PRC_RESID defines the residual existing capacity, by period. With PRC_RESID you can define the phase-out of capacity any way you want, for example, as a constant capacity from 2015 to 2040. The lifetime specified (NCAP_TLIFE) does not affect at all the phase-out of PRC_RESID capacites (unless you define only a single point). If you define the existing capacities by PRC_RESID, and the capacity gets retired gradually till the end of its life time, why do you then define them that way, if you don't want them that way?
NCAP_PASTI is the standard way of defining past investments into new capacity. The past installed capacities work the same way as newly installed capacities: The capacity remains constant until the end of their lifetime.
BTW: I looked at the results from your model, and found that the stack capacity was indeed exactly equal to the electrolyser capacity, in all periods, although the stack lifetime is only 7 years.
NCAP_PASTI is the standard way of defining past investments into new capacity. The past installed capacities work the same way as newly installed capacities: The capacity remains constant until the end of their lifetime.
BTW: I looked at the results from your model, and found that the stack capacity was indeed exactly equal to the electrolyser capacity, in all periods, although the stack lifetime is only 7 years.