REN's capital structure is characterized by significant debt-servicing obligations and a focus on maintaining long-term financial stability in a capital-intensive utility sector. As of the end of 2022, the company has substantial long-term borrowings (1.695 billion EUR) and has demonstrated a commitment to managing interest rate risk (evidenced by significant cash flow hedge reserves).

The market data shows a sharp increase in swap rates in 2022 (e.g., the 10Y swap rate moving from 0.053% in 2021 to 1.927% in 2022). This environment of rising interest rates increases the cost of traditional debt refinancing. Furthermore, the company reported a "Liability Related To The Transitional Gas Price Stabilization Regime" of 1 billion EUR, highlighting potential liquidity pressures and the need for capital optimization.

Hybrid bonds offer a middle ground between debt and equity, providing "equity-like" features (such as deferrable coupons and subordination) that can support credit ratings while providing the company with the flexibility needed for large-scale infrastructure investments. However, given REN's stable, regulated revenue model (Rendering of Services of 588 million EUR) and its ability to maintain healthy dividend payments (102 million EUR), a heavy reliance on hybrids (which typically carry higher costs than senior debt) is unnecessary. A 25% allocation represents a prudent balance to enhance capital structure flexibility without overly diluting the cost of capital or creating excessive subordination issues for senior lenders, aligning with their moderate leverage profile and regulated utility business model.

<answer>25%</answer>