Siemens spent half a billion euros developing the most efficient gas turbine in the world. Last year, it sold no electricity at all, but was only used to stabilize the grid. Now, the unit is to be taken off the market and put into standby reserve next year. Craig Morris says the story shows how important it is not to confuse engineers with policymakers.
“Now stand over here and put your hand on the turbine,” the photographer told me back in 2009. I was visiting Irsching to write a report for the first issue (PDF of my article, including pictures) of Living Energy, Siemens’ in-house magazine. The company was very proud of the combined-cycle gas turbine (CCGT). It had the highest efficiency of any in the world. As such, it demonstrated the prowess of German engineering.
Gas turbines fall into two categories: combined-cycle and open-cycle. OCGTs (the latter) can be thought of as a simple single turbine. Efficiencies are relatively low at around 30 percent. CCGTs consist of two turbines. The first one is like the OCGT, but the second one takes steam (waste heat) from the first turbine to produce more electricity, working just like a normal thermal power plant – hence “combined” cycle. The efficiency of CCGT is generally above 50 percent. Siemens tweaked both of these turbine stages in Irsching to reach a combined efficiency exceeding 60 percent. Exactly what the Energiewende needs, right?
Wrong. German daily FAZ explains (in German) that the turbine is an “ideal bridge towards the age of renewables” and a “fast starter”: “within minutes, it can ramp up and down to compensate for fluctuations in power supply relative to the sun and the wind.” Siemens explains that the turbine can reach its full capacity of 340 MW “in 30-40 minutes.”
Neither of them admit openly that this flexibility is only possible with the first turbine stage, not with the downstream steam turbine. And the first one runs not at 60 percent, but below 40 percent efficiency. In other words, with CCGT you can either have high flexibility or high efficiency, not both simultaneously.
Note that CCGT uses steam to generate more electricity. Lower temperature waste heat can also be recovered for external heating purposes. Efficiencies then easily reach 80 percent – far more than the record-setting 60 percent for power production alone in Irsching – and I see here that Siemens even puts the figure at “up to 95 percent from a well designed scheme.” Such turbines are called cogeneration units.
The process does not require any advances in engineering, however. It does require political cooperation. The waste heat needs to be fed into a district heat network, which not every municipality has. Then, you need to find buyers. If households already have a chaotic mixture of heating systems fired with oil and gas (because homeowners do not generally coordinate such purchases), then there may not be enough buyers of the waste heat even if the city does build a district heat network.
Siemens has expertise in engineering, not political coordination. The company naturally promotes its own breakthroughs. Journalists who do not (but should) understand these details then fail to understand why a plant with record efficiency might not be successful in the Energiewende. Cogeneration, not so much CCGT, is what the Energiewende needs. Cogen units are so flexible that they can ramp up generation according to demand for heat (wärmegeführt) or power (stromgeführt).
Utilities that have banked on CCGT are not doing well in Germany right now. Those that banked on cogeneration and other things that the Energiewende needs are doing better – see this salient example. The situation is similar in other parts of Europe, such as Spain, because natural gas prices are relatively high; in the US, CCGT might have a brighter future. In Europe, emissions trading has also failed to make natural gas cheaper than coal in the power sector, against the assumptions prevalent last decade, when these CCGTs were contracted.
The story of the world’s most efficient gas turbine is thus not one of a failure to produce a technology that the Energiewende needs. It is the story of some of the best minds in Germany focusing on making progress with a particular technology – without properly investigating what role that technology is likely to play. In addition to top-notch mechanical engineers working on specific products, the Energiewende also needs policymakers who can tell engineers whether those products are needed.