Short answer
Keep project economics separate from financing. Compare certain debt cost with uncertain after-tax return on retained capital and preserve liquidity reserves.
Important variables
- Investment after support
- Useful energy, efficiency and degradation
- Energy prices and tariff
- Horizon and discount rate
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Worked example
A €20,000 loan at 5% is not a 5% surcharge on the investment but an amortisation schedule. Only interest and fees are financing cost.
Break-even: What changes the result?
Test the main driver as a cautious, central and optimistic range. Also check whether the ranking reverses at a crossover or remains robust across the range.
Common mistakes
- Treating subsidy or tariff as certain
- Omitting losses and degradation
- Confusing simple payback with return
Terms in this guide
Sources & assumptions
- KfW Bankengruppe — Heizungsförderung ab 21. Juli 2026 (2026-08-17)
- RATIOXA — Methodology and formulas (2026-08-17)
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