Live from the MGM Grand Convention Center in Las Vegas, Nevada, it's the queue at splunk.conf 2014. Brought to you by headline sponsor, Splunk. Here are your hosts, Jeff Kelly and Jeff Frick. Hi, welcome back everybody. Jeff Frick here with the queue. We're at the splunk.conf 2014. The fifth annual Splunkies or Conference at the MGM Grand in Las Vegas, Nevada. They outgrew the Cosmo, they outgrew the Aria, they outgrew everything. I think Godfrey says there's 175 people at the first one five years ago. I think there's over 4,000 Splunk practitioners, employees, partners, customers, and Splunkers I guess is the right word. So we're excited to be here. It's our third year. Joining them by my host, Coase, in this next segment. I'm Jeff Kelly from Wikibon and we're joined by Matt Olson, principal architect at CenturyLink. Matt, I think your first time on the queue, welcome. Thank you, glad to be here. So tell us a little bit about CenturyLink. I think, you know, we think CenturyLink, we think cloud. What are you guys, tell us a little bit about CenturyLink and your kind of value proposition. Yeah, so we're third largest telecom in the US and grown by leaps and bounds through some organic growth but also merger and acquisition. And I think like most of telecom right now, we're in the midst of a massive transformation really into a data services company. That means we're accommodating massive transformation with decline in some areas and just incredible growth in others. Right, so let's talk about that a little bit. So becoming a data services company, what does that mean? Does that mean providing analytics? Does that mean providing data movement? What does that mean from your perspective? First and foremost, it means providing broadband based and internet based services. And it really means also moving from a mode in which we're involved in selling pipes to a mode in which we're selling services that are running over those pipes. So it's really been quite a challenge in terms of monitoring the performance management which is my key responsibility because you need the ability to link what you're seeing in terms of the service delivery with what you're seeing in terms of the underlying infrastructure and the pipes and the network elements and such. So when you're delivering high value services over those pipes, you've got to be able to make sure those pipes are up and running and operating smoothly at all times. And the key is understanding what's happening end to end because in service delivery to a customer from a point within the core of your network, you're going to traverse multiple topologies, multiple network elements and lots of different vendors and each of those elements, each of those segments might look okay but when you add it up end to end you find it's a different story. So talk a little bit about Splunk and how that's helping you do that. Clearly it's a critical part of your job and a critical part of delivering value to your customers. Oh it's absolutely central. And I think the key with Splunk is that we're able to break down data silos very easily. So as a large telecom and a telecom that's grown through acquisition especially, you have a number of different silos, you have a number of different information domains and Splunk has really allowed us to break down the barriers between those silos and provide an integrated correlated view of what's happening across those domains. So previously, maybe take us a little bit before and after. So as you bring, before you started working with Splunk and trying to break down those silos, what was your approach to trying to do that? Was it a manual approach? How would you go about doing it? Well we had a very traditional approach which was based upon traditional row oriented databases and generally you have your DVAs, you have your people focused on schema development, you have your people focused on Java and GUI development and you have generally multiple teams and multiple areas across those domains. So we started using Splunk I think as many businesses do just for simple log parsing, kind of a tactical spot solution and then we realized that we could do prototype development very, very quickly. Because at the time to market, if you want to inhale data, parse it, work with it and then build views of it, if you're working in a traditional environment, you got to work in each of those specialized areas, work with your DVAs and schema and bring in the data and then you go to work with another group in the development. And we quickly ascertain that with Splunk we were able in one place, in a one stop shop very simply to prototype all the way from data acquisition through to the useful views. And then we realized that those prototypes, well they're fully functional as production operational tools. So we began to transition more of the load and more of the focus from traditional, it's actually oracle based solutions over to Splunk and over time actually very quickly and that became our core focus and we kind of pushed aside the old legacy solution. Interesting, so we got to resolve in the CEO at his keynote yesterday, talked a little bit about supporting. We first talked about seeing from customers the need to do this kind of rapid application and development and rolling it out as fast as possible. And we've talked to customers yesterday around kind of the whole DevOps and where Splunk fits in there. It sounds like that's one of the key value propositions for you. Oh absolutely. Can you maybe give us an example, add a little color, what's one of the use cases or one of the coolest things you've found or maybe not coolest, one of the most important things that you've found using that approach? Well I think first and foremost, we start with pain. You work with different organizations, different customer organizations and determine what the pain points are, where they're hurting. Because nobody ever really has the time to produce detailed requirements of what they need. So you find out where the pain is and then you kind of dive in and prototype something. And I think the coolest initial cases were simply situations where something had gone wrong with the service. Something was clearly a mess and yet you had these multiple groups each scrambling in their own little tool sets trying to figure out what was going on. And we were able often with Splunk to very, very quickly link what was being observed in terms of issues with the service to what the platforms were saying regarding the syslog and SNP data and such telling you what's going on with the platforms. And you can really quickly, really easily provide a view that shows you, okay here's where your service is failing and that exactly right there is the underlying cause because you can link what's happening with the machine data from the platform perspective with what's being observed with the service. And we had a number of cases like that where we had a number of people in mad scrambles, they had war rooms, you have these long operations and we're able to just quickly dive in, grab data, whip something together and illustrate the root cause of the problem. So, and not to belabor the point, but with the old approach, the more rigid relational approach where you have to know the question you want to ask beforehand. It sounds like that wouldn't be possible doing that kind of analysis. Yeah. And so clearly that's an area where it's interesting, I'd love to talk more about it. Some point how you see this kind of impacting some of those traditional vendors who take that approach, but I know Jeff wants to get the questions as well. Yeah, it's just interesting too with Telcom and really the growth of data centers and we're constantly hearing about next in data centers and obviously cloud is huge and public cloud and hybrid clouds and private clouds and you guys are the stuff that's actually up in the cloud that's metal and electricity. So I want to talk a bit about how your business is growing and transforming because of this cloud transformation and the additional challenges that that kind of rate of growth is kind of throwing it your way when you've got to fix things. Yep, oh absolutely it's a matter of scrambling to keep up with mad growth in areas certainly cloud is one of them and also service is delivered by the cloud and it's certainly a challenge of tying together all of the pieces involved in the service delivery because you have now I think a scenario where you often have not only bundled the services and functionality but you have everything sort of coexisting in a virtual environment and it does offer though I think some tremendous advantages in terms of not only the simplicity and provisioning but also the ability to establish a more sort of consistent and controllable environment for the services but it's a learning curve. Because for the consumer of the cloud I just wanted to turn on, turn off, add my stuff, pull my stuff down but from your point of view and supporting that and architecting it it's real stuff that's got to be connected it's got to work together and you've got to actually execute on that vision. So I mean is taking a cloud based architecture approach from a delivery point of view actually easier from your side? I think ultimately it's easier, yes but there's a substantial sort of upfront investment in expertise and in establishing an architecture that's going to be very robust and support the rapid deployment that's really the key. And following up on Jeff's question I mean how is this approach with new tools like Splunk so different than the old approach with the old tools? Well and I think the key is that you need tools that are inherently flexible and extensible and you need tools that are within our control to a degree, I mean the thing is as a service provider you need the ability to quickly go in with your knowledge of the particular, the subject matter you're working with and the problem you're trying to solve you need to be able to quickly iterate through the solutions without depending on rigid technologies or undue vendor engagement. Right you can't really iterate if you have to go back to a data model or to build a new schema and it's going to take three months that's not an iterative approach unless you've got to be able to ask a question not get quite the answer you were looking for iterate, ask a new question that's something that some of these new approaches provide. So I want to get your take a little bit on kind of Splunk's model so we've talked to a lot of clients here customers of Splunk and a lot of them started kind of small with Splunk and then moved to different use cases can you kind of walk us through how that evolved in your organization? Absolutely so we've started as I said with the initial tactical focus simply on parsing log data to get at operational issues with platforms and such and extended then into sort