Hartmut Michel (2012) - Photosynthesis, Biomass, Biofuels: Conversion Efficiencies and Consequences

Thank you very much for giving me the opportunity and, of course, you're all aware that we had 2 very controversial talks. And I also would like to make one or the other comment on the controversies. I work actually at the Max Planck Institute of Biophysics. And our institute works on membrane proteins. And membrane proteins is a point which is catalysed by, photosynthesis catalysed membrane proteins, mainly. And so it’s made up in photosynthesis. Importance of membrane proteins is seen here, there’s a text book figure, everything you see is membranes. And there are many important roles of the proteins in it. And for instance the catalyse transfer flow of, transport of substances across membranes are involved in biological electron transfer, that’s mainly for the synthesis in cellular respiration. And also signal receptors. Very important for medicine and also some membrane proteins are enzymes, preferentially for hydrophobic substrates. So primarily what we work at the present is respiration but the whole thing is too complicated. So I deal with easier things and give you more or less synthesis. You have seen already that the controversial discussion and so I will not rely on and go into that. And you also see that carbon dioxide concentration has increased and I think the warming as well as the increase in carbon dioxide concentrations are facts and cannot be disputed. I also should say it’s my personal experience in more than 60 years of life that it got warmer. I used to be a gardener as a child, taking care of the garden of my father, now I’m taking care of my own garden. I know when the first temperature below zero degrees used to be that was 15th of October and when you waited over 15th of October, when you waited until you had ice in your barrels, this happened in middle of November. But nowadays you have the first frost much later. And you don’t get ice before December in your barrels. So my personal experience tells me that there is some warming, but its local warming, not a global warming. But from that I am convinced that warming exists. We also have seen this temperature and Co2 concentration in the Vostok ice cores in the Antarctica, that’s the correlation. But it's true as the previous speaker said that actually it is the temperature rise. The temperature is before the rise in Co2 concentration. And this is, I would think it’s a problem for the climatologists. And the reason for that is that, the reason for this, I come to that later. And temperature rise precedes the rise in carbon dioxide concentration. That cannot be disputed. And the reason is that the temperature rise stimulates the activity of the biomass degrading aerobic bacteria. And this leads to carbon dioxide production more than it helps to increase the photosynthetic carbon dioxide fixation. That is truly a fact. Of course, this correlation and the increase of carbon dioxide concentration by fossil fuel as well as theoretical consideration led to the assumption that the increase in carbon dioxide and other green house gases, mainly methane, of course apart from water, causes the observed temperature rise which I do not dispute. The evidence that global warming is caused by green house gases is calculations, simulations and this is based on the infrared radiation transfer theory. And a person becoming very popular in that work field was Svante Arrhenius. His work was in 1896. He got a Nobel Prize in 1903. And for me the best evidence that green house gases actually cause global warming is the cooling of the troposphere which none of the previous speakers mentioned. There is a higher part of the atmosphere that is cooling down and this can be easily explained. It receives less infrared radiation from the surface on the earth. So this would be... For me this is the best piece of evidence that there is indeed global warming. But that’s the only piece of experiential evidence which I accept. What I really miss is, apart from the calculations, from the simulation, is that somebody fills a very long tube, evacuated with mirrors, puts in a source of infrared radiation and measures at the end how much infrared radiation comes up at the end. And if you come up then with a 2 watt per square meters, I would be completely happy. But I’m wondering why nobody does this pretty simple experiment. Now to...the major point is: Fossil fuels -that’s coal, petroleum, natural gas- are derived from photosynthesis. And in photosynthesis plants fix carbon dioxide from the atmospheres. And the question now is: Can plants be used to produce bio fuels and to solve the energy problem of mankind and reduce thus also global warming? Start off with a leaf, that's the primary site of photosynthesis. Of land plants and I start up with some few basic facts. Photosynthesis is mainly composed of 2 classes of reactions, one are the light reactions. That is: the absorption of light leads to the creation of chemical energy. That is redox energy. You can also call it also fixed hydrogen. And you release oxygen as a side product. So it was a waste product and this was the biggest change in the world was the invention of the oxygenic photosynthesis. And this was a catastrophe in earth and more than 90% of all organisms died when this was invented by nature about 3 billion years ago. Dark reactions, you have the redox energy there and you use that to take out the carbon dioxide from the air and convert it and fix it as sugar. So that’s a picture of that. You have the light reaction, water comes in, you release oxygen, you produce ATP, the universal energy currency in biology. And you produce NADPH and the other products are the oxidised substrate and the hydrolysed ATP. Then you come to the Kelvin cycle, there you fix carbon dioxide and the result of that will be the sugar. The absorption of light occurs by chlorophylls and by carotenoids. The chlorophylls are here the green molecules and the carotenes are the yellow molecules and they are light harvesting antennae. And then, as the next step is the transfer