 to charge a battery of 12 volt, we need 14 to 15 volt. If the VM of the cell is 17.5 volt, we have to operate it less than the VM. In that case, efficiency of the cell is will be reduced. How to compensate for it? No, your VM as per the design is 16, 17, 18 volt, but your cell is not going to operate at a room at 25 degree centigrade. I told you that, your cell because it is encapsulated will always have 15, 20 degree centigrade higher temperature than ambient. So, actually you will not get in realistic condition, you will not get your VM of 17 volt. It will be dropped by 2, 2.5 volt. The actual voltage that you will get is only about 14, 15 volt. So, why we design for higher VM is just to take care of the temperature effect. Jai Chandrajinder college, Karnataka. Sir, I want to know where you, where did you consider the efficiency of the solar PV module? In the design, you are not consider the efficiency of the PV module, but when you give your rating of a PV module, you know rating of a PV module already takes care of that, right. How do we rate PV module? We rate PV module 4000 watt per meter square. So, when you, when you say watt peak condition, when you say that rated power, it already considers the efficiency. It already considers the efficiency. So, as a user, you do not have to bother about what is the efficiency of the module. You have to just see how much is the peak voltage it can provide you and not the efficiency. You do not have to worry about the efficiency of the PV module. It already comes incorporated in the watt peak rating. Sir, what would be the cost, approximate cost of the system you designed right now? What would be the approximate cost of the system that I designed right now? It is a good homework to all of you. Let me see how much it cost in Karnataka and how much it cost in Baramati. So, this is the assignment to all of you. Find out the cost of individual component, do the analysis, send it and if you are happy with the design, if I, if you believe me and my design is okay, you can actually install it and if you are going to install, you will get the real, real cost. Okay. A lot of questions. SGSITS Indore? Sir, which parameter decides the depth of discharge of a battery? It is decided by the material of the battery. It is decided by the electrode design of the battery. Okay. So, for example, Ladasit battery which are used in the car called SLI batteries do not have deep discharge because the electrode is flat. But the deep discharge battery which are used in a PV system is called the tubular battery, right? Because their electrodes are circular and they are kind of kept in the form of the tube. So, that your electrode material is not kind of lost during the charging, discharging. So, it is the electrode, it is the design of the electrode. It is the material of the battery itself will decide all the parameters. Okay, NIT Surath. By the way, I have run out of my time. Professor Fernandes is already here. If you have any question for him also, please go ahead and ask. Professor Fernandes is also here. Okay, NIT Surath. That if PV is gives the output for only one day. So, will it will make the battery charge to use for the three days? No, if you, so, yes, if you design the system for one day and you consider the autonomy of two days, so that we require total charge of three days. Assuming this, assume that yes, battery will get charged because you cannot do the over design, right. The extra battery capacity that you have considered, that is only for some emergency days, right. So, if I, your question, if I understand correctly that your battery capacity you have taken for three day, but the module we have taken only for one day. Now, for that much extra capacity of the battery, we cannot actually have the module also extra because that much battery capacity will be only used for couple of days in a year. And many times, you know, we have done the little bit over design. Remember, you have taken more power than the required power. So, that will take care of that battery charging. Varangal. Sir, good morning, sir. You said that it will be four batteries, sir, but actually 300, when you put it in parallel, I think you need to have six batteries, sir. I think if you see the white board. Okay, let me, let me, let me have a look at that. We have gone for the battery calculation. Okay, so we have, so we have come up with the four batteries, right. So, our energy requirement, sorry, ampere hour requirement was 373. We have chosen 100 ampere hour battery from the market. So, 373 divided by 100, we require 3.73 battery or we require four batteries. Now, this four battery charge capacity. These four parallel sections are okay. These four parallel sections are not four batteries. No, so what was our charge requirement? 