So, just for discussion sake let me just say that we are looking at March, March of an of any given year okay. So, March of a given year is typically at the time, when the northern hemisphere is coming off of winter. It’s had it is winter and says December, January, February and it is just slowly coming off of winter. So, it’s moving towards spring and then eventually it’s going to move towards summer. So, it is coming off of winter whereas, the southern pole is been in summer okay. So, the heat is a little more into the southern side of the hemisphere. So, that’s why you see this red band not centred around the equator, but little towards a little towards the lower side more of it is present towards the lower side little less towards the northern side more towards the southern side. So, the southern hemisphere is coming off of summer, then northern hemisphere is coming off of winter so, but you still see this big band. The big band where there is a considerable amount of sunlight that’s coming down on it fairly harsh sunlight, and you can see, of course, India is right here and which means we receive even as we come off of winter. Most of India receives a lot of sunlight and we know that we know I mean in India almost anywhere in India of course, winters are quite strong, quite severe at least by Indian standards in northern parts of India, we do have places where the temperature drops to 0 degrees C, even in our capital I think in winter you will have some days where the temperature begins to dip close to 0 degrees C, but certainly northern even for the north if you go, temperatures dropping below 0 degrees C is not uncommon, snow is not uncommon. n even for the north if you go, temperatures dropping below 0 degrees C is not uncommon, snow is not uncommon. So, this is the range of temperatures that we have, but generally, for a fair part of India you know at least half of India you get a lot of sunlight, you get a lot of heat and that’s what is quite visible in this picture that we see. We also see that you know as we are perhaps aware almost all of Africa gets a huge amount of heat from the sun, all of Australia gets a lot of heat. So, you have Australia here, you have Africa here, and a lot of South America. So, significant fractions of the world are receiving a lot of heat from the sun and so, these are regions geographical regions where you can potentially have a lot of solar energy devices deployed and you have a great chance of you know getting you are getting good quality sunlight and then others high-intensity sunlight. So, with smaller devices, you can presumably capture more energy. So, the promise of solar energy is highest in these places is what I am trying to say. It is not that it’s not there and other places, but it’s the highest in these places simply because of the natural position of these places relative in the geographical sense, which results in the kind of sunlight they receive at different points of time in the year. So, this is the major band, but we still have a little bit more, we have regions on either side of it which receive a little less sunlight may be on average the temperatures are probably about to say maybe 5 degrees or 10 degrees lower as you go away from you know hotter regions towards the cold regions. So, you can think of two more bands of regions of the planet, where the temperatures and therefore, the amount of or rather the amount of sunlight coming in, therefore, the temperatures are little less because of the position of that planet and the fact that it is you know it is a little bit oblique, that the angle at which the sunlight is arriving at those places. So, but actually, interestingly you find that many of the places. So, essentially most of Europe falls in this category right most of Europe falls in this category. In the southern hemisphere not much this small tips of southern America come into this category South America. A fair bit of North America comes in this category. So, a fair bit of United States, fair bit of I mean essentially all of Canada is all going to come in this category, where they don’t receive as much of the harsh sunlight harsh and direct sunlight that some of the other places receive. And that does not mean that they cannot use solar energy devices many of these places have invested a lot in using solar energy devices and it does work for them, but they just have to accommodate for the fact that they possibly are not going to receive the same amount of same quality of intensity in their sunlight as some of the other nations, which such as Africa, a fair bit of South America, Australia and India are going to receive. work for them, but they just have to accommodate for the fact that they possibly are not going to receive the same amount of same quality of intensity in their sunlight as some of the other nations, which such as Africa, a fair bit of South America, Australia and India are going to receive. So, but this is the other two regions and then, of course, you have the two extremes here the closer to the polar regions here, the closer to the south pole and closer to the north pole. So, those are regions which are you know in summer you are going to get some sunlight, in winter it’s all going to be dark and so on. And so, there again it becomes more difficult to harness this solar energy as effective. So, that gives you some idea that you know graphically also our planet, has some features associated with it and we have to deal with these features, we have to be aware of these features and we have to deal with these features. So, I was also mentioning that you know this delicate boundary that