High-Efficiency Gas Turbines Will Play a Growing Role in the Energy Transition

Alex Forbes

The latest high-efficiency gas turbines aren't just more economical than ever—they're also flexible enough to partner perfectly with renewables. Here's how these turbines are poised to keep power grids stable and resilient.

Renewable energy sources have made huge strides over the past decade. Costs have fallen to levels at which wind and solar power can compete with conventional generation technologies without subsidy. You shouldn't, however, underestimate the role that heavy-duty gas turbines will need to play in power systems as renewables penetration grows. Just as renewables technology has been advancing, so have gas turbines.

Mean Machines

The latest high-efficiency turbines are impressive machines. In 2016, when EDF Bouchain deployed a high-efficiency H-Class turbine in a combined-cycle configuration—meaning it recovered waste heat to drive a steam turbine, instead of venting it into the atmosphere—the plant achieved 62.22 percent net efficiency, according to GE Power. Fast-forward to today, and 65 percent is within sight.

With fuel costs accounting for up to four-fifths of total running costs, even a small increase in efficiency amounts to big bucks, says Jonathan Truitt, product management leader for gas power systems at GE Power. Using data drawn from sources including the International Energy Agency, GE Power recently estimated that in the US—where gas is relatively cheap—a 1 percent rise in efficiency can lead to fuel savings of $50 million over ten years. In Asia, where LNG can cost over $10/MMBtu, the savings would be much higher.

Flexibility Matters

Just as importantly, OEMs are designing these new machines with a focus on operational flexibility.

The once-conventional wisdom that combined-cycle gas turbine (CCGT) power stations should, wherever possible, be operated as baseload has been turned on its head by the energy transition. Today's CCGTs need the ability to ramp output up and down quickly, start up and shut down promptly, and tolerate turndown to low output levels without breaching emissions regulations.

Manufacturers of high-efficiency turbines have responded accordingly. They've designed turbines to ensure that CCGTs and open-cycle gas turbine (OCGT) power plants can accommodate the vagaries of variable renewables.

Girding the Grid

It is increasingly appreciated that—because wind and solar power are variable—conventional generation sources are still needed for when the wind isn't blowing and the sun isn't shining. These complementary sources have to be dispatchable, meaning they have to be available when called on to run.

But dispatchability is only part of the answer. What is not so widely appreciated is that rotating machinery running synchronously brings stability and resilience to power systems, two advantages not shared by nonsynchronous renewables. Keeping a large electricity network resilient is much more complex than just supplying sufficient energy. Voltage and frequency need to be kept within narrow tolerances. This requires the management of reactive power as well as active power.

A Greener Ireland

Take the example of Ireland, a world leader in the integration of renewables into an isolated electricity network. The nation is striving to meet a target of getting 40 percent of its electricity from renewables by 2020, according to EirGrid Group. To make that possible, Ireland's grid will need to handle up to 75 percent of variable renewable electricity at any one time, according to EirGrid Group. This is the system nonsynchronous penetration operational limit, or SNSP.

As part of its decarbonization strategy, Ireland is phasing out the burning of coal and peat in electricity generation, according to the nation's Department of Communications, Energy, and Natural Resources (DCENR). It also has a policy of not investing in nuclear power, reports the DCENR. So, as renewable generation capacity grows, gas-fired power stations—already a big part of the power fuel mix—will play a critical role in providing dispatchable, synchronous electricity to keep the grid resilient.

Mind the Gap

Ireland is not alone in having a policy of phasing out coal in electricity generation. According to Beyond Coal, it's one of eleven countries in Europe that have made such a pledge, a list that includes the UK, France, and Italy. Germany, Europe's largest consumer of coal, is in the throes of a debate over whether to make a similar pledge, and a special commission has been set up to advise on the issue by the end of the year, according to Clean Energy Wire.

In several of these countries, gas-fired power will be one of the few contenders, if not the only contender, to fill the gap that coal's phaseout from power will leave. France's EDF Bouchain power station, for example, was actually converted from an old coal-fired plant. When it started up in 2016, its net fuel conversion efficiency of 62.22 percent prompted Guinness World Records to name it the world's most efficient CCGT.

In the US, natural gas is now the biggest source of electricity generation, according to the US Energy Information Administration, having overtaken coal in recent years simply because gas is so abundant and cheap due to the shale revolution. The more efficient gas turbines become, the harder it will be for coal to compete.

In Asia, nations hungry for power are investing in the latest high-efficiency gas turbines to bring electricity to the hundreds of millions of people in the region who still lack it. Bangladesh and Pakistan are among the nations ordering high-efficiency H-Class gas turbines, according to GE Power.

Blue Sky Thinking

In China, a determined drive to reduce air pollution has caused gas demand to skyrocket—so much so that an expected global LNG glut has not materialized. In its thirteenth five-year plan for electricity development, China aims to have 110 GW of gas-fired electricity generation up and running by 2020.

It has been widely reported that gas turbine orders in recent years have been well below the manufacturing capacity of the main producers. But gas turbine orders will sustain into the future, balancing grids as an increasing percentage of renewable energy sources are added, said GE Power's Truitt.

Opposing forces are at work: On the one hand, a trend toward decentralization of electricity generation; on the other, forecasts of greater electrification of the global energy economy as decarbonization extends beyond electricity generation and into heating and transport.

Hot Stuff

The secret behind the latest generation of high-efficiency turbines is in the firing temperature. H-Class turbines have much higher firing temperatures than the temperatures used in F-Class or E-Class turbines.

The physics involved are complex, but a reasonable simplification is that efficiency shows a direct correlation to firing temperature. In some cases, high firing temperatures cannot be withstood by the materials used to make the turbines.

Manufacturers therefore have had to resort to special cooling techniques: air cooling in the most advanced models, ceramic coatings on the most vulnerable components, and careful management of combustion zones and where the flame sits.

The effort is worth it. Higher efficiency brings many benefits: lower fuel costs, lower capital expenditure, lower maintenance costs, and—crucially, in an age of escalating climate concerns—lower carbon dioxide emissions per unit of electricity generated.

More than ever, with the introduction of these high-efficiency turbines, gas-fired power stations are complementing renewables, rather than competing with them.


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