On the other hand, conventional GT-based plants (simple cycle) are, obviously much lower than combined cycle, and are generally under 50% (top performers being around 40-45%).

Fossil-fired boiler plants are also around 30-40% thermal efficiency. This again, is affected by the type of fuel (coal (anthracytes, lignites, etc.), oil fuel, natural gas or multi-fuel.

Again, there are ways to improve your thermal efficiency by various means (GT inlet air cooling, use of reheat steam turbines, coal pulverization, use of CFB boilers, etc.), but general figures are typically as I specified above.

Hope, that helps.

Alexei