we have to watch, which is where that 0 degrees centigrade is I mean temperature is of about 0 degrees centigrade. So, I mean just to illustrate here, maybe that if I were to use this boundary here as that the region where the temperature just above drops below 0 degrees C. If the mean temperature of the planet goes up by 1 degree C, that boundary may move up okay. So, this means all the ice in this sector will now start melting and that’s a lot of ice; when that’s a lot of ice if all the oceans that side was frozen they all start melting. So, that’s a dangerous situation to have because; that means, also this is there is less amount of ice up here to do the reflection, where our if it happens to be in you know floating around in the water etcetera or even out here, it’s on the land you have ice on the land if it is there let me also start. You will have less because ice on the land that is here would melt. So, these issues are there that is basically what I was referring to. Well before I move forward I asked you a question earlier in the class about the snow blindness and that would affect people that would be here and that would affect people that would be here you know any of these places where you have a lot of ice. So, they don’t have sunglasses, they don’t have what we Indians refer to as cooling glasses. So, what do they do? They have essentially you know maybe even some leather kind of thing or a piece of wood, that is used the equivalent of a sunglass, but it has very tiny slits and because it is tiny slits the amount of sunlight that comes and decreases drastically is this. It’s just the same as squinting your eye and then seeing with the tiny opening of your eye because you have closed the most of your eye and you have a very tiny opening you see only a very dim amount of light coming through to your eyes right, but if you are in a stuck in a place where it is so bright, you cannot keep on walking around with your eyes half-closed, it becomes difficult for you. . It’s just the same as squinting your eye and then seeing with the tiny opening of your eye, because you have closed the most of your eye and you have a very tiny opening you see only a very dim amount of light coming through to your eyes right, but if you are in a stuck in a place where it is so bright, you cannot keep on walking around with your eyes half-closed, it becomes difficult for you. So, they have and they don’t since they didn’t have a technology to make you know sunglasses the way we currently have them, the older form of dealing with this was simply they would have some structure which would sort of the serve the same you know the physical shape of a set of glasses, but it would just be a piece of the opaque item with two tiny slits one for each eye. So, that it’s a narrow slit through which you see, and that was a thing and it could even as I said to be a piece of leather with two tiny slits, which you could you just tie around your eyes and use, and that would make a big difference in the amount of sunlight that the people were exposed to. And therefore, you know significantly you know I mean elevate this issue that they had with extremely bright sun. So, that was the question that I asked earlier and I thought I should clarify to you here, but in any case concerning this plot that we have here, this gives you an idea of what happens geographically, concerning sunlight that’s arriving on our planet. (Refer Slide Time: 47:57) And the last thing that I think I should draw your attention to is what happens as a function of time of day okay. So, what you see here is an again the planet, our planet and we will assume that we have incoming sunlight from here, and this is the north pole. So, directly we are facing down on the North Pole and so, east is here, and west is down here okay. So, what you can see here is this is midday, this is closer to the morning and this is closer to the evening. nd the last thing that I think I should draw your attention to is what happens as a function of time of day okay. So, what you see here is an again the planet, our planet and we will assume that we have incoming sunlight from here, and this is the north pole. So, directly we are facing down on the North Pole and so, east is here, and west is down here okay. So, what you can see here is this is midday, this is closer to the morning and this is closer to the evening. So, we know from our experience that you know in a given day as you come towards the middle of the day, you feel the maximum heat when you are out there in summer when you are out there, outside certainly in places like in India in summer if you are out there in the middle of the day it’s so harsh many places. You have to wear some kind of a hat or a cap or put at least some coverage on your head are or you are going take a lot of heat on your head and So, most of us do not enjoy being out in the sun in the middle of the day, in peak summer right. At the same time, we know that during the evening as well as during the morning it’s quite comfortable in many places, even though it may be summer. So, why is that the case that is because the same amount of energy that is coming in is during the middle of the day is distributed over this larger piece of area, and similarly in the evening it is distributed over this larger piece of area. You can see that this area here and this area here are much larger than this area here right. So, the same amount of energy is getting distributed over a smaller region of the area or smaller area during the middle of the day than it is during the morning or the evening. And as a result, so that’s the intensity. So, the