To determine the appropriate reliance on hybrid bonds in the capital structure for Enel SpA, we evaluate the company's financial health, cost of capital, and prevailing market conditions in 2022:

1.  **Financial Position:** Enel has a high debt burden. "Longterm Borrowings" stood at 68.19 billion EUR in 2023, up from 54.5 billion EUR in 2022. "Shortterm Borrowings" also increased significantly to 18.39 billion EUR. Total liabilities reached 177.5 billion EUR against 42 billion EUR in equity.
2.  **Cost of Funding:** The market data shows a sharp increase in the swap curve for 2022 (e.g., the 10Y swap curve moved from an average of 0.053 in 2021 to 1.927 in 2022). Rising interest rates make traditional debt more expensive and increase the risk profile of high-leverage companies.
3.  **Capital Structure Utility:** Hybrid bonds (perpetual instruments) serve as a critical tool for companies with high debt-to-equity ratios to maintain credit ratings by providing "equity-like" features while managing leverage. However, relying on them too heavily (e.g., 75% or 100%) would be unsustainable due to the "Coupon Paid Hybrid Bonds" (123 million EUR in 2022) and the potential for credit rating agency limits on how much hybrid capital counts as equity.
4.  **Strategic Balance:** With equity at 42 billion EUR and total liabilities/debt rising rapidly, a moderate reliance on hybrid instruments—to bridge the gap between debt and pure equity—is prudent. A 25% reliance on hybrid bonds within the capital structure strategy provides sufficient flexibility to manage the rising interest rate environment without over-leveraging the hybrid market or diluting shareholders excessively. A 0% reliance ignores the benefits of hybrid instruments in managing the current interest rate volatility observed in the swap curves, while anything above 25% significantly increases the risk of coupon payment sensitivity during liquidity crunches.

<answer>25%</answer>