of the service layer where we have a lot more data related to the services we're delivering to our customers and with a focus really on operational support but then we quickly discovered that that same underlying data set and that same functionality provided by Splunk can then be leveraged for executive dashboards and presentation for trend analysis and then true analytics and in fact for business intelligence type functionality as well because often times the underlying data set is actually very much overlapping and often identical so what we've done is really to begin our initial development with an operational focus but then as we've developed the operational tools we've discovered more and more use cases that can be readily supported in other realms in planning and engineering even in marketing and product management and such. Well interesting so does and how does does or doesn't Splunk's kind of licensing model allow you to expand in that way? Yeah and I think the licensing model in my mind is really key because it's simple. It's simple, it's clear cut, there's none of this back and forth around which feature sets you have licenses for and complex higher order math around any of that and the simplicity is extraordinarily important in my mind. The other really key development and something I've been very focused on at Comp is now with 6.2 I think the availability of even simpler pivot type models and I think tools that will really allow those BI type users to quickly become comfortable and productive with Splunk. So when you say BI you mean more kind of on the reporting side versus more the interactive real time operational analytics? And also, well some of it is I think real time because you have impact of various marketing approaches and understanding of what's happening with your various products and it's but yeah it's really I think the analytics in the business realm as opposed to in so much in the operational realm. Interesting because in Godfrey's keynote yesterday he kind of put up that slide that showed the old EDW BI model and kind of the new Splunk approach and in your case it sounds like Splunk is disrupting not just the underlying relational database but also even up to that layer of the EDW and the BI space as well. Oh I think so. It's very interesting. Yeah it is interesting because at the end of the day it's about getting the right information of the right people at the right time so they can take action and they can do something with it and I'm just curious kind of the people that have more of a traditional BI approach, knowledge, experience, expertise, how are they, what's the reception to this style of BI I guess? Well I think the initial reception has been quite positive in that there's kind of shock and awe and when people see what you can produce and how quickly you can produce it it's really very very appealing. I think the next step though is to get to a point where those same users are comfortable producing those views for themselves. You know it's one thing to impress them without rapidly you can develop views of the data. The next step though is to impress them with how quickly they can produce those views of the data and I think these new tools are going to enable that. Right so moving to that self-service. Right, exactly. So expand on that a little bit. Does Splunk make it possible for a really non-technical person to do that or is that something you think they need to invest in anymore? Yeah and I think with the latest though at 6.1.2 and now at 6.2 that's a lot of what's being introduced is the ability to work with the data models and with PIVITS and such which are intuitively familiar to data analysts, people who have grown up using Excel and PIVIT and VLOOKUP and all those nifty tools. Well yeah that's interesting. I mean we've been hearing about kind of that self-service moving to the self-service intelligence model for 10, 15 years and it's still a traditional BI space is kind of stalled out and the metrics you usually hear is 20% of any given organization is actually using these BI tools. They've never really been able to crack that number. So what's it going to take to do that? Is it just simply bringing in tools that kind of mimic Excel and the tools that people know and understand or what's it going to take to kind of break through that number? Oh I think it's the intuitive interface and the intuitive tools and I think that PIVITS are particularly effective in that area. So what else are you looking for from Splunk? I mean as we look forward and we're here next year talking to you what are some of the things you're hoping to hear being announced from Splunk or areas where you hope they invest over the next 12 months? Well I think a lot of what I would be looking for personally is sort of consolidation of some of the functionality that's already been introduced. There are things like the ability to connect to external databases via DB Connect is in my mind extraordinarily important as is HUNK because Splunk has always been very good I think at coexisting with other tools with other solutions and those sorts of capabilities really add tremendously to the functionality. And so I think from my perspective the real key is continuing to sort of extend and harden those sorts of capabilities and integrate them more fully because it's extraordinarily powerful when you can take something like Splunk and have it leverage reference data, topology data and all these external data stores and also coexist with the Duke and HDFS and then potentially do so in a cloud environment. I mean that becomes an extraordinarily powerful environment. You're looking to expand different use cases, different underlying storage and other architectural approaches. Kind of unifying those in a way that you can't do with more point solutions. Exactly. All right, well we're out of time unfortunately Matt. Thanks so much for coming on theCUBE. Really appreciate it, great insights. Thanks for watching. We'll be right back up for this next segment. Please stick around. Excellent.


So, let us start. So, if you recap last lecture, we have looked at the physics of semiconductor, we have looked at p n junction operation and then we have looked at how p n junction works as a solar cell under when the light falls on it and then we have looked at various parameters of solar cell and in the last lecture, we looked at the design of a solar cell. So, where should be your junction, how to design anti-reflective coating, thickness, back surface field, front contact etcetera. And in the last, we were discussing about the series resistance as a one part of the design is to minimize the series resistance. So, that we will discuss briefly today, but today's two of my talks will be mainly on production of silicon and how the silicon wafers is used for manufacturing solar cell. So far, we have looked at the structure, cell structure, how it should be, but now today we should also look at how the cell, how the solar cell is manufactured using the various fabrication technology. So, the recap of the last lecture is that we have looked at the various upper limits of solar cell parameters, open circuit voltage, short circuit current, fill factor, resistive losses, sheet resistance, resistive losses we have started looking at. So, if you look at the device, the solar cell, the current flows as I said in emitter, sorry in base it flows vertical up because that is the lowest resistance path. Your emitter is very thin. So, the current in emitter flows in horizontal direction. One other reason why current is shown to flow horizontal is that the distance between the fingers is normally of the order of millimeter, while the thickness of emitter is of the order of few hundred nanometer. So, one millimeter is 1000 micrometer and 1 million nanometer. So, if you compare the different distances, the thickness of the emitter is very thin as compared to distance between the fingers. And therefore, we have to show that the current is flowing horizontal. Then the current is collected by the fingers, current is collected by the fingers and then it is given to the bus bar. Bus bar is the thicker line, basically bus bar is collecting current from all the fingers and your bus bar is the thicker line. Therefore, the contribution to the resistance comes from the base itself. So, base contributes to the resistance. The emitter contributes to the resistance. The contact between semiconductor and metal is also not a perfect contact, not perfectly omic contact. So, there is some resistance there. The metal fingers have their own resistance. The bus bar has its own resistance. The big contact has its own resistance. So, there are six component of resistance that comes in the path of the current in a solar cell and lower the resistance, better it is. Lower the resistance, better it is. And this is the series resistance. By the way, it comes in the series. So, it is a series resistance. Lower resistance is better because lower resistance means lower i square r losses. So, whatever power that is generated in solar cell by light should not be dissipated within the solar cell. Otherwise, the output power will be lower. So, the whole idea of the design is to minimize these resistances. Normally, the base resistance is very small because the cross section area is very large. So, this resistance component r 2 will be very small. The r 1 that is the back contact resistance is also very small because back contact remember it is everywhere. Back contact is everywhere. So, resistance of the back contact is also very small. And r 4 contact resistance can also be very small. So, main resistances that you have to actually minimize is the emitter resistance, the finger resistance and the bus bar resistance. Solid matter semiconductor contact resistance will also be important. So, the main resistance in the solar cell comes from the top part. Note down this point that the main resistance to the solar cell comes from the top portion. So, if I draw the solar cell diagram again, so there is a front metal contact here, then your back metal contact everywhere. So, current flows like this, then flows like this, then it flows vertically here, flows like this vertically here. So, typically this resistance of this part resistance of this part is almost 0, here r value is almost 0, here r is not equal to 0 means high value. Metal fingers have r not equal to 0 which is high value and the metal semiconductor contact will have r value not equal to 0. So, the main resistance in a solar cell comes from the top portion. Main series resistance R S contribution, main series resistance contribution come from the top. So, that is what people normally try to do that try to minimize this resistance as much as you can. You can do the analysis actually very simple analysis that current flows vertically, here it flows horizontal. So, if you know