Reasoning:

REN is a regulated utility with large, stable infrastructure assets and predictable cash flows, which generally makes it a plausible issuer of hybrid bonds. However, the question is not whether hybrids are possible, but how much of the S&P equity-credit capacity should be used.

Key considerations:

1. Leverage is already meaningful  
   At year-end 2022, borrowings were about:
   - Long-term borrowings: €1.695bn
   - Current borrowings: €0.639bn
   - Total borrowings: about €2.334bn

   Equity was about €1.518bn. This implies debt is materially larger than book equity. On a simple debt-plus-equity basis, debt represents roughly 61% of capital before considering other adjustments.

2. Interest-rate environment worsened sharply in 2022  
   Swap rates moved from very low or negative levels in 2020–2021 to around 1.7%–1.9% in 2022. Corporate bond yields and non-financial IG spreads also increased. This means new hybrid issuance would be significantly more expensive than in prior years.

3. Finance costs already increased  
   Finance costs rose from €54.4m in 2021 to €67.4m in 2022. Although operating profit improved, higher rates make aggressive hybrid issuance less attractive, especially because hybrids typically carry a coupon premium over senior debt.

4. Cash generation is strong but dividends are significant  
   Operating cash flow was strong at €613.5m, but the company also paid substantial dividends classified as financing activities of €144.6m. Hybrids could support credit metrics and preserve financial flexibility, but excessive use may be inefficient given coupon costs.

5. S&P equity-credit cap  
   S&P limits equity credit on hybrids to 15% of total adjusted capital. For a regulated utility with stable cash flows and sizeable investment needs, using some of that capacity is reasonable. But given REN’s already elevated debt, rising financing costs, and the need to avoid over-reliance on expensive subordinated capital, full utilization looks too aggressive.

Overall, REN should make moderate-to-high use of hybrid capacity, but not the full S&P cap. A 50% utilization would be conservative, while 75% better reflects the company’s regulated stability and ability to benefit from equity credit while still leaving headroom under the cap. Full 100% utilization would likely be too aggressive in the 2022 rate environment.

<answer>75%</answer>