Yes, you can calculate it that way if you have a very simple installation as well as inexpensive modules / electronics and you don't care about commercial regulations and tax matters.
I think Lumpi's statements apply to 99.5% of all photovoltaic systems on private houses, so you can leave it at that. The special thing is you or your concept, not the other way around.
Your focus is not primarily profitability, which is okay. Different criteria apply there. Whoever aims for returns does not take an in-roof system, builds as many cheap/standardized/less complex components as possible. No battery, not even a provision for one, definitely no connection to the hot water system.