
30.11.22,08:22:19,0,302,0,,0,10,50

The meaning of the zerofeed.state content can be seen in the code.

Adaption

Additionally there are some values to tweak the power control process:

• reduce safety margin from inverter by increasing this value
  ABSLIMITOFFSET=0

• threshold to trigger the SOLABSLIMIT decrease
  SMPWRTHRESMIN=10

• threshold to trigger the SOLABSLIMIT increase
  SMPWRTHRESMAX=50

• the minimum solar power (Watt) before starting the power control is now
  calculated based on the provided DTUMAXPWR value from the inverter:
  SOLMINPWR = (3% from DTUMAXPWR) + 10 Watt

These values are estimations and work fine in my environment.

Power control functionality

The following pictures were rendered (with LibreOffice Calc) from debug values during the development phase for understanding the general concept of the zerofeed script. The adapted values and the algorithm have been improved after getting the raw values for these figures.

• SOLPWR = blue (solar power yield)
• SMPWR = red (smart meter power consumption from house/flat)
• SOLLASTLIMIT = yellow (solar limit)

Power control example (more solar power than consumption)

This picture shows a day with good solar power (SOLPWR) yield which has to be limited to the house/flat power consumption (SMPWR). E.g. from 13:00 - 15:00 the solar panels are limited. At 15:30 a relevant power consumer is attached with sets the SOLLASTLIMT value to DTUMAXPWR (disabled limit).

Power control example (low solar power mostly unlimited)

This picture shows a day with low solar power (SOLPWR) yield where the house/flat power consumption (SMPWR) is mostly higher than the solar yield and therefore the SOLLASTLIMT value is set to DTUMAXPWR (disabled limit) for most of the time. From 15:00 to 15:30 the solar power exceeds the SMPWR value and the limiter gets enabled to not feed the public network.

Power control algorithm

Inverter startup phase

The script first waits for SOLMINPWR Watts before it starts to control the solar panel power output. This makes sure that the inverter is working and can process requests to the power limiter. The OpenDTU always answers requests to get the current solar power - but in the case the solar power is zero the inverter is completely shut down and not accessible!
When the inverter switches off and the SOLPWR value becomes zero (e.g. over night) the script gets back to this startup phase.

Initializing/disabling the solar power limiter

When the inverter is up and running the limit is disabled (set to 100%). Usually the persistent power limit value is always 100% at power on time until someone modified this value (with persistence). This script only applies non-persistent power limitations to the inverter.

The power control loop

The 'system power' is measured by the Tasmota smart meter interface and provides the value of the power flow from the public network to your house/flat (where the solar modules are connected too). This value SMPWR is usually a positive value which indicates the current power consumption of your house/flat. When the solar modules produce more energy than your house/flat consumes the SMPWR can become a negative value as the power meter measures your feeding into the public network - which we want to avoid with this script.

We mainly have two triggers to start a power limit control action to maintain a low power consumption between SMPWRTHRESMIN and SMPWRTHRESMAX:

1. SMPWR is less than SMPWRTHRESMIN:
   Concept: Set the power limit for the solar panels to SMPWR + SOLPWR. As SMPWR was assumed to be negative the calculated limit is less than the current solar power output SOLPWR and should lead to a SMPWR value greater then zero. This action is now triggered when SMPWR is less than SMPWRTHRESMIN, therefore the calulated limit results from: SMPWR + SOLPWR - SMPWRTHRESMIN. As the inverter might be conservative and too cautious with the limit the ABSLIMITOFFSET value was introduced to increase the calculated limit. The ABSLIMITOFFSET probably needs to be adjusted in your setup.

2. SMPWR is greater than SMPWRTHRESMAX:
   The SMPWRTHRES* threshold values are used to reduce the power limit control commands to the OpenDTU and the inverter. In the best case the SMPWR value remains between SMPWRTHRESMIN and SMPWRTHRESMAX. When SMPWR gets greater than SMPWRTHRESMAX the solar power limit can be safely increased by SMPWRTHRESMAX. Depending on SMPWR we can increase the solar power limit faster to finally remove the solar power limit. When the solar power limit has been increased up to 100% it remains there until SMPWR becomes less than SMPWRTHRESMIN again to restart the power limit control process.