I'll analyze Terna S.p.A.'s capital structure and the appropriateness of hybrid bonds.

**Current Capital Structure Analysis:**

1. **Equity (end 2022):** €6,169.1M, of which €989M is from hybrid/perpetual bonds issued during 2022 (visible in the equity movements as "Equity Instruments Perpetual Hybrid Bonds")

2. **Total Debt:** 
   - Long-term borrowings: €8,416.7M
   - Short-term borrowings: €444.1M
   - Current portion of long-term: €1,909.3M
   - Total debt ≈ €10,770.1M

3. **Total Assets:** €22,802.9M

4. **The hybrid bond (€989M) represents roughly 16% of total equity** and about 5.8% of total capital (debt + equity ≈ €16,939M)

**Key Considerations:**

1. **Regulated utility nature:** Terna is Italy's transmission system operator - a regulated, stable-cash-flow business. This supports moderate use of hybrid instruments as rating agencies typically give 50% equity credit to hybrids.

2. **Already issued hybrids:** The company issued €989M in hybrid bonds in 2022, showing management already views hybrids as appropriate. The coupon payments are visible (€21.1M "Coupon Payable To Holders Of Hybrid Bonds").

3. **Interest rate environment:** Swap rates rose significantly in 2022 (5Y from -0.264% to 1.726%), making fixed-rate hybrid issuance more expensive. Corporate bond spreads also widened.

4. **Leverage profile:** With total debt ~€10.8B against equity of ~€6.2B (including hybrids), the debt-to-equity ratio is about 1.75x. The hybrid issuance helped improve this ratio.

5. **Proportionality:** The €989M hybrid represents about 9.2% of total debt+equity financing. For a regulated utility, hybrids typically constitute a modest portion of the capital structure - usually 10-20% of total capital at most, to optimize rating agency equity credit without over-reliance on a single instrument class.

6. **Rating considerations:** Rating agencies typically cap equity credit for hybrids at around 15-20% of total capital. Going beyond this reduces the benefit.

**Assessment of options:**
- 0%: Too low - the company has already successfully deployed hybrids
- 25%: This represents a moderate reliance, consistent with the current ~16% of equity and typical utility practice of having hybrids as a meaningful but not dominant part of the capital mix
- 50%: Too high - would expose the company to refinancing risk and reduce the equity credit benefit
- 75-100%: Far too aggressive for a regulated utility

The current hybrid allocation (~€989M out of ~€6.2B equity, or ~16%) suggests a moderate approach. A 25% target for hybrid bonds as a share of the capital structure is reasonable and aligns with utility sector best practices.

<answer>25%</answer>