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So, we have to keep all of that in context when you look at any one technology. So, nothing is going to be an all concurring technology. So, in that context, this is also okay this 3 per cent is that all I mean pretty much any course line anywhere you can try and capture this a something great plus right. So, therefore, this is so, efficiencies are about 6 and a half per cent at best and then you are looking at about 3 per cent more likely. So, what can we do? I mean having picked up the cold water one thing that you can do very easily straightforwardly is air conditioning ok. So, if you look at the air conditioning plants if you look at you know AC plants at the various building. So, when they do centralized air conditioning when they do air conditioning of you know multiple buildings using one plant which is which are distributed buildings. Many times what they are doing is you know cold water is being sent off to different places. So, one place only the plant operates and creates cold water then that gets sent into different places from there the local you know heat exchanger will then eventually you make that building cold etcetera. So, will, so things like that are being done you know, so you transport cold liquid to different locations and then work on it. So, here you have already got the cold liquid you have got 5-degree centigrade or 3-degree centigrade liquid you just pulled it out from the bottom of the sea here sitting there you just pulled it from there. So, it is there. So, if you are you know if you set up a network ahead of time. So, imagine you know coastal city let’s say in Tamilnadu in Tamilnadu for example, I mean Chennai, Chennai is very hot in summer it is very hot a lot of people struggle with the heat it is very hot and humid and so there is a great need I mean a lot of people feel the need for air conditioning it would be extremely uncomfortable to operate and function doing the middle of the day with without air conditioning many places in Chennai so that that feeling will be there. So, we are putting air conditioners, but now, if you have cold water from the sea for. So, for that lot of electricity is being used. So, the electricity usage in Tamilnadu or Chennai at least we will go up significantly in summer because of the number of air conditioners that will switch off during summer. So, significant use of electricity, so significant use of energy. So, now, in the process of generating electricity or generating electricity, you just pulled out cold water from the bottom of the sea and if you had a network of pipes which could transport this cold water to various places in the city. You can technically do air conditioning using this water without having to put you know air conditioners in the conventional sense of the word where you have a compressor a lot of different things, that are going on in a lot of electricity being used you already have this cold water that’s available with which you can appropriate design your air conditioner to deliver this cold air to various places in the city. So, technically at various buildings in the city for example. So, technically we can have air conditioning that is significantly dependent on this 3-degree centigrade water that was getting off you know 3 or 5-degree centigrade what are they getting from the bottom of the sea where essentially you are main energy in usage is that pump that is pulling that water outright. So, that’s a major thing that you can do associated with this OTEC plant. (Refer Slide Time: 37:40) Of course, the purpose of it is electricity. So, that is one major activity that we will anyway do. So, there essentially what you are doing we will talk about how the electricity is generated in just a momentum. So, that is one major output from this OTEC
plant. So, air conditioning would be like a sort of a byproduct of this plant because you can do it and then electricity is your primary product. Desalinated water. So, in the process of doing this electricity generation one of how we do it, there will be a couple of different ways in which we can do it I am going to talk about that, but one way in which you will do this desalination would do this electricity generation would result in desalinated water being available to you that of course, can be used both for drinking as well as irrigation. I mean again if you look at Chennai situation water is also major issue like with any major city like with major cities increasingly now, in the news you hear about cities which are which have either out of water or just on the verge of running out of water and for example, they say in Bangalore is one of the cities which is likely to run out of water. So, the scarcity of water is a significant issue in many cities have that problem. So, Chennai also has a problem with the scarcity of water and depending on where you are in India you have differing levels of water scarcity issues through the year or even internationally many cities have this issue. Because populations have grown and they are concentrated in some area and you have to have water available to them. So, if I mean, of course, you may depend on rain or you may depend on rivers you may depend on some perennial rivers you may depend on glaciers etcetera this is one way in which you can get the water where you getting electricity at the same time we are also getting drinking water by doing there because the process of getting the electricity is creating desalinated water for you right. So, you can get that. So, you can get drinking water you can use it for irrigation and to some degree whatever cold water remains you can do mariculture. So, where it’s sort of you know running you know forms where you allow you to know sea animals to grow and you can use them for various purposes depending on what you are interested in. So, as you can see there is a wide range of things that you can do with this associated with this OTEC