  This paper presents an improved mixed-integer model for the Thermal Unit
Commitment Problem. By introducing new variables for the temperature of each
thermal unit, the off-time-dependent start-up costs are modeled accurately and
with a lower integrality gap than state-of-the-art formulations. This new
approach significantly improves computational efficiency compared to existing
formulations, even if they only model a rough approximation of the start-up
costs. Our findings were validated on real-world test cases using CPLEX.
