How Should I Consider Using My BESS?
Along with considering the chemistry for use, the designer is also going to want to consider how to use their BESS.
In this section, we will discuss photovoltaics (PV) smoothing, peak shaving, and frequency regulation, among other topics. This discussion can be helpful for letting the reader know what techniques are available, but they will still have to consider what will be applicable to their use case.
Main Points
- Definitions for the common stationary applications are provided: frequency regulation, peak shaving, voltage support, phase balancing, energy trading, PV smoothing, behind-the-meter storage.
- PV smoothing and peak shaving are some of the more common applications.
- They differ in the state at which the battery is stored, making PV smoothing slightly preferable where possible because it better preserves the lifetime of the battery.
First, Read This
Before choosing how to manage the BESS, it’s important to understand some of the available options for management. The aforementioned NREL study provides great definitions for some of the available options.
“Frequency Regulation: One of the more important ones is frequency regulation. In frequency regulation applications, the frequency is adjusted based on the loads that are active and demanding variable power, as necessary. They provide “up” regulation by discharging and “down” regulation by charging.
Excerpt from pages 6–7 of https://www.nrel.gov/docs/fy21osti/77621.pdf
- Peak Shaving: Another important application is peak shaving, where the energy storage system is discharged during an “on-peak” period and charged during an “off-peak” period.
- Voltage Support: This is also important and is where the power is used to maintain the voltage within specified limits.
- Phase Balancing: Phase balancing is the process of keeping the load at each phase as balanced or equal as possible.
- Energy Trading: Energy trading is where bulk energy is bought or sold and moved to an area of need.
- PV Smoothing: PV smoothing where power is added or taken away to mitigate large changes in the PV power output.
- Behind the meter storage: When energy is generated (usually from wind, solar, or heat) and stored until it is needed to be released but typically at an individual building and ‘behind the meter’”
Next, Consider This
One of the more widely studied use cases mentioned above is PV smoothing. Using a BESS to mitigate spikes in usage can help areas avoid “brownouts” and give more consistent energy profiles to the main system. An example from Sandia National Laboratories is shown in Figure 3. Here they developed an algorithm to have batteries provide supplemental power at high use times while keeping the battery state of charge (SOC) near 50%. Keeping the battery at this SOC is helpful because the battery will still be able to both supply and absorb power while its degradation is reduced (this is discussed further in the Stressors section). In Figure 3, the utility power is plotted in dark purple. There are two batteries providing supplemental power in light blue and light purple/pink. We see that we draw more power from the batteries during an increase in utility power to help lower the power required from the utility and use the batteries to offset this.
Now, Consider This
Another common application for stationary energy storage is peak shaving. Here a battery can be used as a supplemental energy source to provide power during peak times and be charged during off hours. In this case, the battery is often charged to 100% SOC to keep the maximum energy available for peak hours. An example of this is shown in Figure 4. In this figure, the bold red line is the utility use after peak shaving. The dotted blue line is the energy that is needed without a battery helping with peak shaving. As a result of peak shaving, the utility sees a more consistent energy profile. During low use periods, the utility can be used to charge the battery, while at peak fluctuations the battery provides energy to the system. The shaded blue regions are where the battery is providing energy to the utility. Overall, the greater consistency of the use provides better ability to predict remaining life of the battery and improve the duration of the system.
Finally, Read This
We’ve defined several options for BESS applications in stationary situations and highlighted a few of the prevalent applications. Read this excerpt from the conclusion of the “Reliability analysis of battery energy storage system for various stationary applications” article by A. Bakeer et al., which discusses some of the differences between the applications. There is a bit of technical jargon here, and things like the “greedy algorithm” (a machine learning [ML] algorithm) can be ignored. The key takeaways here are that frequency containment reserve applications can help the battery last the duration of the power electronics if we allow the battery to run to 30% capacity (measured Ah) fade. Capacity fade is the technical term for the decrease of capacity compared to BOL. In addition, in peak shaving we have high degradation because we keep the battery fully charged. Other applications that allow the battery to maintain 50% SOC will see less aging when the battery is not in use.
“Three main groups of applications were considered: utility – frequency containment reserve, residential PV – increased self-consumption with a greedy algorithm, and industrial – peak shaving of excessive load power…
In the frequency containment reserve applications, the expected lifetime of the power electronic converter of 24 years allows for one replacement of batteries that fade by 20% of their capacity in 15 years. However, if the fade of 30% is allowed, the lifetime of the converter and battery could be matched.
In the peak shaving applications, BESS suffers from the highest calendar aging due to average SOC close to 100%. On the other hand, the low number of charge/discharge cycles allows for a capacity fade of 20% in 12 years. This is close to 15 years of B10 lifetime expected from the associated converter.”
Excerpt from https://www.sciencedirect.com/science/article/pii/S2352152X22002481