process and they are all associated with activities that were anyway already doing, air conditioning we are already doing some amount of you know the usage of the sea you know related products we already doing, the water we need, irrigation we need. So, all these things I already have electricity we need. So, all these things come together with OTEC plant and therefore, this OTEC plant is a good thing to have despite the challenge of you know having to deal with the depth of water and you know getting the pipe to stay together. (Refer Slide Time: 40:20) So, once you get all this cold water and the warm water what you do. So, there is one way there are two different ways in which you get this electricity out of it at the end of the day you have to run a turbine. So, if you just have water sitting at 36 degrees C that’s just flowing I am you cannot run much of a turbine with water sitting at the temperature you need you to know vapour pushing through the turbine and getting the turbine to run. So, normally what is done is if you can be set up a low-pressure situation. So, that the water you know now, become comes out in vapour form and then can run the turbine. So, so warm seawater will evaporate at low pressure and it will run the turbine and then will be condensed by the cold seawater and you will have some water you can eject. So, this warm water which first comes you know which evaporated is now, clean a because it is a vapour form. So, it the salt is not there in it and then when you again condense it you can have desalinated water. So, you remove the salt separately and then you can this desalinated water and so that desalinated water becomes available as a byproduct. So, when you do this open cycle method of getting electricity out of this OTEC plant are you get desalinated water as a byproduct. Another way in which you can do it is to run this closed-cycle operation were basically what to do if you take you do not use the water directly to run the turbine instead you have a closed system where you have low boiling point liquid typically ammonia is used any other refrigerant could also be used, but with refrigerant, we have already had this issue of you know how the refrigerant creates this hole in the ozone layer. So, many refrigerants are now, banded. So, there are only specific refrigerants that are permitted to be used and so and that contact should be careful what you use. For example, ammonia would be something that boils at minus 33 degrees C and so you can use that in the context of this you know system and then that would be the liquid that would evaporate, that would run the turbine and then be you know condensed and etcetera. So, again warm water will make it evaporate it will run the turbine and then cold water will condense it. So, this kind of operation we can think of. So, we have an open cycle and we have closed a cycle. We will also keep in mind that you know your pumping in large amounts of water. So, everything that comes with it. So, it’s not going to be like clean water you going to have you know you may even have some small sea creatures that show up and you know various things that are available in the sea will show up. So, in some sense yes you may do some disruption to the marine you know the environment that is there and the water that you are ejecting is ejected back into the sea. So, you are doing some little bit of churning of the seawater in this process, but the general calculation shows that you know at least concerning the water I mean the quantity of water we are going to use is so minuscule relative to the amount of water that’s available in the sea and we are just putting it back. So, whatever churning that we are doing it so tiny that it would more or less have no impact at even if you did large scale deployment of this OTEC technology. Okay so, if you did large scale deployment also we would not have much of an impact on the behaviour of the water and just because of our interfere incident. But we have to always be cautious because this is how we thought about the atmosphere and we should know what can we do we are not going to do anything on earth that can disrupt the atmosphere, but we are currently doing that concerning the CO, CO2 emissions. But in this case, it seems like the calculations show that you can use a significant amount of OTEC technology across the world not make a big difference to the water itself. However, we may impact the marine life that exists there because they are accustomed to a certain temperature at various regions and if you keep on pumping in pulling out water your probably disrupting the creatures that all are at the depth and you are pushing backwater at some other level which has a different temperature. So, you are effecting creatures are that depth. Again that is close to the shore. So, if you go away from the shore this is not going to be an issue you can even have offshore platforms which like a ship. So, in the ship some of them even right the early day's people tried all of this they put a ship out there and from the ship that we are pipe going for deep down pulling of the cold water and then doing all the electricity generation. But all of these have been challenging many of those ships have been destroyed in you know the ocean. So, that has happened even in India one of the plants that were put up in 2002, in Tamilnadu it was put up it had issues with the cold water pipelines. So, it was partially successful, but not you know they couldn’t sustain it over some time that they have some issues dealing with the cold water pipeline. So, even in the coastal area, there is a problem even offshore when you when the set up is made there, there can be challenges. So, it is not an easy technology to work with because you are not on solid ground I mean you are dealing with a liquid that is and dealing with depths liquid, flowing and large quantities that we do not have enough control on. So, that is something that we have