the resistance of the emitter and by the resistance of the emitter will discuss while we are discussing the solar cell itself that the resistance is first of all emitter doping is not uniform. And therefore, there is a concept called sheet resistance that we have to define. I will go directly. So, if you have the look at the parameter, if I have the spacing S, the length of the finger is L spacing between the finger is mentioned here D, but actually it is S. If I have that kind of parameter then the power loss in emitter will be given by this equation. So, J is the current density, L is the length of the finger, R is the sheet resistance of the emitter and y emitter. So, we are talking about emitter power loss, S is the spacing between the fingers. So, remember how important S is right cube power of the cube. So, F S increases slightly. So, if this space between the fingers doubles the power loss in emitter becomes 8 times. So, it is very very important design parameter of a solar cell to have the proper spacing between the fingers. It is very important design parameter to have the proper spacing between the fingers. Therefore, it should be carefully chosen. So, now if I have again, if I go back, if I go back here, let me draw again for the clarity. If I have this, if my emitter, if my fingers are here. So, this distance is S, the emitter resistance is normally given as a sheet resistance R sheet because it is a very thin layer, very thin layer and non uniform doping. And then we have seen from the expression that P depends on cube of the spacing. It also depends on R sheet. This is the power loss in emitter. Do we want power loss to happen in emitter? No, we do not want power loss to happen in emitter. We want all the power that is generated. We want all the power that is generated to come out of the solar cell and deliver to the load external not within the, within the cell. So, therefore, what is important? Spacing between fingers is important. Spacing between fingers, S is a spacing between fingers. Now, so you will say that because power loss in emitter is a function of S cube. So, why not to have very small S? Why not to have very small S? Means why not to have very small finger spacing? If you have small finger or front contact spacing, what will happen? If you have small spacing, then your fingers are like this. This is the scenario of small S, but when the scenario, when you have the small S, when your S value is small, what is, what is the problem now here? Your metal coverage of the front surface is larger. So, this your metal is shadowing the light. So, what you are doing? You are shadowing the light because of the more metal contact. So, you have said shadow loss will increase. So, you do not want high shadow loss also. So, this is a very good optimization that is required. What is the optimum spacing so that loss in the emitter is not much. So, typically you have 4, 5 percent, 3 percent loss that is allowed and according to that you can choose the finger spacing. Shadow loss, you do not want to be very high and i square r loss is in emitter also you do not want to be very high. So, therefore, this is very important. In the optimization of finger spacing is very important. Otherwise, if you have very close fingers, your shadow loss is higher, if your very fingers far from each other, then your raise to loss is higher. So, that optimization is required. So, what you can do basically in order to solve this problem which is not easy at all to solve the problem. So, instead of having larger width and less height of the finger, you should try fingers or the metal contact which is having smaller width and higher height. But in practice, this metal contacts are printed by screen printing and it is not possible to get a very thin width. This is called the aspect ratio. The ratio of W widths to height is over H is aspect ratio and people want aspect ratio as much as possible. Typically aspect ratio typically the finger width, typically the width of this finger W is in the range of about 100 micrometer. In the height will be in the range of about 20 to 30 micrometer. So, you will see the aspect ratio is will be about 0.4, 0.3. Typically, you want aspect ratio to be 1 or even higher than 1. So, that is one of the important design aspect in not only the design, implementation practice is still a challenge. You cannot actually, if you try to implement very good contact and very high aspect ratio, then your cost also increases. So, how it is going to affect? So, the series resistance affects the power loss because of internal series resistance, there is a internal losses within the solar cell. Because there is an internal losses within the solar cell, what kind of losses within the solar cell? I square losses. So, the power available to you outside the solar cell or to the load will be lower. So, when you have a high series resistance, what happens? When you have high series resistance for the same current, your voltage available will be lower. So, what I am trying to tell you is that, if I have, if my good solar cell will be like this, a less good solar cell will be like this. So, this solar cell will have high R s, this solar cell will have low R s. So, what is change, what is happening? The slope of the I V curve, the slope of the I V curve is changing, reducing towards the open circuit voltage, the slope of the I V curve reducing or you can also say that because of your R s, there will be I R s drop, voltage drop inside the solar cell because your series resistance, the V drop inside the solar cell will be I R s. So, therefore, you can say that for the same current now, the voltage available to you will be lower. For the same current, the voltage available to you will be lower. So, this is the effect of R s, series resistance. So, that you can see here, also for a solar cell is a non-linear device, but at the maximum power point, if you take the ratio of the V m over I m, you take the character, you get the value of resistance which is the characteristic resistance of the cell. And then, a series resistance at any other point is R s divided by R c h and your fill factor, your power first of all decreases, your power, maximum power that you can get under the series resistance equal to p 0, p 0 is the power when there is no series resistance and 1 minus R s, small R s is given by this. So, basically the impact of high series resistance is to reduce your power and that happens because of the reduction in the fill factor. Your fill factor also reduces, which is very clear. Fill factor is the definition of squareness of the I V curve and if your I V curve is less square, which means the fill factor is less. If your I V curve is more square, your fill factor is also higher. Similar to that, so what main difference happens is the slope of this, slope of the I V curve here towards the open circuit voltage determines the series resistance. So, there are many research papers available which will actually tell you that if you measure the slope here, you can actually measure the series resistance or at least qualitatively if you look at the slope of the I V curve and if the slope is not very high or the slope is not very high, you can say that this is the I V curve of a solar cell which is having high series resistance. I will draw you again. So, if I draw the curve like this, this can also be a solar cell curve, but it is very clear from this curve that this slope, it is very clear from this curve that this slope here is very low as compared to what otherwise is possible like this. Therefore, you can say you can say and impress people that this solar cell has very high series resistance, very high or on the other hand you can say because it is not square at all. So, you can say that fill factor for this solar cell is very low. So, this as a student of this course, now it is should be very easy for you. Similarly, shunt resistance, shunt resistance will have mainly the slope of the curve near the short circuit current will actually give the shunt resistance. Shunt resistance will actually results in the current bypassing the junction. So, bypassing the junction. So, therefore, for same open circuit voltage you are actually now getting lower shunt resistance, but let me tell you that in general the shunt resistance is not a problem for a solar cell. Shunt resistance normally very high it is the series resistance which is always the more problematic. It is the series resistance that is always the more problematic. So, that is it. So, it is shunt resistance normally is not a problem. As I said the earlier the shunt resistance should be very high we looked at the model of the solar cell. So, series resistance should be very low and shunt resistance should be very high and that is normally the case. So, this is the summary of losses. Fine. So, let me move ahead. So, this is the summary and let me give the typical parameters. So, that we have to discuss the silicon production today. So, normally we use silicon substrate because it is abundant all other people are getting clearly. So, just check Sastra. So, normally substrate for solar cell is silicon most commonly then people can use other substrate also silicon is abundance non-toxic. The cell thickness is 180 micron. Remember cell thickness is 180 micron. The doping of the base is normally tends for 15 or tends for 16 atoms per centimeter cube which is corresponding to the resistivity of 1 ohm centimeter or around that. So, typical resistivity is 0.1, 0.2, 1 ohm centimeter, 2 ohm centimeter that is typical. Emitter thickness is less than a micrometer. Emitter thickness is less than a micrometer doping is of the order of tends for 19 per centimeter cube or tends for 1918. Sheet resistance of 50 to 100 ohm per square. Optical losses can be avoided by anti-reflective coating and in normally we do the surface texturing as well as anti-reflective coating. The thick layer which is used as anti-reflective coating is silicon nitride. It has a thickness about 70 to 80 nanometer you can calculate and for the anti-reflective texturing the pyramids are formed which is normally 4 to 5 micrometer and all in the height. Grid pattern is about 20 to 200 micrometer wide fingers which are normally 2 to 5 millimetres too much actually normally 1 to 2 millimetre apart. So, not fine. So, that is the end of the design of the solar cell. If there is any question I will take one or two quick questions and then we will move on to the solar PV technologies. And mainly when you are discussing solar PV technology it is a production of silicon how to produce because we are talking about silicon silicon silicon and we are also talking you know why there is a high cost and so on. So, the production of silicon will answer why silicon is expensive. Then we will discuss the silicon wafer technology and thin film. So, one or two quick questions there is a