Designing for Extremes: Battery Storage in the Mojave Desert

When Doosan GridTech installed a 25-MVA/10-MWh battery energy storage system (BESS) for the Los Angeles Department of Water and Power (LADWP) at its Beacon Solar Plant site in Kern County, California, the company introduced mission-critical design elements that enabled the system to operate reliably in one of the more inhospitable places on the planet while meeting the utility's rapid-response and high-performance requirements.

1. This aerial view shows the Beacon battery energy storage system (BESS) and the Beacon Solar Plant, located in the Mojave Desert in California. The BESS was designed to operate in extreme climatic conditions. Courtesy: LADWP

Due to its location in the Mojave Desert (Figure 1), LADWP required its first utility-scale BESS to deliver maximum reliability-99% for 10 years-while accommodating the following use cases:

a- Frequency control to meet and maintain North American Electric Reliability Corp. and Federal Energy Regulatory Commission frequency specifications as a balancing authority.

a- Energy storage to demonstrate the project's ability to offset renewable energy generation.

a- Voltage support to provide reactive power adjustments at the 230-kV transmission line to help mitigate voltage rise and drop occurring due to wide variations in energy production and load during the day.

a- Performance testing to demonstrate long-term and commercial-scale reliability of the energy storage technology.

Given these use cases, the nascent state of battery energy storage technology, and the extreme temperature conditions of the Mojave Desert, Doosan GridTech used an N+1 design methodology and intelligent failover feature to deliver a BESS with minimum system downtime for maintenance and repair.

The design approach balances economics and reliability while making sure the system will meet its performance guarantees. While the N+1 methodology is commonly employed in critical utility applications, this is the first time that this strategy and its corresponding financial investment was accepted by LADWP to assure the highest degree of reliability in its flagship battery storage installation.

N+1 Design Resilience

Put simply, this N+1 design means that the BESS is designed to meet the performance capabilities for the full 10-year period of service, even if a major piece of equipment is out of service for any reason. In effect, routine maintenance and other downtime can occur without any system derating or limitations. Doosan built in complete redundancy of several critical systems to ensure that the system would continue operating in temperature extremes ranging from 0F to 115F.

Due to the two-hour driving distance from downtown Los Angeles, the Beacon BESS also needed to be designed to minimize maintenance in an extreme weather environment. Here are some of the steps the company took:

a- Oversized equipment was used, allowing for both N+1 design and extreme temperature considerations while still delivering 25-MVA and 10-MWh capability. A more temperate climate would dictate using only 10 2.5-MVA inverters. But because inverter performance declines in extreme heat, 12 2.5-MVA inverters were installed, with an extra unit added to ensure the system would continue operating if one inverter or container failed.

a- Highly insulated battery containers were installed to improve heating, ventilation, and air conditioning (HVAC) efficiency.

a- Hardened control systems were included, with control computer and network switches that can handle temperatures greater than 160F.

a- An on-site backup diesel generator was installed that can power the HVAC and monitoring systems for up to seven days, keeping battery temperature conditions within warranty requirements. Due to the high likelihood of a major earthquake in California, enough fuel for seven days of generator operations was required so that LADWP could focus on higher-priority recovery efforts. If this project had not been built in a high seismic zone, less fuel or a non-permanent solution such as mobile generator connections might have been acceptable.

a- Complete redundancy is provided for the battery HVAC system. The 10-ton design requirement for cooling each container was doubled, providing 100% redundancy for a total of 20 tons of cooling and utilizing multiple stages for efficient operation.

a- Two auxiliary power transformers were installed to provide redundancy of auxiliary power distribution. This allows one transformer to be taken out of service for maintenance while the other is available to continue running the HVAC system.

a- Two on-site control systems were created in a hot standby configuration, so that if one fails, the other will automatically take over and continue to manage the system.

a- A redundant fiber optic network loop was installed between all BESS components, eliminating any single point of communication failure.

a- As an additional safety measure, oversized door hinges, door bolts, and door latches were installed on each container to protect against high winds in the area.

Put to the Test

The battery energy storage business is a fast-growing, rapidly evolving sector within electricity generation and distribution. But some aspects of the technology, and some use cases, are still in an early stage of development. The stakes were high for LADWP's $19 million Beacon BESS, and it was important to ensure that the technology would prove itself under extreme operational conditions and extreme weather conditions.

To prove the N+1 design methodology and meet the 100% redundancy requirement, the system was put through 90 days of Performance Acceptance Testing. The first five days of testing took three hours and included a 30-minute/20-MW charge cycle and a 30-minute/20-MW discharge cycle followed by a 60-minute/10-MW charge cycle and a 60-minute/10-MW discharge cycle, while simultaneously producing and consuming 15 MVAR of reactive power. That was followed by 85 days of 15-MVAR production and consumption of reactive power to support the voltage at the 230-kV transmission line. The system successfully obtained 99.9% availability for the 90 days of testing, exceeding expectations. The only downtime that occurred was a few hours to optimize the feedback control loop to improve performance when transitioning between scheduled setpoints.

Commencing commercial operation in early October 2018, the Beacon BESS has been constructed alongside new solar photovoltaic (PV) power plants totaling 570 MW. It will also enable additional development in one of the best solar PV locations in the country.

-Jason Yedinak, PEis manager of power engineering, andAnna Edwardsis a power-systems engineer, at Doosan GridTech in Seattle, Washington.

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