Enel should utilize hybrid bonds to a **high, but not maximum, extent** over the next 18 months: **11.25% of total adjusted capital**.

Key considerations:

- **Already material hybrid stock:** Enel already has **€5.567 billion** of perpetual hybrid bonds classified in equity at year-end 2022. This means hybrids are already part of the capital structure and the company has market precedent and investor familiarity.
- **Leverage pressure is significant:** Total borrowings increased materially:
  - Long-term borrowings rose from **€54.5 billion to €68.2 billion**
  - Short-term borrowings rose from **€13.3 billion to €18.4 billion**
  - Total liabilities increased from **€164.6 billion to €177.5 billion**
  - Equity was broadly flat/slightly down at **€42.1 billion**
  
  This points to a more leveraged balance sheet and reduced rating headroom.
- **High investment and negative free cash flow:** Operating cash flow was **€8.7 billion**, while investing cash outflow was **€13.6 billion**, driven by large capex:
  - PPE purchases: **€11.3 billion**
  - Intangible purchases: **€2.0 billion**
  - Other long-term asset purchases: **€1.3 billion**
  
  This indicates structurally high capex needs, typical of a large utility undergoing energy transition investment.
- **Heavy shareholder distributions despite weaker earnings:** Dividends paid were about **€4.9 billion**, while profit attributable to owners fell to **€1.7 billion** from **€3.2 billion**. The dividend burden adds to financing needs.
- **Debt-funded funding gap:** Financing cash flow was strongly positive at **€7.4 billion**, with proceeds from borrowings of **€22.4 billion** versus repayments of **€9.4 billion**, confirming reliance on debt markets.
- **Business risk profile remains supportive:** Enel is a very large, diversified utility operating across Europe and Latin America. Its regulated and essential-service activities support investment-grade credit quality. However, the group also has exposure to unregulated power, commodity volatility, and political/regulatory complexity.
- **Hybrid benefit is meaningful:** Additional hybrids would likely receive partial equity credit from S&P, helping adjusted debt metrics and preserving rating flexibility without immediate common equity dilution.
- **But not enough justification for the full 15% cap:** While leverage and capex pressure are high, the case is not clearly “transformational distress” or an imminent downgrade scenario requiring maximum hybrid support. Also, market rates rose sharply in 2022, so new hybrid coupons would likely be materially above Enel’s legacy debt cost.
- **Issuance capacity constraint:** With a stated practical maximum of **€3 billion per year**, Enel could add up to roughly **€4.5 billion** over 18 months. Combined with the existing **€5.6 billion**, this would bring hybrid capital to around **€10 billion**, plausibly near the **11.25%** option depending on total adjusted capital and S&P equity-credit treatment.

Overall, Enel has **high capex intensity, rising leverage, significant refinancing/funding needs, and an existing hybrid capital structure**, making additional hybrid issuance advisable. However, because funding pressure is not clearly extreme enough to require the S&P maximum and because hybrid costs have risen, the most balanced recommendation is **11.25%**, not 15%.

<answer>11.25%</answer>