29th March 2022
Battery Ageing in Energy Storage Systems
In a bid to reduce carbon emissions to zero, industry players are developing better and more sustainable means to store energy. The existing power grids run on an inefficient system and they waste a considerable amount of electricity due to a disconnect between the amount of electricity produced by the generation plant versus the actual consumption. This disconnect has given rise to the need for Battery Energy Storage Systems (BESS).
A BESS is an energy storage system (ESS) that captures energy from different sources, accumulates this energy, and stores it in rechargeable batteries for later use. Should the need arise, the electrochemical energy is discharged from the battery and supplied to homes, electric vehicles, industrial and commercial facilities.
However, like other battery systems, the BESS battery is also prone to ageing and degradation over a period of time. So, if you are wondering what causes ageing in energy storage systems, this post is for you.
Battery Ageing and its Types
The battery’s performance deteriorates gradually throughout its lifetime. This is known as battery ageing, and it is an irreversible process caused by physical and chemical changes over the years. However, certain things can escalate the rate of ageing, such as:
- High charge currents for charging
- Batteries charging for long even after achieving full charge capacity
- Charging a battery at low temperatures, i.e., less than 10°C
- Using or storing battery cells at temperatures higher than 40°C
- Cycling cells more than their operating voltage capacity/range
Primarily, there are two types of battery ageing in energy storage systems.
Calendar aging is a process that occurs while a battery is in resting mode. This is the state when there is no current flowing through the battery. It is a significant factor that causes lithium-ion batteries in Energy Storage Systems to age, especially where the battery time resting is longer than its operational hours.
The cycle of a battery is the number of charge as well as discharge cycles it completes before losing its performance. The depth of discharge is one of the most significant causes that affect the cycle life of your lithium-ion battery.
Cycle ageing occurs when your battery charges or discharges. Some ageing mechanisms include parasitic physiochemical transformations degrading your battery energy capacity and power capabilities.
Factors Influencing Battery Ageing in BESS
Studies suggest that the wide temperature range is the main factor influencing battery ageing in energy storage systems. Technically, your battery starts ageing the moment you start using it. However, the battery charge cycles play a critical role in how long your battery is going to last. Some factors influencing battery ageing are:
Battery Charge Cycle
A battery charge cycle means one complete cycle of battery drainage and full recharge. So draining a battery to 0% and then recharging it all the way to 100% counts as one battery charge cycle. However, using up to 50% battery and recharging it back to 100 also completes one charge cycle.
The more charge cycles your battery completes, the more it will degrade. This process causes your battery to age.
Overcharging and Trickle Charging
Overcharging the batteries by leaving them on charge after reaching 100% can also damage your battery’s life and risk catching fire.
On the other hand, trickle charging, where you top up the battery the moment it goes under 100%, can also diminish your battery’s lifespan and capacity.
This degradation can be accelerated by extreme charging patterns, increased temperature (both ambient and operating), overcharging, or undercharging.
At low temperatures, the reaction of the negative electrode with the electrolyte creates a protective layer on the surface of the negative electrode surface.
This layer never provides complete protection and gradually thickens over the cell’s lifetime. This consumes lithium that is otherwise responsible or contributes to your battery’s cell capacity. The greater the negative electrode’s surface area is, the more layer it will need for complete coverage, increasing the capacity fade.
The battery’s chemical reaction accelerates at a high temperature, making it a defining contributor to battery ageing. Higher temperature increases the risk of a protective layer forming quickly on the negative electrode.
Strategies to Decrease Battery Degradation
The problem of battery ageing is an area of concern for battery energy storage systems. Therefore, cell manufacturers believe that advancements in developing cathode compounds might help improve batteries’ cycle and performance life.
The battery degradation issue may be offset by using silicon compound anodes. These anodes can ensure higher energy density. However, they will also introduce a more significant element of mechanical degradation. The cell manufacturers are already working on alternative chemistries to develop anodes enabling a longer battery lifespan but at the expense of higher energy density.
According to a study, BESS with battery packs close to the floor experience lower temperatures than those on top. This temperature ranges from an average of a minimum of 23°C to a maximum of 32°C. Therefore, the manufacturers of BESS need to design sophisticated cooling systems for energy storage systems.
This strategy will help control and regulate the temperate of each battery pack in the system. Slowing down the battery’s ageing process will be beneficial in reusing second-life batteries to extend the overall lifespan of the entire energy storage system.
Battery energy storage systems are more efficient power storage systems than traditional electric grids. However, battery ageing is an irreversible process caused by various factors, including battery charge cycles, overcharging and tickle charging, and inappropriate temperatures. If you wish to slow down the battery ageing process, practicing adequate charging measures to control and maintain battery temperatures is the most useful technique.
ALTERGO’S BATTERY AGEING MODELS
State of Health estimation is the process of estimating the real performance of a battery post-deployment. This performance is often evaluated as the remaining useful capacity, actual impedance profile and often correlates directly with the state of function when considered within a specific application.
Altergo allows a range of models to be deployed on battery data. These models fall under 4 main categories: a physical, semi-empirical, statistical approach, and machine learning. Each methodology has its advantages and disadvantages and its selection depends on the use case and the availability of quality data.
Calendar aging is modeled using an empirical model which takes inputs of State of Charge, Temperature, and time. The model utilizes a first-order time-dependent ODE. The ODE takes in the aforementioned inputs along with tuning parameters to provide a progressive value of calendar losses. The calendar aging model is developed in reference to the model developed with certain modifications to normalize the output with respect to nominal capacity.
Cycle aging is modeled using an empirical model which takes as inputs the number of cycles, depth of discharge, temperature, and C-rates. The model computes the loss by averaging over the inputs. The model also requires turning parameters. The cycle aging model is developed in reference to the model developed with certain modifications to use equivalent cycles instead of charging throughput as the input for progression.
Altergo is a Modern Asset Management Platform for Energy that empowers new energy companies to create an accurate Digital Twin, a virtual replica of physical components, assets and their contracts. By unifying the internal and external data and leveraging advanced data science, Altergo significantly impacts a business’ ROI and enables companies to make data-driven decisions that improves asset life and performance.