Hello, in today’s class we will continue our discussion on geothermal energy. In particular today we will look at some aspects associated with the technology part of the process we understand that you know inside the earth there is a lot of heat and we are trying to extract it. So, a little bit more on the technological side of it, some aspects associated with some challenges associated with the technological side of it is what we will try to focus our attention on. (Refer Slide Time: 00:43) So, in this context, our learning objectives for today’s class are basically to describe the different conditions relevant to geothermal energy availability ok. So, it’s not available in the same kind of quality or quantity I mean quantity it is not the issue or the quality at different locations. So, if you go about trying to find it, you may find it with different levels of you know heat that’s available their temperature that’s available there even what is available there that is coming out maybe naturally from under the ground. So, these are things that we have to look at. Then we would also like to understand that in this context since what is available underground may be different, at different locations what are the variations in geothermal plant design ok. So, what are the typical kinds of variations that people have about geothermal plant design? So, I think these are the two major ideas that we would like to focus our thoughts on and go through you know related information ok. (Refer Slide Time: 01:49) We saw this in the last class that we saw that as you go deeper and deeper in into the earth the temperature goes up and that’s the idea of this whole geothermal energy process. I also told you that these are all based on models the actual temperatures that you see here are all based on models and so you can see variation from you know a model to model. So, these are not hard and fast temperatures these are sort of estimates based on different models and as of now, we have no real way of actually measuring these. Even though you know the core is only 6400 kilometres below us you can learn a lot about planets that are far away from us, stars that are far away from much more effectively than you can learn about the core that is just directly below us because we cannot access it whereas, you can use astronomical instruments to access all of those. Incidentally, even though the temperature is going up, one of the points that you must I mean find interesting perhaps to note is that the inner core which is where you are seeing the highest of the temperatures even though this may or may not be the exact number that we need to look at the temperature is, so, high there that in principle at about you know if we cross 5000 degrees C and you know if that kind of a temperature you cross essentially all metals will be in the liquid state you will not you are not going to have any solid metal at that point. But if you go to the core the estimates indicate that in the core you actually have solid metal you don’t have liquid metal and the reason is simply that whatever you see as the melting point which you see in the data that you see when you go and look up you know melting point of iron and melting point of copper or melting point of aluminium whatever the temperature that you see there is the temperature which is the melting point of that metal at atmospheric pressure ok. So, melting point T melting point that you typically see assumes that it is at atmospheric pressure. So, that is equal to at one atmosphere and as you can you know as we sort of saw you could have to several million atmospheres if you go down based on you know how much of pressure is being collected there. So, therefore, the pressure is very high there and under those conditions even though you are well past the melting point the metal is forced to stay solid the atoms are pushed close enough that they stay in their solid-state they don’t break free and float away as liquid ok. So, therefore, the inner core is considered to be solid material and in fact, based on all the estimates based on the fact that earth has magnetic properties various other the density of the earth various other things the expectation is that these are the kinds of you know compositions of the centre of the earth. Incidentally, I mean on along similar lines because of all this heat and pressure that is there it potentially this is something that you would this is a form of energy that you could extract in other locations too in other planets to if a similar situation were to exist, of course, that would require some kind of a crust and then some you know hot material being beneath it. So, some places that may not be the case, so if you have a gassy planet and that is not the case then there may be no well-defined surface on which this can be done. But this is an idea that is of interest even for space exploration because at various planets depending on where you are you could get energy directly from within the planet as opposed to say solar energy etcetera. This may be relevant based on where the planet is located this is just an interesting aside. And in all those cases again based on the pressure the central part may be solid, the central inner core may be solid ok. So, for example, the theory suggests that if you look at the centre of saying Saturn or centre of Jupiter the temperature and pressure and composition are all just right that at the centre of those planets it is very likely that you have a big diamond ok. So, the, you know we look for diamonds and it is such as scarce item here and on the planet on our planet and it is so expensive you may have a diamond sitting in the centre of Saturn or Jupiter which is larger than our planet. So, that is possible we don’t know that that is true, but the conditions are vector the high temperature the high pressure and the amount of carbon that is present create circumstances that are very similar to what is