Hybrid bonds are instruments that mix equity and debt characteristics (e.g., perpetual or subordinated debt with features like loss-absorbing). To assess Naturgy Energy Group SA’s reliance on hybrids, we examine provided balance sheet and debt figures. The data shows:
- Long-term borrowings: 12.689e9 EUR (2023)
- Noncurrent financial liabilities: 13.999e9 EUR (2023)
- Current borrowings and current portion: 2.11e9 EUR
- No explicit mention of hybrid or perpetual instruments; equity components show typical equity, including negative components in some equity items, but no dedicated hybrid line.
- Cash flow and interest costs suggest standard debt mix; no clear evidence of hybrid bonds as a material portion.
Given typical industry practice for regulated energy groups, they prefer a mix of senior debt and some hybrid/other perpetual instruments to optimize WACC. However, without explicit hybrid data, we should assume no reliance on hybrid bonds beyond negligible if not disclosed. Therefore, the prudent estimate is near 0% to 25%? The question asks "to what extent should this company's capital structure rely on hybrid bonds?" Based on data, there is no evident use; thus 0%.

Final: <answer>0%</answer>