question from Salim. Government call you Salim. Good morning sir. Sir in the solar simulator why we have to use only hydrogen lamps. In solar simulator we use halogen lamp because the spectrum of the halogen lamp is quite matching with the spectrum of the sun quite matching it is not matching completely, but it matches quite well. And therefore, the performance that you get under the halogen lamp will be close to the performance what you get in a real practice. Real practice means outside this condition. Sir we are having another question. Sir during this in the solar panel is in the dark or condition the batteries full the batteries fully charged. Now will the solar panel draw the will draw the power from the battery or not? Will it act as a load? Solar panel will not act as a load it can act as a load if the battery is fully charged, but normally in each solar panel there is what is called the blocking diode. There is a we will discuss while discussing the module that when the design of solar panel there is a blocking diode which blocks the blocks the reverse current flow. And therefore, solar panel will not act as a load there is a protection there. Any other question on the design of the solar cell ask a specific question to the design of the solar cell? Fine Gandhi Nagar. Good morning sir. Can we use ITO along with the metal fingers on top of the solar cell to get more collection? Those who do not know ITO is the indium teen oxide or the transparent one of the transparent conductive oxide used in a thin film technology for a making a contact. Normally for crystalline silicon it is not advised to use IDO along with your metal contact because first of all ITOs are not transparent they will block the light and they are not their resistivity is also higher than the emitter itself. Remember our silicon emitter is doped tends for 18 tends for 19. So, therefore, because the resistivity is higher you cannot actually you will not have much advantage of using TCO or ITO in crystalline silicon solar cell. Kakinada last question quick. Sir, I ask please research is going on in the field of conducting polymer so that by removing the metal contacts we can put conducting polymers which are transparent and get more light efficiency can be increased for the solar cell conducting polymer. Yes. So, that they collect current from the instead of metallic one where they stop the light we can use conducting polymers. Yeah conducting polymers I do not think we will have the metallic property you know because we want very low series resistance. So, that is one problem. Second problem is our solar cell is going to live for 25 years, but I do not think your any polymer actually can carry the current for 25 years. So, we are looking more for a metallic properties. So, we will get a semi conducting property, but getting metallic property from polymers will be very difficult and using it for the 25 years is even much more difficult. So, let me stop here and let me stop here and go ahead with my lecture otherwise we will run the short of time as always we do. So, now let us discuss the production of silicon production of silicon. One reason why solar cells are expensive is because of the cost of silicon itself and you might have read it if not. Let me tell you that about 50 to 60 percent cost of 60 percent even up to 60 percent cost of the solar cell is nothing but a cost of a silicon itself. So, rest everything else is very small. So, converting silicon wafer into solar cell and then converting solar cell into module and we have detailed lecture about the cells and module performance. So, we will discuss that in detail, but the important point to take home right now is that about 60 percent 50 60 sometimes even 70 percent cost is the cost of material itself. So, therefore, it becomes very important to know why it is so, why silicon is so expensive. So, that we are going to look at very quickly the details about the silicon types of silicon, silicon manufacturing and so on. So, before we go further the current status of silicon I will tell you. First of all the prices of solar cell fluctuates or actually fluctuated in the past and that is because of the prices of silicon itself. So, one there was a prices going down and suddenly in 2003 and 2004 the prices started increasing and that happened because of the shortage of silicon in the market. The history is that microelectronics industry is very old industry right, IC industry is very old industry, silicon is the main material used for IC industry and when solar cell production started in 70s and 80s whatever the material that was coming or the leftover material or you can say even the waste material that was coming from the IC industry or being utilized for the solar cell industry right. So, let us say in 2000 about 2000 only 10 percent of silicon produced in the world was utilized for solar cell only 10 percent which means we were the PV industry was completely dependent on the electronics industry microelectronics industry, but when the production and the consumption of solar cell started in 2002, 3, 4 there is suddenly shortage of silicon. The microelectronics industry was not able to supply the silicon to PV industry and because microelectronics industry can always pay the higher price right because the chips are very small 1 centimeter square half a centimeter square. So, the cost of that material is not very high, but our solar cells are very big right, solar cells are 100, 200 centimeters for each and then you have to use many solar cells. So, solar cell is a very large area device and because of that the silicon consumption in solar cell is higher and therefore, the because of the shortage solar PV industry have to pay higher prices and the module prices started increasing. In this phase about 2003, 2004 lot of people have invested money in making silicon dedicated for solar cell. Many people have invested money for producing silicon dedicated for solar cell and now in 2008, 9, 10, 11 you see that prices are again going down in this prices are going down again because of the good supply of silicon. Still manufacturing silicon is not easy at all it is not easy at all and I will show you by the slides. First of all silicon is used in many other industries, but not in that pure form. So, aluminum alloy for example, alloying aluminum people use silicon and there are other usage of silicon itself. So, actual silicon production which is not very high pure is very high 5 million 5 million metric tons and who are the main producer of silicon. I will show you some other slides. So, it is mainly Hamlock, Wacker, REC, Tokuyama, MEMC, Mitsubishi these are the main player. Now, I want to actually focus your attention to this. So, this is the slide from 2005 look at the scale of this graph. The scale of this graph is 2004, 2006, 80000. This is kind of the capacity of the various manufacturers. So, this is the scale everybody can see. So, 2005 this was the scale. The scale was 2004, 2006, 80000 of various manufacturers in the world. Also note then where is the China? China is very small silicon production. Now, let us look at the this slide. This slide is actually 2010 slide. Look at the scale now. What is the scale? One order higher 10,000, 20,000, 40,000, 60,000, 70,000. So, first of all what has happened in the last couple of years is that huge capacity of silicon production has come. One order magnitude higher than other and because of that you can see that the silicon production has really crossed too much higher level and I will show you the number. Again just this is the give it an idea that when I made this slide in 2008 and 2009 the production estimated production in 2010 was 40,000 metric tons. So, that was the title of my slide when I made in 2008, 2009 40,000 metric tons by 2010 more, but actual production in 2010 of silicon was 209,000 metric tons. This is called polysilicon. Do not worry about it. We will come to what is polysilicon referred here, but it may actually exceed 350,000 tons of silicon by 2012. So, there is a huge production of silicon is happening now dedicated for solar cell which was not the case 10 years earlier. Because of all this, because of all this production volumes are increasing for the solar cell and the cost is going down. So, this dotted line is the cost and you can see the cost of the module were somewhere like 100 dollars per watt and now you can actually get less than 2 dollars 1.5 dollars. So, that is happening this is one of the tutorial problem that I have given you can do very easy problem that if you know the solar cell efficiency and if you know the sizes then you can estimate if you want to make a 10 gigawatt modules in 2010 how much silicon is required or actually current production of silicon PV module is 20 gigawatt. So, if you are making 20 gigawatt module using silicon, how much production of silicon should happen in the world? This calculations are very easy you can do it. I have given in the tutorial. Basically, what you do if you want to estimate the silicon consumption, very quickly let me tell you that silicon consumption. So, what you do is you find out the length width and thickness length with the thickness of the module of the silicon solar cell. This will give let us say volume in centimeter cube you multiply with the density of silicon gram per centimeter cube. So, you multiply your volume of the silicon used by density of silicon. Silicon density is 2.33 gram per centimeter cube. When you multiply this actually you know the mass of your one wafer in the gram. So, one wafer mass you can find out in terms of the gram. Normally typical length you can take anything it can be like 100 10 by 10 centimeter or 12.5 by 12.5 centimeter. Thickness I told you about 200 micron or more precise 180 micron. So, you can find out what is the gram what is the mass of one wafer? Now, this one wafer let us say one wafer your standard test condition is you have 1000 watt per meter square and your efficiency is 15 percent let us say. So, this much power is available to you you multiply by the area of your cell. So, you get how much power you get and this is a watt peak power. So, you will see that some gram of material is required per watt peak. This is finally, you want to find some gram of material is required per watt peak. So, you can find out if 1 megawatt is to be produced how many grams of materials available. 