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Renewable Resources Energy Analysis

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We have been looking at net energy analysis and life cycle analysis we continue with that some examples. Before we do that let me just again tell you about the criteria that we talked of. (Refer Slide Time: 0:33) We talked about the energy return on investment EROI. We also looked at the energy payback period which is E energy payback time EPBT. And then the net energy ratio, similar to the energy return on investment, net energy ratio NER. Remember in the NER we were not using the renewable energy resources in this. In addition to this, there are two other similar indicators which will be used, which is also used in literature, one is called the cumulative energy demand. And this is often done even for products that means we take, let us say we are making steel or we are making cement, we take the total amount of energy which is required in the over the lifetime, energy input over the life and divide that by n which is the number of years of life and the output that we are producing. So, if you looking at the production, M product annual. So, we will, so you take the cumulative energy over the life side, that is the energy input divide that by the number of years into the annual production. So, this is called the cumulative energy demand and we can compare the CED for different process route and see overall whether or not our option is better than the baseline. Similarly, we have what is known as a Carbon Emission footprint and this will be the total carbon dioxide or carbon emission whichever way you would like to do that over the lifetime, emission over the life divided by n into M product annual. And so, what I will now show you is our examples of net energy analysis that we have done in the Indian context, these are all based on different student projects, some of them are at the master’s level, some of them are at the PhD level and so will take, this will give you an idea of how this analysis can be used for different kinds of context. And at the end, we will talk about what are the advantages and disadvantages of using net energy and life cycle analysis and how do they compare with the conventional economic analysis. (Refer Slide Time: 4:14) So, let us start with an example. This is an example of different, you know many of, many researchers believe that the future will be with hydrogen and hydrogen is a secondary fuel, secondary energy source. The key thing is terms of using hydrogen in the transport sector would be how do we store the hydrogen. So, there are, what we looked at here is the different kinds of, we can have like you have the CNG compressed natural gas, we can also have compressed hydrogen storage. And this will be at high pressures and then we can also look at liquefying the hydrogens so that there is volume gets reduced and then you have a cryogenic tank and we could also have solid-state storage, metal hydride and there are several people who are working on different kinds of a metal hydride, so we can look at magnesium hydride and FeTi hydride and in this we can for a certain amount of distance which we are riding, what is the amount of energy which is being consumed. And then direct energy required for travel, the energy required to produce and store the hydrogen, the energy required to produce and store the produce the tank and so we get the total energy required for the tank. And you can see some methods of storage have relatively less energy that is required. So, for instance, magnesium hydride seems to be better than FeTi hydride and if one looks at it in the case of the production and storage, in this case, you will find that for cryogenics there is a significant amount of energy required for this storage. The add on materials is so when we look at the total, it turns out that the FeTi hydride has is lower than the magnesium hydride even though the energy reduced to produce the tank is lower. And so that depends on the performance and we can use for an equivalent amount of performance we can compare. And right now, as it looks like the compressed, the compressed hydrogen tank seems to be the, from an energy point of view the best option, of course, there are issues in terms of safety and solid-state storage account better for the safety. (Refer Slide Time: 7:03) In the case of solar thermal power we have done in the energy analysis for both parabolic trough collectors and Fennel reflectors in all of this first what we did is we defined for a particular amount of output which we require, a 50-megawatt plant with a particular amount of output, we defined the different characteristics for a particular location and then calculated the amount of steam and then the solar field requirement and then the field area. (Refer Slide Time: 7:45) And having got that we then calculate it, the dimensions of the modules, module length, module width, number of modules, the oil volume, the piping volume, receiver volume, the vessel dimensions and then we have an embodied energy factor for each of these materials. So, you have the solar field, steel and the glass and the mirrors and then you have the receiver mirror weight, structure weight, the energy used in this and then we got the energy payback