To determine the optimal extent to which REDEIA CORPORACION SA should utilize hybrid bonds relative to S&P Global Ratings' 15% cap on total adjusted capital, we evaluate the cost of hybrid bonds against the company's cost of equity. 

1. **Cost of Debt (Kd):** 
Using the interest expenses and total borrowings:
Total Debt at the start of 2022 = Long-term Borrowings (5,896,170,000 EUR) + Current Borrowings (1,391,722,000 EUR) = 7,287,892,000 EUR
Finance Costs for 2022 = 116,468,000 EUR
Kd ≈ 116,468,000 / 7,287,892,000 ≈ 1.60%

2. **Cost of Equity (Ke):**
Using Return on Equity (ROE) as a proxy:
Net Income (Profit Loss Attributable to Owners) = 664,731,000 EUR
Beginning Equity (2022-01-01) = 3,685,131,000 EUR
Ke ≈ 664,731,000 / 3,685,131,000 ≈ 18.04%

3. **Cost of Hybrid Debt (Kh):**
Hybrid bonds typically carry a spread over senior debt to compensate for subordination. Adding the Sub-Sen Delta for EUR Non-Financial IG for 2022 (2.295%) to the standard borrowing cost:
Kh ≈ Kd + Sub-Sen Delta ≈ 1.60% + 2.295% = 3.895%

**Conclusion:**
Replacing traditional equity with hybrid debt provides a strong cost advantage because the estimated cost of hybrid bonds (~3.90%) is substantially lower than the cost of equity (~18.04%). This substitution lowers the overall Weighted Average Cost of Capital (WACC) while still offering equity-like characteristics to maintain credit metrics. As a result, the financially optimal move is to fully maximize the hybrid issuance up to the S&P threshold.

<answer>100%</answer>