Operating costs of wind power are for sure not zero. Especially repairs of offshore wind turbines are very expensive.

https://docs.wind-watch.org/offshore-availability-costs.pdf

Hydropower and solar have much lower operating costs.

All thermal power plants experience wear and tear and have to be regularly repaired and maintained. Nuclear power plants can load-follow (within technical limits), but as the operating costs (maintance, repair, staffing, fuel) are much lower then capital costs it makes economic sense to run them at full power.

https://shs.cairn.info/revue-revue-deconomie-politique-2025-...