To determine the extent to which Fortum Oyj's capital structure should rely on hybrid bonds, we must analyze the company's financial standing and the prevailing market conditions in 2022. 

1. **Cost of Capital Considerations:** Hybrid bonds are a subordinated form of debt, sitting between senior debt and equity in the capital structure. As indicated by the "SUB-SEN DELTA FOR IBOXX EUR NON-FINANCIAL IG," the spread (cost difference) between subordinated (hybrid) and senior investment-grade debt widened significantly in 2022 to an average of 2.295% (up from 1.298% in 2021). Relying on hybrid bonds under these market conditions strictly increases the weighted average cost of capital (WACC) compared to issuing standard senior debt.

2. **Debt Capacity and Solvency:** Despite realizing a massive net loss of €10.29 billion in 2022—almost entirely driven by its discontinued operations (primarily the Uniper divestment/loss)—Fortum's continuing operations remained robust. The company reported a Comparable Operating Profit of €1.87 billion and an EBITDA (Operating Profit Before Depreciations) of €1.84 billion. Meanwhile, its interest expenses were relatively low at €179 million. This gives Fortum an extraordinarily strong Interest Coverage Ratio (EBITDA / Interest Expense > 10x) for its ongoing enterprise. 

3. **Optimal Capital Structure:** Because Fortum has ample capacity to service standard senior debt—which is fundamentally cheaper—there is no economic rationale to aggressively lean on hybrid bonds to finance its operations. Hybrid bonds are typically only utilized to protect credit ratings when a company is nearing its senior debt capacity limits, or by financial institutions for regulatory capital requirements. Fortum is a non-financial utility company with high operational cash flow from continuing operations. 

Therefore, standard corporate finance theory dictates that Fortum should fund its operations using cheaper senior debt and internally generated equity, minimizing or eliminating the use of expensive hybrid debt structures. 

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