period and the energy return on investment. And it turns out that for the parabolic troughs collectors the energy payback period turns out to be higher than that for photovoltaic, but even then, it is of the order of about little less than 4 years which means that it is, it could be viable because the solar parabolic troughs collectors last for 25, 30 years. And so, with the result that even though the economics today of solar thermal does not seem to be it is little costlier than the conventional, from an energy point of view recover your, the energy investment in less than 4 years. And then the remaining part is the advantage and you are going to get, the NER is going to be greater than 1. (Refer Slide Time: 9:24) In the case of buildings one can look at different types of, in a building, there is a significant amount of energy which is used in the operations. And one can look at different kinds of materials if we are using more insulation, we are using phase change materials, the initial embodied energy of the building can be slightly higher but that can reduce the operating energy. And so, if you look at a sustainable building you will find that the embodied energy component as compared to the baseline, the share of the embodied energy is slightly higher but the overall energy gets reduced. And this is another area where there is very significant scope for improvement, we can compare different kinds of materials, we can look at what is the embodied and the operating energy and then calculate this. Because buildings overall are extremely important, 30 to 40% of the total energy used is associated with buildings and if we can design the buildings so that the life cycle energy used is drastically lower then we can use renewables to supply that and we can have a sustainable solution which is distributed. (Refer Slide Time: 10:44) So, now I would like to show you some results that we have done for a situation where we are comparing distributed TV, battery and systems and we want to look at different kinds of batteries which are there and we have done an analysis cradle to gate kind of analysis of the different types of batteries and try to see what it means in terms of embodied energy. So, if you look at the batteries, I just like to show you some of the steps involved and how one goes about this analysis. For more details, you can see the paper which is being written by Jani on this project. So, we can look at for a particular amount of, we were looking at a particular amount of electricity which is being generated and if we look at my weight, if you are looking at 1 kg of a lead-acid battery cell, the manufacturing, the battery assembly has anode, cathode, electrolyte and you can see the number of different materials which are there. For each of these again in the case of lead is a question of how much is purchased and extracted and how much is coming from recycled and that share that fraction affects the overall calculation. Similarly, for aluminium and recycled aluminium. So, these factors can be varied and based on this the numbers will change and you can see all the different component, separator, tubular mass, connectors and the assembly of the battery all of that is put into it. (Refer Slide Time: 12:39) When we look at the overall cell we are PV battery system we are looking at the manufacture and transport of the PVRA, production and transport of the frame and the array support of the solar charge controller, the battery, the invertor and then based on this we get for a particular output we can make this calculation. And this gives us all the different steps in the lifecycle analysis so that we can get the total amount of energy that we are getting in this system. (Refer Slide Time: 13:08) So, if you see this, this is the this is another picture, is schematic of this which talks to, which tells us silicon production, PV cell manufacturing, fabrication of the module then frames, the materials which are there in it. And then we have the batteries and then the installation phase, operating phase and then material recycling and the waste disposal. In this case, we just concentrated on this and we have not added the waste disposal phase. (Refer Slide Time: 13:41) So, this is for the this is the cradle to grave gate. If we wanted to do cradle to grave, we would have also needed to take the decommissioning and recycling and the transportation of this. So, in each of this, there are materials, there is embodied energy in the materials, there is the electricity and the energy used which is there. (Refer Slide Time: 14:03) And just to give you an idea, when we talk about lead or aluminium there are a variety of different sources which give the amount of energy per kg. So, you can see here, the from, this is the what is known as the virgin lead. That means if you are just directly getting from the ore it varies from 22 to 39 different, we view this as 39.1, these are for other context Europe and others we have taken the location of the mine, the kind of ore that we have, the energy used in that and we got the value of this and the details are there in the paper. From scrap again, you can see that there is a reasonable range and of course the point to notice that the energy used from scrap is significantly lower than that in this case. And similarly, in