This guide explains how to use the Shelly Pro 3EM to detect your energy surplus and automatically switch on consumers – such as a heating rod – in multiple stages.
The logic is based on scenes that evaluate measured power values and switch the outputs of the Shelly Pro 3 accordingly.
Requirements
- Shelly Pro 3EM for measuring grid power (PV self-consumption or grid feed-in)
- Shelly Pro 3 (used here to control a 3-phase heating rod*, with 1000 W per phase in this example)
- Shelly Smart Control App or browser version (https://control.shelly.cloud) to set up the scenes
Basic Concept
The Shelly Pro 3EM measures the current active power (negative = feeding into the grid).
Depending on the available surplus, a specific number of heating stages will be activated:
More than 1500 W surplus → Stage 1 ON
More than 3000 W surplus → Stage 2 ON
More than 4500 W surplus → Stage 3 ON
Example Wiring: Heating Rod on Shelly Pro 3
Creating Scenes
You will create one ON and one OFF scene per stage, resulting in six scenes in total:
Scene 1 – Phase 1 ON
Wenn:
- Total power: is less than -1500 W
- Trigger: Once
- Condition: valid 2 minutes
And:
- Condition: L1 off
- Condition: L2 off
- Condition: L3 off
Then:
- Switch L1 on.
Scene 2 – Phase 2 ON
Wenn:
- Total power: is less than -1500 W
- Trigger: Once
- Condition: valid 2 minutes
And:
- Condition: L1 on
- Condition: L2 off
- Condition: L3 off
Then:
- Switch L2 on.
Scene 3 – Phase 3 ON
Wenn:
- Total power: is less than -1500 W
- Trigger: Once
- Condition: valid 2 minutes
And:
- Condition: L1 on
- Condition: L2 on
- Condition: L3 off
Then:
- Switch L3 on.
Scene 4 – Phase 3 OFF
Wenn:
- Total power: is less than -1500 W
- Trigger: Once
- Condition: valid 2 minutes
And:
- Condition: L1 on
- Condition: L2 on
- Condition: L3 on
Then:
- Switch L3 off.
Scene 5 – Phase 2 OFF
Wenn:
- Total power: is less than -1500 W
- Trigger: Once
- Condition: valid 2 minutes
And:
- Condition: L1 on
- Condition: L2 on
- Condition: L3 off
Then:
- Switch L2 off.
Scene 6 – Phase 1 OFF
Wenn:
- Total power: is less than -1500 W
- Trigger: Once
- Condition: valid 2 minutes
And:
- Condition: L1 off
- Condition: L2 off
- Condition: L3 off
Then:
- Switch L1 off.
Optimization Tips
Use hysteresis between ON and OFF thresholds (e.g., turn ON at –2000 W, OFF at –1800 W) to avoid rapid switching.
You can set the delay time in minutes to prevent frequent switching during brief shading or passing clouds.
Use time-based restrictions (e.g., active only during daylight hours) to better align with your energy strategy.
For advanced automation (e.g., prioritization or PV forecasting), you may want to integrate external control systems or MQTT.
* Please make sure to follow the technical specifications of your heating element.