To determine the appropriate extent to which REN - Redes Energéticas Nacionais, SGPS, S.A. should rely on hybrid bonds, we must analyze its current capital structure, financial health, market conditions, and the specific characteristics of hybrid instruments.

**1. Analysis of Current Capital Structure and Financial Health:**
*   **Equity Ratio:** As of 2023-01-01, Total Equity is €1,517,534,000 and Total Assets are €6,451,596,000. The equity ratio is approximately 23.5% ($1,517,534,000 / 6,451,596,000$). This indicates a relatively high leverage ratio, typical for utility infrastructure companies, but leaves room for optimization.
*   **Debt Levels:** Total Liabilities are €4,934,062,000. Long-term borrowings decreased significantly from €2,390,852,000 in 2022 to €1,695,362,000 in 2023, while current borrowings increased. The company is actively managing its debt maturity profile.
*   **Profitability and Cash Flow:** The company generated a profit of €111,771,000 in 2022. Operating cash flow was strong at €613,466,000. However, finance costs were €67,394,000, indicating a significant burden from interest payments. Hybrid bonds, which often have deferred coupon features or lower coupons than senior debt, could help manage this cost pressure while maintaining leverage ratios acceptable to rating agencies.
*   **Dividend Policy:** The company paid dividends of €102,150,000 (from the equity statement changes) or €144,602,000 (from cash flow statement, likely including prior year accruals or different timing). The ability to pay dividends is crucial. Hybrid bonds typically require the issuer to have the discretion to defer coupons without triggering default, which aligns with a stable, cash-generative business model like REN's.

**2. Market Conditions (2022 Data):**
*   **Interest Rates:** The swap curves show a dramatic increase in rates from 2021 to 2022. For example, the 10Y swap average went from 0.053% in 2021 to 1.927% in 2022. The "Bear" case (higher rates) shows 10Y swaps at 2.227%.
*   **Credit Spreads:** The iBoxx EUR Non-Financial IG spread increased from 1.298% in 2021 to 2.295% in 2022.
*   **Implication:** The cost of senior debt has risen significantly. Hybrid bonds, being subordinated, usually carry a higher coupon than senior debt but offer equity credit (often 50-100% equity treatment by rating agencies). In a rising rate environment, locking in long-term capital via hybrids can be strategic if the equity credit helps maintain investment-grade ratings, which lowers the overall cost of capital compared to issuing more expensive senior debt or dilutive equity.

**3. Strategic Fit for Hybrid Bonds:**
*   **Equity Credit:** Rating agencies typically grant 50% or 100% equity credit to hybrid bonds depending on their structure (deferrability, perpetuity, etc.). Given REN's equity ratio of ~23.5%, issuing hybrids can artificially boost the equity base without diluting existing shareholders. This is beneficial for maintaining credit ratings (likely BBB/A range for a national grid operator) while funding large infrastructure projects (indicated by high "Intangible Assets" and "Property, Plant and Equipment").
*   **Regulatory Environment:** As a regulated utility, REN has stable cash flows. This stability supports the payment of hybrid coupons. Regulators often allow the cost of hybrid capital to be included in the regulated asset base (WACC), making it an efficient funding source.
*   **Optimal Level:**
    *   **0%:** Too conservative. The company has high leverage and could benefit from the equity credit of hybrids to strengthen its balance sheet metric without issuing new shares.
    *   **100%:** Impractical and inefficient. Hybrids are more expensive than senior debt due to subordination. Relying entirely on them would unnecessarily increase the weighted average cost of capital (WACC).
    *   **75%:** Too high. This would imply replacing most senior debt with more expensive subordinated debt, which is not optimal for a company with stable, predictable cash flows that can easily service senior debt.
    *   **25% vs 50%:** A 25% reliance is a modest addition, often used to tweak ratios. A 50% reliance suggests a more structural component of the capital stack. Given the significant drop in long-term borrowings and the need to fund ongoing infrastructure investments (CapEx) in a high-rate environment, a moderate but significant portion of hybrid capital is appropriate. It balances the cost (higher than senior debt) with the benefit (equity credit). Industry practice for regulated utilities often sees hybrid capital constituting a meaningful but not dominant part of the equity/debt mix, often targeting around 10-20% of total capitalization or a specific portion of the equity-like buffer. However, the question asks for the extent of *reliance* on hybrid bonds within the context of options provided.
    *   Looking at the options, 25% represents a prudent, moderate use of hybrids to enhance equity credit without overpaying for capital. 50% might be considered aggressive given the already substantial equity base relative to some peers, but REN's equity ratio is not exceptionally high. However, considering the sharp rise in rates, locking in too much hybrid capital (which is expensive) might be less attractive than maintaining flexibility. Yet, hybrids provide duration matching for long-lived assets.
    *   Let's look at the "Sub-Sen Delta" and spreads. The widening spreads make senior debt more expensive too. The key advantage of hybrids is the equity credit. If REN issues hybrids, it improves its leverage ratios. A 25% allocation to hybrids (as a portion of total capital or debt-like instruments) is a standard strategic target for many investment-grade utilities to optimize their WACC and rating profile. 50% is likely too high a proportion of the *total* capital structure to be efficient, as senior debt is cheaper. 0% ignores the benefits. 75% and 100% are clearly inefficient.

    Comparing 25% and 50%:
    REN's Equity is ~1.5B. Total Liabilities ~4.9B.
    If they replace 25% of liabilities with hybrids, that's ~1.2B. This is a large issuance.
    If the question implies "what percentage of the *debt* portfolio should be hybrids", 25-30% is common.
    If it implies "what percentage of *total capital* should be hybrids", 10-15% is common.
    The options (0, 25, 50, 75, 100) likely refer to a strategic stance or a proportion of the *flexible* capital raising or debt component.
    Given the high leverage (Debt/Equity > 3), strengthening the equity side via hybrids is valuable. However, hybrids are costly. A balanced approach is key. 25% is a safe, standard recommendation for optimizing capital structure in utilities without taking on excessive cost. 50% would be aggressive.

    Let's re-evaluate based on the "Bear" market scenario provided. In a bear market (high rates, high spreads), the cost of all debt rises. Hybrids, being perpetual or long-dated, lock in these high rates for longer. However, they provide rating stability. With spreads widening (1.298% to 2.295%), the premium for subordination increases. This makes hybrids relatively more expensive compared to senior debt than in previous years. Therefore, one might lean towards a lower reliance to avoid locking in high subordination premiums, or conversely, use them to secure equity credit if the senior debt market is closed or prohibitively expensive.
    However, the most standard "optimal" capital structure advice for a stable utility with moderate leverage is to use hybrids as a *supplement*, not a primary source. 25% represents a significant but supplementary role.

    Another perspective: The question might be asking about the proportion of *new* financing or the target mix of *quasi-equity*.
    Let's look at the Equity vs Liability mix. Equity is 23%. Liabilities 77%.
    If we introduce hybrids, they sit between.
    A 25% reliance on hybrids (of total capital) would mean 25% Hybrids, 23% Equity, 52% Debt. This creates a very strong balance sheet.
    A 50% reliance would be 50% Hybrids, 23% Equity, 27% Debt. This is unlikely as senior debt is cheaper.
    Therefore, 25% is the most reasonable strategic target among the choices to optimize WACC and ratings.

<answer>25%</answer>