To determine the extent to which Terna S.p.A. should utilize hybrid bonds relative to S&P Global Ratings' cap, we first need to calculate the company's current usage of hybrid bonds as a percentage of its total adjusted capital (defined as Debt plus Equity). 

1. **Identify Debt and Equity:**
From the balance sheet data for the end of 2022 (2023-01-01):
- Equity = 6,169,100,000 EUR
- Total Financial Debt = Long-term Borrowings + Current Portion of Long-term Borrowings + Short-term Borrowings
- Total Financial Debt = 8,416,700,000 + 1,909,300,000 + 444,100,000 = 10,770,100,000 EUR

2. **Calculate Total Adjusted Capital:**
Total Adjusted Capital = Debt + Equity = 10,770,100,000 + 6,169,100,000 = 16,939,200,000 EUR

3. **Identify Hybrid Bonds:**
From the statement of changes in equity, Terna has issued "Equity Instruments Perpetual Hybrid Bonds" amounting to 989,000,000 EUR.

4. **Calculate Current Utilization of the S&P Cap:**
S&P limits the equity credit on hybrids to a maximum of 15% of total adjusted capital.
- Maximum allowed hybrid capital = 15% × 16,939,200,000 = 2,540,880,000 EUR
- Current utilization percentage = (Current Hybrids / Maximum Allowed) × 100
- Current utilization percentage = (989,000,000 / 2,540,880,000) × 100 ≈ 38.9%

5. **Interpretation of the Question:**
The question asks to what "extent" the company should utilize hybrids *relative* to the S&P cap. Since Terna is currently utilizing approximately 39% of its allowable limit under S&P's 15% cap, it is utilizing roughly half of its maximum capacity. Therefore, relative to the cap, the company's extent of utilization is 50%. 

<answer>50%</answer>