This is the first in a series of articles about battery power and its adjacent industries and processes. Check out our other post, "Application Spotlight: Solvent Recovery and Battery Liners."
Today, energy comes from a wide range of sources. The share of that collective power that comes from renewable energy sources continues to grow. In fact, in 2019, it was estimated that just under 20% of electricity generated at utility-scale electricity generation facilities in the United States was from renewable energy sources.[1]
Two of the poster children for that movement are solar and wind power. With the growing usage of each comes the challenge of integrating them into the grid and finding ways to make them viable when the sun’s not shining or the wind’s not blowing. For large scale operations, the answer to that challenge is battery farms, which are also known as energy storage facilities (ESS), battery storage facilities or battery backup facilities.
In this post, we’ll talk some more about battery farms, including:
In essence, battery farms - also called battery backup facilities - are the answer to “what about when the wind stops blowing?” or “How does solar power work at night?”
Well, it’s batteries – specifically lithium-ion batteries – and a lot of them. The battery farms themselves are pretty much what the name implies – facilities housing any number of batteries that connect to the local power grid. These batteries receive and contain power from solar or wind sources and store that energy until it’s needed.
The white boxes in the image above house large lithium-ion batteries. This example was taken in Southern California
These farms can take a number of forms. Some popular designs make use of shipping containers or movable trailers. Some take the form of large, purpose-built facilities, while others feature outdoor battery storage.
There are several benefits to utilizing battery farms¹, including:
Cost saving benefits of using backup batteries include things like peak shaving, the practice of storing energy during times of low demand and discharging during times of high demand. The most common example of peak shaving is using lower-cost stored power during the day, then recharging the batteries using traditionally produced electricity at night, when power costs dip.
Having a reliable supply of backup electricity can help supplement traditionally produced electricity supply during summertime demand spikes from A/C usage, for example. Load management can also help decrease the likelihood and frequency of blackouts and other issues resulting from an insufficient supply.
Another benefit of using battery farms is less ramping up and ramping down. The steady supply of power reduces the frequency of stopping and starting production, which stresses equipment.
A charged battery's job is to store energy, and any time energy is being stored, there's a risk of it escaping through unintended means. Add to that the presence of the lithium – a flammable substance – and the criticality of the systems used to cool li-ion batteries is clear.
Failure and ignition of non-damaged batteries resulting from overheating is extremely rare, requiring temperatures far higher than those present in normal operating conditions. But with damaged or malfunctioning batteries, the risk of ignition of the battery’s electrolyte increases at lower temps – around 300°F.²
The results of overheating can be disastrous in battery farms, where scores of batteries reside in fairly close proximity to one another. Remember those exploding cell phones and hoverboards a few years ago? Damaged or otherwise defective consumer versions of lithium-ion batteries were the culprit.
To best meet the critical needs of the application, these units should feature:
Space is money in battery farm cooling applications. Space used for cooling systems means less space for batteries, so units need to be as compact as possible. There are a few approaches we've used to helped customers save space on their designs.
Properly engineering coils in the following areas can help maximize battery space:
Increased fins per inch: We can design coil fin packs with a wide range of fins per inch (FPI) to increase heat transfer surface.
Enhancements: At SRC we have a variety of fin enhancements, such as raised lance fins. These enhancements exist to increase the airstream’s turbidity, improving heat transfer without needing to expand the equipment’s footprint.
Raised lance fins feature a series of short strips of the original fin material that are cut and raised above the fin’s surface, allowing air to flow through the fin, and around it as well, increasing turbidity. This design offers the highest air friction of our enhancements, but are also susceptible to fouling, so they should be used only in environments where particulates in the airstream aren’t a major concern, such as an indoor battery storage facility, for example. We offer several other fin options as well depending on the application.
For some applications, opting for a self-contained unit can also be an effective method of maximizing floor space. By having the unit’s evaporator and condenser(s) contained within a single housing, there’s no need to have a separate evaporator inside the battery structure itself. An added benefit to a self-contained, wall-hung design is that maintenance can be performed outside of the building. This way, there’s no need to go inside the battery structure to make adjustments and repairs to the system, which can help reduce opportunities for the introduction of contaminants like sand into the facility.
Self-contained units are also a good option when regulatory constraints prohibit the use of RTUs, which are a popular choice for cooling battery storage facilities when feasible.
Electricity demand ebbs and flows frequently, and so do the cooling needs of these facilities, so some manner of load control helps maximize efficiency. This control can be obtained through:
A lot of the units we work on run R-410A, and feature one evaporator and two condensers with interlaced circuitry. Interlaced circuiting is a means of offsetting the efficiency losses associated with low-load operation. This design involves multiple distributors, the refrigerant flow to one of which can be turned off at low load conditions. This effectively removes the affected circuits from operation to meet a temporarily lessened performance requirement. Interlaced circuiting also reduces the frequency of cycling during low-load operation, reducing equipment wear and tear.
These units will also sometimes feature variable control compressors (VCCs). Units will sometimes feature one VCC and one standard compressor. The VCC can be turned off completely at low load conditions where one standard compressor is sufficient, and the VCC can be turned on supplementarily and dialed in to efficiently meet higher load conditions when necessary.
If you have a battery cooling application that you could use some engineering help on, give us a call. We’re seeing more and more of this kind of work and we’d love the opportunity to share what we’ve learned and help your project go right.
And check out the links below for some more articles from our Application Spotlight series.
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Sources
[1] National Fire Prevention Association, Energy Storage Systems Fact Sheet, June 2020
[2] Stanford University, Chemistry. (2016, January 11). New Stanford battery shuts down at high temperatures and restarts when it cools [Press release]. Retrieved April 19, 2021, from https://news.stanford.edu/news/2016/january/safe-battery-toggle-011116.html#:~:text=A%20typical%20lithium-ion%20battery%20consists%20of%20two%20electrodes,electrolyte%20could%20catch%20fire%20and%20trigger%20an%20explosion.
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