To determine the extent to which Acciona SA should utilize hybrid bonds relative to S&P Global Ratings' cap, we must first calculate the maximum amount of equity credit S&P would allow, which is 15% of total adjusted capital (defined as Debt + Equity).

1. **Calculate Equity:**
Using the 2023-01-01 balance sheet data:
Equity = 6,304,000,000 EUR

2. **Calculate Debt:**
We sum the noncurrent and current debt instruments, excluding lease liabilities (as S&P typically evaluates lease liabilities separately from traditional debt when assessing hybrid capacity, focusing on financial debt).
- Noncurrent financial debt (Participaciones Preferentes Obligaciones YOtros Valores Negociables No Corrientes): 3,101,000,000 EUR
- Noncurrent loans (Noncurrent Portion Of Noncurrent Loans Received): 2,624,000,000 EUR
- Current financial debt (Participaciones Preferentes Obligaciones YOtros Valores Negociables Corrientes): 1,139,000,000 EUR
- Current loans (Current Loans Received And Current Portion Of Noncurrent Loans Received): 553,000,000 EUR
Total Financial Debt = 3,101,000,000 + 2,624,000,000 + 1,139,000,000 + 553,000,000 = 7,417,000,000 EUR

3. **Calculate Total Adjusted Capital:**
Total Adjusted Capital = Debt + Equity = 7,417,000,000 + 6,304,000,000 = 13,721,000,000 EUR

4. **Calculate S&P's 15% Cap on Hybrid Equity Credit:**
15% of Total Adjusted Capital = 13,721,000,000 * 0.15 = 2,058,150,000 EUR

5. **Assess Optimal Utilization:**
Acciona is a capital-intensive infrastructure and renewable energy company that heavily relies on debt financing to fund its large project pipeline (as evidenced by its significant capex and rising debt levels). Maximizing the use of hybrid bonds is highly advantageous for such firms because S&P grants "intermediate" equity credit (usually 50%) to hybrids, effectively doubling the subordinated capital raised per unit of S&P equity credit. By utilizing 100% of the allowable 15% cap, Acciona can optimally lower its leverage ratio and strengthen its balance sheet to support its aggressive growth without suffering a downgrade. Because it is far below the cap currently and operates in an industry where balance sheet capacity is a critical competitive factor, it should aim to fully utilize this capacity.

<answer>100%</answer>