BESS is for Batteries
Opponents of the Rancho Viejo Solar project are most concerned with safety hazards stemming from battery energy storage systems (BESS) used alongside wind and solar farms. The energy storage system banks excess power and helps regulate output, but they come with risks. Besides the inherent risks of any chemical battery technology, the technology behind these energy storage systems is barely out of its infancy.
Here’s a look at where this new technology came from and where it might be headed, based on available reporting and online resources.
From Under the Hood
First-generation battery storage systems of the 2010s were often housed in large metal buildings. In late 2012, Xtreme Power commissioned a 36-megawatt battery built inside a metal building in West Texas for Duke Energy—one of the first of its kind. The buildings were the right size but inflexible and expensive and inflexible. Self-contained BESS gradually evolved out of the tech and proved easier to move, or scale while being cheaper and showing improved safety.
As for the batteries themselves, first-gen versions were old-school lead-acid based like you’d find in a car. Those first-generation batteries offered high surge currents but had low energy density compared to what is used today. Non-sealed lead-acid batteries can also produce hydrogen and oxygen when overcharged. To avoid that problem, water has to be refilled regularly. Because the inflammable gases they produce must be vented out to avoid explosion risks, high maintenance costs followed.
Enter large-scale lithium-ion batteries, which like the acid-lead version they replaced in BESS, started in vehicles. Turns out batteries for electric cars are a better fit for BESS than batteries for combustion engines. Lithium-based chemistries enabled significantly higher energy density than acid-lead and much longer battery life.
A kind of Wild West for stationary lithium-ion based energy storage technology emerged, bringing battery chemistries like Nickel Manganese Cobalt, Lithium Titanate Oxide, Nickel Cobalt Aluminum, and later Lithium Iron Phosphate into the fray.
Nickel Manganese Cobalt (NMC) was the early favorite. Samsung built one of the first Battery Management Systems in 2013, using NMC chemistry. The company then partnered with Sungrow on a high-quality lithium-ion BESS that set the standard in terms of design and chemistry, making Korea a leading center for BESS technology.
BESS is Born
Portland General Electric (PGE) in Washington commissioned the country’s first grid-scale BESS, which was introduced in October 2012. Today, PGE has three grid-scale battery energy storage systems with an output of 475 megawatts and over 1.9 gigawatt-hours of dispatchable capacity for the Portland metro area.
Most of the BESS systems today are composed of securely sealed battery packs, which are electronically monitored and replaced once their performance falls below a given threshold. Batteries suffer from cycle ageing, or deterioration caused by charge–discharge cycles.
Lithium-ion batteries offer a long lifespan with minimal maintenance, high energy density, and low self-discharge, which makes them ideal for modern utility-scale BESS applications, according to the Electric Power Research Institute.
BESS Burns
Some lithium-ion batteries are a fire hazard, primarily those containing cobalt. The number of BESS incidents has remained around 10 to 20 per year and usually in the first three years of operation. Because the rate has remained static while the size and number of systems increased, the failure rate has decreased, according to EPRI.
The greatest hazard from these systems is called thermal runaway—an uncontrollable, self-accelerating chain reaction that occurs when a device, particularly a lithium-ion battery, releases heat faster than it can dissipate, leading to a critical temperature increase, fires, and potentially explosions.
BESS fire accidents include individual modules in 23 battery farms in South Korea from 2017 to 2019. In the US, reported battery fires have been sparse but dramatic and dangerous. Some recent examples:
Moss Landing, Calif.
On Jan. 16 in Moss Landing, Calif., a BESS made by Vistra connected to a system at the Moss Landing Power Plant lit fire and quickly burst into thermal runaway, causing the evacuation of more than 1,000 residents. The fire destroyed a significant portion of the facility, releasing smoke and contaminants into the air, leading to road closures, health concerns and a class-action lawsuit filed by residents and business owners. Residents complained of headaches and sore throats in the aftermath, and the incident prompted calls for improved safety regulations. The same fire reignited a month later. This incident followed a malfunction in September of 2021 at the same facility that damaged a significant portion of the battery modules. This was the fourth fire incident reported at the facility.
Escondido, Calif.
On Sept. 5, 2024, a fire broke out at a San Diego Gas & Electric battery storage facility. The blaze was limited to one of the 24 battery storage containers, according to the city of Escondido, and no injuries were reported. However, the surrounding area remained under mandatory evacuation orders for a couple of days.
Surprise, Ariz.
On April 19, 2019, smoke was reported from the building housing of the energy storage system at an AES-owned site in Surprise, Ariz. About three hours after the reports of smoke, a door was opened and a thermal runaway ensued. Injured first responders were transported to area hospitals. An extensive investigation finds “to a reasonable degree of scientific certainty that this internal failure was caused by an internal cell defect, specifically abnormal Lithium metal deposition and dendritic growth within the cell.” The lithium-ion battery module that failed was made by LG.
For details about incidents, consult the online BESS Failure Incident Database, which compiles information about stationary battery energy storage system failure incidents. Another website, bess-sdk.com, keeps a map of reported BESS incidents.
Tech Advances
Lithium iron phosphate (LFP) batteries have since emerged as a favorite for large storages due to the high availability of its components, longer lifetime and higher safety compared to nickel-based lithium chemistries. An LFP-based energy storage system that was installed in Paiyun Lodge on Mt. Jade in Taiwan has operated since 2016 without a safety incident as of June 2024, according to a journal entry published by MDPI.com.
Sodium-based batteries are emerging as a contender with lithium chemistries for BESS applications because, compared to lithium-ion batteries, sodium-ion batteries offer improved safety, and similar power delivery. The technology lags in energy density compared to lithium-ion batteries. The largest BESS using sodium-ion technology launched in 2024 in China’s Hubei province, boasting 50 megawatts and 100 megawatt hours, according to a July 2024 article in Chemistry World.
(Dave Cathey)
