I'll analyze REN's capital structure and whether hybrid bonds would be appropriate.

## Company Profile
REN is a regulated energy utility (electricity and gas transmission networks) in Portugal. It operates under concession agreements, with assets primarily classified as intangible assets (concession rights) worth ~€4.1 billion.

## Key Financial Characteristics

**Leverage:** 
- Total debt (long-term + current borrowings): €2,334,306K (2023) vs. €2,766,073K (2022)
- Debt/Equity ratio: ~1.54x (2023)
- Total liabilities/equity: ~3.25x
- This is a highly leveraged company, typical of regulated utilities

**Profitability & Cash Flows:**
- Net income: €111.8M (2022), growing from €97.2M (2021)
- Operating cash flows: €613.5M - strong and stable
- EBIT: €239.7M
- Interest coverage (EBIT/Finance costs): ~3.6x

**Regulated Business Model:**
- Stable, predictable cash flows from regulated activities
- Long-term concession assets
- Low business risk profile

## Hybrid Bond Considerations

**Arguments for hybrid bonds:**
1. **Regulated utility with stable cash flows** - ideal candidate for hybrid instruments as rating agencies typically give 50% equity credit
2. **High leverage** - hybrid bonds could improve credit metrics by receiving partial equity treatment
3. **Interest coverage at ~3.6x** - moderate, could benefit from equity credit improvement
4. **Rising interest rate environment** (swap curves jumped significantly in 2022) - hybrids could be expensive but still help maintain credit ratings
5. **Significant capex program** (€201M+ in intangible asset purchases annually) requiring ongoing financing

**Arguments against heavy reliance:**
- Hybrid bonds are more expensive than senior debt
- The company already has substantial debt; 100% hybrid would be unnecessarily expensive
- Credit spread environment (iBoxx EUR Non-Financial IG sub-senior delta of 0.2) shows modest additional cost
- Regulated utilities typically use hybrids as a complement, not replacement, for traditional debt

**Typical utility approach:**
Regulated European utilities commonly use hybrid bonds for approximately 10-25% of their capital structure to optimize rating agency equity credit while managing overall cost of capital. Given REN's high leverage and stable regulated cash flows, a moderate allocation makes sense.

The 25% option aligns with industry practice for regulated utilities that benefit from equity credit but shouldn't over-rely on expensive hybrid instruments.

<answer>25%</answer>