the case of aluminium, in our case aluminium from ore, the energy, embodied energy is lower than the international number that is because of the current, the basis, the based on our production and our efficiency of our manufacturing and then this is from the scrap. (Refer Slide Time: 15:31) Based on this now we get for each of the different batteries, lead-acid battery, lithium-ion, nickel-metal hydride, nickel-cadmium, sodium sulphur, lithium sulphur and we get the material per kg of the material the manufacturing energy, the recycling energy, the transportation and then we get the mega Joules per Watt-hour of the battery capacity. And you can see that there is quite a bit of variation in this, lead-acid of course seems to be low in terms of the embodied energy and that is why lead-acid is quite popular, its initial costs are also low, life is less and they have environmental impacts. (Refer Slide Time: 16:24) So, the PV panel numbers, if you see this is the breakup of the starting from quartz, the metallurgical grade silicon production, and then the solar grate silicon and then and so on. And then coming into the glass and copper, the frame, aluminium and you can see for each of these components, there are different energy inputs which have been calculated and you can find more details in this paper. This gives us finally the kind of values. (Refer Slide Time: 17:05) So, if we look at the different batteries when we talk about the batteries, here you can see the difference in the cycle life, you see lithium-ion has much higher cycle life than the lead-acid and then the other one something in between and the life and the efficiencies, specific energy, the energy rating and of course depending on the battery efficiency for a particular requirement the ratings on the same functional unit and bases you will have different ratings and that is used for calculations. (Refer Slide Time: 17:37) And so essentially this is kind of, so you can see as we said the storage capacity lead-acid is 150, lithium-ion of is little lower 137 less than 140 and then these others are in that kind of range. And you can see this is the basis by which we have done these calculations. (Refer Slide Time: 18:01) Based on this then we have calculated all the different components, the recycled energy, the embodied energy, the cost of manufacture and per unit mass of the battery. If you see this is how it gets calculated, you can see the energy densities and you can see lithium-ion having the higher energy density, sodium sulphur even higher energy density and then this comes out in this form. (Refer Slide Time: 18:32) So, finally, when you look at the numbers this is how the numbers look, we the interesting thing to see is that per kiloWatt of output which we talked of, this is like the CED which we talked of, the cumulative energy demand, what is the energy input per kilo Watt-hour of output. This is not including the solar installation which is there, this is only the amount we are using to make this and you can see that the lead, the lithium-ion turns out to be the lowest energy, embodied energy. And also, we will find that the battery adds a significant amount of embodied energy to the total and based on that what happens is that we can calculate, you can see that in some cases the battery, nickel-cadmium the embodied energy is very very high and of course this also takes into consideration the difference in the lives because this is the final cumulative energy demand. And it gives us an idea of, a comparative idea of this, it shows that you know sodium sulphur, lithium-ion seems to be the options which can result in cost-effective options. Today they are costly but they are from an energy viewpoint they seem to be promising. And then we can also use this as a basis for seeing if you want to change the process of manufacture, can we change the process so that this, the energy input decreases and it becomes more viable. (Refer Slide Time: 20:38) So, you can look at this more details in the paper and when we compare this, now convert it into the NER and of course, we would, higher NER is better. You can see that the lithium-ion NER is of the order of about 7 which includes the PV plus battery plus the power electronics and seems to be better than the NER of the even the lead-acid and but lead-acid seems to better than most of the others. And you can see the payback period is of the order of about 2, little more than 2 years for lead-acid and lithium-ion. This gives you an idea of, you can compare these results with the numbers that we saw earlier from NREL and global numbers, you see there is some variance and that depends on the Indian context as well as the scale at which we make these calculations. (Refer Slide Time: 21:51) We have also calculated then the embodied, carbon of the batteries and then this can be used to look at the CO2 options. When we talked about batteries, most of these, many of these now where you have prototypes, they are commercial. We want to look at an early stage calculation and how the energy analysis can be used to compare different options. (Refer Slide Time 0:34) So, we talked about hydrogen and the only we can think in terms of making hydrogen viable is if we can make it from renewable sources. So, current methods of hydrogen production typically