power in per unit area is higher during the middle of the day, it’s a lot less during the morning and the evening. So, similarly when you have a device that is trying to capture solar energy, generally if you do nothing with the device; if you just leave the device you know in the best possible condition in one single condition which is whatever is the best data that you got from it, in all your tests you leave it in that condition undisturbed, it will gather the best sunlight during the middle of the day, it will gather less during the evening and gather less during the morning. So, that is another aspect that we have to keep in mind. So in fact, they even call it I A M or incidence angle modifier. We will discuss this more later incidence angle modifier, it simply takes into account the idea that when the light is perpendicularly falling on the device it is it is in the best position to capture the solar energy whereas, during the morning as well as during in the evening, the light is arriving at an oblique angle as supposed to vertically down and therefore, if the device is sitting flat if we have this light arriving at an oblique angle it is in e will discuss this more later incidence angle modifier, it simply takes into account the idea that when the light is perpendicularly falling on the device it is it is in the best position to capture the solar energy whereas, during the morning as well as during in the evening, the light is arriving at an oblique angle as supposed to vertically down and therefore, if the device is sitting flat if we have this light arriving at an oblique angle it is in a it’s less ideally situated to capture that energy, it is also less ideally situated to capture the energy during the other part of the day either the evening or the morning. It is best situated to capture energy when it is in the middle of the day. Of course, so, they have to account for it that’s the point. The point is that you have to account for it. So, if you want uniform energy through the day, you have to keep that in mind that you are not going to get the same amount of energy by if everything else sits the same. So, they have tried various ways to address it, and we will see that in some of our later classes. So, they move the device. So, the device is moved such that, even though the sunlight is coming this way the device also faces that way. Sunlight is vertical it’s facing this way, sunlight is coming from this direction it faces this way. So, you have to do something to address it is the point. The point is you cannot just assume that you just put a sunlight solar device out there, and it has solved all your problems it will take care of everything right. So, that’s something that we have to look at. So, this is the I AM and we will see that in greater detail in one of our later classes, but it sort of conveys to you what happens concerning incoming sunlight and different points in the day okay. So, we looked at three different things in this class, in conclusion, we will try to sum these three aspects together. (Refer Slide Time: 52:17) Slide Time: 52:17) We found that solar energy that arrives on the top of our planet ends up participating in a wide range of phenomena, as it traverses through the planet okay. So, as it comes through the planet, there is a wide range of phenomena in which through the atmosphere and reaches the surface of our planet than a wide range of phenomena in which it is participating. So, we need to be aware of it. So, we understand the complexity of what it is that we are dealing with okay. When it comes from the sun through most of those 149 million kilometres, it is a vacuum, there is nothing there it’s just coming in as you know electromagnetic radiation. So, there is no real phenomenon that of any great significance where is it is you know getting absorbed in any major way, by and large, it is arriving on the planet. Once it arrives on the planet from the outskirts of the atmosphere as it traverses in, lot of things are happening. And as a result of that various aspects are happening about concerning what is getting reflected, what is getting absorbed, what phenomena are happening in terms of cloud formation, hot air rising, weather phenomena, all these things are happening as a result of how this layers of the atmosphere are dealing with the incoming solar radiation okay. And whatever we have as life on the planet is very intricately related to this phenomenon that is happening. But the idea that there is sunlight coming and the fact that there is this atmosphere that that is you know interacting with this incoming radiation and as a result, many things are happening. Rain happens, clouds form storms happen, there are a lot of things are happening as a result of this process of the sunlight coming in and interacting with the atmosphere, interacting with the land, interacting with the water. in and interacting with the atmosphere, interacting with the land, interacting with the water. So, we looked in detail about how this interaction happens and what are all the various steps involved in this interaction. And we found that there is a wide range of phenomena through which the solar energy is absorbed, in and something happens concerning the solar energy and then it is later released through a wide range of phenomena that are happening in the system. And it is important to note that these phenomena are very critical in the grand scheme of what this planet is doing in terms of its weather circumstances, in terms of its equilibrium, in terms of life on the planet. If you do anything that messes up or disturbs this you know set