 Let us now move ahead and look at solar. So in the case of solar, solar is much more predictable and when we talk about solar insulation, we are looking at the direct and the diffused. So we have a direct and the diffused. If you are looking at the direct insulation, this is an instrument which is used to measure the direct beam insulation, this is called the pyrilometer. This is focused so that it is directly depending on the position of the sun, it will be taking the direct normal beam radiation to the sun and you have this is the measurement. You also have what is known as a pyranometer and the pyranometer can be used for measuring diffused radiation or total. This is a blocking sheet which can be used to block the direct and then what is measured becomes only the diffuse. If we remove this, then we will get the total insulation which is on a horizontal surface and that will be the global horizontal insulation. And so the direct plus diffused will give us the horizontal and these are the instruments that can be used to measure. Most of the measurement stations will have these type of instruments and the solar constant ISC which is incident is of the order of 1361 watts per meter square, 1361 watts per meter square. Total amount of solar insulation available per meter square of surface, when it comes through the atmosphere some of it gets scattered, some of it comes down at diffuse, some of it gets absorbed and what we have is what is known as the direct normal irradiance DNI. And DNI at any point of time when we talk about the solar photovoltaic, we usually have a standard which is based on a 1000 watt per meter square and we create the characteristics for that insulation. When the insulation is lower, the output would be lower. So DNI is the flux density of the direct unscattered light from the sun measured on a flat plane perpendicular to the sun's rays and this DNI that we talk about which is so this is DNI is perpendicular to the sun's rays so that it is, you have the normal irradiance which is there and this flux varies over the day as the sun rises and there is a peak and then it goes down in the evening. When we look at the DNI every hour we can measure the DNI and then make a plot, we can take the aggregate amount of the irradiance over the year and that is plotted as the annual DNI. So those are the kind of values which are put. When we look at the spectrum of the solar radiation, if you see this, you have the sunlight which is there, some of it is absorbed and then it reaches, this is at different wavelengths and some of it is in the visible range and in the infrared and in the ultraviolet and all of this is incident onto the device and depending on the characteristic of the device, we have an efficiency which is there and this is used to convert the energy. So if you look at now the solar irradiance, these are formed through a few of the sites which are there in where there have been solar plants and you can see that in some cases you have this pattern but because of cloud cover for some hours there is a drop in the irradiance and this is from a site in Gujarat for a particular day, one of the days you have no cloud cover and you can see that the generation megawatts follows the classic example of what we expect from a solar PV plant and another day there is some cloud cover at this point and then is there is a cloudy days, this one is a cloudy day with number of cloudy hours and disruptions. So these are the kind of things which I told you that in terms of the interruption and the variability which is there in solar. Solar is much more predictable as we said that with the different kinds of you can measure this is with a different unit, it is kilojoules per hour square meter, usually we will put it in terms of watts per meter square and then we can take watt hour per meter square multiplied by the number of hours and then over the year you will get something like a kilowatt hour per meter square per year and this is the global solar irradiance and you can see this is the direct normal DNI which is there and you can see the yellow region, these regions are the ones with high DNI. In the Indian context we have reasonably good DNI across most parts of the country and there is a variation of course see this is the kind of average global solar irradiance and you can see this is in watts average in watts per meter square over the months of December Jan Feb and this is June July August, this is again both of these are from the global energy assessment. In the case of India you find that most large parts of the country have most of the country has DNI greater than 1900 kilowatt hour per meter square and some of these regions for instance this is more than 2200 and so this is quite a good DNI. Now in order to make a calculation if you look at the total amount of electricity that we require we can take that electricity divided by the DNI that we have take the efficiency of the cell and then calculate what is the area that is required and if for instance if you are talking of 500 billion kilowatt hours we can see that this can be met by installing about 2500 square kilometers of 50 into 50 kilometers or 4 smaller squares of 25 kilometers into 25 kilometers and so really speaking this location which has been selected is a location which has the highest insulation in terms of DNI it is also a location which is desert and relatively low population density. However still you know getting 50 kilometers into 50 kilometers is difficult creating the transmission and distribution line creating the storage in actual practice when we try to get land land is always difficult to acquire and the requirement for land the requirement for water in terms of the cleaning the panels and in the case of solar thermal even as a working fluid these are some of the problems in terms of the solar penetration. As I told you for the you can see this is the global horizontal insulation watts per square meter for a particular location of a PV module in the IIT campus and you can see that the generation actually follows the insulation data. We can also look at the DNI variation over the years and you can over this is for a particular site at Noida and you can see that every day that the DNI goes up and down but there is a variation within the seasons and there is a fluctuation and so this is one of the issues when it comes to solar but when we look at solar there are large tracks in the Indian context we have a significant amount of solar radiation most parts of the country have good solar radiation. Most of the solar is happening though in mostly in the west and the south east and northeast