Jet engines are subject to rapid-changes in power demands — revving exponentially up and turning on a sixpence to ramp down again. Technology derived from those engines is proving a perfect companion to Australia’s burgeoning intermittent renewable-energy supply: aeroderivative gas turbines ramp faster than the Roaring Forties into zephyr-less intervals, they’re instantly responsive to cloud cover over the Pilbara, and coolly cope with air-con hour on Australia’s summer grid.
A handy proof point was this year provided by the nine new dual-fuel GE aeroderivative TM2500 generator sets purchased by the South Australian government in response to the late-2016 blackouts. In January they were “instrumental in helping to keep the lights on in South Australia when Victoria was experiencing rolling cuts to supply”, says Aaron Scott, regional sales manager of gas turbines for GE Gas Power Systems.
With a combined capacity to power more than 200,000 homes, the trailer-mounted TM2500s were operational within three months of contract signing, and have spent the year-and-a-half since mid-2017 in a state of readiness to take off — take a load off the grid, that is.
In coming years, they may remain in their two grid-supporting locations, where they are currently diesel fuelled, but as the South Australian government evolves the state’s plan to reach 75% renewable electricity production by 2025, they’re likely to be regrouped as a super-efficient gas-fuelled power plant.
“Aeros” as GE’s aeroderivative turbines are affectionately known, are flexible and adaptable, not just in their ability to respond to grid requirements, but in fuel-source and configuration.
Beyond peaking power plants
“Historically, aeros have been around in gas peaker applications,” says Ihab Chaaban, global commercial development director of Aeroderivative Gas Turbines and Hybrid Technology at GE Gas Power Systems . He’s referring to what are otherwise known as peaking power plants, which are generally only run in times of high demand. But, he adds, “there has been continuous evolution in GE’s product range to match ongoing change in the global marketplace.”
GE’s aero product range is now optimised to provide solutions for contemporary needs: for mining companies running off-grid, which want to take advantage of wind and solar generation and reduce emissions by replacing traditional diesel generation, but at the same time need to ensure constant power to their operations; and for utilities working to reliably integrate more renewables into their operations.
The latest development has been the ability to integrate aeros with battery storage, in a hybrid configuration that further dramatically reduces response time and increases their operational flexibility.
Aeros themselves can ramp up to full power within five minutes of start-up from cold iron. Working in tandem with a battery charged by the aero, response time is reduced to 250 milliseconds. That is, when the hybrid system receives the signal to support grid frequency (in this case maintaining Australia’s 50 Hz requirement) or grid demand, the battery responds to supply electricity within 250 ms, which is replaced by generation from the aero within five minutes.
This means aero-plus-battery configurations can replace what’s known as grid “spinning reserve” — the frequency-stabilising effect of constantly generating large-capacity coal and gas plants.
Hybrid aero-plus-battery solutions can also be directly integrated into wind and or solar farms, thereby providing built-in grid firming for renewables developers who “are finding it more and more difficult to get their projects approved without some sort of grid support or dispatchable generation to back it up”, says Scott.
Ensuring return on investment
Incentive to invest in guaranteed ultra-fast-start capacity that uses transition fuels such as gas (which will continue to be significantly more expensive than wind and solar and current legacy coal-fired generation), is also about to get a boost.
On July 1, 2021, AEMO will implement a new five-minute “settlement” rule (replacing the current 30-minute rule) which will bring the five-minute response requirement of generation in line with the market opportunities for generators to bring in higher-priced firming generation when required. That is, the price signal will match the peak need of the grid, and investment in fast-response technologies will be more quickly recouped.
As the Australian Energy Market Commission writes in its information sheet on the change: “30 minute settlement provides an incentive to respond to expected 30 minute prices, rather than the five minute dispatch price. This leads to generator and demand responses occurring up to 25 minutes after they are required by the power system,” and to distortions in electricity pricing.
The energy landscape is complex, with many variables to consider. Chaaban advises, “Everyone is heading towards higher renewable penetration because it makes sense economically, and it makes sense for the environment, but globally grids are still going through chaotic change and I would say it’s essential to gradually manage transition.”
Maintaining the high-tech flow state
The flexibility of GE’s aero product range is well placed to provide grid firming whatever the weather, and in tandem with emerging technologies.
Chaaban points to one model of a California-based investor-owned utility (IOU) that was running a gas turbine non-stop as spinning reserve, thereby supporting grid frequency; as well as ensuring constant electricity supply. The falling cost of batteries led GE to tweak is original solution by adding a 10-megawatt battery to the system, which could respond within 250 ms, meaning the turbine had time to ramp up from zero when required. The IOU’s gas bill was enormously reduced and emissions were slashed.
In Australia, a number of research centres are focused on developing our capacity to produce hydrogen using renewably derived energy. As the technology and commercial production of hydrogen come into play, GE aeroderivative gas turbines can operate on hydrogen blended with natural gas, as well as fuels with high levels of hydrogen content. The GE Aeroderivative gas turbines can be manufactured, or retrofitted, to run with reduced emissions on that gas blend or on biofuels— allowing their grid-firming capacity to contribute towards a 100% renewably powered nation.
“It’s all being researched and tested as we speak,” says Chaaban.
In the meantime, New Zealand’s Todd Generation is installing a NZ$100 million natural-gas-fired twin-set of 50 MW LM6000s at Taranaki in the north west, in anticipation of ongoing renewable-energy installation. New Zealand has huge hydro-electric capacity, but climate variability and the country’s goal of 100% renewably generated electricity by 2035, have contributed to increasing development of solar and wind resources.
“This project represents a significant investment in the security of New Zealand’s future energy supply, said Todd Generation general manager Tim Cosgrove. “Fast-start natural-gas-fired plants provide a reliable source of power to back up intermittent renewable generation.”