I need to analyze whether Terna S.p.A. should utilize hybrid bonds relative to S&P's 15% cap on equity credit for hybrids as a percentage of total adjusted capital (debt + equity).

**Key observations:**

1. **Terna already issued hybrid bonds in 2022:** The equity statement shows "Equity Instruments Perpetual Hybrid Bonds" of €989 million issued during the 2022-01-01 to 2023-01-01 period, appearing as a new equity component ("Capital Instruments Bonds Hybrid Perpetual") at €989 million as of 2023-01-01.

2. **Calculate total adjusted capital:**
   - Total Debt: Long-term borrowings (€8,416.7M) + Short-term borrowings (€444.1M) + Current portion of long-term borrowings (€1,909.3M) = €10,770.1M
   - Total Equity: €6,169.1M (which includes the €989M hybrid)
   - Total Adjusted Capital = Debt + Equity = €10,770.1M + €6,169.1M = €16,939.2M

3. **S&P's 15% cap on equity credit from hybrids:**
   - Maximum hybrid equity credit = 15% × €16,939.2M = €2,540.9M
   - Current hybrid amount = €989M
   - Utilization = €989M / €2,540.9M ≈ 38.9%

4. **Company characteristics favoring hybrid usage:**
   - Terna is a regulated utility (Italian electricity transmission grid operator) with stable, predictable cash flows
   - Strong operating performance: Revenue grew from €2,534.5M to €2,898.1M (+14.3%)
   - Solid profitability: Net income of €857.7M
   - Good cash flow generation: Operating cash flows of €2,323.7M
   - Regulated business model provides revenue visibility and stability
   - Investment-grade characteristics with significant capex needs (€1,492.3M in PP&E purchases)

5. **Interest rate environment:** Rising rates in 2022 (swap curves moved significantly higher), making the timing of the hybrid issuance relevant. The company locked in hybrid financing which provides equity credit.

6. **Capital structure considerations:**
   - Debt-to-equity ratio is relatively high (~1.75x), typical for regulated utilities
   - The hybrid helps improve equity metrics without diluting shareholders
   - The company has significant investment needs for grid expansion

7. **Current utilization is ~39% of the cap.** The company has already demonstrated willingness to use hybrids. For a regulated utility with predictable cash flows, stable revenues, and significant capital expenditure needs, hybrids are an efficient financing tool.

8. **Should they use more?** Given the rising rate environment, the already meaningful leverage, and the significant investment program, there's a reasonable case for moderate-to-significant utilization. However, the company is already at ~39% utilization, and going to full utilization would mean issuing an additional ~€1.55B in hybrids, which would be substantial. The coupon costs on hybrids (€21.1M shown) are manageable.

Given that:
- The company already actively uses hybrids (~39% of cap)
- It's a stable regulated utility well-suited for hybrid financing
- It has significant ongoing capex needs
- The capital structure benefits from equity credit
- But there are diminishing returns and cost considerations at very high utilization levels

A utilization of around 50% of the cap seems most appropriate - the company is already partway there and could modestly increase, but full utilization would be excessive given cost considerations and the already meaningful hybrid component.

<answer>50%</answer>