relatively have less solar radiation so we have this situation where when we talked about fossil fuels it was mostly in the east and little bit in the center most of the solar and the wind is happening more in the west and the south so there is a sort of regional disparity in terms of the kind of resources which are available. Let us now look at some of the other sources of energy if we look at tidal. Tidal is the renewable energy source where it is not dependent on the sun but it is actually the moon. So the gravitational effect of the moon on the earth causes the high tide and the low tide and the principle typically in a tidal situation of course you can have tidal turbines which are in the stream just like the wind turbines but in the other case we allow the water to come in at the high tide and then we block it and then we release the water at the low tide. This difference between the high tide and the low tide that is called the tidal range that gives us the head for running the turbines which gives us the power generation. So the power generation happens only at a fraction of the time when we are releasing the water during the low tide and it will of course be in so in the case of this kind of data we will need to have what is the tidal you know there will be a daily tide or a semi-diagonal tide there will be a tidal range between the high tide and low tide and this has to be mapped. This has been for all locations of the course there are ranges of tides which are provided and this is the tidal range map which is given in the you can see of course that we are looking at a tidal range of 10 to 20, 10 to 30 meters would be cost effective again depending on the location and the kind of things one can think in terms of. In India we have not yet built there is a plan to build and I am not sure what is the status of that of the coast of in the Bay of Bengal of the coast of Sundarbans there is a plan to build tidal plant there is also a plan at the Gulf of Kach the largest tidal plant is the one in France which is a 240 megawatt Laran's France which has been operational for a for decades and it is also a tourist attraction there is a recent one which has been built in Korea in the Siva lake it is about 254 megawatts. So tidal as of now there is a potential it is not yet a commercial technology there are a few projects they are demonstration projects they can be near cost effective but we do not expect them to have a very major role in the future unless there are technology breakthroughs. In addition to tidal there is also something called the ocean Otec or the ocean thermal energy conversion and this basically is using the principle that the surface of the ocean is much warmer than the water which is there at the depth and because of this it is possible to have a normal ranking cycle where we use the temperature this temperature difference to generate electricity and the advantage that we have is that we have a large volume of water and even though the temperature differences are relatively small in the sense that we are looking at temperature differences of 18 to 20 degrees even though they are relatively small because there are large volumes we can get we can generate a reasonable amount of energy and we had the largest plant being planned off the coast of Tamil Nadu it was a 1 megawatt power plant and the problem was that most of the components were tested however when it was put in the field the pipeline the HDP pipeline 1.1 kilometer pipeline kept getting ruptured and because that was not able to be established that was the project was abandoned there are a number of the this is the most difficult challenge in the sense that it has to be put in the ocean which is the most the most adverse and harsh environment but however there is a significant potential to do this. In the case of wind also in many of the countries in Europe the land for wind is not available and the plan is now to move offshore in the case of offshore we can have essentially we will have much higher wind speeds and we can have large wind farms and that is the way this is going offshore is costlier again there are technological challenges but this is this has been the way we are going in the case of wind also we have gone for larger and larger plants and now we have a single turbine which can generate of the order of 10 megawatts. So, this is in terms of we have looked at tidal and we have looked at ocean thermal then there are also we can also look at these ocean currents and it is possible to use some of these ocean currents in terms of energy generation. The other possibility related to the cost is to have the energy which is available in waves and to harness that and in order to do that what happens is that see on the surface of the water because of the wind we have the waves and the waves have the crests and troughs and we have a number of different devices which can be used you have the oscillating water column and you have the edinburgh duct and you have the pelamis different kinds of devices which bob up and down and that movement reciprocating air is converted into electricity. This has the largest number of patents which are available for wave power the problem is that this is all distributed you need to have a way for taking out that power we need to have a way for taking that power and converting it into electricity and then evacuating that electricity and connecting it to the shore. So, this is again something where we do not a there is a reasonable amount of potential and this is that you can see in different regions you can see that the total terawatt R which we are looking at extra joules is about 106 extra joules very large potential but cost effective extraction is an issue they could be breakthroughs and this could provide reasonable amounts of requirements specially for islands and coastal regions. So, we have looked at tidal we have looked at ottec we have looked at wave the other source of energy as we talked about is the geothermal energy and in the case of geothermal as we said there is that the at the depth the temperatures are much higher and then when you look at the water coming in contact with this we have essentially hot water or steam coming out there are many natural hot springs where these come out and these are usually tourist attractions here there are many different technologies where we can have an injection well and an extraction well where you inject water inside and or a working fluid inside and then you can have an organic Rankine cycle and have power generation. If you have lower temperatures we can also directly use it for heating or we can use a vapor absorption