The efficiency depends primarily on size (different manufacturtes have use similar designs). Bigger Gas Turbines tend to more effiecient. Additional factors such as waste heat recovery and heat exchangers can improve the system efficiency (but not the effiecency of the actual Gas Tubine).
Smaller gas turbines such as the Rolls Royce Avons have around 25% Thermal Efficiency while larger units such as the Rolls Royce Trent-50 have efficiencies of around 42%. A full list of Tubine Efficiencies for different manufacturers can be found at http://www.vibronurse.com/turbmath.HTML
Note that the above comment does not make the Avon a bad unit its simply the case that it is designed primarily for a high power to weight ratio. Some people will also quote very high figures for G.E Frame machines (+50%) but these numbers usually include co-gen (a steam turbine used to recover waste heat) and are therefor not just Gas Turbine Efficiency.
The full calculation for calculating Gas Turbine effieciency is avalaible at VibroNurse at the following page (http://www.vibronurse.com/turbmath.HTML) and program which does the calculation is available at http://www.vibronurse.com/gaseff.HTML. We use this program at our oil and gas platforms and it works well particlauarly as a condition monitoring tool.
A modern combined cycle gas turbine/ steam turbine power plant can reach almost 60% efficiency.
by increasing the turbine inlet gas temperature
Inefficiencies in the compressor of a gas turbine cycle increase the back-work ratio and decrease the thermal efficiency of the gas turbine cycle, since they increase the compressor work.
1.Turbine output is increased for same compressor work. 2.As more heat is supplied,thermal efficiency decreases.
an increase in relative humidity will increase the Gas turbine output. and thermal efficiency. when the ambient tempeature is high at that time also if RH is high it will have a slight positive impact on GT output & Efficiency.
gas turbine's operate at very high temperatures. so a thermal barrier coating is necessary to protect the gas turbine components. TBC's have low thermal conductivity. they also protect against oxidation and hot corrosion.
The efficiency of a Turbine, is roughly 40%.
Gas turbine manufacturers generally state the efficiency of their turbines using LHV. However, natural gas in the U.S. is bought and sold on an HHV basis, so be careful that you don't mix units. Otherwise, you will buy a gas turbine that is too small for your anticipated needs.
The gas (working fluid) having flown through the turbine does some work on the turbine, converting its thermal energy into mechanical work produced by the turbine and coming out as an expanding gas with lower temperature and pressure.
www.muellerenvironmental.com/documents/GER3567H.pdf discusses many factors affecting gas turbine efficiency. It specifically addresses GE turbines, but the factors discussed are relevant to all gas turbine power generators.