[00:00:00] Speaker A: Hello and welcome to the Consulting Specifying Engineer podcast. I'm your host Amara Rozgas and I've connected with Sunil Lakshmipathy and Anil Kapahi from Jensen Hughes. In this episode we'll be talking about energy storage systems, specifically the topic of explosions.
Thanks for joining me today, Sunil. And Anil.
[00:00:27] Speaker B: Thank you for having us.
[00:00:29] Speaker C: Yeah, thank you for having us.
[00:00:31] Speaker A: Excellent. Well, it's great to connect with you both. And before we launch into this discussion, let me offer our audience some insights on your background.
Dr. Sunil Lakshmipathi is lead consultant in performance based design analysis for various engineering applications at Jensen Hughes.
With more than 15 years in the industry, he has developed computational tools and methods and performed advanced computational analysis in industrial process safety, transportation and aeronautics sectors.
Dr. Anil Kapahi is the director of research, development and testing at Jensen Hughes. With more than 20 years of experience in consulting and academia, he's one of the technical leaders with Jensen Hughes on energy storage systems. Anil is also a technical member of NFPA 855, 68 and 69.
All right, well, I'm happy to have both of you with me today because we've covered energy storage systems before in these conversations, but never from the explosions angle. So Sunil, let me kick this off with a really basic question.
What are energy storage systems?
[00:01:50] Speaker B: Sure, yeah.
As the name suggests, these energy storage systems are systems that can store energy when there is an excess production of it, but the demand is less and use that energy or deploy that energy when the demand exceeds the production in some form factor. The energy storage systems have always been existence. I mean, in the ancient times you had these water wheels that would be used to pump water from one location to another.
But here we are talking in terms of electrical energy.
And the demand for electrical energy has greatly accelerated, especially in the past decade.
There is a greater demand, be it more on the data storage and whatnot.
So as the need for electrical energy has also increased, there's, you know, and with the emphasis on using renewable energy resources, that is to, you know, to generate energy in a sustainable manner, we do need to have some sort. And the, you know, these energy storage systems have gone, have become more prominent in their usage and their deployment.
The renewable energy resources, as you know, they're intermittent in their production. The nature of them is that they're very intermittent in terms of production.
So these energy storage systems help in capturing and storing that energy when there is a higher production greater than the demand and use that stored energy and deploy them when the demand exceeds the production. So the utility companies have used, have, you know, have started using these systems quite significantly. And from the technology perspectives, there have been a lot of energy storage systems like, you know, how you batteries in some sense. But the lithium ion battery technology has taken, you know, a significant, significant pie of these energy storage systems, so to speak. It's more than 80% now. And the, the, this chemistry and the storage technology of these lithium ion batteries makes it highly amenable for using them in this manner. And because the lithium ion batteries, even in a small factor, as we know in our cell phones and other micro devices, they can store a high energy in a very small factor. So that is, they have their high energy density and they're easy to maintain and they have a long life cycle and also are fast charging. So there are many advantages of these lithium ion battery technologies that make them very useful and highly desired to be used in this technology for lithium ion for energy storage systems.
[00:05:04] Speaker A: Okay, and I think this is probably a question on everyone's mind, Anil, what are some of the typical hazards for energy storage systems? What do we need to worry about?
[00:05:17] Speaker C: Yeah, so like with any other source of stored energy, if the energy is released in an uncontrolled manner, it does result in some kind of hazards in the world of lithium ion batteries.
This uncontrolled release of energy is what's known as thermal runaway.
So to be specific, lithium ion batteries do have hazards related to fire, explosions and toxicity.
And for this podcast, we'll focus on the explosion hazards.
This explosion hazard comes from the electrolyte within the lithium ion batteries, which is highly flammable.
And when these batteries fail due to any internal or external abuse, the flammable electrolyte can evaporate and it can get fragmented into flammable gases such as hydrogen, methane, and propane and lots of other hydrocarbons.
Now, when these playable gases, they disperse inside in an enclosed ess enclosure, energy storage enclosure with a very high degree of congestion, it could result in a formation of explosible cloud.
