Let’s reason through this step-by-step.

**1. Nature of the business**  
ERG S.p.A. is in the renewable energy sector, which is capital-intensive but generates stable, predictable cash flows once assets are operational. This makes it a good candidate for some degree of leverage, including hybrid instruments, since hybrids can improve credit metrics while preserving equity.

**2. Profitability and cash flow stability**  
- Revenue grew from €601m to €714m.  
- EBITDA went from €397m to €499m.  
- Operating cash flow from continuing operations improved significantly from –€41m to €503m.  
This upward trend in cash generation supports fixed obligations like hybrid coupons.

**3. Existing leverage**  
Total non-current financial liabilities remain substantial (~€2.1bn in borrowings and bonds). However, total equity is around €2.05bn, so the company already uses significant debt. Adding too much hybrid debt could increase financial risk if interest rates rise.

**4. Interest rate environment**  
Swap rates shifted from negative in 2020–2021 to around 1.7%–1.9% in 2022. Corporate bond yields also rose. This means the cost of issuing hybrids is now higher, making 100% reliance unattractive.  

**5. Hybrids as part of the mix**  
Hybrid bonds (treated partly as equity by rating agencies) could help ERG maintain its credit rating while funding growth. A moderate use (e.g., 25%) would balance the benefit of lower reported leverage with manageable additional cost, especially given the cash flow growth.  

**6. Why not 0% or >50%?**  
- 0% ignores the benefit hybrids can bring to credit metrics in a growth phase.  
- 50%+ would be too aggressive, given rising rates and the already large debt load.

**Conclusion:**  
A moderate reliance on hybrids (25%) fits best—enough to support expansion while keeping financial risk controlled.

<answer>25%</answer>