 Let us start now ok. So, what we discussed what we are discussing last time was the PV module design that is what we have done and let me recap. So, in the PV module design we have many looked at how many solar cells are to be connected in series in order to get a required voltage and the important thing is we should take care of a drop in a voltage because of the temperature rise and because solar cell is encapsulated in a glass and because of the greenhouse effect the cell temperature within the module is much higher than the ambient temperature normally 15, 20, 25 degree centigrade higher than the ambient temperature ok. Then if you know the current density of a given technology we can find out how much current a given cell produce and once we know the current we can actually find out the total current of the module we know the total voltage of the module and in this way we can find out the power rating of a module. This is all under standard test condition right. Then we also looked at mismatch in the solar cell why it is important to connect the same kind of solar cell in series otherwise there is a losses and that if there is a mismatch in the solar cell the total power of a module will be a less than the sum of the power of all the solar cells. Normally whenever you put cells in series in parallel this power output power of the module should be equal to sum of the powers of the solar cell which is normally not the case and therefore the module efficiency is typically 1 to 2 percent lower than the cell efficiency. If your cell is 16 percent your module may be about 14, 14 and half 15 percent as the best. So, that is the that is what happens in module design. So, once given a requirement voltage you can design a module with the number of cells. So, typically a solar cell having a made by higher band gate material like cadmium tellerite will actually give you higher open circuit voltage. So, when a solar cell is giving a higher open circuit voltage the number of cells to be connected in series in order to get the same output voltage would be lower. So, crystalline silicon solar cell we have seen the number is 36 now sometime 34, 33 also in amorphous silicon and CDT you will see that number of solar cells to be connected in series in order to get the same 14, 15 volt voltage to charge a battery of 12 volt at any operating condition would be less than 36 and it will come about you can do the calculation, but it will come less than 30, 20, 25, 28 and so. So, that is the design and all those parameters while we discuss in the design is at standard taste condition right, but in practice your module is going to be installed in the field and therefore, the actual performance of the module may not be the same as the performance rated at standard taste condition. So, in this lecture what we are going to look at is how the module is going to how the performance of the module in the field conditions vary. So, in the previous lecture as I said we designed the module we looked at the PV module design number of cells to be connected. Yes we also looked at the mismatch and bypass and blocking diode and the current voltage equation of a solar PV module. So, cell and module and as I said that same current voltage equation can be used for the PV array also when several modules are connected together. So, in this case we looked at the ratings of the module effect of temperature and radiation PV module application and some notes on the field performance of the module. So, if you go to the industry and the lot of industry who are trying to set up a PV power plant today have this very big question which module should I use? Should I use a crystalline silicon module? Should I use 3DTE module? Should I use amorphous silicon module? Which module should I use? And as I told the answer is never easy, it answer is never easy it depends on so many parameters. So, now if you look at the rating of a PV module what we have discussed is the standard test condition. But there are two other ratings that are used for the PV module. One is standard test condition which gives you watt peak power, standard test condition is 1000 watt per meter square, air mass 1.5 G global radiation, cell temperature 25 degree centigrade. Remember cell temperature 25 degree centigrade, wind speed 1 meter per second. But we know that 1000 watt per meter square is normally not available. It is not normally not available and therefore people say let me use some other condition which is called standard operating conditions. Since in a standard operating condition what you do is you get solar radiation not 1000 watt per meter square, but you get solar radiation of 800 watt per meter square. But even then your temperature can also be higher. So, then you say let me characterize my module at what is called nominal operating condition. Let me characterize my cell as nominal operating conditions. So, there are three ratings. So, there are three PV module rating, standard test condition, standard operating condition, nominal operating condition. Here we use 1000 watt per meter square and 25 degree centigrade. Here we use 800 watt per meter square and 25 degree centigrade. Here we say it is 800 watt per meter square and temperature is not 25 degree centigrade of cell. In order to use the temperature we use what is called NOCT nominal operating cell temperature. So, this temperature is nominal operating cell temperature and that temperature is obtained by another way. So, I will show you. So, this nominal operating cell temperature is typically 42 to 50 degree. It assumes ambient. So, the NOCT can itself vary by 42 to 50 degree centigrade. So, here you are not going to use 25 degree centigrade. So, 22 to 50. Now, again for Indian condition this is a low temperature. Our real operating conditions in India is going to be larger. So, in Europe because the temperature in the climate are lower you have the lower NOCT nominal operating cell temperature, but in India it is going to be large. Anyway, under this condition what you are going? So, once you go from STC to AOC, SOC I am sorry what is going to happen because your radiation is going down your current will go down, but your voltage will remain same. Once you go from SOC to NOC because of the lower radiation as compared to 1000 watt your current will go down, but and because of your higher temperature what will also go down? Voltage will also be lower voltage will also be lower. So, that is what we have seen look at here. I will show you the zoomed version of the what happens. The standard people people only give the standard taste condition, but if you want you can actually ask your manufacturer to give me a performance under the NOC or SOC condition. So, look at the NOC condition this dotted line here both voltage is lower current is lower because you are talking about not 1000 watt per meter square 800 watt per meter square and you are talking about higher temperature NOC nominal operating cell temperature and the larger curve is STC the one below is SOC. So, in this way you can actually get the. So, the performance under NOC is more realistic performance performance under NOC is more realistic performance and what you see here in terms of the what you see here in terms of the in terms of the power. So, STC power is higher and you can see here NOC power is going to be lower NOC power is going to