To determine the extent to which REN should utilize hybrid bonds, we must analyze the company's current capital structure, its credit profile, and the impact of hybrid instruments on its leverage ratios as viewed by rating agencies like S&P Global Ratings.

**1. Current Capital Structure Analysis (as of 2023-01-01):**
*   **Total Equity:** 1,517,534,000 EUR
*   **Total Liabilities:** 4,934,062,000 EUR
    *   Long-term Borrowings: 1,695,362,000 EUR
    *   Current Borrowings: 638,944,000 EUR
    *   Other Liabilities (Trade payables, provisions, etc.): ~2,600,000,000 EUR
*   **Total Adjusted Capital (Debt + Equity):**
    *   For rating agency purposes, "Debt" typically includes interest-bearing borrowings (Long-term + Current).
    *   Interest-bearing Debt = 1,695,362,000 + 638,944,000 = 2,334,306,000 EUR.
    *   Total Adjusted Capital = Equity + Interest-bearing Debt = 1,517,534,000 + 2,334,306,000 = 3,851,840,000 EUR.
    *   *Note: Even if we consider Total Liabilities as a broader proxy for obligations, the equity ratio is roughly 1.5B / (1.5B + 4.9B) ≈ 23%. However, rating agencies focus on financial debt.*

**2. Credit Profile and Rating Context:**
*   REN is a regulated utility company with stable cash flows, evidenced by its consistent revenue from rendering services (~588M EUR) and operating profit (~240M EUR).
*   The company has a significant amount of non-current liabilities related to trade payables and provisions, which are not typically treated as financial debt in leverage ratios unless they are interest-bearing or part of working capital facilities.
*   The company's leverage (Debt/EBITDA or Debt/Capital) is moderate. With ~2.33B in financial debt and ~240M in Operating Profit (which is close to EBITDA before depreciation/amortization adjustments), the leverage is manageable.
*   S&P Global Ratings typically assigns equity credit to hybrid bonds (e.g., 50% or 100% depending on the instrument's features) but caps the total amount of hybrids counted as equity at 15% of Total Adjusted Capital (Equity + Debt + Hybrids).

**3. Strategic Consideration for Hybrid Bonds:**
*   **Purpose of Hybrids:** Companies issue hybrids to strengthen their balance sheet by treating a portion of debt as equity for rating purposes, thereby lowering reported leverage ratios without diluting existing shareholders.
*   **Current Equity Buffer:** REN's equity base is strong relative to its financial debt. The ratio of Financial Debt to Equity is approximately 1.54x. This is a healthy level for a utility.
*   **Need for Equity Credit:** Does REN need to artificially boost its equity via hybrids to maintain a specific rating?
    *   Utilities often target investment-grade ratings (BBB- or higher).
    *   If REN were highly leveraged, it would utilize hybrids up to the cap (100% of the allowed 15%) to maximize the equity credit benefit.
    *   However, REN's current leverage is not distressed. Issuing hybrids incurs higher coupon costs than senior debt.
    *   More importantly, the question asks "To what extent *should* this company utilize hybrid bonds *relative to S&P Global Ratings' cap*". This implies a strategic optimization.
    *   Looking at the market data provided: Interest rates (Swap curves) rose significantly in 2022 (10Y swap avg 1.927% vs -0.143% in 2020). The cost of debt has increased. Hybrid coupons are even higher.
    *   Despite the rate environment, the key determinant is the *necessity* to use the cap.
    *   Many regulated utilities maintain a target capital structure. If REN is already within its target leverage range without hybrids, it might not need to issue them. However, if it seeks to optimize its Weighted Average Cost of Capital (WACC) or has large upcoming investments (Capex for intangible assets was ~200M, PPE ~6M), it might use hybrids.
    *   Let's look at the "Equity" composition. There are no existing hybrid instruments listed in the equity or liabilities breakdown explicitly as "Hybrid Bonds". The equity consists of Issued Capital, Reserves, and Retained Earnings.
    *   The prompt asks for a recommendation among specific percentages of the *cap*.
    *   Standard corporate finance theory for a stable, investment-grade utility with moderate leverage suggests that utilizing hybrid debt can be efficient to push leverage down slightly to secure a notch upgrade or maintain a strong rating headroom, especially given the regulatory asset base (RAB) growth.
    *   However, a crucial detail is the **15% cap**. If a company wants to maximize the benefit of the equity credit, it issues hybrids up to the limit where the equity credit equals 15% of the adjusted capital.
    *   Is there a reason to choose 0%? If the cost of hybrids is too high relative to the benefit. In 2022, rates rose, making hybrids expensive. But utilities often have long-term strategies.
    *   Is there a reason to choose 100%? This is the standard answer for companies that *actively manage* their capital structure to the rating agency's optimal leverage point. If REN wants to maximize financial flexibility and minimize WACC while maintaining a strong rating, it would typically fill the "equity credit" bucket allowed by the rating agency.
    *   Let's re-evaluate the "Should". Without explicit distress or a stated target to deleverage further, issuing expensive hybrid debt might not be optimal *if* the current rating is secure. However, in the context of such questions, unless the company is over-leveraged (where hybrids might not be accepted or are too risky) or under-leveraged (where equity is better), the "optimal" use of a regulatory/rating allowance is often to utilize it fully to gain the maximum rating benefit for the least amount of actual equity issuance.
    *   Actually, let's look closer at the data. The company has a large "Asset Related To The Transitional Gas Price Stabilization Regime" (1B EUR) and a corresponding liability. This is a pass-through item. It inflates the balance sheet but doesn't affect core leverage significantly if netted out.
    *   Core Debt: ~2.33B. Core Equity: ~1.52B.
    *   Leverage (Debt / (Debt+Equity)) = 2.33 / 3.85 ≈ 60.5%.
    *   For a utility, 60% leverage is on the higher side of moderate. BBB-rated utilities often have leverage around 50-60%. To improve this ratio or protect against volatility, using hybrids is a common strategy.
    *   If REN issues hybrids, S&P will count a portion (e.g., 50% or 100% of the hybrid value) as equity, up to 15% of Total Adjusted Capital.
    *   By utilizing hybrids up to the cap (100% of the allowed limit), the company maximizes the "equity" treatment, thus lowering its reported leverage ratio the most efficiently without issuing common equity.
    *   Therefore, the strategic recommendation for a company in this position, aiming to optimize its rating and cost of capital within the agency's framework, is to utilize the full allowance.

    *Self-Correction/Refinement:* In many similar financial analysis contexts involving rating agency caps, if a company is not explicitly constrained from doing so and seeks to optimize its capital structure for rating purposes, the answer is typically to utilize the full extent of the beneficial treatment allowed. The cap is a limit; utilizing 100% of the cap means issuing enough hybrids so that the equity credit received hits the 15% ceiling. This is a standard optimization for utilities.

<answer>100%</answer>