62.2 ampere at 24 volt. And okay, yeah, you are right. So, we require. Four parallel, say, eight batteries we need to. Right, right, right. So, the, we have done the design for, yeah, we have done, we have done the design for the 12 volt, 24 volt charge. So, there should be two such strings. So, in each string there has to be four batteries that you are saying. I am sorry, there should be four parallel strings, yeah, yeah. You are right. There should be, I will check it, but I think you are right because we have done the design for once, yeah, yeah. So, two batteries in series and there are four such parallel parts. I will check it again. You also check it that, yeah. Sir, one more question, sir. For grid system also, should the analysis be done in the same way, sir, for grid interface with the PV modules? Yeah, for the grid connected system also, see, remember the energy flow, energy is conserved, right. So, whatever I do, the simple way to actually design is just to look at the energy flow, right. So, even if you are designing for 500 kilowatt or 1 megawatt, your input energy, output energy, if you take the energy flow and efficiencies of the component which are coming in the path, you can definitely do the very good approximate design. Sir, load the effect that inductive load or capacitive load such type of things does not come into the picture, sir? Well, it will come, but I mean, it will come, but I guess the professor Fernandez can answer that better, but I am just taking the efficiencies of each and every component, right. So, energy must be conserved. The simple principle is that the energy must be conserved. See, if I take that into account, I can actually get the approximate load. What is the question? For the grid side, sir, what will be the input means grid load, how do you take as a grid load? Voltage, power and inductive load or capacitive load such type of things should be considered, sir, while you are doing this analysis. No, what sort of analysis? I do not know. See, I do not know. Sir, you want to feed the power to the grid? Let me tell you the question. This question is, I have shown them the design of a PV system for a stand alone. He is asking if I am going to cannot design the PV system, which is grid connected. What I have used a simple principle of energy conservation at each point and I have taken energy flow from one point, one component to other considering the energy efficiencies of the each component. With simple considering the efficiency of each component, can we also design the system which is grid connected? Is that the question? Yes, sir. If I understand correctly, this is what is the question, right? Solar panel, whatever finally the inverter that could be any number of stages and this is the grid. That is what procedure is the same in the sense, this is the rating of the inverters KVA or VA. Now, if you are feeding the power to the grid, generally what the grid wants is, you feed the power at unity power factor. In addition, if the grid wants reactive power, then you have to suitably have a... So, if you are feeding the power to the grid at unity power factor, V and I should be out of phase, that is all. This is V, this is I. So, when you are feeding power to the grid, generally it is expected that you do it at unity power factor. Otherwise, if the grid wants reactive power, then it evaporates at leading power factor. Definitely, it won't be lagging power factor. So, that's it. So, most of the time... Thank you, sir. Most of the time it is unity power factor. Okay, thank you. Javelpur. My question is related to the problem which we have just solved. Yeah, go ahead. For the daily load requirement of 1.2 kilowatt hour, our PV module requirement is almost 1.8 kilowatt hour, which is almost double the capacity of our requirement. Okay. That means we have to install a double capacity PV module and also there will be intermediate cost of other equipment like controller, inverter, battery, etc. Will you think that this type of PV module would be economical for the total load requirement? Well, your PV module... Only if you look at the PV module, power rating, it came about 311 watt only. So, if your energy requirement is 1.27 kilowatt hour, so definitely your input supplied must be higher than 1.27 kilowatt hour. And therefore, considering all the efficiency that is inverter and battery efficiency, your supply is 1.8 kilowatt hour. Okay, it is an energy kilowatt hour. It is not the power rating of the module. Power rating of a module came only 311 watt peak, not 1800 kilowatt hour. Not 1800 watt hour. Okay. The power rating only came 311 watt peak. So, definitely if your consumption is 1,270 watt hour per day, your supply must be higher than that because energy is getting lost in the battery and inverter operations. Okay. And the cost is your perspective, right? Yeah, PV module. Madam, how do you go to office? Do you go by cycle or by walk or by car? How do you go to office by cycle or by walk or by car? The most economical thing is to walk. Okay. Or do you go by cycle? So, why do you come by car? Then it is not economical. Okay. So, it is your perception what is economical and what is not. If you want to use solar power, yes it is. What type of regular maintenance is required for solar PV module once it is being installed? The regular maintenance is, as far as the PV module is considered, it is just a cleaning of a PV module. That is it. And if you are, if you want to generate more energy, you can do the sun tracking as we discussed in the first and second lecture. As far as the battery goes, battery requires maintenance. Battery should not, you should ensure that battery is not going to deep discharge, that the water level in battery is sufficiently high all the time. That is the two main maintenance part. Okay. So, now we are taking a general questions. You can go ahead and ask any question related to the whole course. Okay. Any part of the day, any 10 days. So, for 9 days is also here. You can ask any question. Made in this problem, sir. Okay. Sir, so long, sir, please. Yes, yes, I am hearing. So, the inverter design you made. Yes, yes, I am hearing. 