Let’s work through this step-by-step.

**1. Understanding S&P’s hybrid cap**  
S&P’s methodology limits the equity credit from hybrid bonds to 15% of total adjusted capital (total debt + equity). This is meant to preserve credit quality and prevent excessive reliance on hybrid instruments.

**2. Estimating Iberdrola’s total adjusted capital**  
From the 2022 year-end data:

- Equity  
  - Attributable to owners of parent: €41,119m  
  - Noncontrolling interests: €16,995m  
  - Total equity ≈ €58,114m  

- Financial liabilities (debt-like items)  
  - Noncurrent financial liabilities: €44,216m  
  - Current financial liabilities: €25,079m  
  - Total ≈ €69,295m  

So total adjusted capital ≈ €58,114m + €69,295m ≈ **€127,409m**.

**3. The 15% cap in absolute terms**  
15% × €127,409m ≈ **€19,111m**.

**4. Iberdrola’s current hybrid usage**  
From the balance sheet, instruments classified as "Instrumentos de Capital con Caracteristicas de Pasivo Financiero":
- Noncurrent: €576m  
- Current: €87m  
- Total hybrids ≈ €663m

This is far below €19,111m.

**5. Potential to issue more**  
Given that current usage is only about 3.5% of the cap, the company still has room to issue more hybrids if desired, *up to* the 15% limit.

**6. Strategic consideration**  
The company has significant capex, stable regulated cash flows, and a large balance sheet. It could comfortably issue hybrids for capital structure efficiency without nearing the cap, but the question is “to what extent *should* it utilize hybrid bonds relative to the cap?” Given its current low usage and growth/investment needs, using 100% of the allowed limit could make sense from a financial optimization perspective—balancing equity credit and cost of capital while staying within rating guidelines.

Based on this reasoning, I would opt for full utilization of the allowed cap.

<answer>100%</answer>