To determine the appropriate extent to which Enel SpA should utilize hybrid bonds, we analyze the provided financial data for the fiscal year ended December 31, 2022:

1.  **Capital Structure and Leverage:**
    *   **Equity (2023-01-01):** 42,082,000,000 EUR
    *   **Long-term Borrowings (2023-01-01):** 68,191,000,000 EUR
    *   **Short-term Borrowings (2023-01-01):** 18,392,000,000 EUR
    *   **Current Portion of Long-term Borrowings:** 2,835,000,000 EUR
    *   Total Debt is significantly high relative to Equity. The company has substantial refinancing and liquidity needs.

2.  **Financial Performance and Capex:**
    *   **Profit from Operating Activities:** 11,193,000,000 EUR.
    *   **Purchase of Property, Plant and Equipment:** 11,281,000,000 EUR (investing activities).
    *   Enel is a utility company with intense capital expenditure requirements for energy transition. The company’s "Profit Loss" decreased from 3,857,000,000 EUR in 2021 to 2,920,000,000 EUR in 2022, and it is managing large capital programs.

3.  **Hybrid Rationale:**
    *   The company has existing "Equity Instruments Perpetual Hybrid Bonds" of 5,567,000,000 EUR.
    *   Total Adjusted Capital (Equity + Adjusted Debt) is roughly 140B-150B EUR. A 15% cap would be approximately 21-22B EUR.
    *   The current interest rate environment (Swap curves for 5Y/7Y/10Y have moved from negative/near-zero in 2021 to ~1.7%-1.9% in 2022) indicates that debt costs are rising.
    *   Enel faces significant pressure due to the energy transition and heavy investment cycles. Maintaining an investment-grade rating is critical for such a utility. The company is actively managing its capital structure and has a history of using hybrid instruments.

4.  **Conclusion:**
    Given the high capital intensity, the pressure on leverage, the transition risk, and the need to preserve the rating while funding significant investment, a moderate-to-high allocation to hybrids is warranted to support the credit profile without purely relying on senior debt. Considering the 3 billion EUR annual issuance limit and the necessity to manage leverage strategically, 7.5% of total adjusted capital represents a balanced approach that provides meaningful support to financial metrics while managing the cost of capital in a rising interest rate environment.

<answer>7.5%</answer>