The company currently carries a significant amount of debt (≈ 5.3 bn) against a relatively modest equity base (≈ 2.8 bn), giving a debt‑to‑capital ratio of roughly 66 %. Its interest coverage is strong (≈ 6–7 × net interest) and operating cash flows (≈ 727 M) comfortably exceed interest and dividend obligations, indicating capacity to service additional sub‑ordinated instruments. The market environment offers low nominal rates (5‑year swap ≈ 1.7 % and IG corporate yields ≈ 1‑2 %) and hybrid bonds typically price at a modest premium over senior debt, making them a cost‑effective way to bolster equity‑like capital without diluting shareholders. For a capital‑intensive utility such as ACEA, a conservative target is to allocate roughly one‑quarter of total capital to hybrid instruments; this improves the effective equity ratio and rating metrics while keeping leverage and refinancing risk within acceptable bounds. A higher proportion (≥ 50 %) would overly increase sub‑ordination and cash‑flow pressure, whereas none would miss the opportunity to optimise the cost of capital. 

<answer>25%</answer>