to worry about. (Refer Slide Time: 45:09) So, in conclusion, you know OTEC is available to tap in most all coastal regions. So, except if you go to extremely cold regions then you may not have a big difference between the surface temperature and the temperature of the water much further down. So, that’s something that we can think off, but most other coastal regions this can be done and as I said you can do on large scale it doesn’t make a big difference. It can set up in an offshore mode as well just the way you have offshore oil ricks right you have offshore oil ricks which are sitting floating platforms sitting out in the sea. So, they would have to figure out at what location they can access the depth of water easily. So, a lot depends on how you know sea shelf is, you know what is the topology there because there are places in the if you examine the coast depending on where you are the water will sometimes drop off the depth will suddenly increase a dramatically. There are other places where you know the ocean floor is quite shallow from you know say the coast. So, you stand at the coast you can actually walk quite some distance into the water and you will still be only you know knee-deep or you know waist high and you can still see you know it even for the further distance the water is just maintaining that kind of depth. So, many many of those you know popular resorts that are there with you see beautiful photos of our all places where this kind of a situation is there that the depth is very shallow for a long distance. So, you can get into the water, but you are not in any deep water for quite some distance very visible distance we can see. But many other places for example, in Chennai, in and around Chennai lot of people say that the water floor falls off quite dramatically even if you go a little distance into the water therefore, it is not safe to go unless you know what you are doing it is not at all safe to just you know the way into the water beyond some very short distance. A lot of people do not realize the risk there, but that is the safety issue that is there. So, the point being the depth from the coast, from the surface can change significantly from location to location. So, in some places, you can have an onshore setup which can be which is the typical way in which you would probably think of an OTEC plant because you can have the whole plant sitting on the shore and just a pipe that goes out into the water because in a short distance the pipe can just drop down in great depth it can go down and then from there you can pull up the cold water. There may be other places where you have to go quite a bit away from the coast before the depth in water is significant enough right. So, then it doesn’t make sense to start at the coast and send a pipe which goes long distance on the floor and then eventually goes down. So, it helps there to have an offshore platform where like an oil rig you are just sitting you know this whole platform is sitting out in the sea and you just have a pipe going vertically down then that will be an easier pipe to you know put together and manage. So, it goes straight down vertically down to that location which is you know as deep as it can get about a kilometre deep and then from there you can pick up the cold water and then the warm waters is on top. As I said the efficiencies are low it is only about you know 3 4 per cent functionally your only getting about 3 4 per cent, but that is adequate because you can do I mean you are just more or less getting it for free there is nothing of any great significance there. And its clean your, you know except for the fact that you are churning up the ocean and you are getting a lot of marine creatures or marine organisms out which could be significant if you doing this in large scale over some time there are no emissions as such it’s clean kind of energy and that therefore, that is fine. And then the big challenge the structures are stable in the presence of waters, water and water currents is a fact that you have to address. Even be you know you know all the piping and what not you are you are using salty water. So, you have to make sure that you know corrosion is not an issue. It’s not just the salty water it is flowing salty water you are pulling up you know water pumping up water. So, it is going to flow. So, you also could have some abrasion of the surfaces and so the material should be such that they are abrasive resistant and they don’t corrode even if there is abrasion and you have this salty water conditions. So, these are all some of the challenges. So, that is the overview of the OTEC technology. As I said it has been deployed some few places in the world has been tried in India and I think more attempts are going to be made because it adds an interesting mix to the energy scenario. Some places it will make a lot of sense to have may not be in every location and to the degree that it makes sense its worth time ok. So, this is what we want, I would like to discuss this topic and gives you a reasonable overview of this technology. Thank you. Hello, in this class we are going to look at geothermal energy. Interestingly much of the time that we have you know looking at the solar energy for example, and particularly let’s say solar energy and then how it related to say wind energy even ocean thermal energy, much of the time it was the energy that was coming to us from outside ok. So, you are looking at the radiation from the sun reaching the earth those through some radiative process and from there we extracted that energy. So, various things happened. So, we had the sun, and then the earth. So, we have radiation here and then on the surface of the earth if you magnify this on the surface of the earth we had various weather phenomena. So, we have direct sunlight. So, that we had as photovoltaic or you know solar thermal and then this would affect the wind and then you have wind energy. So, you have all the