of events that are happening, by either overplaying one event or underplaying in some event, then we risk the chance that we are going to push the atmosphere into one direction, from which it may further slide into that direction without any control okay or without our being able to control it. So, you cannot simply say I just raised CO2 by 2 per cent, it’s okay let’s continue rising CO2 to into 3 times the current value and then we will quickly bring it down we will find something to you know bring it down quickly. So, let’s not worry about it. The point is when you go from whatever is the current value to 3 times the value of 2 times the value, you will trigger certain other things, which will push it so far into the other direction so fast, that you will not have any it is unlikely that you would have technologies that will urgently bring it back circumstance to bring it back right. So, you may even actually you may tip the scale in one direction, you make move by just a going from one value of CO2 to double the value of CO2, you may tip some set of circumstances into one sequence of events, where then if you simply bring it back from the double that value to the original value that alone will not suffice that’s the point ok. So, from 0.04 per cent CO2 if you suddenly climb to 0.08 per cent CO2, you will trigger a chain of events where you are putting yourself in a situation where then if you bring it back from 0.08 to 0.04 that will not alone be sufficient, you will not bring all the events back to where it was original. They have started one sequence of events just bringing that from 0.08 to 0.04 is no longer going to be sufficient for you, you have to do many many many more things to bring that back to some kind of a situation that you are originally comfortable with. So, that’s the critical thing that we have to remember, it’s not just one number that we are worried about, and you can look at it and say it’s for another 50 60 years, we will figure out this little later. We are we have the danger of triggering other events in this process. with. So, that’s the critical thing that we have to remember, it’s not just one number that we are worried about, and you can look at it and say it’s for another 50 60 years, we will figure out this little later. We are we have the danger of triggering other events in this process. The second thing we looked at is that geographical locations and seasons are important aspects impacting solar energy received by specific locations, and this has an impact in terms of what kind of how we will go about deploying solar energy devices in those locations. We have to be aware of the fact that they have a geographical location, and as a result, it has some characteristic associated with how the solar energy arrives at, how much solar energy arrives at, what is the quality of the solar energy arriving there in terms of intensity and so on. And therefore, if there is a certain power demand in that of that for the population of energy demand for the population in that region, we have to account for the fact that the solar energy has a certain intensity, and those devices have to be correspondingly put in sufficient numbers that with that intensity those devices will provide enough energy for that population. So, that calculation has to be taken into account and based on which region it is for the same total population, you can have a different set of solar energy devices addressing the needs of those populations. So, that’s the second aspect of it. And the third aspect as I pointed out is the fact that during the different times in the day the quality of the sunlight is going to vary, and it is something that you have the address. You have to have a mechanism of addressing, you cannot assume that it is going to be the same and that is why in many of the solar energy-based applications, they will always have some additional storage devices because the best amount of energy that they are going to get is during the middle of the day and. So, they would like to have some storage devices that will help them take care of requirements during the rest of the day as well as through the night. So, you have to put a combination together, when you work with such devices. So, these are a whole bunch of parameters that work together, that we have to be aware of when we try to build solar energy-based systems. And I think that gives you a broad overview of these circumstances. So, as we look at as we look forward into greater detail on what is that solar radiation, how we can trap it etcetera. These are other these are the kinds of aspects that are also to be looked at when you try to deploy it as a technology you know it is nice to do something in the lab. In the lab we will we are going to look at how they test these things in the lab and what circumstances they put the lab conditions on the experiment. are also to be looked at when you try to deploy it as a technology you know it is nice to do something in the lab. In the lab we will we are going to look at how they test these things in the lab and what circumstances they put the lab conditions on the experiment. What you will see is that real-life circumstances are what you saw in the class today and. So, from those lab conditions, when you want to make a product, let’s say you open a factory to make those solar panels and put it out as a product, from your test conditions in the lab you have to account to for these real-life conditions in the real-life circumstances for it to be a successful product. And that’s the perspective that you need to have and that was the purpose of today’s class. Thank you.