Source: RWE connects its first utility-scale battery storage project to the California grid
Preface. In 2024 if all of the BESS battery storage time were added up, they could store 8 of the 8,760 hours of annual electricity generated in the USA. Only 5% of their energy is used to actually store energy, the rest is arbitrage to quickly balance fluctuations caused by wind and solar living and dying. Yet we need from one (720 hours) or three or more months of energy storage (2160) of 4200 TWh annual electricity to cope for the seasonality of wind and solar in a 100% renewable grid. But it isn’t simply a matter of building more energy storage batteries, because the technology they rest upon is shaky and unstable and complex.
Most states are too flat to develop pumped hydro storage, the only commercial option today. PHS is also very expensive and can cost billions of dollars in the few places where one might even be put since the best spots were built decades ago. One of the few ways to balance wind and solar without using natural gas are batteries. Other posts explain why these won’t scale up, but that’s just the beginning of their problems as you’ll see in the two articles below.
This paragraph especially struck me: Cell imbalances can occur because battery energy storage systems comprise of hundreds of thousands of individual battery cells, and while these cells are part of the same system, they vary in quality and aging. The weakest cell among them dictates the performance. Thus, when the BESS is charged, not every cell will charge to the same targeted value (e.g., 100% SoC). At the same time, when discharged, not every cell will be discharged to the same planned value (e.g., 0% SoC).
Twaice is selling a product to help detect these issues, but yikes, imagine the effort to figure out which of the hundreds of thousands of batteries to yank out and replace. Dad used to take the vacuum tubes out of the TV and go to a TV/stereo store to plug them into a testing machine to figure out which one was bad and replace it. This technology is far from being ready to balance wind and solar power, and too complex in a simplifying world to do so. Or even in a complex one with all the time in the world and no peak oil in 2018.
Fantham (2020) pointed out that “Lithium-ion BESS cells each have an upper and lower voltage limit. It is both dangerous and detrimental to battery health to exceed these limits. In a BESS, once a single cell reaches a voltage limit, the BESS must stop charging/discharging in order to prevent over-charge or over-discharge of the battery. However, due to imbalance, not all the cells will be at their limit and therefore there is unused capacity in the system. There are some important questions that this issue raises that are difficult to answer using a large scale BESS. Given that in a large scale BESS there can be tens of thousands of cells and upward, it is unfeasible to log the data for all of the cells.”
This also reminds me of how Lawrence Berkeley National Laboratory and other national labs spent hundreds of millions of dollars on improving batteries to electrify cars in the 1990s. I used to go to their open house every year, and remember chatting with one of the battery scientists who lamented that they had greatly improved small batteries, but not larger sized ones designed for vehicles. And that is where Elon Musk comes in, he strung thousands of batteries together into battery packs. The Tesla Model X has 7,256 cells for example. How many millions of batteries are in these “jelly jar county fair” BESS containers I wonder?
Alice Friedemann www.energyskeptic.com Author of Life After Fossil Fuels: A Reality Check on Alternative Energy; When Trucks Stop Running: Energy and the Future of Transportation”, Barriers to Making Algal Biofuels, & “Crunch! Whole Grain Artisan Chips and Crackers”. Women in ecology Podcasts: WGBH, Financial Sense, Jore, Planet: Critical, Crazy Town, Collapse Chronicles, Derrick Jensen, Practical Prepping, Kunstler 253 &278, Peak Prosperity, Index of best energyskeptic posts
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Gage E, Scoblete G (2024) Line of Thought: How the Growth of Battery Energy Storage Systems May Impact Commercial Property Insurers. Verisk.
Lack of Uniformity May Hinder Risk Analysis One challenge when examining the potential risks of a BESS is the general lack of uniformity in the product.8 They may employ different battery technologies or different design configurations—and that lack of uniformity is reportedly increasing.9 But no matter the tech, one concern seems to loom large: fire. For commercial property insurers, the prospect of a BESS fire could mean damage both to the unit itself and to any property near enough to the flames or flying debris (for example, if there’s a related explosion).
The insurance industry is finding it hard to calculate risks because the precise failure rate of lithium-ion batteries is not available. Or how many fires there have been. One study found that through 2021 fires may have impacted about 4% of the total BESS capacity in the US, and researchers have cataloged over 8,000 lithium-ion battery fires/incidents. 10 11 12
Over a quarter of BESS revealed quality issues related to their fire detection and fire suppression systems. Almost 20% had issues with thermal management systems. BESS units can feature numerous battery packs with hundreds to thousands of lithium-ion battery cells that are connected to one another—inconsistencies in their performance can trigger thermal runaway. 13 14 15 16
Additional Battery energy storage system fire risks
Environmental conditions: BESS failures can potentially be triggered by environmental conditions such as excessive humidity, flooding, extreme swings in temperature, or the accumulation of dust.17
Solar Connectivity: If solar panels are providing energy to a BESS, they may continue to pump energy into a system when firefighters are battling the blaze.18
Fire Suppression: Ironically, fire suppression systems may also contribute to battery overheating. In one instance in California, a sprinkler system reportedly sprayed cells operating under normal temperatures, triggering an overheating.19
Age: Another irony: It’s not aging units that appear to be going up in flames more frequently. By one estimate, the majority of BESS fires globally tend to occur when the unit is between 0-1 years old. 20
Battery Energy Storage System Cyber Vulnerabilities
Like many aspects of our energy infrastructure, BESS appear vulnerable to cyberattacks.21 According to one report, the operational technologies employed by some BESS units to collect data or remotely manage these systems may lack basic cybersecurity protections.22 Cyberattacks targeting those technologies could not only disrupt or possibly exfiltrate data but could tamper with the physical components of the unit in such a way as to potentially trigger fires or malfunctions—particularly if those attacks target the unit’s battery management system.23 Some battery management systems may leverage cloud computing architectures for improved processing, but the migration of some of these systems to the cloud may create additional cyber vulnerabilities and entry points for bad actors.