be lower. So, so if your if your ST if the module is in STC condition like this your your NOC condition will have something like this lower current lower voltage why lower current because you are talking about 800 watt per meter square and why lower voltage because you are talking about 42 to 50 degree centigrade. So, therefore, your power in this case STC is here and in case of NOC your power is going to be lower. But what I am saying NOC will give you idea about more realistic picture. NOC gives idea about the more realistic picture just to keep in mind the module temperature or actually it is not module temperature cell temperature within the module can be obtained like this. So, if you know your NOC you know your ambient condition you know your P in P is in kilowatt per meter square if you know this you can actually find out your cell temperature in the module. So, this are a this is some empirical way of getting that. So, if you put your ambient temperature power in at a given place you can try in your your location today. So, if your you know your power density you can measure, but remember you have to put in kilowatt. So, 1000 watt per meter square is 1 kilowatt per meter square and 800 watt per meter square is 0.8 kilowatt. So, if you do that you can find out your cell temperature and if you know your cell temperature you can calculate how much voltage drop will occur per cell. When you are calculating the voltage drop for the whole module you have to calculate the voltage drop per cell and you have to multiply the number of cells in series then you will get the total voltage drop in the module because of the temperature. So, this is a standard power this is I have shown you the IV curve and the power versus voltage curve this kind of line dotted line here is the power versus voltage curve and the IV curve of a 75 watt peak module and this watt 75 watt peak module will have different value of current and voltage under different conditions. So, this we have seen already, but just to emphasize again that look as we go from the lower and lower and lower radiation power your current decreases and as you go and because your radiation because your current decreases voltage is also decreasing why? This voltage decreases not because of the temperature this voltage decreases not because of the temperature this voltage decrease because the voltage is also a log function of current right. We know that voltage is also a log function of current your VOC is equal to kT by Q we have we have written this expression so many times that you should be knowing it by heart. So, your IL is proportional to light generated current is proportional to P in and because of that your voltage is proportional to log of P in proportional to log of input power and because your input power is decreasing your VOC will also decrease. So, this decrease in voltage is not because of temperature, but remember that temperature will have additional effect of decreasing the voltage right keep that in mind temperature will have additional effect of decreasing voltage. So, if this curves are plotted so this must be this is plotted at 25 degree centigrade, but if this curves are plotted at 50 degree centigrade cell temperature or 60 degree centigrade cell temperature this will have even lower voltages it will have even lower voltage. What will happen to the current? As I told you earlier yesterday's lecture the current increases with the temperature, but increases very small 0.05 percent, but the voltage decreases significantly. So, this is the effect of radiation on cell on the module and this is the effect of temperature. So, as the temperature so if I take the same plot if I take the same plot look at what is happening the current is increasing look at the same. So, this is the plot at 0 degree this one the lowest one at the 0 degree centigrade gives highest voltage and lowest current. Here the difference the increase in current is actually much smaller as compared to decrease in the voltage increase in the current because of the increase in temperature is much smaller than decrease in the voltage because of increase in temperature. So, 75 degree centigrade you see the voltage almost come from 22 to almost over 16 volt. So, much 6 volt difference of the voltage can occur because of the temperature. So, there is a effect of temperature and there is a effect of radiation and I told you that when you are calculating the actual output of a module in the field you should take both of this into account you should take both of this into account. So, here I have given the typical parameter for a crystalline silicon solar cell. So, normally current this is for crystalline silicon solar cell the normally current is 30 to 35 milli ampere per centimeter square and the change in current with temperature is plus 0.06 percent to 0.1 percent per degree centigrade. This is positive sign means it increases. Voltage typically you will get 0.5 to 0.6 in that is for the solar cell in the module the voltage is 18 to 21 for the module open circuit voltage and the decrease in voltage at the cell level is 22 to 2.3 milli volt per degree centigrade. Decrease in is 22 to 2.3 per milli volt per degree centigrade for the cell level and 0.075 to 0.085 volt per degree centigrade for the module. Simply you multiply this number by number of solar cell you will get this number. So, for the module the decrease in voltage is about 0.075 to 0.085 per degree centigrade and remember there is a negative sign here. Fill factor is typically 0.6 to 0.8 that is 80 percent 0.6 is 60 percent typically it is in between 70, 72, 74 percent and the decrease in fill factor is about 0.12, 0.2 percent per degree centigrade. Power is here given milli volt per centimeter square power is milli volt per centimeter square. We know that our solar radiation is standard test condition solar radiation is 1000 watt per meter square or you can say this is 100 milli watt per centimeter square in terms of centimeter 100 milli watt per centimeter square right. Now, if my solar cell is having if cell efficiency is 15 percent then I am converting 15 percent of this ok. 15 percent of this will be how much? 15 percent of this will be 15 milli watt per centimeter square or you can say if I take a 15 percent of this power it will become from 1000 watt per meter square becomes 150 watt per meter square. So, same thing you can say either in watt per meter square or you can say in milli watt per centimeter square. So, that is how output power. So, 10 milli watt per centimeter square is corresponding to 10 percent efficiency 15 milli watt per centimeter square is corresponding to 15 percent efficient and the decrease in power this is most important parameter. Decrease in power for a crystalline silicon solar cell is 0.042 0.05 percent per degree centigrade ok. Now, I have I wanted to show you the same numbers for others other technology. So, percentage decrease in power for other technology also I will tell you there was one slide which is missing from here I will send you may be some time which actually summarize all the parameters current, voltage, fill factor and power. The power is most important. So, P m for crystalline silicon or the power output for crystalline silicon decreases by as I said negative 0.4 to 0.5 percent per degree centigrade. This percent of what? What peak? The percent of peak