This is the way.

I’m sure the original comment had incorrect units as used, but this explanation that cumulative units “can’t peak” seems wrong.

If you consider the total stored energy (Wh) over time of a solar-battery system under load, there certainly will be peaks or, in other words, maximal excess capacity of the system.

So no, it’s not impossible to define a unit of Whp as such. “Cumulative” and “momentary” values are not exclusive and also do not have any bearing on whether a function of such values has maxima and minima.