Help for renewables: new GE natural gas turbine meshes flexibility with combined-cycle efficiency

Natural gas-fired power generation has generally been considered necessary for the transition away from dirty electricity generated from coal toward clean electricity generated from renewables. Wind and solar are intermittent so integrating them into the grid means we have to be able to balance their intermittencies against another source of power generation that is flexible. That “other” source is natural gas, which despite its own controversies (particularly around emissions and water contamination as they relate to shale gas production) is generally much cleaner than coal.

But here’s the problem: There are two basic ways of deploying natural gas-fired power plants. One is in single-cycle mode, where you run the fuel once through a gas turbine. This kind of plant is usually used for peaking purposes because it can ramp power output up and down quite quickly, and because of this flexibility it is generally matched up with renewables — i.e. when the wind stops blowing the single-cycle peaking plant ramps up accordingly, and when the wind picks up the gas plant ramps down. This assures demand and supply on the grid remain in proper balance.

Unfortunately, single-cycle plants are not efficient. Only between 33 and 40 per cent of the natural gas fuel that goes into it produces electricity. The rest is lost as waste heat. Now, the alternative is to build combined-cycle plants. With these plants, natural gas fuel goes into a gas turbine, but the waste heat is captured and used to power a steam turbine. A combined-cycle gas plant can be between 55 and 60 per cent efficient. But the tradeoff is that it doesn’t have the flexibility that comes with single-cycle mode. So combined-cycle plants tend to run more like baseload generation, but with minor flexibility to adjust to slow-moving changes in system load. In other words, combined-cycle gas plants and intermittent renewables can play together but not very well.

Now, all of this is background for what I really want to tell you: General Electric announced yesterday in France that it has developed a new power plant design that achieves the flexibility of single-cycle with the efficiency of combined-cycled. The new plant, called FlexEfficiency 50, is basically a combined-cycle plant with 61 per cent efficiency that’s based on jet engine technology (a newly developed 9FB Gas Turbine) and waste-heat capture for driving a steam turbine (109D-14 turbine). GE has rated the plant’s output at 510 megawatts. According to GE, the plant can ramp up by 50 megawatts per minute, which is apparently double the ramp-up┬árate that exists today.

This might not seem like a big deal, and it’s certainly not the sexiest of stories, but if we’re going to rely more on natural gas as we transition to renewables, and if more of that gas is going to come from shale resources (meaning it will have a larger carbon footprint), then having a natural gas plant that’s both efficient and flexible is actually a very good thing to have over the coming years. This is especially true in regions such as California and Ontario that are hoping to integrate a large amount of renewables into their systems over the next decade.

One thought on “Help for renewables: new GE natural gas turbine meshes flexibility with combined-cycle efficiency”

  1. Tyler, it seems like a step in the right direction, but I’m afraid it might be a small one.

    In order for gas to play well with wind, it has to be happy to stop generating whenever the wind is blowing hard. That translates into a low Capacity Factor, low production, and low income to cover the cost of building the plant. There’s a range, a continuum, ranging from plants that are almost always needed, down to plants that are literally never needed except as non-operating reserve capacity. Plants at the very top of that continuum could use this new technology. Plants in the middle or below might not, and plants anywhere near the bottom should be coal-fired, if economic efficiency or hydro rates mattered to any of the Powers That Be.

    Another approach to improving gas-fired efficiency is co-generation, aka combined heat and power (CHP). Unfortunately, it doesn’t play well with wind AT ALL, because the “heat client” demands heat independently of the wind. So it competes with wind and nuclear, rather than complementing them.

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