required to create diamonds. So, this is just something that is of interest. So, different planets have different circumstances, ah, but many of them have, have there is a chance that several of them have some energy in them certainly on earth we have this energy that we are trying to tap okay. (Refer Slide Time: 06:24) So one of the big activities associated with you know locating and tapping of geothermal energy is this idea of prospecting ok. So, prospecting is simply exploring, exploring to find out what is available where that’s essentially what it is. So, people do prospecting for all kinds of different things I mean they may be prospecting for a particular ore, they may be prospecting for gold, they may be prospecting for diamonds etcetera. So, even for geothermal energy that is the idea the, there are people who study you know the geology of various locations of our planet and then, so they try to understand what are better locations for the plant. As we discussed potentially you could dig a hole at any place and based on the kind of temperature you get at some depth you can run a geothermal plant. So, in some sense you know location is not critical you can do this at multiple locations and it is not impossible to do it that way, but there are better there are locations that have considered better locations and to identify those locations you have to do prospecting. So, a considerable amount of time is spent to locate various regions that people think might be of interest maybe because there is some you know hot water already coming out from under the ground which suggests that there is some hot spot below where you can access the heat at maybe a much shallower depth, you can access higher heat at a shallower depth. So, therefore, there may be better locations and therefore, there is interest to you know explore those locations and see what you can obtain in those locations. So, to do that actually what they do is they try to make a chart of some sort where you have a map and then at in the map at various locations you indicate, what is the temperature at various depths? So, therefore, you will get some kind of an isothermal line you will get find out that at which depth you get the same temperature at various places. So, if you are getting you to know higher temperatures at lower depth then potentially there is you know some hotter region below. So, that may be a region that is more interesting for us to explore from the perspective of geothermal energy. So, for example, a place when they are trying to set this up they have done this kind of geological exploration in several places in India. So, there is this Balrampur district in Chhattisgarh, a particular place called Tattapani in Balrampur district Chattisgarh which is where they are you know doing putting to set up a geothermal plant and so that is where we are likely to see some activity come up from the Indian perspective. But all of that again as I said it relates to this initial step of prospecting. (Refer Slide Time: 09:15) So, prospecting also does multiple other things. I mean, so it is not just locating the region which is of interest you have to understand what is that region they also you know drill course I mean drill through that location and pick up what kind of material is located at various locations in that region as you go down in depth. So, it’s a temperature, so they are locating you know finding out temperature as a function of depth and composition as a function of depth. So, composition means not necessarily chemical composition we are looking at you know what kind of rocks are there what kind of I mean is it sandy, is it full of rocks and if so, what is the thickness of the rock layer, how much of sandy area you have to go through, what kind of clay is there in that region, what kind of soil is there how deep it goes. So, those kinds of information this is very this may not seem immediately relevant, but it is very useful in identifying low-density regions. Even within the same area, so supposing you have located a particular region where it seems like there is some hotspot below even in that region you can check out multiple neighbouring locations to see if there is one region where the drilling seems to be going much more easily right. So, that enables setting up of the plant in a much more easy manner and therefore, this is a very important initial activity and incidentally, I mean here this is done. So, extensively to locate these plants nearly 40 per cent of the cost of geothermal energy is associated with this exploration process. So, and that is because they set up you know sort of you know small scale plants are set up, small scale drilling is done. So, small scale drilling is done small scale meaning the plant is almost like a mock plant they will set up they will have to drill, I mean a hole into the ground to some reasonable depth, to understand everything, to understand the temperature as a function of depth, to understand what you know geological features are there as a function of depth, you can also see there has been some relatively recent melting and solidifying in those regions that give you an idea if you know that has been a relatively active location so to speak and then get this information together. So, you have to drill these holes and these are being done at various locations and each of them costs a fair bit of money. So, nearly 40 per cent of the cost of geothermal energy is associated with exploration. So, lot of you know work is done on this remote sensing to get a better sense of what features are available at larger you know, a larger area of land so that they can identify these locations much better and therefore, in fact, the general thinking in the field of geothermal energy is that it is much more important to invest in technologies that help you in this exploration process, that will help you do this exploration much more effectively, much more efficiently, in a much