most of it 90 % of hydrogen comes from natural gas from steam methane reforming. One can also coal gasification and electrolysis mostly it is based on fossil fuels which are not sustainable from the overall viewpoint. So, we need to look at hydrogen production from renewable energy sources like wind, solar, biomass. (Refer Slide Time 1:08) And this study we are going to talk to you about is to look at biological methods of hydrogen production. These are still at the laboratory scale, where it can operate at ambient temperatures and pressures. They are expected to be less energy-intensive and they have a variety of feedstocks as carbon sources like sugars, lignocellulosic material, wastewater and there are several reactions, there are substrates and bacteria, so you have the biological feeds stock something like C6H12O6 with water giving you hydrogen, CO2 and then another compound. So, this is the hydrogen we would separate and use. (Refer Slide Time 1:50) And we would like to this you can see this is a slightly old paper, it is in 2008. There is a comparison of biohydrogen production processes. So, what we said is all these processes today are still at the laboratory scale based on what has been done in the laboratories scale and the performance can we assess and see whether these are likely to be viable and how do they compare from energy or a net energy point of view. So, we would like to calculate the NER and see if those NER’s are greater than 1. (Refer Slide Time 2:28) And to do that, so the production at a commercial level not reported, pretreatment methods and hydrogen production depend on the feedstocks, which feedstock is viable which is not, which process is viable, which is not. So, the analysis of different feeds stocks and processes is necessary before we invest in scaling up the process. (Refer Slide Time 2:46) And this is the methodology that we have used. We have shown, we were looking at biomass to hydrogen there are thermochemical methods pyrolysis and gasification larger scale. We are here, we are looking at the biological processes; biophotolysis, dark fermentation, photo fermentation. I am not going to go into the details of the process I am just going to illustrate for you the methodology and some of the results and those who are interested can look at the paper and associated papers and this can be an area where there, still this is an area where there is a scope for doing active research. (Refer Slide Time 3:21) So, we would look at four different processes dark fermentation, photo fermentation, two-stage fermentation, bio catalysed electrolysis. And we will take an input feeds stock sugarcane juice. (Refer Slide Time 3:32) So, the functional unit that we have defined is 1 kg of hydrogen to be produced at 25o C temperature and 1-atmosphere pressure. We compare this with a base case of steam methane reforming with natural gas and we would like to calculate one, two couples of things, one is what is the net energy ratio output by the nonrenewable energy input, the NER should be greater than 1, also what is the kg of CO2 equivalent per kg of hydrogen and then the energy efficiency. We have used the LCA software SimaPro but we can also do this just our calculations. (Refer Slide Time 4:10) And the heat which is being used in the processing we need to produce steam, we used diesel with 90% combustion efficiency. For the electricity, we use the Indian electricity mix and this is the kind of mix and we said that biomass-derived CO2 is 100% carbon closure so zero CO2 impact and we look at natural gas and biogas as well as the residue. (Refer Slide Time 4:39) This is the electricity supply mix that has been assumed in this case. (Refer Slide Time 4:44) There are different kinds of, for steam methane reforming as the base case we use natural gas, coal and these are all the different kinds of inputs which are used for the net energy analysis of hydrogen forms steam methane reforming which is used as a base case for comparison with these options. (Refer Slide Time 5:03) This one was the dark fermentation. In the case of Photo fermentation, we have the sugarcane mill to get bagasse then we get photo fermentation which goes to the anaerobic digester to produce methane and the photo fermentation output is separated using pressure swing absorption so we get hydrogen. In each of these processes, there is some energy input which we quantified. (Refer Slide Time 5:31) In the third process that we have is the two-stage fermentation process where again we have milling and bagasse, we have dark fermentation as well as photo fermentation and then you have anaerobic digester for methane and pressure swing adsorption for hydrogen. (Refer Slide Time 5:47) In the next process is with bio catalysed electrolysis where we have an anode and a cathode and bacteria where you have this, this is where you have the electrolysis and hydrogen is being produced. (Refer Slide Time 6:02) And these are the input data in terms of the electricity used in the sugarcane crushing. And the production in the dark fermentation, photofermentation, methane to CO2 ratio, the recovery in the PSA, the compressor needs electricity input so we have the isothermal efficiency and then we have the loading of the bio catalysed electrolysis, based on this we buildup for each of the process