[go to online article for citations here]
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Twaice (2024) Improve the safety, availability & performance of energy storage systems with battery analytics.
The increasing numbers of BESS that are supplying electricity to the grid come with risks, which is why the North American Electric Reliability Corp (NERC) continues to develop new reliability standards for inverter-based resources (IBR) – including battery storage, wind and solar (UD 2023). Batteries are such complex systems that a lot can go wrong, such as risky increases in temperatures which can cause the system to trip offline, or cell imbalances, which over time decrease the amount of energy that can be discharged. Battery energy storage systems as well as other renewable energy assets must be able to reliably provide the amount of electricity to the grid that they have agreed to. If they are not able to do this, they are liable for penalties and in the future, will risk noncompliance with regulatio
BESS availability is just as important for owners and operators who are not providing grid services but are engaging in energy trading. To take advantage of price fluctuations to purchase, store and release energy on-demand, the energy storage system must be reliable. It must be available when required and perform to its optimal potential, otherwise trades could be interrupted or rendered unviable. Also, extreme price spikes in the market mean that energy storage systems can earn a large portion of their planned income in just a couple of events – for example during extreme windy weather. If these rare events happen, the system must be up and running and performing at its optimal level, otherwise asset owners and operators leave money on the table
Companies need to ensure there are measures in place to ensure high availability and safety of energy storage systems. However, this isn’t easy. Asset owners and operators are juggling many different tasks and often lack transparency into what is going on with their ESS, making it practically impossible to identify what problems might occur and how they can be avoided. While there are many different root causes of poor availability or downtime, cell imbalances are one of the main ones. Identifying and solving problems with cell imbalances can go a long way in ensuring BESS safety and availability. In this whitepaper, we discuss the challenge of cell imbalances and how battery analytics can help to overcome it.
Imbalanced modules and cells lead to inverter faults and can cause wasted energy. This can be hugely problematic and lead to losses of billions of dollars/euros over the lifetime of an asset. An internal analysis carried out by TWAICE showed that if a 100 MWh system experiences a State of Charge (SoC) imbalance of 15% within half of all strings, this could lead to a revenue loss of 10 million EUR over the entire lifetime of the asset.
Cell imbalances can occur because battery energy storage systems comprise of hundreds of thousands of individual battery cells, and while these cells are part of the same system, they vary in quality and aging. The weakest cell among them dictates the performance. Thus, when the BESS is charged, not every cell will charge to the same targeted value (e.g., 100% SoC). At the same time, when discharged, not every cell will be discharged to the same planned value (e.g., 0% SoC).
This has profound implications for the BESS. On the one hand, this can cause considerable stress for the battery and drive systems out of the pre-defined and safe operation windows, leading to safety issues, downtime and shorter lifetime. Additionally, this leads to wasted energy, meaning that BESS are less likely to be able to fulfil their market obligations.
[So basically if just one of four batteries is 100%, the others in its clusters stop charging, and same on the discharge side—the first one to finish determines prevents the others from fully discharging, causing a considerable waste of energy].
While SoC imbalances can occur naturally due to quality differences among the individual battery cells, they can also occur due to the way in which the battery management system (BMS) calculates state of charge. The BMS usually calculates the state of charge based on the Coulomb Counting method or voltage. The Coulomb Counting Method measures the current of the battery, but errors accumulate when the battery is used for a long time without being fully charged or discharged, making it difficult to accurately estimate SoC. The limitation of using the voltage method to calculate the SoC is that the open circuit voltage (OCV) changes with temperature and aging. This is particularly problematic for LFP storage systems because these have a flat OCV, therefore small errors in voltage cause huge distortions for the SoC estimation. This whitepaper explains about the different methods of calculating battery State of Charge in more detail).
When several cells or modules are aggregated, the inaccurate SoC provided by the BMS means that some cells are overcharged and some cells are undercharged, leading to even stronger SoC imbalances – thus more wasted energy, and higher safety risks
Summary
Cell imbalances are a key indicator that can lead to low availability, revenue loss, safety risks and shorter battery lifetimes. Cell imbalances cause low availability as they lead to wasted energy and over time, lead to increased stress on the battery.
While it is helpful to know when and where cell imbalances are occurring, it is even more helpful to understand the root cause of the problem. This could be a problem that occurred during manufacturing or construction, it might have to do with HVAC components such as the cooling system, or it might result directly from the way that the storage system is operated.
After this a product is explained that can help to detect these problems
References
Fantham TL et al (2020) Impact of cell balance on grid scale battery energy storage systems. Energy Reports. https://doi.org/10.1016/j.egyr.2020.03.026
UD (2023) FERC directs NERC to draft reliability standards for wind, solar and storage. Utility Dive.