of the energy of the absorbed photon in a radiationless process to the photosynthetic reaction centre. There the charge separation takes place and you get a transport of electrons across a photosynthetic membrane. You reduce the electron receptor and you create an electric voltage across the membrane. That’s the machinery. We determined that structure in 1986 and that was, the result was the Nobel Prize in 1988. So here you have the primary electron donor that gets excited and you get transfer of an electron across the membrane. People now have learned to do the same work with plant systems. And you see here, this is a picture of the photo system 1 of the green plant, it’s very complicated. There are 100’s of chlorophylls, molecules, many, many proteins but we can determine the structure. We can find out the position of each non hydrogen atom in that huge complexes. Which is really I think a remarkable achievement. The electron flow in the photosynthetic membranes of chloroplasts and also cyanobacteria is seen here. You have in the plant and in cyanobacteria, you have first photo system 2. Photo system 2 is where the water splitting occurs with the release of the oxygen. You get a transfer of the electrons across the membrane. And there the electron moves on to another complex. Then you’re going to a PC1 complex where you transfer the electrons back across the membrane. You produce another molecule, called plastocyanin, this donates electrons to the photo system 1. Then the electrons are transferred here to another, to ferredoxins and at the end you reduce NADPH, which is a co-enzyme. So this is what happens in the light reaction. In addition the gradients formed across the photosynthetic membranes drive the synthesis of ATP here. And that’s a rotatory engine and the rotation here leads to the synthesis of ATP. So this is what happens in the basic steps of the light reaction. The conversion of the sun light in photosynthesis is considered to be very high with a really effective quantum yield. But one has to say that less than half of the sun light which reaches the earth is photosynthetically active. So it’s only the wavelength from 400 to 700 nanometres which can be used by the land plants. And quantum yield is high as I said but this means that each photon absorbed leads to electron transfer across the photosynthetic membrane. This does not mean that the energy yield is high. If we look at this schematic drawing with respect to energy, then we saw as I said with photo system 2 and went up with NADPH and that’s an energy scale. And most of the light energy is lost in the primary light reaction already. Theoretically you need 8 photons to rise the energy for electrons by 1.2 electron volts. That’s a difference here between the water and the NADPH up here. And this means that only between 19 and 33% of the energy of the absorbed photons are stored in the form of NADPH. So already most of the energy is lost in the photosynthetic electron flow here. And experimentally you always find and you need about 9.4 -the 8 is theory and the reality is 9.4- in order to reduce 2 molecules of NADP to NADPH. And if we consider that only 47% related to energy of the sun light are photosynthetically active you have to conclude that 11.9% must be the absolute maximal efficiency of photosynthetic light energy conversion of plants. This value is reduced substantially further by inhibition of photosynthesis as high light intensities, damage at high light intensities and the inefficiency of carbon dioxide fixation. Let me start off with the inhibition of photosynthesis at high light intensities. And this shows you here the Co2 fixation. The dependence of the strength of the sun light. And you see here that already at this rather low value here of about 200 you reach saturation. And the full sun light is about at the value of 1,600. So it would be well to the right of the scale. And this means that at 20% of the full sun light is the maximum already reached and 80% of the energy of sun light is not used by the land plants, of the full sun light. We have further losses of energy caused by photo inhibition, by photo damage at high light intensities, by photo respiration. That’s a process in which oxygen is used by the enzyme ribulose-1,5-bicarboxilase instead of carbon dioxide in Co2 fixation. The wrong product has to be removed by respiration and by other metabolic processes. At the end the theoretical limit for the efficiency of photosynthesis is around 4.5%. That’s the theoretical upper limit. But in reality it’s less than 1% of the sunlight energy which is stored in the form of biomass. And in particular I didn’t mention much about the photo damage and actually the plant is able to repair the photo system once every 20 minutes. So the plants repair their system 3 times an hour. And I don’t think that we can do that in a technological process. Now let’s start with some examples, we have here. Let’s start with biogas, that's produced by archaea, methanogenic micro organism. Biomass, contains 60% methane. The rest is mainly carbon dioxide but there’s also some danger in it because you produce hydrogen sulphide which caused some fatal accidents already. And this is how you can operate, you have the cows. You produce some products apart from milk. And this goes into the fermenter, you add mainly green stuff, mainly maize, leaves from the corn. Add this to the fermentation. And you get heat, you can use... the farmer can use this for heating the house. And you produce biogas and the biogas, the methane there is... drives a gas engine in a generator and you produce electricity. And you can use of course a residual stuff here as a fertiliser on the field. You can simply calculate, look up in the tables and you get about 4,600 cubic metres of methane per hectare. The energy yield is about 46,000 kilowatt hours. And this would convert to about 17,000 kilowatt hours electro energy or about 1.7 kilowatt hours per square metre and year resulting in 0.2 watt per square metre on a continues basis averaged over the year. And if you look about the distribution of the average