mass and energy balances. (Refer Slide Time 6:42) I am not going to go into details of these and look at the details in the paper and essentially what happens is that for each these the sugarcane input, electricity input, the ammonia, platinum, the outputs which are there and for each of these processes we create the inventories in terms of masses and then we also create energy content. (Refer Slide Time 6:59) And then in the case one, the final results without byproduct, with the byproduct, of course, it much looks better. You can see that in all these cases the CO2 emissions, kg CO2 per kg of hydrogen that we have is significantly lower in all the bio catalysed, in the biohydrogen processes and it turns out that the two-stage process seems to be the best in terms of the CO2 emissions. Similarly, if you look at the nonrenewable energy use photo fermentation and two-stage process look to be similar while bio catalyzed electrolysis uses much more in terms of energy. So, this gives us a way a direction in terms of how to move forward, in terms of processes within the process we can again use it if you can process model and we can again it to make the comparison between making a viable process and making a process which can then go to the next stage where you can do the economics. (Refer Slide Time 8:16) This has been, this is, these are the series of charts which have been used by Ashby which has been proposed by a UK researcher Ashby and this is reported in Allwood et al., you can see essentially the idea is that when we choose materials we often do that based on the particular application we choose from a particular set of materials. And people often historically use a particular set of materials but for some properties, it is possible to have a whole host of materials. So, for instance, if you look at ceramics, metals, polymers and we look at let say the property that we are interested in is a Young’s Modulus. So, you can have for a given Young’s Modulus a whole set of different materials between metals and ceramics and different materials have different amounts embodied energy. Similarly, we can also draw this in terms of embodied CO2 so we can choose a material that uses less energy or less GHG equivalent emissions and this could be a basis for looking at the sustainable design for the future. (Refer Slide Time 9:26) And this is just to illustrate, this is another parameter when we look at the strength and so one can actually create this kind of curves and these can aid the designer in terms of choice of different kinds of materials and we are now in an era where we have nanotechnology and we are creating designer materials. So, this can be even more useful because we can look at materials with a particular capability which has a low energy footprint, low carbon footprint. (Refer Slide Time 10:09) So, with this, I would like to just give you the last example where we are talking of sustainability analysis where we are looking at combining all of this, the LCA, the thermodynamic analysis techno-economic analysis. We would like to screen different kinds of technologies and compare them and see what are the prospects for the future and this can help us in the decision on investments. So, we look at in the case of life cycle assessment these two criteria we will look at, the cumulative energy demand and the carbon emission footprint. And in the thermodynamic analysis, we can look at the energy efficiency, the exergy efficiency. Exergy is the second law of, using the second law where we convert everything into work equivalent which is exergy. And then we can look at the primary energy consumption per kg. We can look at the current cost, future cost and bottom-up cost. So, will take an example this is from a PhD thesis done recently by one of our students where we looked at the possibility of using for zinc which we manufacture currently using an industrial process using fossil fuels, how can we make the zinc manufacture process sustainable. So, we have a whole host of different options where we make it zero carbon and we would like to compare this. (Refer Slide Time 11:31) So, one of the processes that we are looking at is a solar carbothermal reduction where we start with zinc oxide and the carbon source which could be biomass or coal. (Refer Slide Time 11:51) We have this reaction which is essentially zinc oxide plus carbon giving us zinc plus CO and this is a carbothermal reaction which we are carrying out at a high temperature. We generate those temperatures by getting solar thermal concentrated heat and there has been this reactor which has been there for the carbothermal reaction of zinc, 300 kiloWatt reactor, compound parabolic collectors and this has been done in Israel. You can see here that on the ground you have these heliostats which are focusing on to a reactor and this is a beam down reactor which again focuses, this translates it to a mirror and this goes to the reactor which is here and this is getting very high temperatures and you can have, you concentrate it. This is one reactor which has been built and some performance data is available. We took that performance data and try to analyze what does this process mean if we wanted to implement this process to manufacture zinc. How would it look like in terms of the energy and the carbon?