Arizona Public Service Is Back on the Grid-Scale Battery Scene
The utility completed installation of two identical AES batteries to test how this technology really works on the Arizona grid.
JULIAN SPECTOR MAY 25, 2017
Arizona Public Service Is Back on the Grid-Scale Battery Scene
Arizona Public Service Is Back on the Grid-Scale Battery Scene
Photo Credit: Julian Spector
With two grid-scale batteries newly in place, Arizona Public Service is learning the elements of energy storage operation that you can't read in a book.
The utility is using the pair of 2-megawatt/2-megawatt-hour lithium-ion battery systems from AES to test how the technology performs in the desert climate of the greater Phoenix area, where summer temperatures routinely crest 100 degrees Fahrenheit.
The Advancion systems have been inserted into a distribution grid that has seen rapid uptake in distributed solar generation as a result of the Solar Partner Program, which places APS-owned PV modules and smart inverters on customer homes. Advanced battery vendors tout the technology's ability to ease renewable integration and correct power quality on the lines. APS wants to find out just how well this works in practice.
"No utility, to our knowledge, has ever done two identical batteries specifically sited in two different locations along a feeder," said Scott Bordenkircher, director of technology innovation and integration at APS.
That distinction enables a controlled experiment wherein Bordenkircher and his colleagues can test the locational value of storage for voltage control and power quality. Typically, equipment at the substation regulates voltage for the whole feeder; voltage runs high at the head of the feeder to ensure it maintains an appropriate level at the end. Grid-scale batteries open up alternative solutions.
Local, reliable data
APS put the batteries on a distribution feeder in a wide open valley northwest of Phoenix, where the Festival Ranch housing development has created a load pocket.
The West Valley has the highest penetration of rooftop solar in the Phoenix area, helped by the frequency of new builds with west-facing roofs that can capture the late afternoon sun. The Festival Ranch feeder already has 68 homes participating in the Solar Partner Program, in addition to other solar customers.
One battery went in at the substation, and the other sits in a walled enclosure halfway down the feeder, on a swath of open land adjacent to the housing tract. Now the utility can test whether one works better than the other, and how they compare to the traditional approach to voltage control.
"You've got a lever point in the middle of the feeder that has a much better chance of acting on both ends as opposed to having to force it from just one end," Bordenkircher said.
Similarly, it could be better able to smooth out fluctuations from the rooftop solar and smart inverters by being located in the midst of them. If a cloud passes overhead and knocks out 200 kilowatts of midday rooftop capacity, the utility has to call up additional generation elsewhere. The battery can do it from across the street.
"It's a shock absorber – it tends to level out the entire feeder by being able to quickly absorb or discharge depending on the situation," said project manager John Pinho.
The trial run will also test the batteries for peak shaving, although the 2-megawatt-hour energy capacity somewhat limits the usefulness for absorbing 4- or 5-hour peaks.
APS has access to the land for the mid-feeder battery for two years. If the demonstration proves successful, it may seek an extension, but it will also be possible to pull out the 60,000 pounds of batteries, lift the 100,000-pound container out, and move it to some other useful location.
Future battery installations will be informed by the data these systems gather on basic operations in the Arizona heat. Bordenkircher wants to make sure they charge and discharge as expected in a real-world field setting. The testing will also measure parasitic load, which is how much energy the battery consumes in the course of operating. That number impacts the ultimate cost and value of ownership.
That kind of data exists for batteries elsewhere, but different feeders have different effects on battery operations, Bordenkircher said. Data on a battery's performance in Southern California don't necessarily translate to how it will behave on an APS feeder in the outskirts of Phoenix, so a local calibration is needed.
The climate control keeps the interior of the battery at a balmy 75 degrees, even in the middle of a desert valley. (Image credit: APS)
Emerging mathematics
The batteries aren't doing anything that can't be done by conventional distribution equipment, like regulators, capacitor banks and integrated volt/VAR control.