refrigeration system use it for cooling there are also geothermal heat pumps and geothermal so you can have ground from the ground if you take things the temperatures are 5 or 5 degrees 6 degrees lower and you can run you can save energy when you are trying to heat or cool a space. So, that is again another application there are many different countries where this is a this is a commercial technology cost effective but it needs it needs it will be in areas where there is already the faults and you have the steam emerging at high temperatures in the case. So, this is this gives you an idea of some of the different countries and the kind of geothermal installed capacity and you can see Indonesia, Iceland, Philippines a number of different countries where there is a geothermal capacity and this is a map showing the geothermal faults before we look at that in the case of India these are the geothermal provinces and if you see the in the Indian context the around the fault areas these are the areas where you have the geothermal but the temperatures in most of the cases the temperatures are relatively low. In some cases in the Puga Valley we are getting temperatures of 200 centigrade and so this can be used for power generation there is a pilot being planned at Puga Valley. Many of these other places you can use it for cooking you can use it for heating and in we do not expect geothermal to have a very major role in the Indian context but locally this can provide some of this requirement. The supply curve for we talked about supply curve the supply curve for geothermal with current technology you can see that we can get of the order of 200 exa joules or 300 exa joules at different kinds of prices and with new technology of course the prices will go down and that is for the supply for geothermal electricity and this is for supply for geothermal heat. So, similar kinds of supply curves are available for many of these and this is available in the global energy assessment resource chapter. We come to now another energy source which is in the Indian context quite important it is biomass and biomass could be agricultural residues crop residues it could be waste which are there and cattle dung and then this biomass of a variety of such biomass is available. There are many different processes and process routes for conversion of this biomass. When we try to map this biomass each of these biomass has the depending on the ash content and the moisture content you have a certain energy content of the fuel and you can see that in all of this has the energy content between we are talking of between 12 to 19 mega joules per kg. Remember that we were comparing this with when we talk of oil it is about we are talking of 40 mega joules coal is about half of that but it is a reasonable source. So, it is slightly lower than the energy content in coal but it is something which is abundant and of course in some cases they already have alternative uses it is being used biomass is being used as fodder for cattle it is being used as a feedstock it is being used in patching for houses. So, we have to see whether what about the supply and demand and we have to also look at if you talking of animal dung we look at how do we collect it how do we process it but we can estimate and all of this when we look at getting the estimates of this is these are now stocks. So, we will have to have distributed ways of making these calculations. When we do these calculations we would need to look at for instance we know in different regions of the country or regions of the world what is the wheat production the rice production and based on that based on the production we can find out per ton of product how much tons of residues are produced and we can multiply that we can take the yield in terms of how much area under plantation what is the yield multiply that by the residue ratio and then we will get the amount of residue we can get the energy content of the residue also depending on the growing season and the harvesting season the residues will be available at a particular point of time. So, one of the recent controversies and which has been in the news is has been about the pollution in many of our cities including Delhi and the problem with the air quality has been blamed on the stubble burning which has happened in Haryana in Punjab and the crop residues and the stubble and it is possible of course to gasify it use it for energy and we have to work out these things. So, this is the kind of potential so in all of this you can take the rice again the quantity of residue the residue ratio and the residue energy. So, that is how we can calculate the biomass in the case of biomass there are different possible processes there are thermochemical processes where we can look at if it is combustion just like we have in a power plant the Rankine cycle power plant we burn coal and then we get steam and then we use that steam to run a turbine in this case we can take biomass you know we can take baggers we can take rice husk we can burn it and generate steam generate power the efficiencies are slightly lower than that of a coal based power plant but it could be also cofire you can have coal plus some biomass and the other root is instead of combusting it completely we can gasify that means we add less air so that it is partially gasified it is gasified and you get carbon monoxide and hydrogen which is the producer gas and that producer gas then can be used to can run an engine a diesel engine or a dual fuel engine or a dedicated producer gas engine or we can pressurize it and use it for a gas turbine most of our Indian experience has been with atmospheric gasification and we have been using that gasified output for heating thermal or for running an engine and generating power shaft work we can also think in terms of using this biomass for pyrolysis and getting liquid fuels so this is thermochemical the rates of reaction are higher these are all chemical reactions biochemical is where we let now the microbes do the work for us in the case of digestion anaerobic digestion we get biogas it settles down and we get biogas and we also get slurry and we can use this also for fermentation get ethanol you can have oil extraction and you can have biodiesels and biofuels in the GA and in this special report on renewables you can find all of this again in terms of different different biomass feedstocks different kinds of conversion routes and different heat outputs in terms of heat or power or liquid fuels or gases fuel so there are many different things which are possible in the case of biomass the issues is that if we want to dedicate