Power generation turbines for the electrical grid are generally used in one of two different configurations;
combined cycle to meet base load power demand, and
simple cycle to meet transient and peak power demand.
A combined cycle power plant employs both gas turbines and a steam turbine together to produce up to 50 percent more electricity from the same fuel than a simple cycle plant. The waste heat from the gas turbine that escapes through the exhaust in a simple cycle gas turbine is routed to a heat recovery steam generator, where the heat of the exhaust gas is used to generate steam for the steam turbine. In a combined cycle configuration, two gas turbines are often paired with a single steam turbine. Combined cycle power plants are generally designed for base-load (full-power) operation because they lack the agility to ramp up and down rapidly. It is challenging to efficiently integrate a plant designed for base load with renewable energy sources that provide intermittent power. Although the plant efficiency of a gas turbine operating in simple cycle is less than a gas turbine operating in combined cycle, a gas turbine operating in simple cycle has far greater operational flexibility in terms of its ability to accommodate swings in power while operating under partial load.
We suggest that the following aggressive goals can form an exciting way ahead for owner/operators of power generation gas turbines. (It isn’t easy but ambitious goals rarely are.)
The five power generation goals below are relevant to simple cycle and combined cycle gas turbines. Each of these goals directly addresses a key criterion used to select aggressive goals for gas turbine development:
Efficiency
Compatibility with Renewable Energy Sources
CO2 Emissions
Fuel Flexibility
Levelized Cost of Electricity
Power Generation Goal 1: Efficiency
Goal Summary Statement: Increase combined cycle efficiency to 70 percent and simple cycle efficiency to more than 50 percent.
Large state-of-the-art gas turbines for power generation are currently operating with a combined cycle efficiency of 63 percent or more and a simple cycle gas efficiency of about 40 percent. Increased efficiency gains are probably more important for power generation and aviation applications than for those used in oil and gas applications.
In addition to improving efficiency, achieving this goal would reduce environmental impact to the extent that reducing fuel burn results in a commensurate reduction in emissions of interest (i.e., NOx, carbon monoxide [CO], CO2, and particulate matter). This may be difficult to achieve with respect to NOx because some approaches to improving efficiency involve increasing combustion temperatures, which tends to increase the formation of NOx.
Achieving this goal would also reduce life-cycle costs to the extent that reduced fuel consumption exceeds the cost of implementing associated design changes.
The technical risk of this goal is high because achieving 70 percent combined cycle or 50 percent simple cycle efficiency may require the introduction of revolutionary rather than evolutionary technology. Changes to the underlying configuration of the turbine may be required. Development, testing, and validation may be paced by the ability to design and manufacture the necessary hardware. Solutions may require new materials, which have historically required longer development timelines.
Power Generation Goal 2: Compatibility with Renewable Energy Sources
Goal Summary Statement: Reduce turbine start-up times and improve the ability of gas turbines operating in simple and combined cycles to operate at high efficiency while accommodating flexible power demands and other requirements associated with integrating power generation turbines with renewable energy sources and energy storage systems.
Integration with renewable energy sources will be most critical for turbines being used to meet transient and peak power demands. However, all future turbines would benefit from the ability to use renewable fuels and supplement power from renewable sources.
Achieving this goal would increase compatibility with renewable energy sources and reduce environmental impacts because a fast start capability and flexible operations will enable grid operators to quickly balance the electrical output of gas turbines with the variable quantity of power supplied by wind and solar.
The demand for fast start may be impacted with the introduction of grid-scale energy storage systems such as batteries. Hybrid gas turbine/battery systems may reduce the number of turbine starts and extend the time available to bring gas turbines online. Such systems have the potential to reduce fuel burn, maintenance costs, and harmful emissions.
Achieving this goal would improve fuel flexibility, as one aspect of an integrated energy infrastructure with renewable energy sources is the ability to burn renewable fuels.
The technical risk of this goal is medium to high depending on the nature of the renewable fuels that gas turbines would be expected to use as fuel; using 100 percent hydrogen would pose the highest technical risk. Compatibility with electrical generators powered by renewable fuels would also be challenging due to the rapid and frequent fluctuations in the amount of electricity available from renewable energy sources.
Power Generation Goal 3: CO2 Emissions
Goal Summary Statement: Reduce CO2 emissions to as close to zero as possible while still meeting emission standards for NOx.
There is growing pressure to reduce emissions of various types from power plants. Reducing emissions of CO2 is of primary importance, however, because the threat posed by global warming and the corresponding drive to decarbonize the energy industry makes the status quo increasingly unacceptable. New gas turbine designs that reduce CO2, however, will not be competitive if they come at the cost of decreased performance or if they prevent gas turbines from meeting standards for NOx and other harmful emissions.
In addition to reducing environmental impact, achieving this goal would increase compatibility with renewable energy sources and the future electrical grid by enabling greater use of renewable fuels.
The technical risk of this goal is medium because high efficiencies generally require operating at higher pressures/temperatures, where NOx formation rates are accelerated. New combustion paradigms are required to enable acceptable NOx, while still maintaining adequate turndown.
Power Generation Goal 4: Fuel Flexibility
Goal Summary Statement: Enable gas turbines for power generation to operate with natural gas fuel mixtures with high proportions (up to 100 percent) of hydrogen and other renewable gas fuels of various compositions.
Fuel flexibility is particularly important for power generation and oil and gas applications. In addition to improving fuel flexibility, achieving this goal would reduce environmental impact by decreasing the reliance on conventional carbon-based fuels, and moving toward zero or near-zero net carbon emissions.
Achieving this goal would increase compatibility with renewable energy sources and the future electrical grid by having the ability to burn fuels, such as biofuels, derived from renewable energy sources.
The technical risk of this goal is high because of the target to burn 100 percent hydrogen.
Power Generation Goal 5: Levelized Cost of Electricity
Goal Summary Statement: Enable reductions in the levelized cost of electricity from power generation gas turbines to ensure that these costs remain competitive with the cost of solar and wind power systems over the long term.
Levelized cost is becoming one of the key criteria to determine whether a utility company decides to purchase and operate a gas turbine. It is likely that sales of gas turbines will be negatively impacted once the cost of renewable energy is consistently undercutting the cost of gas turbines. Two recent assessments predict that this could happen in the 2021 to 2024 time frame.
It will be challenging both to meet the increasing performance goals and to remain cost competitive with the renewable energy sources. The ever-changing power generation landscape makes it increasingly difficult to predict gas turbine research with the highest potential paybacks. For example, large and unforeseen reductions in the cost of renewable energy could potentially mitigate or reverse long-term projected growth in the demand for gas turbines for power generation.
Given record-low prices for renewable energy, Bloomberg New Energy Finance has stated that “some existing coal and gas power stations, with sunk capital costs, will continue to have a role for many years, doing a combination of bulk generation and balancing, as wind and solar penetration increase. But the economic case for building new coal and gas capacity is crumbling, as batteries start to encroach on the flexibility and peaking revenues enjoyed by fossil fuel plants.” Even so, the pace at which changes in power sources could take place would depend on many factors, such as the pace at which lower-cost renewable sources of energy could be scaled up and deployed and the rate at which demand for electricity is growing.
This research area would directly reduce life-cycle costs. The technical risk of this goal is high because the increased efficiency targets will require more expensive solutions such as higher performing materials and more complex component geometries leading to higher manufacturing costs.
But we said it wouldn’t be easy!