Add Discharged energy [W.h] as variable

[TomTranter]

Summary
Add Discharged energy [W.h] as variable

Motivation
Like discharged capacity but using current * voltage. Useful for performance metrics and minimal overhead

[valentinsulzer]

Took a look at how you started this. You don't need to create a new pybamm.Variable for discharged energy, just calculate it as a post-processing step

[TomTranter]

Ok - is there an official way to do this? Or you just mean manually with the entries

[valentinsulzer]

add it to this function somewhere

PyBaMM/pybamm/models/full_battery_models/base_battery_model.py

Line 828 in 51ee22a

def set_voltage_variables(self):

[valentinsulzer]

My bad, you do need an additional variable