energy of the sun light reaching the earth that you see here. We are now here in Constance, that would be about 150, we are in Lindau, not in Constance, we are at the Lake of Constance, we are in Lindau. So we are here. And in the Sahara you get about 315 watts per square metre so it’s only a difference of about 223 in the sun light energy between Sahara and Germany. If we use that energy here in Lindau, if we compare that, then we would only convert 0.2 watts into electric energy. That is about 0.13% of the sun light energy comes into the electric energy via biogas. So that’s a highly inefficient usage of land. And we have not considered with that value that we have to put in about 40% of the energy by using fertiliser, by tractor fuel to produce the biogas. So the real value here is below 0.1% if we go via biogas to produce electricity. And if we ask eventually could we produce Germany’s energy amount by that. And then we come up with a calculation that we would require 720,000 square kilometres. When we consider also the energy input by the energy, the entire area of Germany is about 350,000 square kilometres only. The agricultural area including meadows is about 170,000 square kilometres. So we cannot do that within Germany to save our energy crisis by biogas. Let’s go on with bio ethanol. In Europe it comes from sugar beet or wheat. And in the US it comes from corn. And the ethanol produced per hectare has energy content slightly higher than the biogas from the maize field. But 80 to 88% of the energy of the bio fuel has to be invested into the growth of the plants, harvest and into the concentration of the alcohol, the ethanol to 99.5% by distillation and other chemical processes. And if the energy for concentrating the alcohol comes from coal, then there is an increase of carbon dioxide emission, about 30% compared to the direct usage of fossil fuels. If natural gas, methane, is used as an energy resource, then there is a reduction of carbon dioxide emission by about 35%. And there is no effect when petrol is used for providing the energy as an input. So it depends on the energy input. And sugar cane in Brazil is very popular and there it’s competitive and saves carbon dioxide because it’s the only, it’s only cut for harvest, it’s re-grown, you don’t need to plough the field and to plant freshly. The squeezed stems are dried and burned for distillation. And the energy input there is about 1/9 of the energy contents of the ethanol. But when you compare the energy of the sun light and the bio ethanol that you get, it's still less than 0.2% of the energy of the sun light which has fallen on the sugar cane plantation. Also this is a pretty inefficient process. My vision for the whole thing is that we have to, for increasing the yield of biomass in general, improve carbon dioxide fixing enzyme RuBisCo, Ribulose-1,5-bisphosphate carboxylase, by genetic engineering and selection techniques. And I think it might be possible to increase the efficiency of carbon dioxide fixation and therefore the overall yield of photosynthesis by 50 to 100%. One can try to expand the wavelength range used by plants, by introducing light arresting system which absorbs also UV light and more to the infrared light and also the green light. But if you do that, then your leaves will be black. And you can consider walking in a black forest and the meadows will be black. The grass will be black. How would you like that? Another point is one could try to reduce the photo inhibition at high light intensities. I said that already, at 20% of the full sun light photosynthetic apparatus is saturated. And this is potentially possible when you reduce the size and number of the light harvesting complexes. So that less energy from the light harvesting complexes is transferred to 1 reaction centre. Another crucial point is that the water availability will be crucial. Water is a limiting factor in photosynthesis of the plants. And actually there are reports that you need about 60,000 litres of water to produce 1 litre of German bio diesel. People are then also talking about the next generation of bio fuel. That is a process called biomass to liquid, BtL. Because conventional present day techniques like bio ethanol production from sugar cane or sugar beets or bio diesel use only rape seeds or use only parts of the plants. A future BtL production uses the whole plant which is gasified or converted enzymatically to be used to produce the biogas and less land is required to get the same amount of fuel. And the Fischer-Tropsch process is used for synthesis, called the FT diesel or sun diesel. And the raw material has to be dry, it would be wood or straw and other kind of biomass. And the claim is that you can get about 1 litre of this bio diesel from 4 kilograms of wood. And it was estimated that about 1 hectare provides 3,000 to 4,000 kilogram of FT diesel per year. But I have to say this is not a fair value here because the people don’t tell you that you have to add hydrogen in order to get a high yield in the synthesis process of the diesel. But the hydrogen comes from fossil fuels, is made from fossil fuels, from methane or from petrol. So you need... In this process also you have to put in fossil fuel. But also more recent estimates, there was a study sponsored by the European Union and they ended up with values of 890 to 2,300 kilograms per hectare, so much less than was the original claim. Poplar would be a pretty good source for wood because it has a pretty high efficient photosynthesis rate and it produces about 1% of biomass from the sun light’s energy. Similar this kind of grass, miscanthus, does in a similar way and you wouldn’t have to seed it every year. So that’s a good source for biomass. And if we assume that about 3,000 litres of this FT diesel per hectare can be produced but we have to consider also the input of external energy for its production. Then we would require the entire area of Germany to grow either poplar or the miscanthus in order to supply the present consumption of gasoline and diesel for cars and trucks in Germany. So that is not a viable way