10 gigawatt is produced how many grams of material is required. So, this is small, but a very interesting simple problem that you should be. So, we should be able to estimate the silicon consumption require for 1 megawatt, 5 megawatt, 10 megawatt, 10 gigawatt, 20 gigawatt, 100 gigawatt whatever is the number. So, that you should do. How to obtain silicon is the main question that we are trying to understand here. First of all silicon comes in various types. So, there is a raw silicon which is available in the form of silicon oxide. There is a metallurgical grade silicon MGS, MGS is 98 to 99 percent pure. There is a solar grade silicon which is having purity of 99.999 percent and there is a electronic grade silicon which is having impurity of 99.9999999 percent. Many 9s are there 11 9s 10 to 11 9s are there that is the purity of silicon. By the way do you know any other material which is having this purity probably not. Do you know any other material which is this pure like electronic grade silicon and produced in the quantities of 200000 tons probably not. So, silicon is by the way the most purest material and purest and largest quantity producing the largest quantity on the silicon is the only material which is so pure and produced in so high quantity on the earth. So, this is electronic grade silicon. There is one more grade called detector grade silicon which is even more pure.  So, these are the various levels are the terminologies for silicon. Now, there are lot of impurities that are there in silicon silicon oxide which is available in the raw and that you have to you know remove. So, aluminium boron, phosphorus, titanium, tungsten, nickel, gold, iron, molybdenum, lengthenum all this impurities must be removed. How much to remove? So, that we can get purity level of this. So, that we can get the purity level of this kind of purity level. If your material is for example, only 99 percent pure or even 99 percent 99.9 percent pure you will not be able to make your solar cell. Why you will not be able to make your solar cell? If your material is only 99.9 percent pure or even 99.99 percent pure because impurities will be so high that the recombination lifetime will be higher. I am sorry much lower and therefore, diffusion length will be much lower and you will not get efficiency. So, therefore, you cannot make you cannot use raw silicon you cannot use MGS silicon also to make your solar cell. You can use solar grade silicon or you can use electronic grade silicon. So, impurity level in the solar cell or in the silicon is presented either in form of percentage either in the form percentage or it is or it is given in the parts per some parts per x atoms of silicon. So, this parts is normally given at parts per million ppm or it is given as parts per billion ppb or it is given as a parts per trillion ppt. How to get this parts of impurities per x silicon atom is you get the density of silicon atom density of silicon atom in crystalline form is 5 times transfer 22 per centimeter cube and you divide the density of impurity atoms in per centimeter cube. So, when you do this you will find out how many for how many what is the impurity level for a given number of silicon atoms. So, when you say parts per million. So, we say how in 1 million atoms of silicon how many atoms of impurity that is parts per million. When we say parts per billion in 1 billion atoms of silicon how many impurity atoms of how many atoms of impurity are parts per trillion. So, in 1 trillion atoms of silicon how many atoms of impurity. So, typically we talk about parts per million parts per billion and you can actually do the calculation again I have given tutorial problem to solve it. So, this is the way you can find out. Now, the production steps for silicon is that you actually start with the raw silicon you get the metallurgical grade silicon from metallurgical grade silicon you get the electronic grade silicon which is normally referred as a poly silicon, but you have to convert this poly silicon into the silicon wafer you to convert poly silicon into silicon wafer. So, electronic grade silicon high purity silicon containing gases first you get and then you convert that high purity gases into the solid which is of high purity, but not crystalline. What is crystalline when atoms are arranged in order then we say crystalline. When you talk about poly silicon, poly silicon is a pure silicon high quality pure silicon, but it is not crystalline in the in the form. So, therefore, what you have to do you have to convert this solid poly silicon which is pure into solid silicon which is crystalline silicon wafer. This process is called production of silicon wafer. So, you first convert poly silicon into what is called silicon ingot ingots are big rods of silicon or cubes of silicon and then you cut those ingots into the wafer. So, we look into this process quickly. First of all we have talked about three types of material metallurgical grade electronic grade and SOG solar grade metallurgical grade electronic grade and solar grade. So, look at the what kind of impurities that is allowed and this impurities are given here in terms of parts per million. So, in 1 million silicon atom how many atoms of impurity is allowed when 1 million silicon atom how many if it is metallurgical grade silicon aluminum is allowed so and so, so much 1517 atoms of 1 is allowed of aluminum in 1 million silicon. But, if it is solar grade only 0.7 atoms are allowed or if it is electronic grade 0.001 0.001 atom in 1 million which means about 1 atom in 1 billion. So, the impurity level or the purity level of silicon as far as aluminum is concerned is parts per billion. Look at the gold AU even much lower 0.0007 parts per million. So, about 0.07 parts per billion or which means 70 only 70 atoms of gold is allowed per trillion atoms of silicon. So, from this numbers you can imagine the kind of purity that is required and to purify a silicon which is high melting point. Silicon has a melting point of about 1400 80 degree centigrade. So, considering the high melting point of silicon and considering the kind of purity level that you require it is very difficult and challenging task to manufacture silicon of high quality, manufacture silicon wafer of high quality and produce silicon solar cells. For that matter so far as of today in the country nobody, nobody, nobody makes silicon. There are some efforts which are going on to manufacture silicon, but right now nobody is doing. So, let us let us look now step by step how to make a metallurgical grade silicon. So, metallurgical grade silicon before we go further as you increase the purity level of silicon your cost also increases. So, this slide here what you show what I have shown here this is a impurity contained in terms of the parts and this is the cost. So, if you look at the cost of a electronic grade silicon which is here is about 70, 80, 100 dollar per kilogram. The cost of a detector grade silicon is even 200, 300 dollar. The cost of a solar grade silicon can be about 10, 20 dollar per kilogram. The cost of the metallurgical grade silicon is about 1, 2, 2 dollar. So, as you increase your purity level your cost also increases. How increases? Look it is a log scale. So, it increases exponentially almost. So, it is a very important factor. Today's term the cost of the silicon that is used for solar cell application is available at about 40 to 50 dollar per kilogram that is that is what is available. So, silicon is available in nature you can have the sand has containing silicon oxide there are sand stones there are clays are available which is containing silicon and you can actually get a silicon from here. So, first step is to get the metallurgical grade silicon from raw silicon that is silicon oxide. In order to get the metallurgical grade silicon where the price can be the metallurgical grade silicon can have price 1, 2, 3, 4 dollar per kilogram. Very simple thing to do is you take raw material that is silicon oxide fuse with the carbon. So, you actually do this process at 2000 degree centigrade I will show you the slide here. So, you actually take put your raw material to carbon electrode supply very high voltage. So, that you know this material get heated and when the melting when the melting occurs this liquid silicon gets settled on the bottom which is about 98 to 99 percent pure and this silicon can be extracted and this silicon is referred as a metallurgical grade silicon. So, simple take silicon oxide fuse with the carbon or burn with the carbon you will get silicon and the cost can be higher. Normally this is produced in the country where electricity is cheaper because ever energy requirement remember you are melting it almost about 2000 degree centigrade 1800 to 2000 degree centigrade because that much melting requires lot of energy and therefore, if your electricity cost is cheaper than this cost of metallurgical grade silicon will be cheaper. So, not in India. So, it is produced in the countries like Brazil, Canada, USA where electricity is cheaper. So, once you get your metallurgical grade silicon what you have to do now you have to get a purified further. Now, purifying the solid metallurgical grade silicon further to a level where impurities are only in the range of parts per million and parts per billion. It is not possible to do it in the liquid phase. So, what people have done is you have to convert into the gaseous phase. So, we can we convert metallurgical grade silicon into silicon gases containing silicon and this gases are actually having very low boiling point. So, the gases which are which we convert for purification is silicon containing gases. So, we have a silane these are the silicon containing gases which are having low boiling point and can be purified by distillation. Silicon n can be purified by the distillation. So, there is silane there is a Si HCl3 tri-chlorosilane there is a Si H2Cl2 and there is also Si Cl4. So, these are the various gases which people use for purification of silicon. So, you get this gases for example, silane this is called silane and your tri-chlorosilane it is called TCS tri-chlorosilane this is called the DCS di-chlorosilane and this is tetrachlorosilane. So, normally this silane is used for purification you get a silane as a pure gas because you can do the distillation at low temperature, but what we want we do not want silane gas we want silicon in the solid form right. So, then there is a another state one thing also wanted to know tell you is when you want to make your amorphous silicon when you want to make your amorphous silicon people use silane. So, actually you can get this purified gas and directly do the deposition of silicon amorphous silicon. So, various impurities that you have to get rid of and what again you do is you have to convert the silicon into silicon containing gases. So, Si Cl4 then your Si H4 silane. So, various reaction that takes place in presence of HCl. So, you treat with HCl and you get your silicon containing gases and this gases as I told I am telling you that because of the lower boiling point can be purified by distillation and you get silicon containing. So, once you get high purity silicon containing gases what you have to do you have to get the pure solid right eventually want solid. So, you have to convert this gas pure gas into pure silicon. Once you get pure silicon, but this polysilicon is actually a not crystalline this polysilicon is not crystalline. So, then you have to convert into crystalline form. Once you convert into crystalline form then you have to cut it in the form of silicon wafer. So, then it cutting wafer. So, this is the various state. So, I will show you this I will show you the states. So, one is already that you know that it is raw silicon. Next step is to get a metallurgical grade silicon. Next step is to get a pure silicon gases or silicon containing gases next step is get a pure polysilicon. This is the polysilicon is high quality, but this is not this is not crystalline. This is not crystalline then you have to convert to crystal. So, then you have to get silicon ingot this is crystalline. What kind of crystal? What kind of crystal?  