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As more and more states pass laws mandating that up to one-third of their power come from renewable sources by 2020, utility companies are wrestling with how to make the energy mix work.
A persistent problem for wind and solar power is intermittency – the wind doesn’t always blow and the sun doesn’t always shine when power is needed most. And batteries large enough to store massive amounts of power for these down times are too expensive to deploy.
Now, an emerging consensus holds that wind and solar coupled with natural gas-powered turbines could be the best way to balance green energy with reliable power supply.
Turbines fire up rapidly
When electricity from wind and solar aren’t available, natural gas turbines are ideal for bringing backup power online quickly, according to a recent study by the Center for Strategic International Studies (pdf), a bipartisan policy center.
The 7FA turbine can reach 75 percent of its peak output in 10 minutes. Photo/Courtesy GE
Bryan Sixberry, a product manager for 7FA gas turbines at General Electric, this magazine’s sponsor, said natural gas turbines can fire up rapidly and provide power to the grid when renewable energy falls short.
“Just like a stock portfolio, you have to have a diverse energy mix,” Sixberry said.
The 7FA turbine working in simple cycle – which means there is no steam turbine attached to catch waste heat – can reach 75 percent or more of its peak output within 10 minutes of being switched on, Sixberry said.
Power without interruption
Over the years, GE engineers have increased not only the turbines’ energy output – a new generation 7FA gas turbine can generate 211 megawatts of power – but also their ability to start and stop rapidly.
A gas turbine in the GE manufacturing center in Greenville, South Carolina. Photo/Courtesy GE
By comparison, coal-fired electricity generation cannot adjust output as rapidly and its considerable environmental impacts would effectively negate the benefits from the wind and solar that it backs up.
Sixberry said that about 60 percent of GE’s 7FA natural gas turbines in use are already operating on stop-and-start cycles, while the balance of turbines run almost constantly.
So if wind power can’t meet demand on a hot summer day, when consumers have their air conditioners blasting, the gas turbine can come online quickly and supply the additional power without any noticeable interruption.
“An essential partner to renewables”
This capability is often referred to as “wind firming,” which is necessary because a world powered only by renewables is not feasible right now.
Perhaps just as important for a renewable energy backup system, natural gas turbines have become increasingly efficient and clean, Sixberry said. The turbines emit just 9 parts per million of both nitrous oxide, which is produced by combustion at high temperatures, and carbon dioxide.
With low emissions and quick start ups, natural gas for electricity generation could be, as the report by the Center for Strategic International Studies called it, “an essential partner to the development of renewables.”
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