power ok. Decrease is a whenever given percent is percent under the percentage of standard test condition. For cadmium telluride because the band gap is higher the drop in the voltage is lower and therefore, drop in the voltage is lower the power decreases lower. So, you get about you get about 0.252 0.28 percent of what peak per degree centigrade ok. Similarly, amorphous silicon amorphous silicon is even higher band gap. So, sometime you get very very low 0.2 0.22 to 0.26 percent what peak per degree centigrade. This are the typical decrease in the power and this is called the temperature coefficient of power. Similarly, decrease in voltage you can say old temperature coefficient of voltage you can say temperature coefficient of current and so on. Temperature coefficient of power temperature coefficient of voltage. So, these are the important. Once you know that once you know your temperature then you can actually estimate and I give example that if you have suppose let me take another example slide. So, suppose you have a module rated 800 watt peak this module is rated 100 watt peak 825 degree centigrade. So, in operating condition let us say in operating condition your cell temperature not ambient temperature your cell temperature is 50 degree centigrade. Then and I am talking about crystalline silicon PV module ok. This module is crystalline silicon PV module. So, how much is the power you will get? The power you will get for input radiation of. So, your input radiation remains same 1000 watt per meter square. What has changed? Your temperature has gone this. So, I am looking at the effect of temperature only. Your temperature has gone this. So, how much is the power now you will get? So, your power and 850 degree centigrade will be equal to actual your peak power ok. This is actual power minus the drop drop is how much for crystalline silicon? Let us say 0.4 to 0.5 percent per degree centigrade. So, let us say I am taken number middle number 0.45 percent. So, divide by 100 of watt peak power. So, that is 100 watt. Then this is per degree centigrade and I should multiply by the difference in temperature. So, 50 minus 25. So, 50 minus 25. So, this will give me the new power ok. So, my 100 minus this is cancelled out this is 25. 45 multiply by 25 is how much? So, about 12.5 you will get about 12 watt about 12 watt about 12. This is approximately number I am taking. So, your actual power you will get is 88 watt. This is the effect of this is the effect of temperature only. So, your 100 watt module at 25 degree centigrade which is the rated power at 1000 watt per meter square and 50 degree centigrade at this condition and at this condition it will only give you 100 watt. Now, suppose somebody says my 1000 watt is not there, but I am if I go in the 3 o clock afternoon and I am that time I am measuring my module and that time my solar radiation perpendicular to the plane of the module. So, my module is like solar radiation this. So, this solar radiation is my only 600 watt per meter square or let us say even 500 watt per meter square easier to calculate. If my solar radiation is this then how much is the power then very simple this 88 watt you are getting at 1000 right. So, you have to. So, you are getting at 1000 watt per meter square you multiply by 500 watt per meter square. So, what will become your 48 watt will actually become 44 watt. So, a crystalline silicon module of 100 watt peak rated at 25 degree centigrade and 1000 watt per meter square under a temperature of 50 degree centigrade and the radiation of 500 watt per meter square will give you 44 watt right. So, in this way by you can actually find out the effect of temperature and the radiation in a module and at at any given instantaneous value you can find out how much power it will give at any given instantaneous value you can find out how much power it will give fine. And this is how as I said the voltage decreases power decreases current increases slightly and this is the percentage change. Let me show you this in detail. So, that you can realize how much is the effect of temperature. So, look at the percentage change in the parameter. So, if I look at the current my current is positive right. So, some people are asking what will happen if the temperature is lower than 25 degree centigrade. If temperature is lower than 25 degree centigrade look at the power curve power is actually higher than positive it increases then the standard test condition. If my voltage is my if my temperature is higher this is a temperature axis my temperatures are your power decreases your voltage decreases and your current increases. So, these are the relative change as you go from standard test condition of 25 degree centigrade to about 80 degree centigrade look at the percentage decrease in the power it is almost 7 almost 20 percent power change occurs. So, this is this graph is just to give an idea how much changes occur fine various types of module we have already discussed you can see that looking at this module what type of this module is this what type of the module is this. First of all when there when you look at the crystalline silicon module you will always see the fingers right fingers are of aluminum silver white ish. So, whenever you see the fingers line going across the module you say this is definitely crystalline silicon, but now your two choices there can be monochrysaline silicon and there can be multi crystalline silicon. So, there is this identification for monochrysaline silicon is this void patches that you see there and this this void patches that occurs because of the rounded corners. So, this is monochrysaline module monochrysaline silicon module this is multi crystalline silicon module this is monochrysaline silicon this is multi crystalline silicon this is multi crystalline silicon, but this module here and this module here and this module here and this these are all thin film modules these are thin film modules typically amorphous silicon looks grayish like this this is most likely going to be amorphous silicon module and this is normally the color of C I G S module. This is normally the color of C I G S module, the one I have showed you yesterday. Module application. So, these are couple of pictures that I will show you. The module applications can be anything for rural electrification. So, this is one picture from Africa where the modules are installed in each household and basic electricity is supplied using this module. You can use this module for solar lantern charging and nowadays solar lantern can be very very small and your module can be very small. Can you show me this lantern? I just have a lantern here. So, there are solar lamp which actually gives you very significant light, but use LED of only quarter watt. So, this module here, this lamp here, this is a lamp and there is a LED sitting there and this LED is, this LED is only quarter watt and I used it and gives a sufficient, it gives a sufficient light. It is called a steady lamp and the module that is used with this lamp, the module that is used with this lamp is having only half a watt. The power of the module is only half a watt, 0.5 watt. So, now you can see that how solar panel and there is a cost of this is very low. The cost of this entire thing, it has a battery, nickel metal hydrate battery inside, it has a power, it has a LED inside, then there