Why can the headline yield of a renewable energy project be misleading?

A headline yield can leave out the risks that matter most. A "9% gross annual yield" may not reflect grid connection delays or permitting risk.
Small changes in assumptions move returns a lot: a 10% lower wholesale electricity price combined with a 6-month construction delay can reduce the project's IRR by 1.5 to 2.5 percentage points, which for an 8% offer is the difference between attractive and barely competitive. Projects that leave out legal contingency costs can show returns 2 to 3 points higher than what follows once problems arise. Incentives that are not yet awarded can also overstate returns.
A practical test: pick the two or three variables that drive the model (power price, production, timing) and see how the return changes if each moves 10 to 20% the wrong way. Check too whether "asset-backed" in the marketing matches the legal documents. Capital is at risk: crowdfunding investments are not covered by deposit guarantee schemes, can lose part or all of their value, and may be hard to sell before the end of their term.