Photovoltaic system or geothermal energy

Hello, The property is a multi-family house with 4x residential units. Kfw 55 is achieved through the building envelope plus an [LWWP]. Additionally, a controlled ventilation system is planned for each residential unit. However, this is not a "must have." The question now is: - To stick with the air-water heat pump, and additionally install a photovoltaic system for electricity generation. - Or to forego that and use geothermal energy for heating through deep drilling? What do you think makes more sense now in terms of costs and/or KFW subsidies?

None of the additional measures will improve the Kfw standard if 55 is already achieved.

If you want to use the photovoltaic system, my question would be about the usage scenario. Should the system feed in completely or should the electricity be sold to the tenants? Are you aware of the effort involved?
Basically, a photovoltaic system could yield a return in both scenarios.

Geothermal energy ultimately reduces the tenants' consumption costs or ancillary costs. You would have to recoup the additional investment through a higher basic rent.

I wouldn't do anything at all.

Hello, for a pure rental property, I would not have even considered Kfw55, but rather kept it at the Energy Saving Ordinance standard or Kfw 70. Best regards.