more time-bound manner so that you can get all this information without a whole lot of delay and a whole lot of expenditure of money and resources. So, if you can cut this down you know if you can cut down this exploration cost significantly the cost of the plant itself comes down because this exploration cost is all getting you to know tied into the plant eventually when the plant comes you have to recover this exploration cost from whatever it is that the plant produces. And at if you take that into account 40 per cent is very high 40 per cent of the cost being the exploration is very high. And that is mainly because you have to make those tools drilling holes at various locations it is not something that you cannot easily just get this information by taking photographs etcetera you have to drill and that is the reason why this seems to be expensive. So but prospecting is a very important activity in this context. (Refer Slide Time: 13:41) Incidentally, so plants have been set up around the world in this in this context and as I said in India in Chattisgarh they are working on setting one of these up. The largest such plant is in California it’s about the 1500 megawatt plant has multiple I think multiple drills are there at that location and you have 1500 megawatts have been generated there. Several other countries have been involved in this process. You can see here in the Philippines if you take the 10 largest plants that are around internationally then you have three of them being in the Philippines. So, there it seems to be quite an important form of energy capture that is you know being pursued actively. So, in the Philippines we have three of them in the US and Indonesia there are two each two of these large plants are there including this one in California and Mexico Italy and Iceland you have one each. So, this is you know worldwide phenomenon lot of nations are looking at it, we are we have not actively pursued it to the extent that these plants are already set up and generating electricity and so on, but we are also considering looking at it and we are you know in the process of setting up a plant. So, the again the nice driving force for this is that I mean you don’t need any there is no pollution coming out of it is kind of a clean form of energy and potentially infinitely renewable. I mean it is going to last for such a long time that you don’t have to worry about it running out of it so to speak. So, this is the sort of global scenario in this context. (Refer Slide Time: 15:25) Now, let’s say we have done some prospecting ok. So, you have done some prospecting and you locate a particular region where there is very high temperature and in fact, when once you drill you find there is a lot of hot material coming out from there typically steam. So, that is what is coming up. So, based on the location and the temperature essentially based on the temperature you have multiple possibilities of what you can get from that location right. So, either you can get big because if the temperature is pretty high then you may end up getting what is called superheated steam ok. So, water boils off and then you get steam and that point as just about boils off and just you just about created create steam that is called saturated steam. So, that can condense relatively easily because you have just past the boiling point if you heat it distinctly above that boiling point that steam is heated distinctly above the boiling point then it is called superheated steam ok. So, superheated steam is that you know steam at a temperature distinctly above the boiling point okay. So, that is superheated steam right. So, typically superheated steam and so the advantage of superheated steam is it’s not going to immediately condense in generate water ok. So, this is may not seem like much, but we will discuss that in a moment to understand what is the big significance of it if we say you know it’s not going to condense all of a sudden so to speak. First of all in the grand scheme of the fine that people have as they go about prospecting this is relatively rare to find relatively, it is there in some locations, but it is relatively rare to find superheated steam directly coming out from underground, but if the if you do find it in a location it’s a big positive because; that means, you can directly start putting a plant there and start operating it and you can directly use it to run a turbine ok. So, you can run a turbine directly using it we will just see some schematics of this in just a moment, but basically, the steam can be taken to turn the turbine. The one issue that you have to be cautious about is that even in thermal power plants they are creating superheated steam and then sending it in to run a turbine. So, that in that sense conceptually once the steam has generated the processes is the same we send it to run a turbine. Now, the only difference between say thermal power plant situation and this geothermal situation is the fact that when you do this superheating and you generate this steam and you send it in the thermal power plant you started with clean water ok. So, the water is clean it is something that you had control on and therefore, the steam that you get is also clean and that is used to run the turbines. Now, in the case of the geothermal plant what is coming from underground may not necessarily be 100 per cent steam you may have some other gases in it, you may have even some radioactive material in it etcetera, so which may be coming out. So, therefore, what goes into the turbine especially under these conditions when you are sending it directly into the turbine is potentially something that can damage the turbine ok. So, therefore, you have to be cautious about it and you have to take appropriate precautions concerning the turbine materials to ensure that it is more corrosion resistant then maybe you would normally set it up to, set it up to be. So, they put coatings on turbines you