And if this cloud gets ignited, it could result in some sort of a pressure eventually that could compromise the structural integrity of the enclosure.
It can also hurt people in the vicinity of enclosure, such as firefighters who may be around attending to a failure incident.
So in summary, explosions are definitely bad, but explosions in an enclosed environment with high degree of congestion can be devastating.
[00:07:29] Speaker A: Okay, well then, Anil, Anil, you just talked about thermal runaway. So Sunil, what are some of the mitigation measures to handle the explosions or the thermal runaways? That we just talked about here.
[00:07:44] Speaker B: Yeah, so, because I think, as Anil mentioned, these explosion hazards, you know, they could be, you know, they could cause a significant damage. So we need, we do need to put in some mitigation meas to control or either to prevent or control these explosion hazards. And this is the design of these systems. Because of the hazardous nature, there are some regulatory guidelines that need to be followed when designing these systems. You have the NFPA 855 that Danil is a member of, that it's a technical group or a technical committee that puts forth guidelines on recommendations on how to design these systems. So you also have the international codes that also provide some sort of regulatory guidelines on how to design the systems. So in terms of mitigation measures, we can either look at designing the system from an active control perspective or a passive measures. So active measures for these systems are where you have a system that is monitoring the space within the ESS constantly. And if there is a thermal runaway event, it activates automatically. And what we mean is, here we are going the route of what is called as minimizing the combustible concentration of the mixtures inside the enclosure. That is to prevent an explosion from occurring in the first place.
So these active measures, that's one way of preventing an explosion system.
And another method is what is called as a passive method.
And so this is a system where you have, you know, if there is a release of these battery gases and they get accumulated, you have a system where, you know, if there is an explosion event, these passive systems called as explosion venting.
So essentially, if there is a high pressure inside these enclosures, you have these openings that are the vents that open up and release that high pressure gas from inside the enclosure to the outside, thereby mitigating the effect of these high overpressures and controlling the damage to these enclosures.
Those are some of the ways that we can mitigate this explosion hazards.
[00:10:27] Speaker A: Got it. So we have passive and active mitigation measures. Anil, what are some of the pros and cons there?
[00:10:37] Speaker C: So I think before getting into the pros and cons, let me give your audience some context.
So both active and passive strategies, they have been used in the process safety industry for many years.
But the design of modern ESS systems provides unique challenges.
And the first one is, as I mentioned earlier, it's a highly congested geometry in an enclosed environment.
And the second one is the stochastic nature of this hazard. And what I mean by that is it is not trivial to quantify the Scale and the duration of hazard for ESS system.
So, keeping these two challenges in mind, if we look at passive and active protection methodologies, as Sunil mentioned, NFPA 68, which is a passive protection methodology, although it is, you know, nearly maintenance free solution, the prescriptive methodology of performing calculations and quantifying deflagration vent areas according to NFPA 68 has some limitations and its applicability to ESS type enclosures is questionable because the underlying data on which this methodology is based that was collected using experiments that did not look like what we have in the ESS employer. So there's a big gap there and industry needs to do some work to address that.
Now, if we look at the 69 system that requires mechanical exhaust ventilation, this mitigation methodology is common in the ESS industry.
But the design here is also based on limited test data and engineering analysis is required to come up with the progression of the failure event.
And one thing which is important is the single most important parameter to size and exhaust fan is the release rate of flammable battery gas.
And right now there is no standardized methodology to quantify that.
Furthermore, especially for the active system, the, the need to perform routine inspections, maintenance of the backup power during a failure event does get into the, the reliability of active systems. So, so overall there are technical gaps that exist in Both NFPA and NFPA 68. And NFPA 69, especially when we talk about ESS containers. And the fire protection industry has a lot of work to do to fill those gaps.
So right now, in my personal opinion, a redundant approach of using both may help in enhancing the safety.
[00:14:17] Speaker A: Okay, well then this leads to an obvious question.
What are the tools to perform the explosion control analysis?
Sunil, can you fill us in there?
[00:14:28] Speaker B: Yeah, sure.