to get the fuel for our cars and engines. Another point which comes up is bio diesel from the oil palm. And from the palm plant here, the point is, the yield is pretty good, about 5,000 to 6,000 litres per hectare. But the point is, the forests are cleared primarily in South-East Asia, in Malaysia, Borneo, Sumatra are the most terrible examples. And the palm oil is exported to Europe and it even receives subsidies because it’s considered to be renewable energy. But with that actually we do a very bad job because the tropical rain forest in South-East Asia, they grow on peat. And the underlying organic material on the soil here is oxidised when you remove the forest. Its oxidised by yeast and bacteria and it takes about 430 years until you get a compensation of this carbon dioxide released by the bio diesel saving. And in my opinion we should stop to produce bio diesel in the tropics from the oil palm. And we should not allow the import of palm oil derived bio fuels in Europe. I also think that the result of the climate will be very negative because it is much, much drier than the original forest. And on the other hand we kill our eco systems. We kill many species and our natural resources which may have many, many unknown compounds which could be used in medicine to treat one or the other disease. And to reduce the carbon dioxide release it would be much better to grow poplars on the land used for bio fuel production. And to convert the bio mass to coal by a process called hydrothermal carbonisation. And you have to heat the biomass in water to about 160 degrees and this would actually save 207 kilograms carbon dioxide per hectare. Whereas when you produce bio fuels you save about 0.3 kilograms per square metres. So not producing bio fuels and instead reforesting the land saves you 10 times more carbon dioxide than the actual bio fuel production. This is why I think one of the most stupid things is bio fuel production. And I think the major reason why it is so popular is because there is subsidies for farmers. Particularly in Europe and there’s lots of lobbyism in parliament, to governments and that's why we have now also... we have 10% ethanol, bio ethanol in some kind of our super gasoline and diesel has to have 7% of bio diesel in it and with that actually we kill our environment. If we now compare the systems and we go to efficiency of commercially available photovoltaic cells, then here we have a yield of about 15 to 20% in electric energy compared to the sun light energy. And also you have seen such things as this thermal power plant where you have reflectors focusing the sun light onto absorber tubes. You can heat the liquid up to 400 degree and then you can produce electricity in a classical process via steam. And this is considered also to be very effective and you could produce energy also during night when no sun is shining in contrast to the photovoltaic cells. And the space requirements for solar cells providing all electric energy for the world is listed here. For Europe or for Germany, Germany would be a square of 50 times, 60 kilometres only of the Sahara would be sufficient to produce the energy, electric energy for Germany. My vision there is if we would be able to transport electric energy without losses by super conducting electricity cables then we would require 3 to 4 big photovoltaic fields, maybe one in north Africa or one also maybe in South Africa, Kalahari, one in China, one in Australia, one in Mexico. And if these cables would span the globe then we could have continuous energy all over the world, we wouldn’t need, there would be no need to store energy because the sun is shining somewhere at each hour. But even now without super conducting cables we can transport electric energy from the Sahara to central Europe with high voltage direct current cables and this is what is planned in the Desertec. But on the other hand the yield also in Germany is pretty good. And probably we don’t need that. Coming to the alternative to bio fuels and we have that car and this car is electric car and it uses 80% of the energy stored in the electric batteries for propulsion. So 80% of the energy in the electric battery is used for driving the wheels. If we see, have a look at this car with a combustion engine and then only 20% of the energy of the gasoline is used for driving the wheels. So there is an advantage of a factor of 4 of the electric system over the bio fuel system. So if we take that into account and we consider that bio fuel contains less than 0.2% of the energy of the sun light. And we can easily calculate that the combination of photovoltaic cells, electric battery, electric motor, uses the energy of sun light at least by a factor of 400 better than the combination biomass, bio fuel combustion engine. Clearly we need more powerful batteries and I don’t think that is... To get that is realistic and they are in the lab, in the development, they are tin-lithium-sulphur batteries and they store 10 times more energy than the present lithium batteries. Present day lithium batteries are the technology of 1995. The technology has improved and we, I think we will be able to drive our cars with the same range as by gasoline cars in the future. So with that I’m going to come to the end and summarise. And production of bio fuels from various kinds of biomass is a very inefficient land use. And we have to put too much fossil energy into the production of the biomass, into conversion into bio fuel. And the direct usage of biomass for heating or electricity conversion in power plants, replacing bio fuels is more efficient by a factor of 2 or 3 with respect to carbon dioxide fixation than the bio fuel production. Solar energy can and will be used to generate electricity either by solar thermal power plants or by photovoltaic cells. And cars have to be driven by electric batteries, electric motors. But I think with jets we have a problem, for that we cannot use. For our jet traffic in the air we’ll still need kerosene. But I think this can be solved. With that I want to come to the end and thank you for your attention. Applause.

