Let’s walk through the key points.  

First, **equity credit on hybrids** is valuable if a company wants to maintain leverage ratios without diluting shareholders. S&P caps the equity credit at **15% of total adjusted capital** (debt + equity).  

From ERG’s data:  

- **Equity at end of 2022**: ~€2.055 billion.  
- **Total liabilities**: ~€3.172 billion.  
- **Total adjusted capital**: €5.227 billion.  
- **15% cap**: ~€784 million of hybrids could get equity credit.  

Second, looking at **leverage**:  
- ERG has net financial debt (roughly) of €1.75 billion non-current financial liabilities + €0.39 billion current financial liabilities minus €0.39 billion cash = ~€1.75 billion.  
- Debt-to-equity is already ~0.85x, which isn’t excessive, but the firm is capital-intensive (renewables).  
- In 2022, they had significant expansion (PP&E and service concession rights increased) and high CapEx (€307 million).  

Third, **earnings stability**:  
- EBITDA is strong (€499 million in 2022) and growing.  
- However, discontinued operations heavily inflated net profit—continuing operations profit was €89 million.  
- Rising interest rate environment (swap curve up sharply in 2022) means new debt or hybrid issuance would be more costly.  

Given their growth needs and the benefit of non-dilutive capital, using some hybrids makes sense. But **full 100%** of the 15% cap might be unnecessary and expensive—especially when traditional debt could still be issued at reasonable spreads. A **middle-ground usage** (50%) would help balance cost and credit metrics without saturating the structure.  

<answer>50%</answer>