I need to analyze whether REN should utilize hybrid bonds up to S&P's 15% cap of total adjusted capital.

First, let me understand the company's capital structure and financial position.

**Key Financial Data (2023-01-01 / year 2022):**
- Equity: 1,517,534,000 EUR
- Long-term borrowings: 1,695,362,000 EUR
- Current borrowings: 638,944,000 EUR
- Total debt: 2,334,306,000 EUR
- Total adjusted capital (debt + equity): 3,851,840,000 EUR

**S&P's 15% cap on hybrid equity credit:**
- Maximum hybrid equity credit allowed: 15% × 3,851,840,000 = 577,776,000 EUR

**Analyzing REN's suitability for hybrid bonds:**

1. **Credit Profile and Rating Considerations:**
   - REN is a regulated utility (electricity and gas transmission networks in Portugal)
   - Regulated utilities typically have stable, predictable cash flows
   - The company has significant intangible assets (4,077,471,000 EUR), likely representing concession rights
   - This is typical for infrastructure/utilities with regulated asset bases

2. **Current Leverage Position:**
   - Debt/Total capital: 2,334,306,000 / 3,851,840,000 = 60.6%
   - This is moderate for a regulated utility but has room for optimization

3. **Interest Rate Environment (2022 data):**
   - Swap rates turned significantly positive in 2022 (5Y: 1.726%, 7Y: 1.806%, 10Y: 1.927%)
   - Corporate bond spreads: iShares Core Euro Corp Bond at 1.085%, sub-senior IG at 2.295%
   - Rising rate environment makes fixed-rate instruments more attractive to lock in

4. **Hybrid Bond Attractiveness:**
   - Hybrid bonds are subordinated, perpetual or long-dated instruments with coupon deferral features
   - They receive partial equity credit from rating agencies (typically 50-100% equity treatment depending on structure)
   - S&P caps this at 15% of total adjusted capital

5. **REN's Specific Considerations:**
   - **Stable cash flows**: Regulated utility with predictable revenue streams - good for hybrid coupon service
   - **Existing leverage**: At 60.6% debt/capital, adding hybrid equity credit would improve optics
   - **Intangible-heavy balance sheet**: Large concession intangibles mean traditional debt capacity may be constrained by tangible asset coverage
   - **Dividend policy**: Company pays dividends (102,150,000 EUR in 2022, 113,426,000 in 2021), so coupon deferral on hybrids would need to be structured carefully

6. **Strategic Value of Hybrids for REN:**
   - Improve debt/equity ratio by getting equity credit
   - Diversify funding sources
   - Potentially lower overall cost of capital if equity credit is achieved
   - Match-fund long-duration intangible/concession assets

7. **Constraints and Risks:**
   - S&P's 15% cap is a hard limit
   - Full utilization (100% of cap) would mean hybrids = 577,776,000 EUR
   - Need to ensure not to over-leverage or create refinancing risk
   - Coupon deferral features may conflict with dividend policy if not structured with "look-through" provisions

8. **Market Context:**
   - 2022 was a rising rate environment - hybrid issuance would be more expensive than historical lows
   - However, spreads were widening, potentially making the equity credit value more worthwhile

**Assessment:**

REN is a classic hybrid bond candidate:
- Regulated utility with stable cash flows
- Need for equity-like financing given intangible-heavy balance sheet
- Moderate leverage that could benefit from equity credit optimization
- Long-term assets that match well with perpetual/long-dated hybrids

However, I need to consider:
- Should they use the full 15% cap or be more conservative?
- The 15% cap is a maximum, not a target
- Utility sector typically uses 50-100% of available hybrid capacity
- Full utilization (100%) is common for investment-grade utilities with strong regulatory frameworks

Given:
- Strong regulatory environment (Portuguese utility)
- Stable cash flow profile
- Need to optimize capital structure with significant intangibles
- Investment-grade characteristics typical for hybrid-eligible issuers
- The 15% cap is designed as a maximum safety limit, and utilities with REN's profile typically can sustain full utilization

The answer should be **100%** - regulated utilities with stable cash flows, significant intangible assets, and moderate leverage are ideal candidates for maximizing hybrid equity credit within rating agency caps. The 15% limit is designed precisely to constrain safe issuers like REN, and full utilization optimizes cost of capital while respecting rating agency boundaries.

<answer>100%</answer>