Can I fudge the numbers to make it look better?
Nope.
The calculation is not entirely complete, for example, the VAT for photovoltaic and storage will still be refunded (provided there are separate invoices for this and it is not included in the total house construction cost), but in KFW 40 the heating load also decreases, which results in lower consumption, possibly requires a smaller heat generator (probably not in your example), and with a planned ground-source heat pump the drilling depth is reduced... on the other hand, there are expenses for operating the photovoltaic system (tax issues, maintenance, risk, but also income from feed-in tariffs or savings through self-consumption). Whether the photovoltaic system is correctly dimensioned to match the storage is also questionable. There is a lot of nonsense being done in that regard too.
I think you don’t even need to make this kind of calculation with general contractors/prime contractors because the factor "fluffing up" and/or "I don’t want/can’t" destroys any chance of profitability. Ultimately, you usually don’t have control over the individual components. It might be different when building with an architect, but that’s just my feeling.
One should ask who got cozy with whom to anchor this district heating crap there. That really rubs me the wrong way. But on paper, it’s certainly especially "green".