is some electronic circuit is there and there is a module also with this. So, the cost of putting all this together is only about 400, 450 rupees fine. So, modules can be used for the solar lantern or it can be used for the grid connections. You can put many modules together and this particular picture shows the modules installed on a tracker. There is a tracker here. So, this module follow the sun and there is a grid you can see and this module, this power can be fed into the grid as professor Fernandes must have explained you. Modules can also be used as a building integrated photovoltaics. So, in this particular building, in this particular building the wall of the building and the facade of the building is actually covered with the photovoltaic modules. You can see the thin film modules are sitting there. The modules can also be made transparent. So, if you use the back, tedlar which is transparent. So, whatever the gap which is there in between the cell, the gap will actually transmit the light. So, if you are using the module as a roof, which you can see here this modules are actually being used as a roofing material. You will not only generate the power, but you will also get the light during the daytime. So, there is a double use. Your modules can be very, very long strip as I showed you yesterday and this long can be 1 kilometer long strip. Your modules can be roof integrated. Here there is a module which are. So, you probably you may not notice, but these are the modules solar PV modules which are integrated on the roof. So, that is another way you can look at. It does not require any additional structure. You can just put your module laminate onto the roof. Your module can also be made transparent. You know the thin film technology, how much material you want to deposit is in your hand. So, if you are using amorphous silicon and if your absorption length is let us say about 1 micrometer and instead of 1 micrometer you deposit only half a micrometer, then your module is going to be transparent because there is not enough material to absorb the even visible light and therefore, you can make your module transparent also. Or you can make your module and use it for the big power plants. So, this is one picture and where modules are used for 18 megawatt, but nowadays this is the very old picture. You can see the monochrist line modules are being used here. Monochrist line modules are being used here, but nowadays people are setting a huge power plant. There is one power plant which is coming in. Marasta is 150 megawatt, one single PV power plant, 150 megawatt and there is a announcement that I have seen that in the next two years in California, there is one single power plant which is of 500 megawatt, 500 megawatt. So, PV is really making a huge inroads in the power generation also. This is an example of another photovoltaic module, but this is module is a not normal module. This is a concentrator PV module. These are the concentrators your cell is sitting here. And what is this? This is a heat sink. I will tell you because of the shortage of time, we have not discussed the concentrator photovoltaic, but there are many people who are doing research on a. So, what is happening is you have the concentrator, your solar cell is sitting here, the light is coming here and getting concentrated on the solar cell. And now this solar cell will get heated and this concentration can be of 300 times, 500 times or it can be lower 20 times or even people are talking about 1000 times. So, your concentration can be 1000 times. So, when you concentrate light by 1000 times, your solar cell is going to be in trouble. And therefore, you have to get heat of the heat generated and sometime people use what is called heat sink. So, that is the picture that you see here. The heat sink will actually cool down the cell. So, this is the heat sink. This is actually heat sink is actually heat pipe. Heat pipe is the some mechanism by which you can reduce the or take away the heat. In this solar cell, the 3, 5 solar cells are used. That is the gallium arsenide and the concentration is 400 times, 400 times. So, this are various application and the some application which PV module has started its main thing is in 1960s is a satellite application. The solar PV modules are satellite, the people are using PV modules for running their cars, people are using PV modules for running the aircraft also. Some of the unmanned aircraft, you might have seen the stories that unmanned aircraft completely powered by solar can fly on their own. So, these are very many applications you can use solar PV and that is the one good thing about solar PV. No other power technology can supply you as little power as solar PV can do. For example, in micro watts, milliwatt as we use in our calculators and no and PV modules can also give you mega watt. So, for example, I give my example to my student that if you want to run your watch on a power, electric power, you cannot put coal power plant in your watch. You cannot fit the coal to your watch every day and say power plant. You cannot make it nuclear, you cannot make it hydro, you cannot make it wind based. What you can make it is a PV based. So, the PV is a really versatile technology in that way. So, now, I will give some examples of a performance and I am mainly going to compare with the thin film technology because how which model to use in a field is a one big question in front of anyone. So, look at the various technology I am revisiting here. So, we have C I C crystalline silicon, amorphous silicon, CDT, CIGS, look at the various band gaps and the cut-off wavelength. So, 1.12 is corresponding to 1107 nanometer. So, this is this wavelength is nanometer. So, all the photons which is longer than 1107 nanometer will not get absorbed in crystalline silicon. This number is very easy to remember because it is 1.12. Amorphous silicon is a band gap of 1.7. So, any electron which is any photon which is having energy less than 1.7 electron will not get absorbed or any photon having wavelength longer than 729 nanometer will not get absorbed. Cadmium telluride 855 nanometer is the cut-off wavelength and CIGS 1181 is the cut-off wavelength. Look at the graph here. This is my spectrum. This is the actual spectrum taken from the actual solar spectrum data and look at what happens. So, amorphous silicon cut-off is here. What does it mean? Almost 729. What does it mean? All the food all this energy from here onwards will not be absorbed in amorphous silicon. CDT cut-off is 855. Where is 855? Somewhere here. So, all the photons beyond this will not get absorbed. So, this is already the loss. CIGS is highest. The loss in crystalline silicon and CIGS is the lowest. So, that is one aspect of different technologies. Other aspect is that when you put a PV power plant or there are many things that happens and if you are putting your 1 megawatt. So, 1000 kilowatt power plant there, if you are putting your 1 megawatt power plant or 1 kilowatt, I am sorry 1000 kilowatt actual SE output you will get under standard test condition only about 775. So, actually you will get about what is called the factor, the performance factor. People refer as performance factors. If you are putting 1 megawatt in the good condition you will get 75 percent of it. Why? Because this 1 megawatt is first of all your DC. So, there are various