So there are, you know, these, the design of these explosion control systems can be evaluated either through, you know, simple engineering tools or more at complex and advanced computational cfd, computational fluid dynamics tools. And when we look at, you know, the explosion prevention system that is based on the NFPA 69 analysis.
So where the goal is to reduce the combustible gas concentration, the engineering tools that are there, what is called, as you know, in there's a common term called the well mixed model. So these can be used and they are simple and they do give that answer only in terms of whether the system that is installed in these ESS passes or fails the acceptance criteria that is required from an NFPA 69 perspective. That is the, the concentration of the combustible gases within the enclosure should be less than 25% of the LFL. So the simple models can give that particular answer. But that is from an NFPA 69 perspective. And from an explosion protection perspective we have the NFPA 68 engineering model that is described in the NFPA 68 guidelines. So this does. These are some mathematical formulations that are based on previous experimental data. They are, you know, so they're derived from that and they can also be used to con to what is called as sizing these explosion vents. So both these well mixed models and these NFPA69.8 methodology of doing, you know of use doing the explosion control system design, they are very, they're not very advanced. They do give the answers but they don't consider the complexities or the nitty gritties of these ESS design because these systems are highly congested. And from, you know, when we do the 69 analysis, the simple models do not give where do not capture the effect of the local concentration of the gases where you could have a potential for an explosion.
So we have to use, so that is why we typically recommend more advanced CFD methods.
See performance based tools because they are, you know, they simulate a realistic scenario. They help in you know, defining or designing the system in a more accurate manner.
So those are, you can either go simplistic methods or do a more advanced formulation using CFD models.
[00:17:31] Speaker A: Got it, Got it.
[00:17:32] Speaker B: All right.
[00:17:32] Speaker A: Anil, I know you do a lot of research and testing at Jensen Hughes. What kind of testing is required here?
[00:17:41] Speaker C: Yeah, so I think if we focus on NFPA 855.
So NFPA 855 requires to perform UL 9540A test to evaluate thermal runaway hazards in the battery energy storage systems.
This is a tier level test series that is performed at cell level and then at module level and then unit level and finally at the installation level. To understand the hazard specific for explosion mitigation measures. The cell level test is probably the most important test.
It provides the flammable gas volume.
In addition, it tells you about the individual concentration of those flammable gases, flammability characteristics such as laminar burning speed, maximum explosion pressure, all these things are required to perform the explosion hazard.
The other test, like a module level test, it does provide you data related to cell to cell propagation times.
And that data can be used to define the duration of the failure event.
So the next one is the unit level test.
It can provide you some data on module to module propagation, if there is any.
Finally, the installation Level test provides information on the operation of any deflagration production system installed.
The key is there is lot of other information one can get from.
[00:19:43] Speaker B: This.
[00:19:43] Speaker C: Kind of testing which could be relevant to designing a fire suppression system.
But there are a lot of challenges within this test and our industry is still working to address those challenges.
We'll probably need a full podcast to get into that.
But couple of things that I would like to highlight is UL9540A is not a certification test, certification standard, but a test method.
And the intent is to generate data that can be used to define the hazard for designing mitigation measures by folks like Sunil and I.
And the key is for, for most of the systems the, the data available lacks statistical significance.
And the practitioners who are working on these mitigation layers, they need to be cognizant of deficiency deficiencies in in test methodologies to make sure, you know, the design basis they are using is sufficiently conservative. So, you know, a lot of work needs to be done in this area by our industry.
[00:21:10] Speaker A: Right. It does sound like we have a lot more information to gather here then that kind of leads me to my last question, Sunil. What are some other inputs that are required to perform this analysis?
[00:21:24] Speaker B: Yeah, so you know, as Anil mentioned, one of the primary inputs is the, the battery gas characteristics.
So in addition to that we also do need to have more information when we do in these analysis. First is what is the, the enclosure characteristics.
