The rapid growth of California’s solar industry has changed the Golden State’s grid from a camel into a duck — and no, we have not been sitting out too long in the midday sun. California’s baseload curve, or bare minimum electricity source, used to look like the profile of a camel with 2 evenly equally humps since thermal plants came online twice a day to meet power demand peaks. And this tech is Ducking The Duck Curve.
That camel has morphed into the form of duck over the past decade as California added around thirteen gigawatts of solar power capacity. The solar generation booms at lunchtime and then disappears at sunset. This means that thermal plants have a moderate morning physical exercise, are mostly idle in the day, and return at dusk to do the grid’s heavy lifting. They create a baseload curve that looks like the pert rump, sloping back and long, high neck of a right-facing duck.
The duck curve may sound jolly, however, it's no fun for the operators of the state’s gas-burning plants. “Solar generation has made it even more difficult for utilities that provide baseload power to respond to the steeper peaks and troughs of California’s power demand,” says Alexander Pistner, an Atlanta-based senior product manager for GE Power.
He says many of California’s gas-burning plants were constructed long before solar and other renewable plants joined the state’s grid, and they were designed to remain on almost 24/7 as baseload power.
They often deliver their best possible fuel economy and lowest emissions once they are at high load, or when they are pumping out power uninterrupted for many days at a time. “Now they’re struggling to determine the balance between coming offline completely and operating at minimum load,” Pistner says.
He explains that you cannot turn gas-burning power plants on and off sort of a light-weight switch, or increase and reduce their load, while not a negative impact on their potency and emissions. In this respect, they're similar to car engines, which usually burn much less gas per mile — and emit less — once purring at high speed on the highway compared to once they are stopping and beginning in the central city.
But assistance is at hand for operators that are struggling to ride California’s growing duck curve. GE engineers have devised a neat shortcut to make its gas turbines deliver cruising-speed efficiency and emissions, even after they are being used as a city run-around. They have rolled out a turbine upgrade known as in industry expression 7F DLN2.6+ Flex, where DLN stands for Dry Low Nox (nitrogen oxide-based air pollutants), and 7F refers to GE’s turbine nomenclature.
The upgrade uses Axial Fuel Staging (AFS) technology — which splits the combustion of the turbine’s natural gas and superheated air into separate upstream and downstream zones. Derrick Simons, the Greenville, South Carolina-based specialist in turbine technology, who heads up the team that has designed the AFS system, says cacophonic combustion into 2 zones permits the injection of a comparatively cool flame of burning gas and superheated air into the warmer downstream crucible. This bumps up the flame’s temperature, which controls the turbine’s emissions and raises its efficiency.
Simons, who has worked for GE for nearly 20 years explains it works a bit like a jet's afterburners, you can inject additional fuel and air downstream to optimize performance.
If you have ever used a bunsen burner in a science laboratory, you know how to vary the flame between billowing yellow and roaring blue by regulating the airflow into the bottom of the barrel. The yellow flame is cool, fuel-rich and air-poor, whereas the blue, lean flame is fierce and hot since it burns with a higher ratio of air.