To determine the appropriate extent to which TenneT Holding B.V. should rely on hybrid bonds in its capital structure, we must analyze the company's financial health, the cost of capital in the prevailing market environment, and the strategic role of hybrid instruments for a regulated utility.

**1. Analysis of Current Capital Structure and Financial Health:**
*   **Equity Position:** As of 2023-01-01, Total Equity is €7,713 million. This includes €2,125 million in Hybrid Capital.
*   **Hybrid Ratio:** The current proportion of Hybrid Capital to Total Equity is $2,125 / 7,713 \approx 27.5\%$. The proportion of Hybrid Capital to Total Assets (€38,509 million) is $2,125 / 38,509 \approx 5.5\%$.
*   **Leverage:** Long-term borrowings are €19,006 million. The Debt-to-Equity ratio is high, typical for capital-intensive infrastructure companies.
*   **Profitability:** The company reported a net loss of €879 million for the year ending 2023-01-01. However, this loss is largely driven by non-cash items and specific accounting treatments (e.g., remeasurements of defined benefit plans, huge increases in operating expenses likely due to inflation/energy costs which are often pass-through in regulated environments). The core business generates significant revenue (€8,299 million) and operating cash flow (€1,196 million from operations).
*   **Credit Quality:** As a state-owned (Dutch State) transmission system operator, TenneT has a very strong implicit sovereign guarantee and stable cash flows, supporting a high credit rating.

**2. Market Environment and Cost of Capital (2022 Data):**
*   **Interest Rates:** The swap curves indicate a sharp rise in interest rates in 2022 (10Y average swap rate jumped from -0.143% in 2020 to 1.927% in 2022). This increases the cost of straight debt.
*   **Credit Spreads:** The iBoxx EUR Non-Financial IG spread average was 2.295% in 2022, up from 1.298% in 2021. This indicates tighter credit conditions and higher risk premiums for corporate debt.
*   **Hybrid Bond Appeal:** In a rising rate environment, hybrid bonds (which often have fixed coupons but are treated as equity for rating agencies) can be attractive if issued before rates peak or if they offer tax-deductible coupons (though accounting treatment varies). However, the primary benefit of hybrids for TenneT is **rating agency equity credit**. Rating agencies typically grant 50-100% equity credit to hybrids, which helps maintain the company's investment-grade rating without diluting existing shareholders. This is crucial for keeping the cost of straight debt lower.

**3. Strategic Considerations for Hybrid Capital:**
*   **Regulatory Framework:** Regulated utilities like TenneT are often allowed to include hybrid capital in their regulatory asset base (WACC calculations), meaning the cost of this capital is recovered from consumers. This makes hybrids a cost-effective tool compared to pure equity, which might demand higher returns.
*   **Optimal Level:**
    *   **0%:** Too conservative. Ignores the tax/regulatory benefits and the ability to optimize the WACC.
    *   **100%:** Impossible and impractical. Hybrids are expensive compared to senior debt and do not provide the same control/stability as common equity. Rating agencies cap the amount of hybrid capital they recognize as equity (usually around 15-25% of total capitalization). Exceeding this leads to diminishing returns and higher coupon costs.
    *   **75%:** Far too high. This would severely distort the capital structure, increase the weighted average cost of capital significantly, and likely trigger rating downgrades due to excessive subordination risk for other creditors.
    *   **25% vs 50%:**
        *   The current hybrid level is ~27.5% of equity.
        *   Standard practice for strong investment-grade utilities is to maintain hybrid capital at roughly 10-20% of *total capitalization* (Debt + Equity) or up to 25-30% of *equity*.
        *   If we look at Total Capitalization (Equity €7,713m + Long-term Debt €19,006m + Short-term Debt €0.7bn ≈ €27.4bn), the current hybrid share is $2,125 / 27,400 \approx 7.7\%$.
        *   Increasing this to 25% of total capital would require massive issuance, which is unlikely.
        *   However, the question asks about reliance in the *capital structure*. In the context of "equity-like" instruments, hybrids often complement common equity. A common target for utilities is to have hybrids represent about 25% of the *equity component* or roughly 10-15% of total capital.
        *   Looking at the options provided (0, 25, 50, 75, 100), these likely refer to the proportion of the *equity tranche* or a strategic target for *hybrid vs common equity* balance, or potentially the percentage of total capital that *should* be hybrid (which is usually capped).
        *   Let's re-evaluate the options as a percentage of *Total Capital* or *Equity*.
            *   If 25% of Total Capital: €6.8bn. Current is €2.1bn. This is a significant increase.
            *   If 25% of Equity: Current is 27.5%. This suggests the current level is already near the 25% mark.
            *   If the question implies "What percentage of the company's *equity-like* funding should be hybrids?", a 25-30% mix is standard.
            *   If the question implies "What percentage of *total assets* or *total capital* should be hybrids?", 25% is too high for a utility (typically max 15-20%). 50%, 75%, 100% are definitely too high. 0% is too low.
            *   Therefore, **25%** is the most reasonable strategic target among the choices, representing a significant but not dominant portion of the capital base, aligning with the current actuals (~27% of equity, ~8% of total capital). It reflects a balanced approach where hybrids provide equity credit without overcrowding the capital structure. Most rating agencies allow up to 15-20% of total capitalization to be treated as equity via hybrids. Given the options, 25% is the closest realistic upper-bound target for a specialized instrument's share in a broader context, or it refers to the share within the equity bucket. Given the current state is ~27% of equity, maintaining or targeting **25%** is the most logical "steady state" answer.

**Conclusion:**
TenneT currently holds hybrid capital at approximately 27.5% of its total equity. This level is consistent with industry standards for regulated utilities seeking to optimize their Weighted Average Cost of Capital (WACC) while maintaining strong credit ratings. Increasing reliance to 50% or more would be excessive and costly, while 0% would forfeit regulatory and rating benefits. Therefore, a reliance level of 25% is the most appropriate strategic target.

<answer>25%</answer>