So, then you have to do the dicing then you get the silicon wafer. So, this is the whole root of silicon from raw silicon to silicon wafer and then you make solar cells. I hope it is clear metallurgical grade silicon is only 98 to 99 percent pure. Pure silicon containing gases these are electronic grade silicon gases and then you polysilicon, but not crystalline then you convert into the crystalline form and then wafer. So, I hope now you are starting to realize that how difficult it is to make silicon. There are so many processors required then all these processors are high temperature processors and because this processor high temperature processors lot of energy goes into making silicon and because lot of energy goes in making silicon the cost of silicon that eventually get for making your wafer is higher and because the cost is higher the cost of solar cells is higher cost of solar module is higher and cost of electricity is higher and that is why the whole worldwide effort is actually to minimize the cost of silicon or can we make can are there are other processors where you spend less energy in making silicon is it possible that we use more impure material. So, not electronic grade silicon, but we use solar grade silicon and without compromising with the efficiency. In fact, there are some people which is who are working on I told you that metallurgical grade silicon cannot be used for making solar cell, but there are some people who are trying to upgrade metallurgical grade silicon and it is called upgraded metallurgical grade silicon. So, can we use upgraded metallurgical grade silicon to make. So, let me come to the next slides. So, these are the this is the root will quickly go through it. So, when you when you want to convert pure silicon into. So, when we want to convert pure silicon into pure silicon containing gases into solid silicon there are two ways of doing it one is called Siemens reactor and other is called fluidized bed reactor. Pure silicon gases to solid silicon there are two roots Siemens reactor and fluidized bed reactor then pure solid silicon to crystalline silicon again there are two roots one process is called CZ process and other is called FZ process. And again from crystalline silicon to silicon wafer there are two roots inner diameter sawing. So, you have to saw it and the wire sawing. So, these are the two roots each two roots for different pure silicon gas to solid silicon solid silicon to crystalline silicon crystalline silicon to silicon wafer.  The silicon gets deposited in the form on this rod here I can see the picture here you can see the picture here that eventually this gets deposited here on the on this rod green line and actually you can get a stone of silicon like this which is pure in the form. So, one is Siemens reactor other is called fluidized bed reactor in the Siemens reactor the problem is that the silicon gets in contact with the electrode on which the deposition is taking place. And because of this contact some of the impurity of the electrode is transferred now our purity levels are so high parts per billion parts per million that even any contact with the any other surface can be a problem which is the case for Siemens reactor. So, therefore, people have come up with a fluidized bed reactor where silicon gas when you put like silane you are putting the conversion of the gas into solid silicon happens in the air it is not in contact with any other surface. So, this particles are actually floating silicon keeps get deposited on the particle and when it is heavy enough it just fall down. So, it is called fluidized bed reactor the bad is fluid it is not fixed and because now silicon is not making contact with any other surface then there are two so once you get the solid silicon you have to convert into crystalline silicon. So, definitely you have to melt it right you have to press so you have to melt it. So, there is a process called Chokralsky process it is the name given by the scientist after the scientist. So, you actually melt you put your silicon in a crucible as shown here you put your silicon in a crucible this again you melt in high temperature and you take seed silicon crystal you put in contact with the liquid and you keep rotating it so the atoms which gets deposited to the seed. So, seed is already a p type or n type and it is already monochrist line very important thing to note here is the doping level when we discussed for the solar cell the doping level is actually determined at this point. So, here in this case you put your impurities right. So, you put your boron you put your phosphorus and the desired amount right. So, if you want doping of 10. So, 14 atoms per centimeter cube or 15 or 16 you decide the doping level at this point. So, together with the pure silicon you also put the dopants in it. So, Chokralsky process is one of the most commonly used process for making silicon wafers. So, almost 70 80 percent of the material produced in the world I mean the crystalline silicon material produced in the world is coming from C Z process Chokralsky. So, this is what steps happens you put your stone here pure silicon stone it melts you put your seed crystal then you start pulling.  So, here the silicon was non crystalline or you can say polycrystalline and that is why we call it as polysilicon. Here silicon is a crystalline form and typically when you have the circular shape this is the format when you get always the monochristalline silicon your monochristalline is always circular keep this point in mind because we will use this information. So, your monochristalline your monochristalline ingot monochristalline silicon ingot is circle always it is always circle it is form of ingot and cylindrical. Then you have your float zone silicon float zone silicon again the problem with the mono this kind of C Z process is that silicon comes in the contact with the other surface and impurity level can be higher. So, another way of doing it is floating the melting a particular zone in without any contact, but first of all you have to make the ingot and then you have to make another process to melt it. So, you get actually even higher purity. So, float zone silicon F Z silicon is having higher purity as compared to C Z silicon, but actually you are doing that process twice and because of that it is more expensive float zone silicon is more expensive as compared to C Z silicon, but because of its high purity many times the high efficiency records or the solar cell with the high efficiency are actually manufactured using F Z silicon, but all commercial solar cell people use C Z silicon. So, that was the case for the mono crystalline silicon for multi crystalline silicon it is done in a bit of bit of faster way.  So, in this case the whole chunk it can be 1 meter by 1 meter by 1 meter. So, whole chunk of silicon can be melted and solidified together. So, this much faster, but the problem is you do not get mono crystalline you get multi crystalline. So, there are different grain boundaries that you get here, but multi crystalline is easier to make means cheaper also. So, the multi crystalline silicon is not circle it is normally rectangular or square. So, this is how you get the multi crystalline silicon and in order to cut this silicon ingots into silicon wafer there are two techniques inner diameter and wire sawing inner diameter you have actually a thin sheet of metal which is coated with the diamond and that goes over the silicon ingot and cut it or you have the wire which is coated with the diamond. So, wire sawing. So, one of the problem is that lot of material is wasted you see almost 50 percent material is wasted in the inner diameter sawing. This loss of the material is referred as a kerf loss right when you also saw our wood whatever the wood that goes out is actually a kerf loss. Similar to that whenever you saw your silicon wafer from ingot you have to also lose some of the material because of this mechanical process and this process remember we have actually put so much of effort to make the silicon and now 50 percent of silicon is wasted because of the kerf loss and 30 percent is wasted in wire sawing because of the kerf loss. So, that is a very significant loss eventually at the end you will get this kind of wafer. So, when you get the circular wafer you should understand that it is monochrist line, but when you put circular wafer the packing density will not be very high in the module and therefore, sides are cut normally. So, we get what is called the pseudo square. So, this pseudo square you can see, but always the rounded corner then you will as soon as you see the solar cell with a rounded corner you should be able to find out that it is a monochrist line, but if you look at the multicrist line you can definitely see the different grains as shown in this photograph this is a photo of multicrist line. So, different patches are actually different crystals as shown here different patches are different crystals and normally you can see now whereas, the manufacturing is so nice that actually you cannot see the different grains. So, if you look at your solar modules try to see the experiment when you are doing one of the module will have will be of the monochrist line type and other module will be of multicrist line type. So, we have given you two modules of mono and two modules of multi try to see today when you do the experiment which modules are mono and which modules are multicrist line. So, this is the whole process as I have shown you earlier also that you start from mining get metallurgical grade silicon you get gases polysilicon then you get the ingot and you dice it then your solar cell and then wafer. So, it is a very long process and it takes lot of energy to do that and that is why silicon is expensive that look at the phases that silicon goes through it goes from solid then liquid then solid then gas then gas then solid then liquid then solid and eventually silicon wafer. So, silicon actually goes through lot of processes and because of that silicon is expensive. So, I hope that