windmills wind turbines etcetera this would affect the water and then you had OTEC. And I mean as I discussed earlier really these two are the more significant ways in which renewable energy is being explored internationally and therefore, we also correspondingly spend more time on it, those technologies are much more mature there are many companies which you know actively work towards putting these products out. Many of the other technologies we are looking at are not that mature at least ocean thermal energy conversion is not that commonly present, even though it is something that people are looking at you don’t have many companies which are deploying it although that is increasingly being considered. Geothermal energy is an interesting concept in this context because unlike this situation where you had this radiation coming in which is what you know is the starting point for many of these other technologies here we are looking at something different you are looking at what is coming from inside earth ok, so what is coming from inside earth that is geothermal energy. So, that is already there that is the energy that is sitting inside the earth. So, if you see if you look at this you know the spectrum of renewable energy sources people are considering a wide range of ideas looking at a lot of different possibilities and, so there is no real restriction you if you can think of some other interesting way of utilizing energy that is around which we may not have recognized as something that we can tap then this is something that we can look at. So, this is energy geothermal energy that comes from within the earth and it is interesting to see what is the possibility of us capturing it and utilizing it in a manner that is useful for us ok. So, and in terms of it being renewable I mean we will soon see that you know for all practical purposes it is infinite I mean from the perspective of you know lifetimes of human beings and you know the age of the planet etcetera its significantly I mean it’s not something that we are going to run out of in you know pretty much the entire years that lye ahead of us. (Refer Slide Time: 03:39) So, it is in this context that we look at geothermal energy. So, we will begin by first describing the principle behind tapping the geothermal energy so that’s the basic idea that is being utilized here to extract this geothermal energy and put it to some use. And also in that context look at any limits and it is particularly challenges associated with geothermal energy usage. So, these are the two that we will focus on two objectives that we will focus on as we look through the content of this class, ok. (Refer Slide Time: 04:07) So, if you look at the cross-section of the earth and this is where I think you get a sense of how more or less unlimited it is right. So, on this cross-section, we have not shown the atmosphere actually if you look at you know it is also a very thin layer around this planet the effective atmosphere that we use. Ah. So, wind energy etcetera would fall within that thin layer, but the land area that we live one is essentially part of the crust ok. So, the crust is, in general, some thickness of the order of about 30 kilometres. So, that’s the thickness of the crust. So, and it is also not completely stationary, the crust you know essentially consists of different plates which are sort of moving against each other and that is how you have all these you know, for example, the Everest is still growing, that is how we get earthquakes. So, many things happen. So, in a fairly long scale of time it looks I mean at least a human lifetime scale the movement is not dramatic, but it is there I mean it is there and that is what leads to like I said earthquakes when it when there is an earthquake of course, it is dramatic at that point and significantly affects human life, but in general even though you know you may say that say the Everest is growing by so many centimetre every year or so, many millimetres every year whatever it is. That’s not dramatic in our scale of time. I mean you don’t look down and then you look up and then you suddenly see Everest as grown it does not work that way it is a relatively slow process. So, for all practical purposes, the crust is relatively stable relatively stationary in from that perspective although there is some movement that is going on. Below the crust, we have the upper mantle. So, the crust is the only part that is I mean truly solid. So, to speak then up below that you have different layers below it and so the thickness of the upper mantle is about 720 kilometre. So, the thickness would be this then. So, you are looking at a crust being just this thick and the upper mantle would be this thickness. So, that’s the upper mantle thickness 720 kilometres then below that is the lower mantle 2170 kilometres. So, that is quite significant. So, from here to here you cannot see that there, up to that. So, we will just select something else here, from here to there that’s the lower mantle. And then the outer core which comes from here to there that’s the thickness of, the outer core is about 2260 kilometres thick that’s the thickness and then the inner core. So, it is from the centre here. So, I will just a, so the inner core is from here to here. So, that’s the thickness of the inner core which is about 1220 kilometres thick. So, if you total up all of these that’s the thickness of the earth from the surface up to the centre essentially the radius of the earth. So, if you total this up you will get roughly about 6400 kilometres that are the radius of the earth ok. So, the core contains iron, nickel, some noble metals are present in the core-mantle consists of sulphide and oxide has is both sulfide and oxide rich and the crust is mostly oxides. So, you have all this silica and everything that’s all in the crust. So, this is how we get this is how the earth is, so this is what we are looking at ok. So, if you look in terms of depth this is