So you know, you know, we need to know what is the free air volume of these enclosures. That the type of congestion, what is the amount of congestions that's there? That is when I say congestion, those are the battery racks, the electronics and the cable trays and all that. And you need to know what are the material properties of these enclosures and also to know what is the enclosure strength. Like if you were to design an explosion protection system, we do need to know what is the enclosure strength and how much it can, you know, do that. We need to design too.
So that is one aspect. Another aspect is the operational system characteristics. So by that I mean, you know, in these ess we typically have a cooling system that is active to maintain the environment inside these ESS to nominal values. Because the batteries operate within a certain temperature range, need to be maintained within a certain temperature range. So you know, we need to know how, what is the H VAC cooling system that is, you know, that's active, the recirculation of these system and also the supply and the return air locations and what are what is the, the CFM of the.
In which that is, that is the, the, the, the, the.
The. The rate or the, the flow rate that is maintained within, within these systems. So that's, that's another aspect. And when it comes to the explosion system characteristics, now for, as I mentioned from, for an active system, we do need to have the gas detectors, we need to have the location where we need to place these gas detectors so that they can detect any thermal runaway event. What is the response, the threshold at which these gas detectors get activated, the response time in terms of how the detector passes on this information to activate any mechanical exhaust systems. That is for the prevention system. Now when we look at an explosion protection system, we need to see what is the panel size that is available for us to install and what is the yield pressure of these panels and the specific weight. So there are quite a few system details that we need to know to, to design these systems. And finally, you know, as you know, these ess have a lot of batteries and you know, and that are placed and the footprint is very small. And the, the thermal runaway event can occur from any of the battery, you know, modules that is there inside the system.
So there is some sort of an uncertainty associated that we need to account for when we do our analysis. So we need to see know what is the module design when, how these modules are designed so that if there is some sort of a pathway for the released battery gases to escape out into the enclosure. So these are all some of the inputs that we need to know to, to design the explosion control systems.
[00:25:07] Speaker A: Yeah, well, there are quite a few details there. So now. Thank you.
But let me switch gears on you. What other podcasts do you listen to right now? Sunil?
[00:25:18] Speaker B: Yeah, so I think, you know, for me I've been, you know, drawn to podcasts because the convenience of listening to them, you know, when I'm either commuting to work or when I'm exercising. I, you know, one of the things that I've been drawn to listening in the recent past has been on Indian mythology and world history. So those are some something that's, you know, I want to know, learn more about. And I've been trying to search for podcasts that, you know, that talk about these things occasionally. I do also like podcasts on behavioral economics and also on productivity, you know, helping me to understand, you know, what are, you know, what's, you know, in terms of what, you know. Behavioral economics is an interesting field as you know, and also on productivity and how to increase or to how to, you know, concentrate on things. Those are some topics that, because of the long form of these podcasts, it's, it's, it's a good, good. I, I find it very enjoying to listen to those and yeah, I know I do like listening to podcasts to be entertained and you know, and I'm always open to recommendations to, to you know, that would do new podcasts that would be of interest to me.
[00:26:45] Speaker A: Right, right. Well, it sounds like you definitely keep busy.
So Anil, what about you? What do you do for fun?
[00:26:52] Speaker C: Yeah, not as interesting as, you know, cooking dinner is something I enjoy a lot.
I try to do it almost every day.
You know, other than that, traveling with my wife and our 3 year old son can be fun half of the time.
Yeah, I think those are the couple of activities I, I do for fun.
[00:27:18] Speaker A: Did you say fun half of the time, Anel? Was that what you said?
[00:27:23] Speaker C: Yes, I did.
[00:27:25] Speaker A: Okay, got it. Thank you.
[00:27:28] Speaker C: Tear will have their own definition of fun. So half of the time you can like it and half of the time you just hold your head and see, you know what I'm getting into.
[00:27:41] Speaker A: Good way to put it. Thank you.
Okay, that was Sunil Lakshmapati and Anil Kapahi from Jensen Hughes talking about energy storage systems and understanding the explosion issues around them.
For more information on explosion control and mitigation, energy storage systems and similar topics, visit Consulting specifying
[email protected]. thanks for listening and catch you next time. Bye Bye.