after going through this lecture you will realize that why silicon is expensive and why silicon solar cells are expensive never the less huge progress has been made and the cost of silicon based module which was 100 dollars per watt some 20, 30 years ago has brought down to less than 2 dollar per watt or almost 1 dollar per watt. So, there is lot of progress has been made both in terms of the silicon manufacturing and solar cell efficiency. My next lecture will be about how to use this silicon wafer to fabricate solar cell. Now, we are using a silicon wafer how to use silicon wafer to fabricate solar cell. So, the summary of silicon manufacturing is that you get first of all silicon of various type raw silicon metallurgical grade silicon solar grade silicon electronic grade silicon detector grade silicon and the purity levels can be different and the cost of manufacturing can also be different right the cost of manufacturing can also be very different. I have showed you how to go from raw silicon to metallurgical grade silicon metallurgical silicon to gases, gases to poly silicon which is pure silicon but not crystalline and then you go to crystalline silicon in the form of ingot and then you cut this ingot into wafer. So, that is the whole process and why it is expensive that we have discussed. Question from Vijaywada. Sir, in ingot we are having some flatness, why we are having such flatness while preparing the ingot or wafer, wafer is not round it is having some flat surfaces certain area. Why we should have some flat areas? So, in wafer, so what happens in this when you have the wafer, when you have the silicon wafer like this. So, when you are going to put in the module, in the module you put many solar cell. So, this solar cell will be actually your active area if I make solar cell like this. So, this solar cell will be your active area but the area in between like here will not be active. So, you are not utilizing your module area properly. So, therefore, what we call is this pecking density. What is the area of the solar cell? What is the percentage of cell area in the module? So, if you are using circular then you will find that the best pecking density you can get is only about 70 percent. So, your 30 percent area will not be active. So, therefore, what you do is you cut from the sides, you cut this from the sides like this. When you cut from the sides, so your wafer, you shape of the wafer becomes like this. So, then you call the pseudo square and your monocrystalline silicon is always circular. When you produce it, because of this circular motion that you have to do in CZ process, it is always circular. So, if you want good pecking density, you have to actually get what is called this kind of process, pseudo square. Sudo square shape and now when you put a pseudo square shape, you can actually make solar cell closer to each other. When you put solar cell closer to each other, your pecking density increases and that is what you can see also. Is that your question answered? Sir, one more thing is regarding monocrystalline and multicrystalline. In monocrystalline itself, on all the phases, we are not having equal mobility. Mobility varies from phase to phase. That is, in 1-1-1 plane, we will think that mobility is high. How can we think of mobility regarding multicrystalline crystals? So, in mobility, monocrystalline silicon varies from one direction to other direction. In multicrystalline silicon also, it will be kind of you have to take average mobility. So, then it is not possible to define mobility based on the direction. So, you cannot say mobility in 1-0-0-1-1-1 because there is no such thing because all the grains are very different. But then you have to, you can always say the average mobility, which will be the average of all. Nirunjali, last question, one question only. Nirunjali. Sir, which type is more efficient and why? Which type of silicon is more efficient and why? I will not answer that question. You should know that answer. You know that monocrystalline silicon is a defect free and multicrystalline silicon because of the different orientation, there are many defects, there are many grain boundaries and therefore, there are defects in multicrystalline silicon, but there are no defects in monocrystalline silicon. So, that hint should be enough to tell you that which one should having, which one should have more efficiency.


I'm here from Lauren systems and I'm here to hopefully sort out some cable confusion a few people may have you may even be seeing this As a reply to some of the comments I see on well anytime. I've done videos about cable because the what abouts kick in and The what about cat 6 cat 6 a cat 7 cat 8 direct-attach copper with SFP I want to talk about where we use these different cable types different connections between switches or between servers or around the office and This is going to be a general guideline for their use There's always an exception because as so many things in technology when you ask the question of when do we use this? Well, it depends but those factors and there's some things you can generalize about those factors to kind of determine Generally where cables go where and of course I know there's always going to be an exception and that's fine But as long as you know which cables are which you know when to use those exceptions and I'll be leaving a link to some blog articles and Just talking about you know how to plug things in and where these all go before we dive into the details If you'd like to learn more about me and my company head over to Lawrence systems calm If you'd like to hires for a project such as network consulting There's a hires button right at the top if you want to support this channel in other ways There's affiliate links down below to get you deals and discounts on products and services We talk about on the channel including the shirts and swag in case you like shirts with cats on it matters back We have this shirt that has six cats on it And if you didn't notice their tails represent the different colors of Some of the cables for the category five six seven and eight cabling. All right now I also want to shout out to FS comm for sending me some of these cables is where we got like these dat cables Which actually this one's a 25 gig cable and this fiber They sent these to me along with some modules because I have some reviews I'm doing but this is also part of that review process Which does include as well the switch I have sitting right here so this is a Unify aggregation switch and I will be doing a review in the future and if that Future has already occurred and I will go back and edit this video put a link down below to that review But I've also reviewed this micro tick and this other unify switch here These are just for reference. This is not specifically about them But questions do come up about those switches and about these cables and about the connectors So I figured they made good props now. Where do we use what is? Going to depend on how far away things are is one of the factors in the next one is of course What speed do you need and of course the most speed would be the easy answer But then that also means the most budget so there's a happy middle that always have to be met first is Connecting switches with DAC cable matter of fact switches and servers that are all located for example Within the rack like I have behind me in our lab rack right here This is all has a series of ten and twenty five gig connectors in there And those are best facilitated with SFP using DAC DAC is a cable that is really simple really easy to use you just plug these DAC cables in they come pre Terminated with these type of ends on there or not something you custom fabricate But DAC has a really good advantage SFP in general has an advantage of being very low latency Very low power especially these direct attached copper the downside is of course You're not running this 200 feet away because well it doesn't go 200 feet They do make some active ones that go further, but generally when you're within the rack or within the server room This is where the DAC cables are great Then especially if you are connecting with some of the cards for example This is a 25 gig card right here And you can see has a relatively small heat sink despite having two 25 gig ports on here And this isn't even older 10 gig card These are really affordable so if you're building out your home lab or getting started in this these are common But I think the question that comes up people assume that oh, I should be able to just grab an inexpensive rg45 type connector But that's usually not the case because the rg45 is substantially more wattage Substantially more yes, it's all a small amount of wattage But that is compounded over the number of connections you have so it generates more heat requires more wattage Therefore can be a little bit more expensive and back to latency intensive applications such as a storage server So if you're connecting like a virtualization system to a storage server, you want the lowest latency possible and Yeah, that goes back to using SFP with like a DAC cable here now What about fiber isn't fiber faster? Well, that's still in the same category as SFP Because you're gonna use an SFP module connector and fibers generally speaking really low wattage Not much more not substantially more. I should say then using a DAC cable fibers more though Not for use inside of here. You can it will work But it's more for when the switches are further away And that's for all references article from fs.com rg45 versus SFP Which should be used to connect to switches and this article is january 17th 2020 I bring the date up because it is currently august of 2021 because with technology when you're referencing What should be used where the date matters a lot as technology changes fast But they break down the use cases and really it comes down to this right here when it comes to max distance One-year building and for example, we do a lot of infrastructure for building in warehouses And when you talk about building in a very large scale warehouse You may have 400,000 square foot warehouse and you have the front office And maybe they have some servers and office space up there And then they have the shipping office at the furthest corner of the building In those cases the distance is going to make a big deal and fiber makes a lot of sense And for example, the multi-mode fiber that I have in my hand right here has no problem at 550 meters If we were going to use rg45 ethernet cable 100 meters now I know I've done reviews on like game changer cable And I'll leave a link to that below and game changer cable is able to break that 100 meter limit But generally speaking you'll want to run fiber for a couple reasons one It only goes so much further than the 100 meter distance And if you have to certify a cable with a cable