To determine the extent to which Iberdrola SA should utilize hybrid bonds relative to the S&P Global Ratings cap, we must analyze the company's current capital structure, the cost of capital environment, and the strategic benefits of hybrid instruments.

**1. Analysis of Capital Structure and Hybrid Usage:**
From the provided annual report data for the period ending 2023-01-01 (representing the 2022 fiscal year):
*   **Equity:** 58,114 million EUR.
*   **Noncurrent Financial Liabilities:** 44,216 million EUR.
*   **Current Financial Liabilities:** 25,079 million EUR.
*   **Total Debt (approximate):** ~69,295 million EUR.
*   **Hybrid Instruments:** The report lists "Instrumentos De Capital Con Caracteristicas De Pasivo Financiero" (Equity instruments with characteristics of financial liabilities).
    *   Noncurrent: 576 million EUR.
    *   Current: 87 million EUR.
    *   Total Hybrids: ~663 million EUR.

S&P Global Ratings typically allows up to 15% equity credit for hybrid capital within the "Adjusted Capital" base (Debt + Equity). Let's estimate the current utilization:
*   Adjusted Capital ≈ Total Debt + Equity ≈ 69,295 + 58,114 = 127,409 million EUR.
*   15% Cap ≈ 19,111 million EUR.
*   Current Hybrids ≈ 663 million EUR.
*   Current Utilization ≈ 663 / 19,111 ≈ 3.5%.

The company is currently significantly under-utilizing the allowable hybrid capacity.

**2. Market Environment and Cost of Capital:**
The market data shows a significant shift in 2022:
*   **Swap Curves:** Rates jumped from negative/low in 2020-2021 to positive/high in 2022 (e.g., 10Y Swap average 1.927%).
*   **Credit Spreads:** The iBoxx EUR Non-Financial IG spread increased to 2.295% in 2022.
*   **Implication:** The cost of pure debt has risen. However, hybrid bonds, which carry higher coupons than senior debt but offer equity credit, become attractive for optimizing the Weighted Average Cost of Capital (WACC) and strengthening the balance sheet without diluting existing shareholders. In a rising rate environment, locking in hybrid capital can be strategic if the equity credit improves the overall credit profile, potentially lowering the spread on senior debt.

**3. Strategic Considerations for Iberdrola:**
*   **Credit Rating Maintenance:** Iberdrola is a large utility with significant infrastructure investment needs (CapEx). Maintaining a strong investment-grade rating is crucial for low-cost funding. Hybrids provide equity credit, which lowers leverage ratios (Debt/Equity), supporting the credit rating.
*   **Regulatory Context:** Utilities often face regulatory constraints on returns. Optimizing the capital structure to minimize WACC is key.
*   **S&P Cap Utilization:** Most highly-rated utilities with significant CapEx plans tend to utilize a substantial portion of their hybrid allowance to balance leverage and cost. Leaving the capacity almost entirely unused (as is currently the case at ~3.5%) is generally suboptimal for capital efficiency. However, going to 100% of the cap might be aggressive depending on the specific rating agency's view on the company's business risk profile.
*   **Standard Practice:** For a stable, large-cap utility like Iberdrola, utilizing **50%** to **75%** of the available hybrid capacity is a common strategic target to enhance financial flexibility while maintaining a robust credit profile. Given the substantial gap between current usage and the cap, and the need to fund ongoing transitions (renewables, grid), increasing hybrid usage is logical.

However, the question asks "To what extent *should* this company utilize... relative to the cap". This is often a theoretical question about optimal capital structure policy for such entities. S&P's methodology explicitly sets the cap at 15% of adjusted capital for equity credit. Companies often aim to fill a significant portion of this "bucket" to optimize their leverage metrics. A common benchmark for optimized capital structures in this sector is to utilize roughly half to three-quarters of the allowable headroom to balance the higher cost of hybrids against the benefit of equity credit.

Let's look at the options: 0%, 25%, 50%, 75%, 100%.
*   0% is clearly wrong as they already have some and benefit from equity credit.
*   100% might be too aggressive, increasing the cost of capital unnecessarily if senior debt is still cheap enough relative to the hybrid coupon spread.
*   25% is conservative.
*   50% is a balanced, standard approach for many investment-grade issuers to optimize WACC.
*   75% is also possible for companies aggressively managing leverage.

Given Iberdrola's strong cash flow and the specific mention of the S&P cap, the "optimal" theoretical utilization often cited in corporate finance contexts for maximizing rating benefits without overpaying for capital is often around the midpoint or slightly higher. However, looking at peer groups and general treasury management principles for AAA/AA/A rated utilities, they often keep a buffer. But considering the *current* under-utilization (3.5%), a move towards **50%** represents a significant strategic optimization step that is widely regarded as prudent for balancing cost and rating strength.

Another perspective: The question might be interpreting the "cap" as a limit not to be exceeded, but asking for the *target* utilization. Many rating agencies and investors view hybrid usage of around 10-15% of total capitalization (which is the full cap) as acceptable for strong issuers, but companies often self-impose a lower internal limit. However, without specific internal targets, the most robust "textbook" answer for optimizing capital structure within a regulatory/rating constraint is often to utilize the instrument to the point where the marginal benefit equals the marginal cost. For hybrids, this is often substantial.

Let's re-evaluate based on the specific data provided. The company has very low hybrid usage. The market data shows rising costs. Issuing hybrids now locks in equity credit. A utilization of **50%** of the cap is a very common strategic target for companies seeking to optimize their capital structure without appearing overly leveraged to rating agencies. It provides a significant buffer below the hard cap while capturing most of the benefit.

<answer>50%</answer>