some land for biomass production if you want to dedicate some land for biomass production then there is an issue of food versus fuel and we can if we on the other hand if we just use the resources the waste which are coming from the animals or waste which are coming from the harvest and then we can look at this has alternative use and then we can look at the surplus which is there go for energy conversion and then we look at the end use if you are doing dedicated plantations there is a fossil there is a food versus fuel and that is a problem we need to see we also need to see if we are getting biofuels what is the amount of energy that we are putting in into creating that biofuel so in a later lecture we will talk about net energy analysis and we will see how this looks so when we look at biomass plantation with the different kinds of fields this is the kind of yields which are available in different parts of the world and this has given given this has again been classified in terms of a technical potential of biomass the problem in the case of biomass is that aggregation and creating a number for the country or number for the world is a difficult exercise and it is subject to many uncertainties this is a local issue and we really need to identify locally the supply demand and the maps. In the case of bioenergy the supply curve which has been drawn in the GEA if you see this supply curve gives you at different we can go up to 80 exa joules per year at about 6 dollars per giga joule. Biomass can be reasonably cost effective there is an issue of as we said the use of land use of water and we have to look at it in terms of the sustainability. But biomass bioenergy systems have not been growing at the rate at which PV and wind have been growing bioenergy systems have the added advantage that most of the technology and most of the it generates local employment and these are something where we think in the future that there will be much more in terms of potential. In Europe there have been some estimates of the kind of from different kinds of there are again there are different technologies for conversion the first generation second generation and with genetic engineering we are looking at different kinds of conversion routes. In all of this we have to look at the overall sustainability in terms of energy as well as other issues in terms of land and water. But this is some of the things which is there and this is an aggregate supply curve with municipal solid waste animal waste crop residues. So, if we combine all of this you can see then this is a image which is there from the global energy assessment which talks about electricity heat and primary energy and talks about the exajoules available we can clearly see that in the case of renewables we are not constrained by the potential there is significant amount of potential this may be distributed we have to see how and where we can do it in terms of cost effective methods. When you analyze any particular location we can find out what are the local resources in terms of renewables whether it is solar or wind and then identify for the demand how much we can require we can then look at the cost effectiveness of such things. One of the key things when we talk of renewable situation and when we are looking at large scale renewables is that we have to match the supply and the demand and matching the supply and the demand means that we will look at solar. The solar supply is starting from let us say 6 o'clock or 7 o'clock in the morning and going up to 5 or 6 in the evening. When your demand is in the night and we are looking at the commercial load and the lighting load coming in from 6 in the evening till about 10 or 11 in the night where we have a high demand we need to then store the energy which is coming in from solar and then use that energy in the night. This involves an additional cost and the total amount of storage that we have installed for the energy sector is not even 1% of the total energy that we supply and this is also there are many different storage options and this is of course another topic but when we look at you can look at the economics of different kinds of storage and it could be large scale storage it could be distributed storage and when we talk in terms of storage large scale storage it is mostly we are looking at today the most cost effective large scale storage is the pumped hydro where we look at hydro having a low reservoir and a high reservoir and you pump the energy from the low reservoir to the higher reservoir even that today at today's prices that costs you another 5 rupees per kilowatt hour. So, this is going to be an issue when we talk in terms of high renewables the matching of supply and demand we try to see so far in the electricity grid we were looking at thermal and hydro scheduling now when you have renewables we have thermal hydro solar wind scheduling mostly today in order to encourage renewables when we supply renewables we consider them as must run that means when the PV generates we try to use it when the wind generates we try to use it this will result as we saw in some cases in the backing down of thermal power. So, when we look at a future demand and we have high renewables what we do is we take that future demand subtract from it the renewable share and then see the net energy which has to be met by the fossil and this leads to what is known as that California dark curve. So, we have to see whether or not the supply system is able to meet that and this involves so at the system level when we talk of high renewable energy penetration we have to plan our systems differently in the GA as well as in the special report on renewables there are some supply curves given for renewables and you can look at this in a little more detail. So, to sum up we have looked at today we have looked at the different methods of assessing renewable energy resources. We saw that these resources are distributed and depending on the type of resource we would map the distribution of the supply we would also see how it would vary over the day and the season whether it is wind, whether it is solar or it is the tidal or the biomass we have seen different ways to estimate and look at the potential. Today these renewables are relatively small but they are going to be an increasing part of our energy mix and when we look at a particular application we need to estimate what is the technical potential and the economic potential and then design our systems for that. With this we will close our chapter on renewables we will also now look at what is the situation in terms of materials that we need for the renewable sector.