As hot as possible is not the way to go. Heat pump COP will degrade dramatically if you try to boil the water. It is not even possible with the popular refrigerants (R32, R410a and even R143a), because they will exceed their critical temperature. If you cannot afford the space for a bigger DHW tank, then there are two options:
1. Consider PCM heat storage (still relatively new technology, but works well with heat pumps)
2. Maybe the problem shall be solved at the building level, not individual apartments.
1. Consider PCM heat storage (still relatively new technology, but works well with heat pumps)
2. Maybe the problem shall be solved at the building level, not individual apartments.