Hartmut Michel (2012)

Photosynthesis, Biomass, Biofuels: Conversion Efficiencies and Consequences

Hartmut Michel (2012)

Photosynthesis, Biomass, Biofuels: Conversion Efficiencies and Consequences

Abstract

Photosynthesis, Biomass, Biofuels: Conversion Efficiencies and Consequences

Hartmut Michel
Max Planck Institute of Biophysics,
Max-von-Laue-Str. 3,
D-60438 Frankfurt am Main, Germany

It is generally accepted that the global warming which we undoubtedly observe, is the result of an increased concentration of greenhouse gases like carbon dioxide and methane in the atmosphere. Within this scenario it is evident that we have to reduce the emissions of carbon dioxide in order to stop or to decrease global warming. It will be necessary to switch from energy mainly based on fossil energy with petrol, coal and natural gas as energy carriers to renewable energy. One big hope is the usage of biofuels like bioethanol, biodiesel, sundiesel, biogas and so on. Biofuels are obtained from biomass, and as such derived from the photosynthetic activity of recent years, whereas all fossil fuels are the result of the photosynthesis millions of years ago.
In photosynthesis plants and algae use the energy of sunlight to take out carbon dioxide from the atmosphere and to synthesize sugars and other forms of biomass. The lecture will focus on the efficiencies of the individual steps in photosynthesis and discuss potential ways to improve their yield. The overall efficiency of photosynthesis is very low: less than one percent of the energy of sunlight is stored in the form of biomass, and there is not much hope for a substantial improvement. Biogas and biodiesel per area unit and year contain about 0.4 % of the energy of the sunlight which the area unit has received in the same period. In addition at least 50 % of the energy which of biogas or of biodiesel had to be invested from conventional (fossil) energy sources to produce the biogas or biodiesel. Therefore, production and usage of biogas or biodiesel is not carbon dioxide neutral. By comparison, usage of photovoltaic cells is more efficient by a factor of 50 to 100 with respect to energy conversion, and electric engines are fourfold as efficient as combustion engines. Consequently driving a car using electric batteries, loaded by photovoltaic cells, and electric engines requires only 0.2 % of the land that would be required when driving a car with a combustion engines using biodiesel. Growing energy plants and biofuel production therefore is a very inefficient way of land use. The usage of biofuels made of palm oil or soy beans from tropical countries will enhance deforestation, lead to a loss of the tropical rain forest and increase climatic changes. In addition we shall lose biodiversity and many biological compounds which might help fighting human diseases. Most importantly, need the land to feed an increasing population.

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