What is the efficiency of converting the heat energy generated by a power plant due to combustion/fusion to electric energy?

This greatly depends on the design and mechanical characteristics of combustion (exhaust temperature, etc.) and steam turbines (reheat/non-reheat), and, especially, HRSGs (duct firing, single-or multi pressure, economizer, etc.).
It also depends on the type of fuel.
For example, CC plants based on H-series GE GTs can achieve up to 60% thermal efficiency (LHV) burning natural gas. Integrated Gasification CC plants (burning syngas), built on the same units, are at around 45-49%.

Alexei

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

We are running a Siemens CC with 2 GTs Siemens SGT5-4000F /2 x HRSG/ 1 x ST and have an official rating of 56,87% which in reality is about 56% producing approx. 809MW max.

All the best

Jester

Combined cycle - typically 7000 - 7500 BTU/Kwh

Conventional Steam - 9800 - 10,500 BTU/Kwh

Coal is still the cheaper MW because of the fuel cost per BTU. Typically <$15 per MW.

Conventional Natural Gas Plants would have to see <$1.50 per MCF (million cubic ft.) to truly compete with Coal.

A combined cycle plant can compete with coal power. $2.00 per MCF Natural Gas puts a Combined cycle plant at $15 - $17 per mw.