losses that happens. There is losses because of the mismatch in the module. As I said, there is a losses because of the in the module because of the mismatch in solar cell. Similarly, when you are putting many modules together, there can be losses in the mismatch. So, in a power plant, I have done some of the design of a megawatt power plant. So, if you are looking at 1 megawatt power plant, typically you will have the inverter. Your inverter input you would require something like you know 600 to 800 volt. 600 to 800 volt is what you require. If you are making a crystalline silicon power plant, you use big modules. These big modules are not 130, 140 watt peak, but you have 210, 220, 250 watt peak, where the output VOC of the module can be about 30 to 32, 35, 36 volt. So, when you do this, you will find that when you divide this number by this number, you can find out how many modules you require. So, you normally use about 15 to 20, I do not know depending on the number, 15 to 25 modules in series. I am talking about design of a 1 megawatt power plant. If you have 1 megawatt power plant, your inverter can be of any, it can take voltage. Inverter is normally designed to take large range of voltage because your voltage is varying because of the two parameters. Your voltage of the module varies because of the two parameters. What are those parameters? One is temperature and other is radiation. So, typically you will have 15 to 20, 25 modules in series in a megawatt power plant. Now, when you are having 15, 25 modules in series, definitely the current of the all modules are not going to match exactly. There may be small difference and because of that, people try to match them exactly as much as possible, but there are some losses occurs and this is 3 to 5 percent losses. Temperature derating from the rated capacity. So, because your cells and as a high temperature, your actual power will lower dirt and soiling losses. So, because your modules are in the field, some dirt, the soil or the dust will be sitting. There are DC wiring losses. So, many modules are connected and there will be some resistance in the wires and I square R losses. There is inverter losses, AC wiring losses and all transformer losses. So, when you combine all the losses together, if you are making one megawatt power plant, in real condition, you are one megawatt power plant under the best operating condition, 1000 watt per meter square, but temperature you cannot do any. So, you will get about output performance of about 75 percent. So, let us say 75 to 70. So, this is, so 75 percent to 77 percent is typically your performance factor, plant performance factor, 75 to 77. And this number can be different for the different technology, but typically it is about 70, 75, so on. So, that is what I have shown here that you actually expected output, AC output, if you are having one megawatt DC, you will be about 75 percent of that. Now, the effect of PV module efficiency, as I said, why, I mean, when thin film modules technology can be cheaper, can be cheaper, but they are not always cheaper, they can be cheaper. If they can be cheaper, but they are also less efficient as compared to crystalline silicon. So, when your efficiency is less, your PV module efficiency is higher. I am sorry, when your efficiency is less, your land area or when your module efficiency is higher, your land area requirement is lower, your wiring requirement is lower, your support structure requirement is lower. And therefore, some time or many times, in fact, the people try to prefer or people go for higher efficiency, even though they are little expensive, because if you go for lower, less efficient and less expensive modules, some of the extra cost incurred here is here. I have done some calculation for how much land area is required for a given efficiency of module. Now, this does not take the additional area which is required for the maintenance and roads and these and that. I am just calculating the area of the module only. This is not the area of the plant size, because when you are going to put the plant, what other things you have to take care when you are going to put the plant. So, when you are going to put the plant, if I am having a, if my sun is here, if my one module is, you know, if this is my horizontal, if my one module is here, then there will be some shadow and because of the shadow, I can put only my next module here. So, you have to have some spacing, row spacing and I can put the next module here. So, when you are putting the plant, you will require lot of additional area. One area is because you want to avoid the shadow of the module, so putting on the other. Other area is you want to have the maintenance road and all. So, there is an area for the road. Then you also put what is called the control plant or the control power, where you are going to put your inverter and all. So, that will require some area. So, actually your PV plant area will be higher. I am just considering the area of the module itself. So, if you are having 6 percent efficiency module, then your land area per megawatt is 4.1 and if you are having 16 percent, your land area, sorry your module area depends on the configuration of module. This is the, then your module area is only 1.54 acre per megawatt. This is the condition if you install the module flat on the ground. Flat on the ground means, where we are putting module flat on the ground means you do not have to leave any space. So, therefore, this area, this land area is actually the module area. This land area is actually the module area. So, you can see the efficiency can have significant effect impact on the module. So, this one goes in favor of crystalline silicon. Now, there is another feature that, because in thin film module, your cells are like vertical strips. So, even if there is some shadow causing, if this shadow causes and it really blocks one full solar cell, then your module is not going to produce any power. But if you are going to block the same area of a thin film module, because the cells are like this, small percentage of a small percentage of current will decrease, but your module will perform well. Similarly, if you do the vertical, now this is shown particularly in reference to the power plants. In power plant, if you have one row and then your next row, the shadow of this row will fall definitely. So, if the module are installed like this, then the shadow will actually block the whole single cell. They should not be, you should not install like this. So, you should always install your modules, thin film module in the power plant like this, vertical strips, vertical solar cell. This is the message. Because of the temperature, the kilowatt hour generated per kilowatt peak, this is the one important parameter many people have. How many, how much energy I get per kilowatt peak of installed power? Kilowatt hour, how many kilowatt hour get per kilowatt peak of installed power? And this I am showing only the effect of temperature. So, under a standard test condition, let us say that my normalize value is 1, that every, every module is giving him 1 million unit. Suppose, crystalline silicon, cadmium chloride, amorphous silicon, crystalline silicon, at 35 degree centigrade ambient temperature and 55 degree centigrade cell temperature in the module, I am going to get 87 percent energy only. As