Power plants' efficiency

Being an ex-chief draughtsman with Enemalta Corporation I read with interest the letter of Robert Ghirlando (Power Plants' Efficiency, October 27).

I met Prof. Ghirlando on projects when he was occupying the post of chairman of Enemalta and have known him to be an authority on thermodynamics. I too studied the basics of this subject under the guidance of Unesco lecturers at the Polytechnic in the early 1960s.

Could Prof. Ghirlando explain why and how ABB (now Siemens) claim that their gas turbine GTX100 can achieve 54 per cent efficiency as indicated on their official catalogue and MAN B&W show 55 per cent for their two-stroke low-speed diesel engines on their power efficiency comparison curves at ISO 3046, both in combined cycle form?  

Enemalta Corporation claims that their combined cycle power plant at Delimara power station running with two gas turbines Frame 6B from General Electric was purchased at the guaranteed efficiency of 46 per cent. Exact present efficiency figures of the plant are not made public and one wonders if these can be known. Perhaps Prof. Ghirlando has access more than anyone else and can give us the information.