certifier, it is only certified to work at that distance Second is Any type of copper based rg45 ethernet cable will also be subject to electromagnetic interference Especially in the manufacturing area where you have lots of machines that may give this off That can cause or pose a problem over distance Because all the different electromagnetic interference that it picks up along the way from point A to point B Causes an issue. You don't have this issue of fiber. It's fiber optic now 550 meters for multi-mode fighter and 150 kilometers for single-mode fiber Means one of those two options is going to get you the distance generally speaking You need to get connect either like a scenario I played out with the warehouse or if you have a large facility with multiple buildings And you know you run an underground fiber between the parking lot site to site is great from building to building But a lot of times if if you're in the construction phasing or able to do either directional boring underground We will have a fiber pole that goes between the buildings We worked with the client to do this for example Or they had six buildings on a property and they wanted really fast connections So fiber was run underground between each of the buildings and brought to the main distribution Now mdf or idf main distribution frame where their server room is essentially, you know Where all the equipment may be This is why you have these switches like the unified aggregation switch like I have right here You would then put fiber modules in here and this has Lots of sfp ports that you're able to pop those in and be able to all right put all these together and Then spider it all out to all the switches creating, you know Your hub spoke type of topology or sometimes you could create some different topologies outside of that once again There's always an exception or why you may want to do that for redundancy Where you have the buildings connected to each other as well as to a central server So if one link goes down or some unfortunate parking lot event occurs that destroys it because that does happen when construction people Don't check for what's there before they start digging You can have redundant links, but that get too far off topic the advantages of sfp are kind of obvious They're fast. They're low latency But of course running this 10 gig right here and it's microtik switches are reviewed is still a great budget switch For people starting out and that want those connections. This is why there's so many different sfp options But you're probably thinking alright, but my computer my office is too far away to run DAC And maybe we'll just run fiber everywhere because you know fibers great and this question seems to come up a lot and It's just not practical to run fiber to every workstation and run this all through into everywhere That's of course why we have this right here. I'm not seeing fibers, you know, impossibly hard to terminate It's just not as simple as running a cable But this is where the cabling comes in and we're going to talk about which cable you should use I'm holding some cat 6a and then I'm holding right now some cat 6 And this is where there's always confusion of cat 6 cat 6a And then cat 7 and cat 8 I for those of you that want to go away into the deep in the weeds Me and damber rare did a great video where we talk really in depth about cabling standards I'll leave a link to below But let's just talk about the practical where we are here in august of 2021 about what cable we deploy for building out a office network And the first piece to start with is another article thinks at fs.com Running 10g base t over cat 6 had 6a cat 7 and we can throw cat 8 in there. Uh, this was in january of 2017 So I don't think they had cat 8 ratified then but cat 6 supports 100 base tx 100 base t 10g base t your 10 gig standard for frequencies up to 250 megahertz and it can handle 10 gigs and conditions Of throughput without most length of 55 meters I want to highlight that because there's this constant comment and misinformation that people seem to have That cat 6 is only capable of doing one gig No Cat 5e is capable of doing the one gig connections. No problem And of course you can go a little out of spec and yes, you can probably squeeze not certifiable But squeeze some 10 gig into short runs of cat 5e if it's a good quality cable But as far as what actually is documented in the standard You can do 10 gigs with cat 6 up to 55 meters And if all the computers that also have to connect at 10 gig are less than 55 meters away It's fine to run it now. You're not future proofing if you're Or Building it all in with cat 6 right now cat 6a would probably be a little bit better future proofing But it's still pretty common and we'll get to the why in a second most use price But then we have cat 6a now cat 6a is 10 gig over copper, but it can do the entire 100 meters I wanted to point that out because there is that kind of myth like I said before one that you only can do The 10 gig with this second is yes, you can run poe over both of these It didn't mention an article, but that seems to be a question people come up with oh I have a poe application in you know, the poe switch Maybe only two meters away or three meters away from where the for example a wi-fi access point or whatever poe device That happens to also need 10 gig pretty much wi-fi access points are popular use case for that And yeah, you can definitely run with standard cat 6 poe over that I don't know where that misinformation comes from But if you read the standards that is supported and of course it's supported over cat 6a And these are some of the differences right here when you start looking at the cat 6 or cat 6a You do get better shielding This is what allows cat 6a to go that greater distance and carry the full 10 gig But then what about cat 7? Shouldn't I just future proof my building with cat 7 or cat 8? Let's talk about that now Now this is not an endorsement specifically of mono price They had nothing to do with this video I just thought hey, why not use one place to compare a little bit of pricing prices may vary But at least from one source you can kind of get the price variations you'll see in these cable So here's your thousand foot box of cat 6 ethernet bulk cable cat 6 ethernet cable is relatively easy to work with and Mono price is 125 dollars for a box of thousand foot. What about cat 6a? well a thousand foot costs 279 and This is where budgetary concerns coming. You can see it's got better shielding. That's great Makes it a little bit more to work with and the cat 6 not that much harder It's a little bit of shielding to peel back But of course if you're doing 200 drops and you need, you know 30 40 boxes or more depending on the length and layout of the design you're doing That adds up really quick and becomes a budgetary concern because where the boxes cost Roughly more than double right now in august of 2021 If you find a video for me a few years ago talking about why we were still running cat 5e a number of years ago some of that had to do with the fact that that was Really more budget friendly and for people that just need basic connectivity and are just going to run Basic office applications and their work stations don't really have a lot of speed dependency that just need to be connected Well, you could have years ago gotten away with it now. You can still Same answer get away with cat 6 but cat 6a is going to be a little bit better But this is where the confusion comes in as people start saying why not just run everything cat 8 and i've had people Leave comments on youtube that say that i'm sorry. I don't think that you're running cat 8 everywhere Some people say, you know, it's what we settled on. We only run cat 8 everywhere one cat 8 500 foot box 339 dollars second cat 8 has a lot more shielding So there's a labor cost that goes up with this cable And it's one of the things that really has to be calculated into a job is the patch panels the connectors The little ends and putting them on just when you look at the difference between this is a cat 6 cable and the Cat 6a cable you notice there's a large bulkier difference to it. This actually is more of a challenge than people realize the Challenge is when I have to run 200 drops You have to calculate the size of these cables The size of the cables makes a big difference when you're running 200 drops because you have to have a system That can handle the extra bulk and what I mean by it like System is the suspension that you do for the cable the paths you choose to run when you're building these cabling jobs And the j hooks and everything else that build the support systems to hold these that all has to be factored in So it's not just a cost of cable There's the cost of labor the cost of the patch panels And this all just goes into the budgetary concerns if companies have an unlimited budget to do things awesome Run the best in cable out there But it's a scaling issue that goes back and forth. So generally speaking Here in august 21 cat 6 is still pretty the dominant one you're running But cat 6a is pretty popular But the fact that cat 6 can do 10 gig over up to 55 meters and you take a normal office They kind of are future-proofed at least up to the 10 gig standard if they even need that standard I say if there's always someone saying you should always install the fastest and there's times when Hey, if the company's budget allows it, we will but like I said staying within scope of what's reasonable So hopefully it's cleared up some of the confusion that comes with what cable goes where And why the DAC cables and sfp cables are still really popular and why they're still probably an even better choice Because of the low latency for things that are within the rack But this is still where you run things and I'll mention too people building a new house Cat 6a. Yeah, great if you're doing a new construction for the house But no running fiber all throughout your house is probably still not practical that question is frequently repeated Um But you know there are some advantage to fiber But I've also talked about those in a couple other videos when I talk about the different modules and comparison And final note. Yes, there will be some future videos for those wondering if these modules are sfp 28 We'll be talking about those in a separate video. That's the new 25 gig standard And yes when I review the switch that's part of the reason I have all this because the switch has four 25 gay sfp ports as opposed to just the standard sfp plus 10 gig ports All right, I will leave links to the different blog posts that I referenced in here And uh, allow you to dive in to do some further reading leave questions comments Concerned below or head over to forums where you can find me and have a more in-depth discussion. All right. 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