254 watts. In your whiteboard slide, it is there. Okay. So, if you made it as 254 watts, sir, when you make it as a VA, you wrote it as 250 EA. Okay. Yes. Sorry, inverter is 254. The VA, I think it must be greater than that. It must be greater than, I have just taken approximation that. Approximately. I just taken approximate, suppose you know 250 volt ampere inverter is available, but yeah, normally it should be greater than this. Also, I have assumed that all the loads are operating at the same time. Now, that may not occur and that is why I have taken it to be lower side, but yes, in order to be the safe side, you can take higher side. This 254 came assuming that all the loads, all three CFLs, all two fans and a computer is operating at the same time. Now, that situation may not occur all the time. Okay. And also, you know, if you operate your inverter at a part load efficiency are normally lower. So, if you try to match the load with the full rated capacity, then the inverter efficiency is higher. But to be on the safe side, you can take higher, but one of the disadvantage could be a little lower efficiency because in that case, your inverter will not always operated a full load condition. Right. Jaipur College, Kukas. Sir, how does this... We are using DC load. The first system which is shown in which a panel is connected to the DC load. Okay. Sir, in that case, the voltage, the power of the, power of the panel is changing according to the intensity or it is varying. So, at what, according to what power, which, how, load, according to load power, how much panel should be decided? Jaipur, so one simple thing you should do is try to match the rating. One simple thing you should do, try to make the rating of the load with the PV panel. Okay. So, if you are going to do the, at least the power rating should match, but not only the power rating, you should actually have your module should have sufficient voltage. So, that will determine the choice of your module. Okay. So, not only the power, but the sufficient voltage level also should be matched. So, that will determine the choice of your module. So, it may go for 40 watt module, 6-volt module or it may require 40 watt, but 12-volt module, depending on the load requirement. But what you should do is actually the, the maximum power you can get from the module and the, and the load power requirement, at least that much you should match. And you see that in the morning, evening, in the evening conditions, the radiation is lower. So, actually you should choose the module of higher voltage. Professor Fernandes will answer this. No, no, no. Don't get offended. Don't you think, can't you do of your own all this? You know the, you know the load requirement. How much of, what should be the rating of the solar panel that is required? Given the, why can't you do of your own? Why you want to, why you want an answer for all this? The sense is better that you do of your own. You may commit a mistake here and there. It's fine. You'll learn. Otherwise, if you take suggestions every time and go and do, you may not have the confidence to do by yourself. And these are very, basically very simple concepts. At maximum, he's saying power balance. That's all. Yeah, while choosing the power, you should choose appropriate voltage and current. Now, please don't get offended. I, I was here. I've been listening to the answer. What is the cost, sir? What is this? What is that? I think most of the questions, I think answer, I think you need to find out by yourself. Thank you, please. This is for all the participants. Don't get offended. That's the way one learns. I'm sure even Solanki also has learned through his own experience. Lampur. Hello, sir. I have two questions. How can we make the solar PV models durable when specifically used for solar water heater? And my second question is what is greenhouse gas effect and how it affects the efficiency of solar cells? Greenhouse gas, madam, you might have studied in your 12th standard, 9th, 10th, 11th, 12th. Okay, so it is result in increase in cell temperature. And the first question I couldn't understand clearly. Solar models durable or hot precautions we can take when we use it as a solar water heater. Solar PV module, you are not recommended to use solar PV module as a solar water heater. Amrita. Amrita. For previous analysis we have did, for converting a DC to AC, we have facing lot of power losses. So why not we convert all the home appliance to a DC and instead of that AC? Because the household loads are consuming the large power consumed. Consuming the large power. So why not we convert all the households to a DC equipment and better we utilize our PV modules for higher power plant as AC? For AC distribution. Good idea. Yeah, we can do that. No problem. In fact there are all, if you wish, you can find out the DC components of all types. You can find DC refrigerator. You can find DC light. You can find DC fan. Everything is available in DC. You just have to work little bit harder to get them. But nobody will stop you to do that. No, no. It is, it is found that. No, no, no. It is found that 48 volt DC direct DC transmission for residential. It requires less resources than equivalent AC. I was supposed to show today. I do not know why I did not bring the transferences. If you wish, I will upload those two papers in the module. You go through it. Our study shows that. Our study shows that 48 volt DC DC transmission for