compared to 1, now my energy output is reduced because my cell temperature is higher. Where is the reduction is minimum? Look at this cadmium chloride, the reduction here is 13 percent reduction, here only 7 percent reduction. Here also 7 percent reduction. So, this technology is actually reduction in power due to the temperature is lower. And you can do the 45 degree centigrade ambient and 86 degree centigrade module and look at the reduction. So, you can see the, this goes negative for crystalline silicon. The decrease in power output or a decrease in energy output per kilowatt peak is higher for crystalline silicon as compared to the thin film. This is the sum of the standard module that I have collected from the, from the practice. So, these are the modules that are produced of the crystalline silicon and thin film. Typically, you can look at the wattage of the crystalline silicon module which are used in the big power plant. Now, yesterday we showed that from single connection, single series connection of 36 solar cell, you cannot get with the current size of the solar cell, you cannot get more than 150 watt. So, when the modules are 230, 225 and all, so what does it mean? There are two such series of 36 solar cells. So, these are the modules having double of 36, 72 watt, 72 solar cells. So, look at the voltages, you get voltage of 36. Here the configuration can be different. So, there, so there is a one and there is a configuration is different. You will have the two of them in series of 68, 37, 37, Vm is this, Isis. So, here the cells may be of very high efficiency or you have already, so here you have the four such series, right. Here you are getting double of, what normally we will get 18, you are getting 36. Here you are getting double of 36. So, this number of cells, here is this case will be much higher than 72 also. The currents that you can get, here because your voltage is higher, your current of the module is lower for the same or power. Your fill factor, look at the fill factor 73, 73, 75, 77. Look at the ratio of Vm versus V0. I told you that normally Vm is 80 percent of or 85 percent of the VOC and this is the commercial module. Look at the ratio of this, 0.8, 0.8, 1.8, 1.8, 2, almost same that I told you. In thin film modules, your wattages can be lower and look at this module, 440 watt. This is only 70 watt. Look at your voltages. Voltage of crystalline silicon is much lower. Voltages of a thin film modules are higher. Currents, currents of a crystalline silicon is higher currents of a thin film modules are lower. Remember, thin film modules are higher resistance and therefore, typically you design for the low currents. Fill factors are lower. Look at here, 62, 61, 64 as compared to 73, 74 and the ratio of Vm versus VOC. The Vm is much lower. So, Vm is about 76 percent, 74 percent as compared to 80, 81 percent. So, these are the various parameters and these parameters affects the design and performance of the PM modules in the field. How it affects? So, typically crystalline silicon module will have lower voltage, higher current and thin film module will have higher voltage, lower current. But the both of these modules are for the same power. The both these modules are the same power. Look at here, the power versus voltage. Look at the peak power. Almost both the modules have the same peak power, but crystalline silicon has a lower voltage and thin film modules are designed for higher voltage. Why? Because we want to keep the currents low. So, these are the some of the parameters and now it will affect your and what inverter you are going to choose because your thin film modules is using higher open circuit voltage. So, number of modules to be connected in a power plant will be lower as compared to crystalline silicon because your crystalline silicon has a lower voltage. So, there may be less chances from mismatch in this case, but then your choices can be difficult because you know deciding between 6 and 7 module to get the same voltage may be different. So, these are the various, various impacts that different modules will have in the design of the power plant, performance of the power plant, performance of the module itself. The main factors is a temperature and the radiation and I think with the whatever I taught you, you should be able to estimate the module output power at any given temperature at any given solar radiation. You will be able to do that? Yes, you should be able to do that. So, let me stop here. I will take couple of questions. If you have any questions, please go ahead and ask your questions. Now, I will start getting questions. Sir, yesterday you talked about the selection of the voltage for a particular battery, PV module output voltage for a particular battery. So, you said that if the battery voltage is around 12 to 13 generally, so we select 14 to 15 volts as a PV module output. But the problem is the voltage, the current of the PV module is highly dependent on the light intensity. So, what I believe is in between the PV module and the battery, there should be a buck converter. Oh yes, definitely. Then only we can effectively regulate. Definitely. So, between the normally, normally you do not put a PV module directly to the battery and there are charge controllers that are put sometime it is through the inverter and the electronics in between takes care of those points. So, there is a maximum power point tracker and all those things. So, that is what I have, because the complexity is too high. Because the battery also, as the voltage level increases, it will need less current. Yes. So, all these factors should be taken. All should be factors should be taken, but the minimum voltage that should be available to charge a battery should be something higher than the battery terminal voltage. That is the main message that I wanted to give. Okay, thank you. Okay, K. G. Somaya. Different solar cells having different VOCs are connected in parallel. Then what, how can you predict the VOC? Can you explain that? Again, so in series the current has to be the same. So, in parallel, when you are putting the parallel voltage has to be the same, right. So, as we discussed yesterday, if you are putting the many solar cells in series, the solar cell by adjusting its parameter, the mainly the operating voltage will try to make sure that the same current flows. Similarly, when you are putting the cells in parallel or the modules in parallel and if there is a difference in voltage, some change in current will occur in a such a way that you actually match the same voltages. So, that you will be able to get it from the your IV curve. So, let me try to do that. What we have seen yesterday? The VOCs are different for different cells. Yeah. So, for example, if I if I look two different curves, like this are the two different curves of a different short circuit current, right. Now, when I am putting in series, when I am putting them in series, I have to have the same current flowing. Okay, I have to have the same current flowing. So, if operating point is here, okay. So, then my second my second curve that the solar cell with the lower short circuit current will actually operate here, the solar cell with the higher short circuit current will operate here. So, this is why in this way the voltage. So, this is the positive voltage, this is the negative voltage. In the solar