During a customer acceptance test run on 11 May the Siemens designed and built Irsching 4 H-class combined cycle plant in Germany achieved an efficiency of 60.4% (net), at a net power output of over 550 MW. A few days earlier, on 6 May, during a TUV certified test run, the plant recorded an efficiency of 60.75% (net) at a net power output of 578 MWe.

These remarkable numbers set a new benchmark for combined cycle technology, breaching the 60% efficiency barrier that for some years has been seen as a key target for the major gas turbine makers. Testing at the Irsching 4 plant, due to be handed over to the customer, E.On, this summer, has also shown it to be extremely flexible, able to put 500 MW on line in about 30 minutes with load ramps of 35 MW/min.

The steam conditions, 600 deg C/180 bar, achieved in the new plant, which employs a Benson HRSG designed and built by Siemens (following its 2007 acquisition of the Balcke Durr HRSG business), also represent a step change compared with F class conditions, typically 130 bar, 565 deg C. Looking beyond Irsching, Siemens believes there is scope for attaining even higher efficiencies with its H class combined cycle platform, which employs a fully air cooled gas turbine. By about 2015 it expects to have inoperation a plant capable of 61.5% efficiency at an output of over 600 MWe.