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Tag Archives: Photosynthesis

Renewability and sustainability are two critical factors that will decide the future course of the world. We have to learn from Nature how sun is able to sustain life on earth for millions of years without the slightest hitch. The sun provides light energy for the photosynthesis to generate Carbohydrate using carbon dioxide from the atmosphere and water. The green pigment in the leaves of the plant ‘Chlorophyll’ catalalyses the photosynthesis. The plant grows and serves as food for animals. After certain period both the plant and animal dies and becomes carbon. New plants and animals are produced and the cycle continues. The dead plant decays and serves as manure for the new plant. A sequence of combinations of atmosphere, photosynthesis, micronutrients in the soil, absorption of carbon dioxide from air and release of Oxygen into the atmosphere, food production, life sustainenace, death and decay play like a symphony in an orchestra. Microorganisms too play their role in this cycle.

It is obvious from the above process that life cycle is based on ‘Renewability’.The  death and decay of the old plant gives way to the birth of new plant and new cycle. There is nothing static .It is a dynamic and cyclic process, where ‘Renewability’ is the key. Only with renewability the process can ‘sustain’. Without a cyclic nature, the process will end abruptly. In fact ‘renewability’ and ‘sustainability’ are closely linked.

When we try to develop a new source of energy it is absolutely critical that such a source is renewable and available directly from Nature. Sun is the prime source of such energy, though it is also available in other forms such as wind, wave, ocean thermal etc. Such renewability can come only from Nature because human life in intricately linked with Nature such as earth, sun and wind. Everything that happens in Nature is to support life on earth and not to destroy. This is a fundamental issue.

When we dig out Carbon from the earth  that was deeply buried by Nature and burn them, we release Carbon dioxide as well as Oxide of Nirtogen.Though our primary interest is only heat, we also create by-products such as greenhouse gases that upset the natural equilibrium. Nature can make some adjustments in order to maintain equilibrium; but when this limit exceeds, the equilibrium is upset creating a new environment, which may be alien to human life. This is unsustainable. Nature does not burn organic matter indiscriminately to generate Carbon dioxide to promote photosynthesis. It judiciously and delicately uses atmospheric Carbon dioxide without the slightest disturbance to the equilibrium. Many chemical reactions are irreversible and can cause irreversible damages, similar to ‘radiation’ from a nuclear reaction.

Whatever we do in the name of science, we will have to face their consequences, if we fail to understand the process of Nature completely and thoroughly. Fossil fuel sources are limited and burning them away to meet our energy demands is neither prudent nor sustainable. Human greed has no limit. We live in a finite world with finite resources and there is no place for infinite greed and destruction. There is no solution in Science for human greed.

 

One of the wonders of Mother Nature is her ability to sustain life on earth with sun light, water and Carbon dioxide from the atmosphere producing food. No toxic chemicals, no polluting gas emissions and no noise. We can only admire the majesty and power of Nature with our  fragile knowledge of science and try to duplicate Nature to satisfy our growing energy needs. Nature produces Carbohydrates C6H12O6 using sun’s light, Carbon dioxide from atmosphere and water by a chemical reaction as shown below:

6H2O + 6 CO2  ———–   C6H12O6 + 6O2

The same Carbon dioxide from the atmosphere is now threatening the globe with warming. Can’t we grow more trees so that all the carbon dioxide emissions from our power plants and cars can be converted into more carbohydrates? It sounds very simple and logical but is it feasible? The carbon dioxide in the atmosphere before industrialization was about 280ppm but it has now increased to 392ppm which is almost double. It has grown roughly 2.2% exponentially in the last decade. It is the highest in the past 800 years and likely higher than in the past 20 million years. (Ref: Wikipedia). Couple of things happened during this period. The industrial and population growth increased rapidly building up carbon dioxide level in the atmosphere and at the same time displacing tropical and rain forests with people and industries; it resulted in the buildup of greenhouse gases to a level, which scientists say are unsustainable. We don’t have enough forest to absorb so much of carbon dioxide.

Alternatively, scientists are now trying to interfere with Nature’s photosynthesis process using micro algae called chlamydomonas reinhardtii that will support the production of Hydrogen instead of Oxygen in a normal photosynthesis reaction. This was based on the discovery that if an algae growing culture medium is deprived of Sulfur, it will generate Hydrogen instead of Oxygen. They also found out that such an algae can thrive in a Carbon source such as Carbon dioxide or even in  Acetic acid medium. They tested the process using a pilot Photo bioreactor and concluded that the cost of producing Hydrogen by this route will be about $ 42/kg.The cost is high compared to the target cost of Hydrogen by DEO  (Department of Energy,USA) at $2.80/kg which is fifteen times lower. However scientists are still working to cut the cost.

Meanwhile scientists are also working on Hydrogen production using Photoelectrolysis.The water electrolysis using Direct current is a known process but the cost of energy in this process is still high. The high cost is due to several stages involved. In the first stage, one has to generate power using PV cells. In the second stage the PV generated electricity will be used to split water electrolyticlly.But scientists are now trying to substitute both the above steps with a single step of utilizing direct sun light to split water into Hydrogen and Oxygen.Thie requires a catalyst known as Photocatalyst which will use light energy instead of electrical energy to split water into elements. Using TIO2 (Titanium dioxide coated electrode) and ultraviolet rays of the sun they believe that a 20m2 PV solar panel can generate about 5m3 of Hydrogen ad 2.5m3 of Oxygen in 24 hours, equal to a power generation capacity of 15kwhrs or roughly about  2.01 gallons of Gasoline from 4 liters of pure water.

Scientists are now  hoping that light energy, more precisely ultraviolet rays from the sun will come to the rescue of human beings in solving one of the greatest  energy crisis  in the history of mankind. At last we can hope to see some ‘light’ at the end of the tunnel.

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