The "photosynthetic efficiency" you describe as being 50% probably refers to the percentage of light absorbed over a small range of wavelengths or something similar; it thus has little to do with the overall percentage of energy extracted from the sun. Otherwise I can't rationalize the figure of 50%. The actual percentage of the sun's incident energy is much lower. Additionally, metabolic processes inherent in creating sugars, hydrogen and oxygen, or whatever else in the cell, use a large fraction of the energy. Plus, the cell has to use lots of energy to maintain its other functions. The most efficient biosystems, in fact, are algal ponds, packed with photosynthetic oragnisms, basically exactly what we're talking about here; again, they use less than 1% of the sun's incident energy towards the synthesis of chemicals. I referred to cycling in the biological systems, because the authors of this paper referred to these organisms requiring periodic sulfur innocuations to perform their hydrogen syntheses.
In the most energetically efficient biosystems, less than 1% of the visible light (and much less than 1% of the total light energy) radiated to the Earth from the sun is converted to chemical energy. This figure is for photosynthesis, which is clearly a more evolved (and therefore efficient) metabolic pathway. If you want figures, look in any introductory Biology textbook. Current solar cells are capable of extracting at least 10% (maybe more, I'm a biologist, not a solar panel designer) of incident solar energy. Plus, the electrical energy they extract can be converted to work at a much higher rate than chemical energy (because work from chemical energy needs to be extracted from a heat engine). While capital costs of solar cells are high, they (unlike biological systems) require virtually no maintenance or cycling. So, what you're looking at is at least a factor of 10 higher cost (probably closer to 100) for extracting energy from biosystems, even assuming the bacteria can be evolved to be extremely efficient at splitting water. Synthetic chemicals are another matter; here, bacteria might occasionally be used for mass production of bulk chemicals, if current enzymatic technology improvse. However, the only current example of commodity (i.e. large scale) chemical bioproduction is the isomerization of sucrose to fructose in the making of high-fructose corn syrup for carbonated beverages. Which is sort of a semi-example, because sucrose is a bioproduct anyway, not a hydrocarbon.
What's really going on here? The energy from sunlight is harvested by the bacteria to split water into hydrogen and oxygen. So, essentially, this is a form of solar energy. Is it realistic to expect this source of solar energy to compete with solar panels, which provide direct electric current, and which do not suffer from the inate energetic inefficiencies (I'm talking metabolic pathways here, not current efficiency levels) of biological processes? I doubt it, especially considering the storage problems of hydrogen. I don't think this discovery will revolutionize the hydrogen industry, much less the world energy industry. It's fun to go nuts over these reports, and dream of a care-free life, but please, let's think about the overall thermodynamics of the situation.
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The "photosynthetic efficiency" you describe as being 50% probably refers to the percentage of light absorbed over a small range of wavelengths or something similar; it thus has little to do with the overall percentage of energy extracted from the sun. Otherwise I can't rationalize the figure of 50%. The actual percentage of the sun's incident energy is much lower. Additionally, metabolic processes inherent in creating sugars, hydrogen and oxygen, or whatever else in the cell, use a large fraction of the energy. Plus, the cell has to use lots of energy to maintain its other functions. The most efficient biosystems, in fact, are algal ponds, packed with photosynthetic oragnisms, basically exactly what we're talking about here; again, they use less than 1% of the sun's incident energy towards the synthesis of chemicals. I referred to cycling in the biological systems, because the authors of this paper referred to these organisms requiring periodic sulfur innocuations to perform their hydrogen syntheses.
In the most energetically efficient biosystems, less than 1% of the visible light (and much less than 1% of the total light energy) radiated to the Earth from the sun is converted to chemical energy. This figure is for photosynthesis, which is clearly a more evolved (and therefore efficient) metabolic pathway. If you want figures, look in any introductory Biology textbook. Current solar cells are capable of extracting at least 10% (maybe more, I'm a biologist, not a solar panel designer) of incident solar energy. Plus, the electrical energy they extract can be converted to work at a much higher rate than chemical energy (because work from chemical energy needs to be extracted from a heat engine). While capital costs of solar cells are high, they (unlike biological systems) require virtually no maintenance or cycling. So, what you're looking at is at least a factor of 10 higher cost (probably closer to 100) for extracting energy from biosystems, even assuming the bacteria can be evolved to be extremely efficient at splitting water. Synthetic chemicals are another matter; here, bacteria might occasionally be used for mass production of bulk chemicals, if current enzymatic technology improvse. However, the only current example of commodity (i.e. large scale) chemical bioproduction is the isomerization of sucrose to fructose in the making of high-fructose corn syrup for carbonated beverages. Which is sort of a semi-example, because sucrose is a bioproduct anyway, not a hydrocarbon.
What's really going on here? The energy from sunlight is harvested by the bacteria to split water into hydrogen and oxygen. So, essentially, this is a form of solar energy. Is it realistic to expect this source of solar energy to compete with solar panels, which provide direct electric current, and which do not suffer from the inate energetic inefficiencies (I'm talking metabolic pathways here, not current efficiency levels) of biological processes? I doubt it, especially considering the storage problems of hydrogen. I don't think this discovery will revolutionize the hydrogen industry, much less the world energy industry. It's fun to go nuts over these reports, and dream of a care-free life, but please, let's think about the overall thermodynamics of the situation.