a household requires less resources compared to AC. Okay. Because we believe that. Yeah, yeah. Okay. Shivaji Nagar, Kolhapur. Question. What we... Sir, what, what are the... We have to consider considerations to increase the efficiency of inverter. Sir, I do not have time. No, God. But you tell me if you want to increase the efficiency, what do I need to do? I have to reduce the losses. What are the losses in inverter? What are the losses in inverter? The device, turn on, turn off and conduction losses. Okay. Now conduction losses, you may not be able to reduce or you may not have a choice. Okay. But then turn on and turn off losses, you may be able to eliminate by using what is known as the soft switching. I did mention to you that. Okay. But then if you use soft switching, you may be able to eliminate or you may be able to reduce the turn on and turn off losses. Conduction losses will remain the same. Okay. But then the process of complexity, circuit complexity increases. That's all. So if you do soft switching, you can try to improve the efficiency. But then complexity, control complexity will increase. That is expected. That whatever that you do in life, you have to pay a price. So if you try to improve the efficiency, your control complexity will increase. These issues I have already discussed. Okay. I have nothing more to say on this. Let's take home the many. Yeah. There are plenty of questions. Okay. Okay. Okay. Okay. Okay. Okay. Okay. Okay. Okay. Okay. Okay. Okay. Okay. Okay. Okay. Okay. Okay. Okay. Okay. Okay. Okay. Okay. Okay. Okay. Okay. Okay. Okay. Okay. Okay. Okay. Okay. Okay. Okay. Okay. Okay. Okay. Okay. Okay. Okay. Okay. Okay. Okay. Okay. Okay. it is a same thing, right. If you look, if you put the, if you put the PV cells in series, the current does not get added, right. Same current has to flow. So, when you put the things in series, it is a voltage that will get added, right. We have discussed different solar technologies to improve the efficiency of the solar cell. How we can use concentrators to improve the efficiency of the solar cell? And is there any PV module provided with the heat sink? Because we have discussed under the technology under the STC condition. Standard PV modules do not come. I got your question. Standard PV modules do not come with the heat sink because the cell, they are designed to, you know, designed to operate at 40, 50 degree centigrade easily. It is part of the design. The concentrator technology we have not discussed because of the lack of time. But if you look at the efficiency of the solar cell, you know, you have the open circuit voltage, you have the short circuit current, you have the fill factor and they are divided by P n, right. So, if you are now going to concentrate light, if you concentrate by x times, ok, if you concentrate by x times, what will happen to your efficiency of the cell? Your VOC will increase. How it will increase? Log function. What about the current? It will become x times directly because of linear function. Assuming your fill factor remain constant, which is normally not the case, then your input power is increasing by x times, right. So, this x gets cancelled with this x. Assuming your fill factor is constant because your open circuit voltage is increasing logarithmically, your efficiency will also increase logarithmically as a function of x concentration. So, in this way, if you can manage your fill factor constant, which will also depend on temperature, if you can manage this as a constant, if you avoid your losses, then actually you can get higher efficiency than the normal efficiency without concentration, ok. So, this is without concentration and this is with concentration. So, that is possible, but this is a big question, whether you can manage your fill factor constant and it requires lot of investment in the new design of solar cell, it requires investment in the cooling of solar cell because temperature losses will increase if your concentration increase, ok. So, that is the answer in very brief. We do not have time to go into more detail. Manipal. Yes sir. Actually under the concept of this distributed energy system, each household can the SPV can generate power, it can use in the whatever the partial can be used and the partial energy can be delivered to the grid, but under the condition of variable voltage and frequency of the grid and also the varying input of the because the solar energy also variable, how effectively we can tackle this technologically, ok. I have told this may be empty number of times. One, somehow I do not agree with you that you have grid voltages, we have variable voltage, variable frequency. Voltage might change at the distribution level, but then frequency does not change, frequency varies for a very narrow range, ok, does not matter, ok. But then you have a solar panel, inverter grid, you have an MPPT here, it will extract the maximum power and transfer is to the capacitor and this inverter will transfer the power to the grid in such a way that it tries to maintain the DC link voltage constant, ok. You might have a variable voltage and variable current source at the input, ok, but then at this point voltage is maintained constant. How do I do that? Whatever the power that is coming from the solar, I am saying power, whatever the power that is coming from the solar cell, if I transfer it to the grid, this energy storage element will not do anything. If there is a mismatch of power either