what we are looking at you are looking at about 30 kilometres depth for the crust and then from there, the upper mantle will I mean down if you go to the end of the upper mantle you are looking at a 750-kilo meter depth then you can go further down nearly 3000-kilometre depth is where the lower mantle would end and there your outer core would start and then from there to the end of the outer core is about 5180 kilometres and then from the surface all the way deep into the centre of the earth is about 6400 kilometres. So, this is what we have in terms of the structure of the planet and incidentally. So, we will also get an idea of the temperatures that we are looking at here in terms of what is expected at different locations in this on the planet. So, we will just look at that we will revisit this information in a few moments. (Refer Slide Time: 09:03) So, this is the kind of temperatures we are looking at the crust is anywhere from 0 to 700 degrees centigrade in temperature ok. So, you start at the topmost layer of the surface of the earth which is where we are you know essentially standing. So, based on which part of the world you are sitting in it could vary you know it could be 10 degrees, 15 degrees, 20 degrees, 30 degrees, something like that it can go down to about 0-degree centigrade can even go negative based on which part of the world you are and so an approximate number we are looking at. Forgiving ourselves a range, so we are looking at about say 0 degrees centigrade as the starting point of the temperature here and then it continues you can go warmer and warmer and then as you go deeper and deeper into the crust you could reach about 700-degree centigrade is what you can expect in the crust. The upper mantle will have temperatures of the range of about a 1000 degree centigrade then you go to the lower mantle that’s about 3500-degree centigrade. The outer core is about 4000-degree centigrade and the inner core is about 7000-degree centigrade. So, like I said we will look at these numbers again in just a few moments. This is just to give you an idea of the kind of numbers we are looking at when we discuss the planet. So, the question is actually how do we arrive at all of this information ok. So, how do we arrive at all of this information? So, although you may have read science fiction you know books along with the nature of the journey to the centre of the earth and so on. If you look at the temperatures here right these temperatures they are so high that we have no technology that can do this we have no technology you cannot just dig a hole and arrive at the centre of the planet of the earth and there is no way any human being is going to survive that, there is no technology that we know that is going to survive that. So, in fact, in the foreseeable future, we have no means of actually reaching the centre of the earth and finding out what exactly is happening there. So in fact, almost everything I have shown you in this slide in terms of depth in terms of thickness depth and temperature and even this information that you have down here. Very little of this is available to us as an experiment that you can conduct physically conduct you know you take a sample you put it and put it in for some analysis and come up with all this information saying that as per the sample which was picked up from the core this is the composition of the mantle and so on. So, we are not in a position to do any of this stuff. So, the situation is that using a lot of incidental information about the planet we have theories which predict what is inside the planet, interestingly. (Refer Slide Time: 11:50) So, for example, if you look at what you see here we look at what is the flow of heat from inside the earth. So, based on let’s say just the temperature of the earth as you go deeper and deeper into the let’s say even the crust. So, where is that heat coming from? That heat is not coming from the sun here it is already heated inside the planet. So, there is an expectation that you understand that something inside deep inside the planet is hot. So, we do understand that you do have volcanoes which are you know sending out material from under the ground. So, we know that below the crust there is something molten that is hot that can come out. So, we can you know look at those temperatures you can look at the composition of what is coming out. So, you have some idea of what is underneath right. So, that that is that is another piece of information we have. So, the flow of heat from inside earth we also have volcanoes that give us a lot of information about what is at least just below the crust. So, that gives us a lot of direct information. So, that is again a place where you can see a sample where you can actually do something with the sample, we can also do experiments on surface minerals and rocks right, both surface minerals and rocks under high pressure and temperature ok. So, you can do experiments under high pressure and temperature, but this is an actual little bit tricky because temperature you can heat up if you want to reach you know a range of temperatures. So, for example, if you look at this temperature that we are seeing here 7000-degree centigrade okay even though 7000 seems like a large number technically getting 7000-degree centigrade is not an impossible task is a very doable task there are many places in the world where we have experimental setup which is crossing 7000 degrees centigrade. So, any place there is a nuclear reactor, for example, some nuclear power plant is there. You are crossing 7000 by a long margin you are you know right now you are running fission reaction or something like that. So, you are looking at a temperature which may be approaching even a million-degree centigrade. So, a very high kind of temperature is not unusual to accomplish reaching about 1000-2000 degree centigrade occurs in labs routinely. So, 7000-degree centigrade that will be ways to reach if you run a plasm