cell voltage got adjusted in such a way that your current is a constant, okay. Now, if you are doing the if there is a mismatch in parallel, you can actually do the similar thing. So, now your currents are same, okay, currents are same, but your voltages are different. So, in your parallel thing, you are in parallel, if your one solar is operating here, this is the voltage, the other cell should operate at this point, right, because your voltage has to be same, the voltage axis, okay. So, what is happening by some way your current, which was in this point, your current should have been this, but this particular solar cell with the lower open circuit voltage will have following current, okay. So, it has the voltage will become positive, current will become positive, it will actually dissipate some power. Normally, these are the difference in this is not so much. So, this is how by adjusting the current voltage characteristic of the solar cell, they automatically make sure that the voltage is same in the terminals when it is parallel connection or when you are doing the series, the current is same when you are series connection. Sir, what voltage you get at output if this is the? The combination of the two. So, this voltage get adjusted in a such a way that it matches all the conditions, right. If you are putting 10 cells in parallel, you will get this voltage, okay, because voltage has to be the same, all terminal voltage has to be the same. Also, solar cell will make the adjustment, so that there is they all operated a common voltage. And what you see here? This solar cell is a higher voltage, this solar cell is a lower voltage and what is the operating common operating point? It is the voltage in between. Got it? This actual operating point is a voltage in between the two voltages. So, if this is the open circuit voltage of cell 1, this is the open circuit voltage of cell 2, your actual operating point is this, okay. So, this is your operating point, okay. It does not seems to be totally convinced, but so you will go and read the book, my book, it is explained how the you get the operating voltage, okay. PVG college Pune? Which would be ultraviolet resistant? Oh yes, it glass is preferred because glass is fantastic, it is very well known, it is produced in a large quantity, it is transparent, it is stable for 25 years and so on. So, therefore, you will not find better material than glass, but when you are actually going for the flexible modules, you cannot use the glass and there definitely people try to use some other plastic material which are transparent in nature, you know, which are resistant to ultraviolet and which are long life. Okay, as I said, since it gets heated up, the module gets heated up and so that will affect the efficiency. So, then the glass is to say, I think even if you are going to use any other, if you are going to use any other encapsulate, which is transparent to the visible spectrum, it may likely be, you know, opaque to the infrared or far infrared. So, I think even if you use some other plastic or polymer, you may have similar behavior. So, some heating will always occur. Okay, College of Engineering, Pune. What is the maximum thin film technology is adopted for silicon? What is the maximum efficiency of a thin film technology? If thin film is adopted for silicon, is it? Yeah, so if you have amorphous silicon, amorphous silicon, there are single junction modules which can give efficiency maximum about 7 percent. Then amorphous silicon, there are double junction modules where efficiency can be about 8 percent. Then amorphous silicon triple junction modules, not many people manufacture it. The efficiencies can be about 9 percent maximum. This is for amorphous silicon thin film module. So, whether this technology is not adopted in India? Amorphous silicon technology, as I showed you in my slides, that because of the very low efficiency, if your module is 6 percent or only 6.5 percent. So, these are the modules which are available commercially and some people also supply modules at about 8 percent because the efficiency of thin film amorphous silicon module is low. You require larger land area, you require larger wiring, you require larger losses, larger frame, everything is larger and therefore it is not preferred to use thin film low efficiency amorphous silicon module. But there are many people who do that also. If your cost is really low. So, whether the initial efficiency and the stabilized efficiency of a thin film module is the same? Thin film modules, especially for amorphous silicon, the initial efficiency when the module is manufactured in the plant is higher, but when it is put under the light, it degrades very fast. But the people manufacture actually give you the degraded efficiency only because it is well known fact. So, initial efficiency may be 8 percent, but it is known fact that amorphous silicon module efficiency decreases by about 20 percent after initial some 500,000 hours of exposure to the light. So, people actually mention the degraded stabilized efficiency only. Chandinagar. Yes sir, my question is, which is the base of software for circuit simulation means in SPICE, then SQL, MATLAB, all are in all the software, we can simulate solar PV model. Yeah, the SQL I mean, Professor Patil who has actually developed the SQL at IIT Bombay will be able to better answer that, but what I have seen from his presentation is that a circuit simulation in SQL is very fast as compared to the SPICE simulation. So, the anyways given the example also if you are very complicated circuit like a solar PV module, where there are many cells are put together. If you want to simulate same in SPICE, it will take more time, but the SQL simulation is faster. This is the circuit. Okay. Okay. Three solar cells connected in series and such three modules connected in parallel. And if we connect from the middle, if we connect all the cells from the middle. Go ahead, first of all the… You might have thought this kind of architecture. So, what is the problem with that? First of all, there is a problem in the drawing. Your drawing is not correct. The drawing you shown is actually diodes. Okay. Solar cell is not a diode. Right? We have looked at the equivalent circuit of a solar cell. There is a current source and parallel to that there is a forward bias diode. The both of them work in opposite. Okay. So, when you draw the proper equivalent circuit, you will get answer yourself. And what is the problem with this? I do not know why you are doing this. So, until unless I know the purpose of doing this, then only I can tell what is the problem. Okay. Sivaji University. Hello. There is temperature increase. As the temperature increases, the power plant performance decreases. So, why the power plant installers are running to the Rajasthan and north Gujarat as there is more increase in temperature and as there is also good radiation. Okay. So, yes, as the temperature increases, power decreases. But in Rajasthan, if you look at the solar radiation, it is probably higher as compared to other locations. So, it is definitely location dependent. And other factor may be the availability of land, the policies of the government, the support that is provided for the state government and so on. So, those are the other important factors. Okay. R C Patel Shirtpur. So, what is the concept of 3D solar cell? What is the concept of 3D solar cell? Okay. The 3D is normally referred to the three-dimensional junction. Okay. So, in some cases, for example, in our crystalline silicon, okay, our crystalline silicon is like this. So, there is n and there is p. Okay. And this is your junction. This is what kind of junction is this? This is a planar junction. Right? Junction is plain. But some of the materials like organic solar cells or even disensitized solar cells, the materials are very poor, but organic materials can be very cheap also. Right? So, therefore, in that case, the diffusion lens is very, very small. How small? 