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On Edge of Phoenix, APS Tests the Relationship of Solar and Batteries

September 05, 2018

Project analyzing capabilities of energy storage in neighborhoods

Drama took center stage for Arizona Public Service the morning of Aug. 21, 2017. From 10 a.m. until noon that day, the company faced the vanishing act of the young century when the moon passed in front of the sun and created a near total solar eclipse across the state.

APS had researched and modeled what was expected to happen on the grid in the weeks before the eclipse. Still, questions remained about the full effects when nearly all of the solar energy on the APS system disappeared with the sudden blotting out of the sun. Fortunately, not much happened. The plans APS put into place did the job. At the forefront were advanced technology innovations like the identical 2-megawatt (MW)/2 megawatt-hour (MWh) grid-scale batteries on the Festival Ranch and McMicken feeders that help supply specific West Valley neighborhoods in Surprise and Buckeye.

Batteries just part of larger program

These energy storage resources are part of a larger pilot project APS has embarked on to learn how to better integrate the growing amount of intermittent renewable energy resources into the system, especially private (rooftop) solar. Batteries have the potential to smooth out gaps in solar production when clouds pass over panels and deliver surplus solar energy captured during midday to customers as they arrive home from work and the sun goes down.

The two batteries have been integrated into the company’s Solar Partner Program, a project which includes 1,500 customers. Many of the systems are deployed in the West Valley, where more intermittent solar placement has been particularly – and unpredictably – disruptive to the grid.

Participating customers are receiving $7,200 – $30 a month over the next 20 years – to install a collective 10 MW of photovoltaic rooftop solar panels so the company can study the use of smart inverters and energy storage. APS wants to learn how to improve reliability for customers in areas where a high penetration of solar has created instability in the system. The information APS is gaining from this study will help craft what the future of renewable energy integration looks like for utilities across the country.

“The best renewable energy is the type a customer never thinks about. A light goes on, a load of towels gets washed and life goes on as reliable as ever before, all powered by the sun,” said Scott Bordenkircher, APS’s director of technology innovation. “This is the future APS looks toward as it studies energy storage.”

Construction began on the two batteries in late 2016 and they became operational in early 2017, supplying power to up to 1,000 homes for an hour. That might not sound like a lot, but they displace more expensive resources at times of the highest customer demand, and they also can provide substantial information that will help APS to decide when, where and how much energy storage to deploy in coming years. This is particularly important with company projections forecasting population and economic growth in Arizona that will increase the state’s energy needs by as much as 25 percent by 2025.

It is part of the company’s determination to take the lead in Arizona’s deployment of energy storage, advanced inverters and other controllable resources to better manage peak demand, minimize CO2 emissions and solve renewable integration challenges for the benefit of all of APS’s customers.

A stabilizing influence for customers

The solar eclipse provided the perfect opportunity to see how energy storage can minimize one of the biggest problems with solar power – when the sun does not shine, solar power resources stop producing and completely. That can be disruptive – even destructive – to customers, the grid and sensitive equipment on both sides of the electric meter.

The identical batteries sit on the far edge of development in the West Valley, an area where some probably don’t realize how far civilization has crept out into the desert. Festival Ranch is 52 miles northwest of downtown Phoenix, 14 miles west of the confluence of the 303 and Bell Road. McMicken is about 12 miles due east of Festival Ranch, just north of Sun City Grand. The batteries are surrounded by lots of empty land for now. That won’t last long and their importance will only increase.

Both sites were strategically selected as the locations for these sleek, single-story, supercooled steel structures that inside contain 32 cabinets resembling lockers a high school basketball team might use. Each cabinet is filled with modular units called nodes that together make up the 2 MW batteries.

They are also installed at different points on the feeders to see if location adds value to power quality and reliability for customers. The Festival Ranch battery is installed at mid-circuit, while the McMicken unit is contained at the head of the feeder in an existing substation.

The battery arrays were primed and ready to go the day of the eclipse. Both batteries were fully charged before the eclipse began. As the moon began passing in front of the sun, they were discharged to power the load precisely. As expected, the needle never moved.

“It was as if the eclipse never happened,” said Erik Ellis, then manager of energy technology assessment for APS. “The batteries responded perfectly and sustained their performance through the entire event. We wanted to know if they could help maintain reliable service to customers. They passed their first major test with flying colors.”

An education in advanced technology

Reliability is essential, but only part of the story as APS takes the lead among electric utilities across America in understanding and deploying energy storage resources.

Solar power is clean and abundant, but the way it is utilized today on rooftops scattered across the system can be disruptive. When power is produced at a specific point along the distribution system, voltage is increased at that point and that is a problem. The system must be kept in balance or it will become unstable. Sensitive equipment can easily be damaged and large swaths of customers could lose service. Power quality could be at risk, producing further havoc. These are well-known issues, but much more prevalent with the presence of so much private solar newly installed on the system (more than 80,000 installations in APS territory alone).

Advanced inverters for solar and energy storage systems can enable grid operators like APS to maintain proper control and keep power flowing seamlessly. Inverters transform DC power to AC power so it can be used by customers; advanced inverters allow the utility to have a measure of control over the private solar array to better maintain system voltage in desired ranges, thus protecting sensitive appliances like computers, HD televisions and other important devices that run off electricity.

“We have learned so far that energy storage is superior to advanced inverters in allowing us to operate the system as needed,” Bordenkircher said. “Both are important, but medium-sized batteries like those at Festival Ranch and McMicken are the bigger wrestler in the ring. If every inverter was an advanced inverter we would be good to go, but they are not. Batteries can act as a grid regulator and enable us to restore stability to the sections of our system where we have high solar penetration.”

Many lessons learned

These battery pilots have produced invaluable data. As a result of a single year of operating the energy storage at Festival Ranch and McMicken, APS has learned:

  • How to operate and utilize battery storage
  • How to operate batteries and advanced inverters together so they work in tandem
  • How to use batteries to minimize or prevent power outages
  • Where batteries are best deployed
  • How to follow the load and voltage and a combination of the two
  • How to relieve the local grid during times of peak usage, extending equipment life, and
  • The ideal rate of charging and discharging the batteries

“We have found problems and solutions and we have shared that information far and wide, including with our research partner EPRI (the Electric Power Research Institute), which we believe will lead to greater innovation and broader solutions,” said Bordenkircher. “The work that is being done on energy storage here in Arizona is truly groundbreaking. It is important work and a part of our contribution to the energy welfare of our state and customers.”

In the end, it is customers who will benefit most. Energy storage today is expensive, but as it becomes more efficient it will become more economical. Part of understanding how to unlock the full value of storage is to test its full range of applications. Customers will get more out of the renewables either installed in large installations on the APS system or on individual homes, and Arizona will have a cleaner, more efficient energy future.

“Not all that far into the future, our customers will live in homes that are powered by resources that are cleaner and smarter – and ultimately less expensive,” said Bordenkircher. “The batteries at Festival Ranch and McMicken are an early step toward that future, but an important step. Projects like this will help us to decide how best to deploy advanced technology. The lessons we learn here will resonate for years.”


Energy storage batteries used for the APS pilot program are housed in cabinets that resemble gym lockers.

Categories: Innovative
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