it will receive or it will supply. If it receives, this voltage will increase, if it supplies, this voltage will fall. If I try to keep this voltage constant, there is a power balance, that is all. So, this is the input voltage, I am assuming that power is transferred at unity power factor, ok. So, current is out of phase just by changing the magnitude of this current, I can change the power transferred, that is one way, that is one way. Just by changing the magnitude of this current, I can change the power transferred to the grid because B into I cost it assumed to be 1 is equal to power, ok. How do I choose the magnitude of this current? It is same thing, same close loop that I had discussed, VDC reference that the suitable value that you need to regulate. Actual error, PI regulator, now this could be either, either the magnitude of this current waveform or angle between the two voltage sources, B1, V2 divided by X into sin delta. All this time, I have been saying B1, V2 divided by X into sin delta. So, under that condition, output of the PI regulator is delta. So, I have been, this is not the first time that I am discussing, I might have told this at least three to four times. Simple circuit theory, power balance is the concept that has to be used. Now, how to generate a wave from whose frequency is same as that of grid? For that you need to use PLL, that is all. Ok, Calicut. At the back side of the PV panel, we can increase the cooling rate of the PV panel, thereby we can reduce the temperature aside. Then why industries are not going for this concept? No, it is, so how do you replace, if you are going to replace Tedlar with something which can take heat away, that material has to be metallic in nature. So, if you are going to put an aluminum sheet on the back side with some kind of fin arrangement, it is going to increase the cost. So, when it comes to industry, when it comes to economy, you have to optimize which component will aid the cost, which component will reduce the cost. So, under the optimized condition, it is economical to use Tedlar and not any cooling arrangement. Even if you use any cooling arrangement, the cell temperature you may reduce by two or three degree centigrade, because your cell is still encapsulated. You have to still encapsulate with the polymer sheet on the top and bottom. So, even if you are using a cooling arrangement, it will have, it will come after the cell and then your encapsulant and then your metal sheet. So, even if you have good cooling arrangement, your cell temperature may reduce only by couple of degree centigrade. So, your cell will still be working at a higher temperature and therefore, it will not any solution which brings down the, try to look at the decrease in temperature by having some fin arrangement is not economically viable. Nagpur, last question, then I will answer two quick question on a chat. Nagpur. My question is for the empathy tracker. Sir, in the empathy tracker, are we referenced as well as the actual voltage goes and changing? So, how will the PI regulated, because both the reference as well as the actual voltage is changing? How can the PI handle this, sir? Which contest are you talking about? The MPPT tracker. Yeah, sorry. MPPT trackers are MPPT. So, what happens in MPPT tracker? I don't know. Pay the reference voltage with the actual voltage of a DC to DC converter. Our reference as well as actual voltage goes and changing. How will the PI regulate? Ma'am, what the MPPT does? MPPT tries to operate the solar cell at the maximum power point. At a given operating point, it calculates the power. And it just gives a disturbance. Goes to another point. In that power, if that power is higher than the previous one, it goes on, goes to a higher point. That is so called the hill climbing. Which voltage and currents are changing? See, it does not matter. Operating point at the input may be changing. Operating point at the input may be changing. Yes, depending upon the sun's insulation, the operating point will change. Therefore, both V and I change. But then you are transferring power to the output stage, where it is stored in a capacitor. And that power from the capacitor either is dumped to the grid or it is being consumed. That output voltage is being regulated by the inverter, not by the MPPT regulator. So, what is the converter? Not about the inverter side. I am trying to understand. Don't confuse with the boost converter or volt controller loop. No. What the boost controller does is, the MPPT generates a duty cycle for the switch, such that it extracts maximum power from the solar cell and it is transferred to the output capacitor. That's all. That power has to be transferred to the grid by the inverter. Therefore, the inverter does the voltage control. Boost controller does not do the voltage control. It is the inverter which does the voltage control. If there is only a boost controller, then yes, the controller of the boost regulator will have to regulate the output voltage. Fortunately here, output power is being processed by the inverter. So, the inverter has to do the voltage control. So, you have to consider the entire system and then you have to decide which block will do which control function. So, DC to DC converter will extract the maximum power. It is transferred to the capacitor, inverter from the capacitor, it transferred to the source. Okay, sir. Thank you, sir. Thank you. Okay. So, let us stop here. Thank you to all of you.