ACEA has a very large, capital-intensive asset base and significant leverage, so hybrid bonds could be useful as a balance-sheet management tool. At year-end 2022, equity was about €2.76bn, while financial liabilities were substantial: non-current financial liabilities of about €4.72bn and current financial liabilities of about €0.62bn. This implies a debt-heavy capital structure, with debt well above equity.

However, the company is also not under acute distress. It remains profitable, with 2022 net profit of €311m and operating profit of €566m, and it generated positive operating cash flow of €727m. Revenue increased strongly year over year. That said, net profit declined from 2021, free cash flow was pressured by heavy investment spending, and interest costs rose in a market environment where swap rates and credit spreads increased sharply in 2022.

Because S&P’s hybrid equity credit cap is based on 15% of adjusted capital, the company has room to benefit from hybrids, especially to support credit metrics while funding infrastructure investment. But given higher 2022 rates and the higher cost of hybrid capital versus senior debt, maximizing hybrid issuance up to the full cap would likely be too aggressive unless ACEA needed to protect a rating urgently. A moderate-to-high use is more appropriate: hybrids can strengthen adjusted credit metrics without overreliance on expensive subordinated funding.

Therefore, ACEA should use hybrids meaningfully but not to the full S&P cap. The best choice is 75%.

<answer>75%</answer>