know you can put different kinds of coatings on turbines just to ensure that there is greater resistance to corrosion greater resistance to any abrasion etcetera. So, that kind of precaution needs to be taken. So, but in any case, if it is superheated steam it can be run to it can be sent to run a turbine and also we will look at this we can follow it up with a condenser that we will see in a moment and we also need to if it is coming straight from the ground if the superheated steam is coming straight from the ground we don’t want to exhaust that superheated steam. So, whatever happens at the end of the process the water that is generated is pulled back into the ground at that location to ensure that the cycle stays operational ok. So, this is the general idea that people would like to do concerning superheated steam. So, if you look at you know the sort of a schematic we will see a schematic here. (Refer Slide Time: 20:04) So, we have somewhere further deep down we have hot spots or some hot spot is there where we have very high temperatures and you can get steam. So, normally what they will do is having found such a location they drill two wells. So, one is called a production well which is what you see here. So, this is the well from which they tap the steam. So, the steam comes up the way you see here and then goes into this turbine because it is already superheated steam. So, this is for superheated steam it enters and there is just a schematic of some turbine that I have put here. So, let’s say this is the turbine and this turbine then rotates you get this generator. So, this turbine goes and then the steam goes past the turbine gets the turbine to rotate and then the turbine is then connected to a generator here. So, the generator generates electricity and then you have electricity out. So, this is the basic idea that we have. Now, after you cross the turbine the steam would have cooled or at least completed it’s a task and then at that point we can send it back this is what we say referred to as by saying that we can we should replenish the well, the point being that you know you have taken something out from under the ground and if you exhaust it off you may no longer be able to easily get the steam from that location. So, you send the condensed water back into the ground. So, this way you can keep it running indefinitely as long as there is heat down there. So, there is typically an injection, but through which you complete the loop. So, you send this material back in and this is called the injection well. Now, when you complete this when you go past the turbine right, so the steam hasn’t completed it is work it has done rotated the turbine and you are about to exit the generator I mean the turbine, turbine chamber. So, at that point, you may still have it as steam. So, what should you do? I mean if you directly put steam back in here it may not be as effective in terms of going back down into the injection well and you may it may still have some energy or you are you have not fully captured the energy if you are just sending it back as steam, just you know steam which was superheated significantly it is now, steam that is either you know just about saturated or just marginally superheated. So, you have not fully captured all the energy that is available in this process, if you just do what is being demonstrated by this schematic. So in fact, whenever we find superheated steam they do one more step which is which happens in this region at the exit from the turbine area where we say that we don’t take what is coming and we exit we do not directly send it into the injection where we do one more step before we send it to the injection well and that is what you will see here. (Refer Slide Time: 23:05) So, what we do is we put in a condenser. So, what comes out is sent into a condenser ok. So, here it is allowed to cool down further till it becomes liquid water ok. So, it becomes liquid water and then it is sent into this injection well ok. So, this is what is done. So, this may not seem like much. So, you would say, so what I mean you have you anyway across to the turbine. So, already crossed the turbine what is the big deal in putting it into a condenser and then sending it into the injection well there is a big difference. The moment you put it in a condenser you have taken steam and made it water, liquid water ok. So, when you do this the drop in volume the drop in volume is significant. So, steam is going to have a significantly higher volume than this the same amount of steam when it is converted into liquid water. So, there is a huge drop in volume when it goes from steam to water. So, now, this drop in volume means what. So, you had supposed you have a chamber in that chamber you have steam ok. So, you have let’s say someone meter cube chamber 1 meter by 1 meter by 1 meter, 1-meter cube chamber that is filled with superheated steam. Now, suddenly you cool this and then this whole superheated seemed suddenly condenses into some you know a handful of let’s say I will just give some example maybe 100 ml of water it is what it is let’s say 100 ml or 200 ml of water ok. So, now, suddenly there is a huge drop in volume which means a significant amount of vacuum is being generated inside that chamber ok. So, when you do this condensation you are generating vacuum because whatever was there you suddenly reduce the volume the container still has the same volume, but the interior you know the material that was inside that the vapour that was inside that has suddenly condensed to a very small volume. So, you have generated a significant drop in pressure which is essentially you are creating a sort of vacuum. If you create a vacuum then you pull the gases pull the steam that is coming up here even much more effectively ok. So, and in that process, you make the turbine work even better ok. So, by just the condensation process, by creating a vacuum on the exit side you will make the