To assess the extent to which Électricité de France (EDF) should utilize hybrid bonds over the next 18 months, we evaluate the company's financial metrics, capital requirements, and credit profile based on the provided annual report data for the year ended December 31, 2022.

**1. Transformational Capex and Extreme Refinancing Needs:**
EDF's capital expenditures and refinancing needs are exceptionally high. In 2022, the company recorded cash flows used in investing activities (primarily purchases of property, plant, and equipment) of €18.3 billion. Simultaneously, its operating cash flows turned deeply negative to -€7.4 billion. To cover this massive cash burn and investment requirement, EDF raised over €34.1 billion in borrowings in 2022 alone. This level of spending and refinancing places extraordinary pressure on the company's capital structure. 

**2. Material Downgrade Risk and Credit Metric Deterioration:**
EDF's operating performance collapsed in 2022 (due to nuclear fleet outages, tariff caps, and the European energy crisis). The company reported a net loss of €18.2 billion and a negative operating profit before depreciation and amortization of -€4.98 billion. Consequently, S&P FFO to Net Debt fell to -15.79% and Net Debt to EBITDA to -8.22x. Moody's also flagged a deteriorating adjusted leverage trend. Without substantial structural support, these metrics would point to massive downgrade risk. 

**3. Historical Utilization of Hybrids and Balance Sheet Optimization:**
EDF has been issuing hybrid bonds since 2013 and paid €606 million to holders of perpetual subordinated bonds in 2022, reflecting a substantial existing stock of hybrids. Given the acute pressure on its balance sheet, the preservation of an investment-grade or baseline credit rating depends heavily on maximizing S&P's equity credit allowance for hybrid instruments. Raising hybrid capital helps limit the explosion of pure debt metrics by being treated as 50% equity. 

**Conclusion:**
Considering EDF's massive capex program, unprecedented financial deterioration in 2022, and its heavy historical reliance on hybrid capital to defend its rating, the company sits squarely in the highest urgency tier for hybrid issuance. It is strongly advised that EDF aims to maximize its hybrid capacity up to S&P's limit to stabilize its adjusted leverage trajectory.

<answer>15%</answer>