Helper for shelly/meter selfconsumption

Dear Forums,I am asking for help because I am not shre how to add a helper to show the consumption of various metering devices eg. shellies which is based on the estimated consumtion and availability of the device.
To make it somewhat clearer, lets say i have 2 Shellies that consume 5W each and 2 Accesspoints which consume about 10W each - From their availability I know they are powered on, so within n hour it’d be 30W.
So I’d like to add a helper that represents their powerconsumtion, that may be not 100% accureate but good enougth for me.
This helper may be integrated into the energy dashboard, that would reduce the amount of non metered consumption and help to monitor the total consumption.

Thanks in advance for any Ideas.
c909