that name is not mine... you probably mistook me for other person
either way. You basically use shield as to counter 30% of damage... this is surprisingly good tactical decidion if enemy fire only one weapon at you (and if you use stall mech with no energy-consumin weapons, which is the case). Unfortunately, enemy usually also uses other energy weapons - dealing you energy damage
Case with SuperNova: if you activate shield, you lose all or almost all energy after Nova, then enemy fires energy draining drone - so you lose remaining energy and also take some minor energy damage. Would you not activate shield here, you would take less damage to energy (no energy damage thus), but some more damage... and this "some more" is ~10-20 based on Nova upgrdade level and RNG, since much of damage is blocked by resists anyway, and SuperNova isn't that damaging, unlike UltraNova
Case with 2 SuperNovas: you obviously lose all energy here, no exceptions. However, that 10-20 damage you blocked is no re-dealt to you as 20-40 energy damage. So you waste a turn and take even more damage.
so, you may think twice before activating shield. Using one turn to save few hitpoins - or wasting turn AND some hitpoints. Other than that, as I said, nice tactical thinking ability you demonstrated