10 nanometer, 5 nanometer, 20 nanometer. And therefore, it is not possible for any amount of carrier generated to reach the electrode, reach the contact. And therefore, what people do is they have three-dimensional junctions. So, the junction is everywhere. Okay. Junction is everywhere. And therefore, as soon as the electron hole pair generated because they cannot move very long distances because of the low diffusion length and low carrier lifetime, you put your junction everywhere and then carrier can actually get generated, get transported in various ways and come down. Okay. So, typically, 3D junctions are used with organic solar cells, organic cells, disensitized, disensitized solar cells. Okay. And we are, in fact, also trying to have, do this in a crystalline silicon if your material is poor. Okay. VNIT in Akhpur. Go ahead. So far, we have learned about silicon solar cell in more details. I would like to ask you, is it feasible to fabricate organic polymer solar cell using thin film technique? Yes, it is possible. Organic solar cells are thin film and you can actually make very easily thin film organic solar cell. There are very simpler ways you can spin coat, you can use a simple low temperature process to make organic solar cell. Thank you, sir. So, one more question. About the grid parity, the cost calculation was given in the first lecture, very first lecture. Okay. So, I feel that we should use carbon economic calculation so that we can actually see what is the cost of the environment also. And balance will always be towards PV cells if you use the carbon credit system. Yes, this is wonderful idea that if the whole world starts taking the cost of the emitting carbon from the conventional power plant into picture, it will become much easier for a green technology or renewable energy technology to get into the market. Unfortunately, that is not done in the practice and that is why the cost of conventional power is low. But you are very right, if you start taking care of the carbon emitted into the atmosphere because of the conventional power plant, the cost of electricity coming from the coal, oil, etcetera will be much higher. And the grid parity will be achieved much, much faster. Okay. Sir, please explain me the effect of temperature on energy band. Sir, I want to know the effect of temperature on energy band. Okay, the effect of temperature on the energy band gap is to reduce the energy band gap. Okay. And now this explanation will not be simple because you have to go to the quantum mechanics. As the temperature increases, the arrangement of energy levels within the item and their interaction within the crystal will be such that the available energy states will be little bit lower than the age of the conduction band, which actually effectively results in decrease in the band gap as temperature increases. Okay, sir. Thank you. MNIT Bhopal, cells of different VOC and ISC ratings in parallel connection. Then to calculate the resultant voltage rating, it is given in your tutorials that it should be in between of all these. So how we can calculate the exact value of VOC in that case? Okay, I think I told some other that this, right, this is the method. So if you are having two different, if you are having two different solar cells put parallel to each other having different open circuit voltage, then whatever you look at the operating point and you draw the line for the constant voltage, which will be a vertical line perpendicular to the y-axis and you will meet x-axis or the curve of another solar cell. So this will be the common voltage that both the solar cell can operate, right. In a parallel connection voltage must be common and the solar cell must adjust with respect to each other their current and voltage so that you can have the common voltage point. Like same thing as I showed earlier in series that if the cells are connected in series they must adjust itself themselves such that the common current can flow. Now the voltage the cell with the higher open circuit voltage try to force the higher voltage and therefore it will actually push the voltage of the lower open circuit voltage solar cell to little bit higher level and by doing so the operating region itself will change. So open circuit, the solar cell 2 which is having lower open circuit voltage will actually get pushed to this region where voltage become, where the current now becomes positive. Thank you, thank you sir. Okay, Bharamati. Solar cell, solar cell, what is cost and life for the thin film solar cell? In thin film solar cell as I said every manufacturer I do not know the real picture but every manufacturer guarantees you the same life as any crystalline silicon manufacturer, okay. So thin film module provider if you go and buy the modules for a megawatt power plant they will say that my module is also going to work for 25 years, okay. So every manufacturer guarantee the same life as you get from the crystalline silicon. Now the cost is a, cost is difficult to say because normally thin film modules are supposed to be cheaper that they are about 5 tens, 5 cents or 10 cents maybe 20 cents cheaper than the per watt peak, okay. 5 to 20 cents cheaper per watt peak as compared to crystalline silicon. I am talking about dollar cents. One question I will take from the chat, kindly explain the percentage power decrement in cadmium telluride being nearly double than crystalline silicon. That is not correct, it is opposite. Percentage decrease in the power in cadmium telluride is lower than the crystalline silicon because of the higher band gap, okay. Higher band gap what is the meaning of higher band gap, higher band gap because of the higher band gap as a result of temperature less carriers can get actually to the excited state because less carriers can go, your Ni will be lower. If your Ni is lower your I0 is going to be lower. If your I0 is going to be lower your VOC is going to be, the change in VOC is going to be lower and therefore the percentage decrease in power in case of cadmium telluride is less than the percentage decrease in power as compared to crystalline silicon. Can we place solar cell one above another in some 60 degree aligned with proper gap to harness more solar power in small area like our building. If you are going to put solar cell on the top of each other, if I understand your question correctly I do not understand what is the meaning of 60 degree aligned. But if you are going to put solar cell on top of each other and if your top solar cell is absorbing the whole solar radiation, the bottom solar cell will actually get shaded and will not generate power. But if you are making some angle arrangement, your generation may not be optimum, okay. So, thank you. Let me take a break.