whole turbine system work much better. So, you get even more energy you can extract even more energy out of the turbine and as well as from you know superheated steam that arrived at the turbine and through the turbine. So, you end up creating much more energy or extracting much more energy. So, therefore, a condenser is a very important part that is there that is added to this system of this geothermal energy process when you have superheated steam and it significantly helps improve you know the operation of that plant and therefore, this is always done ok. So, we never typically in this kind of a situation when you have superheated steam we are not exhausting this I mean we are not venting the steam out into the atmosphere instant we send it through a send it back to the same location from which we took it out by using an injection well and on top of it we also use a condenser to create liquid water and then only then we inject it back into the air well. So, this is what you will typically see. Now, this condenser may have some other you know maybe may have water I mean low some water involved in the condensing process cold water may be available locally which is used for condensing process. So, typically condensers you will see some vapours coming off of it, but that is from water that is other than what is being used for this that is coming through, the steam coming from the steam ok. So, this is the kind of layout that is used if after prospecting you find the location where you have superheated steam. And of the possibilities that you can have when you do this prospecting or when you do this, you know surveying for this geothermal energy this is your best case scenario where you found steam and you were directly able to use it. So, then the plant complexity is much simpler and it is much more capable of extracting this heat for you, but this is not what you always find ok. (Refer Slide Time: 27:43) Often what you find is saturated steam. So, saturated steam means it is just past the boiling point I mean. So, you boil the water you are just past the boiling point you have created steam, but you are sitting at a temperature that is very close to the boiling point and at that point if you do anything that cools the steam even marginally you are going to get droplets of water ok. So, if you would take even the tiniest bit of heat out of it you can get droplets of water. So, many places this is what is being formed relatively speaking, significantly more often much more often then you find superheated steam you are likely to find saturated steam. Now, there is an issue with this. I mean in some sense conceptually it is the same you can still send the same steam into a turbine and make it operate and. So, in that sense, you should not consider it dramatically different than using superheated steam, but we cannot use it directly because the condensation that happens creates droplets of water and that droplet we of water can damage the turbine over a progressive period. In all these cases, in all these technologies many of these parts are expensive parts and we don’t want them damaged, turbines are kind of expensive to make and they are expected to last a considerable number of years. So, you don’t want the turbines to be damaged, but when you have droplet us of water you know physically going through the process they can damage the turbines they can lead to corrosion many issues can arise. So, what can we do? So, the possibilities are different, different possibilities, we can think of we can try heating the water. So, you have reached steam. So, in the in a thermal power plant, you are taking water at say room temperature and then using coal and heating it up two 100 degrees C and then you heat it to get steam with, then you heat it to get superheated steam and then you send it into the turbine right, so that much of energy you are getting from coal. Here you already have steam ok. So, it’s just saturated it is saturated steam. So, it is already there in that you know you took it 100 degrees C got it past the boiling point and it is in steam. So, with relatively less amount of coal for example, if you had to use coal with relatively less amount of coal you can get it to become superheated steam. So, that’s simple. So, you are not, you want to be 100 per cent clean in that sense because you are going to use some fuel maybe coal may be oils something to do this final bit of heating to get it to become superheated and then you could use this you can use the same turbine that you used before etcetera. So, that is one possibility. But generally, that is not done because of course, this whole idea is to run this in a very clean manner and by including this burning of this coal you are not you are sort of destroying that good aspect of this technology. And more than that there is also the economic aspect of it these plants are as I said you know they are not located just about anywhere some prospecting is done and it is located at some maybe even in some remote location which is where the hot spot happens to be. So, to run this plant if you are going to adopt this strategy of you know heating it then you have to keep transporting fuel to this remote location. So, and these are not small plants these are typically you are trying to set up a plant which runs you know significant power capacity is there, so corresponding to that a significant amount of steam will have to be used and therefore, corresponding to that a significant amount of fuel will be required. So, if you have a remote location and you have to keep transporting this on a day a regular basis and these plants are you know set up to run for several decades if not more than this is a big process you are setting up which is not at all a convenient process. So, therefore, this is not taken into this is typically not done. So, heating is not pursued in this context. The other option you have is that anytime any liquid. Let’s say you say