This project uses a Shelly Pro 3EM Smart Meter to measure the PV "Balkonkraftwerk" overproduction. An ESP8266 fetches the data. The ESP8266 sends the measured power via serial interface to an Arduino. The Arduino then controls a RobotDyn AC Dimmer. The output of the AC Dimmer can then be used to power e.g. an electro heater.
In the first version of this project I only used an ESP32 to do all the work. The system crashed on a regular base. It seems like the AC Dimmer library and the Ethernet stuff doesn`t work all to well together. So I used a board which contains both Arduino & ESP8266 which I had used in other projects already. The ESP does the networking stuff and the Arduino has a simple & therefore safe regulation task.
I thought about building my own dimmer but then I discovered the RobotDyn AC Dimmer Modules. They are cheaper than building it yourself and there is a library already available on Github. So I decided to "stand on the shoulders of Giants instead of reinventing the wheel" 😉
- Select & Buy Hardware
- Connect the ESP to the Shelly and fetch data
- Connect the AC Dimmer to the ESP and check functionality
- Programm the control software to use only the overproduction
- Connect everything together
- Tests
- Switched to new architecture -> ESP8266 & Arduino combi board
- Final Tests
- Add a housing
- Optional: Add a measurement method and store the data
A 1.5 kW electro heater was the first test device that I want to power with my overproduction. As I am working on this it is winter and warm air is needed. In summer one can think about replacing the electro air heater with a heating blade for a water boiler. (This is more complicated to install because I have no experiences with plumbing work.)
While testing the air heater I realized that I need min. 400W so that the fan starts spinning. I decided to decouple the fan from the heating resistors. So now I have to plugs: One only for the fan and one for the rest of the device.
The electric heater consists of:
- Fan: Min. 20 W
- Resistors: Stage 1: Max: 700W, Stage 2: Max: 1500 W
So the software should start the fan at 20 W overproduction and then the AC dimm can start the heating resistors. Perhaps a threshold of a minimum (10 W) feed-in would be useful to avoid electricity costs at all. The switch of the electric heater shall be set to On and only Stage 1 shall be activated.
I did already a Shelly data readout in my Shelly3EM_to_InfluxDB Repo, see this file. Funny to see my progress since these beginnings. The old code definitifely needs a rework...
To get the data from Shelly device simply use the rpc endpoint with a http client: http://shelly_ip_address/rpc/EM.GetStatus?id=0
You will get a response in json format. This needs to be unpacked to get the raw values.
The regulation loop is very simple and only based on thresholds. The Shelly sends updated values every ~500msec. So the regulation loop is adapted to this speed.
It turns out that the regulation works very well and the system is always around ~-10 W.
Debugging via the serial console is controlled by Makros:
- Debug Off:
#undef DEBUG_MODE - Debug On:
#define DEBUG_MODE
You will get a serial report with the current state & output, e.g. for the Arduino:
