Hi Shelly Team & Forum members,
the shelly app is missing a subtraction/addition helper function for energy scenes. I have the following use case (problem):
- I have the Shelly Pro3EM to measure the negative grid power of my solar energy plant (energy I sent back to my energy supplier but want to use it by myself)
- I want to buy the Shelly Dimmer 0-10V (as input signal for a heating controller - industry standard 0-10V controls)
- I have the Shelly PM connected to the Heater plug for my warm water boiler to measure the heater power consumption.
Problem: I can add a scene with an action if 3EM has a certain value. Example: If the negative grid power is smaller than -500W then put the dimmer to 50%. But this does not consider that the dimmer (or heater ShellyPM) is already ON with e.g. 30% = 300W.
Solution/Required Scene (addition/subtraction - new HELPER value function):
Part1: Helper1 [W] (in my case new Heater/Dimmer value) = Shelly pro3EM [W] - ShellyPM [W]
Result: Helper1 = -500W - 300W = -800W
Part2: Scene: IF Helper1 [W] =< -800W then set Dimmer to 80%
I believe this small Helper function would bring you a lot of new paying customers for the new app. I know this could also be done with home assistant but more complex (I am not HA expert) 
