To estimate the Net Debt / EBITDA ratio for A2A Energia S.p.A. based on the 2022 financial data using S&P methodology, we first calculate the components:

1. **EBITDA:** The report explicitly lists "Gross Operating Income EBITDA" for the period 2022-01-01 to 2023-01-01 as **1,505,000,000 EUR**.

2. **Net Debt:** Net Debt is typically calculated as (Short-term Debt + Long-term Debt) - Cash and Cash Equivalents.
   - **Other Noncurrent Financial Liabilities:** 5,867,000,000 EUR
   - **Other Current Financial Liabilities:** 1,022,000,000 EUR
   - **Total Financial Liabilities:** 5,867,000,000 + 1,022,000,000 = 6,889,000,000 EUR
   - **Cash and Cash Equivalents:** 2,584,000,000 EUR
   - **Net Debt:** 6,889,000,000 - 2,584,000,000 = 4,305,000,000 EUR

3. **Calculation:**
   - Ratio = Net Debt / EBITDA
   - Ratio = 4,305,000,000 / 1,505,000,000 ≈ 2.860465

Rounding to a standard number of decimal places:

<answer>2.86</answer>