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

First, let me identify the relevant data from ENEL's financial statements:

**Hybrid Bonds in Equity:**
- 2022-01-01: 5,567,000,000 EUR (Equity Instruments Perpetual Hybrid Bonds Member)
- 2021-01-01: 2,386,000,000 EUR

**Total Equity:**
- 2023-01-01: 42,082,000,000 EUR
- 2022-01-01: 42,342,000,000 EUR
- 2021-01-01: 42,357,000,000 EUR

**Total Debt (Liabilities):**
- 2023-01-01: 177,536,000,000 EUR
- 2022-01-01: 164,598,000,000 EUR

**Total Adjusted Capital = Debt + Equity:**
- 2023-01-01: 177,536 + 42,082 = 219,618,000,000 EUR
- 2022-01-01: 164,598 + 42,342 = 206,940,000,000 EUR

**Current Hybrid Bonds as % of Total Adjusted Capital:**
- 2022: 5,567 / 206,940 = 2.69%
- 2023: 5,567 / 219,618 = 2.54% (assuming same hybrid amount, or we need to check if changed)

Wait - let me check 2023 hybrid bonds. Looking at the equity components for 2023-01-01:
- Equity Instruments Perpetual Hybrid Bonds Member: 5,567,000,000 EUR

So in 2022 (year-end 2022, which is 2023-01-01), hybrid bonds were 5,567/219,618 = 2.54% of total adjusted capital.

This is well below the 15% cap.

**Analysis of whether to increase hybrid bond usage:**

1. **Current utilization**: ENEL is only using ~2.5% of the 15% cap, so there's significant headroom.

2. **Financial benefits of hybrid bonds:**
   - Hybrid bonds are treated as equity by rating agencies (up to the cap), improving leverage ratios
   - They typically have lower cost than equity (no dilution, tax-deductible coupons in many cases)
   - They provide long-term stable financing

3. **ENEL's financial position:**
   - Significant debt load: 177.5 billion EUR
   - Equity: 42.1 billion EUR
   - Debt/Equity ratio: ~4.2x (quite high)
   - The company is capital-intensive (utility sector)

4. **Market conditions in 2022:**
   - Interest rates rose significantly (5Y swap from -0.264% in 2021 to 1.726% in 2022)
   - Corporate bond spreads widened (iBoxx non-financial IG from 1.298% to 2.295%)
   - Higher rate environment makes fixed-rate hybrid bonds more attractive for issuers (locking in rates)

5. **Strategic considerations:**
   - ENEL has significant capex needs (energy transition, grid investments)
   - The company needs to maintain investment grade ratings
   - Hybrid bonds can diversify funding sources

6. **Risk factors:**
   - Higher interest rate environment increases cost of new hybrids
   - But equity is also expensive (dividend yield, dilution)
   - The 15% cap is a hard limit from S&P

**Optimal utilization assessment:**

Given:
- ENEL is significantly under-utilizing the hybrid capacity (2.5% vs 15%)
- The company has high leverage and would benefit from equity-like treatment
- The energy transition requires massive capital expenditure
- Hybrid bonds are cheaper than equity and improve credit metrics

However, in 2022:
- Rates rose dramatically, making new issuance expensive
- ENEL already has high absolute debt levels
- The company may want to preserve capacity for future stress periods

A reasonable strategy would be to increase hybrid usage toward the cap, but not necessarily max it out immediately. Given the rising rate environment of 2022, some increase makes sense to lock in long-term financing and improve credit metrics, but going to 100% of the cap might be aggressive.

Looking at the progression: ENEL increased hybrids from 2,386M to 5,567M (2021 to 2022), showing willingness to use this instrument. The 2022 rate environment suggests caution, but the structural benefits remain.

For a utility with high capex needs, stable cash flows, and need for investment grade ratings, utilizing a meaningful portion of the hybrid capacity (but not all) seems prudent. **50%** of the cap (i.e., ~7.5% of adjusted capital in hybrids) would be a balanced approach that:
- Meaningfully improves credit metrics vs. current position
- Leaves headroom for future stress or acquisitions
- Doesn't over-rely on this instrument in a rising rate environment
- Provides diversification of funding sources

This is significantly more than current usage but leaves buffer below the cap.

<answer>50%</answer>