The worldwide energy crisis

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We all seem to be aware of the economic credit crunch but how many people really understand the world wide energy crunch and the importance of solving this problem. The ongoing use of natural gas and crude oil over the past hundreds of years has resulted in much destruction to the environment. The use of energy between 1970 and 2001 has increased twice as much [1] resulting in increased atmospheric levels of carbon dioxide and this has led to global warming. Global warming is when greenhouse gases, such as carbon dioxide capture heat and light in the atmosphere hence causing temperature changes. The world is dependant upon fossil fuels for energy which are rapidly depleting and so utilising renewable sources of energy, such as solar energy to generate biohydrogen which is a biofuel, is a guaranteed potentiality of producing hydrogen in a sustained manner. Biofules are biodegradeable so provide various advantages to the environment and they are readily accessible from biomass [2]. In time, solar energy will be able to be used to produce biohydrogen effectively with the help of the following approaches; photosynthesis and the generation of hydrogen via biological systems. Hydrogen holds the greatest amount of energy in comparison to other fuels in a gaseous state and it generates water as a result of combustion therefore, hydrogen is the 'fuel of the future' [3]. This is where biohydrogen production technologies using solar power energy prove to be valuable as it has been predicted that consumption of energy will increase to three times as much by 2025 [1].

The problem with fossil fuels

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Information obtained recently indicate that the burning of fossil fuels has resulted in carbon dioxide levels of the atmosphere increasing to 370 ppm [1] and more seriously, a level of 550 ppm [1] will lead to an approximate increase of five metres [1] in sea level. Additionally, it will cause the elimination of over twenty percent [1] of vegetation and mammals. Therefore, it is vital that the level of carbon dioxide is kept constant at 450 ppm [1], if not lower. To do this, a non carbon dioxide emitting fuel available in plentiful supply is required without delay. Furthermore, thirteen years ago, a figure of almost twenty four billion tonnes [4] was recorded as the product of carbon dioxide and this was the result from burning fossil fuels. It has been predicted that the continual burning of fossil fuels will result in an elevation to the worldwide temperature by an average of 2.2 degrees celsius in the next one hundred years [4]. The global energy demand of the world is approximately thirteen TW per year [1] and this is set to increase to around three times as much by 2100 [1]. However, it must be noted that the predicted values for the effects of global warming could be over estimated.

More importantly, there will be no fossil fuels left by 2100 and so substitute energy sources are essential. Solar energy can be used as a substitute for fossil fuels because it is readily available and in plentiful supply. In addition, the sun is extremely powerful and an adequate amount of the sun's energy reaches Earth each minute and supplies enough energy that would be capable of providing the global energy demand but we need to be able to utilise it efficiently. There are many advantages to solar energy including, it is a clean source of energy and it is not diminishing. In comparison to other renewable sources of energy, such as wind, geothermal or even tidal power; solar energy is available to various types of technologies without difficulty, involving both low and high technology systems [1].

What is photosynthesis?

Photosynthesis is the conversion of sun light into chemical energy and is a crucial biological procedure that occurs here on Earth. It is the physical foundation of both our food and energy resources. Photosynthesis has enabled the development of potential technologies to seize solar energy and convert it into chemical energy; this is why photosynthesis is at an advantage in comparison to various other solar technologies. Photosynthesis has allowed the advancement of prospective systems to seize solar energy and modify it into chemical energy however, Kruse, et al., (2005) think 'photosynthesis is an undervalued blueprint for future solar energy capture and conversion technologies'. I believe it is crucial that the principles of photosynthesis are understood better in order to enhance the transformation of solar energy.

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In addition, photosynthesis is unable to take place without the existence of chlorophyll and this reaction occurs in two phases [5]. The initial phase is the light dependant reactions of photosynthesis and it includes reactions which create the electron transport chain when combined and which generate ATP and also NADPH [6]. Next, the ATP and NADPH produced are utilised to transform carbon dioxide into carbohydrates [6] and are reserved for later use, this phase is also known as the dark reactions of photosynthesis. Moreover, antenna light harvesting proteins are also known as antenna pigments and they are found in the chloroplast of plants within photosystem I and II but also in photosynthetic bacteria such as cyanobacteria. They are responsible for seizing the light required for photosynthesis to occur. There is a vast array of antenna pigments and this is because they absorb light at different wavelengths, they include chlorophyll a and chlorophyll b.

Additionally, a photosystem is a structure which consists of chlorophyll as well as various pigments gathered together in the thylakoids. Photosystem I and II induce the electron transport chain and this occurs within the chloroplast's thylakoid membrane [1]. Photosystem's I and II consist of antenna systems which I have previously mentioned as containing light harvesting complex proteins and these seize the light [1]. This light energy is then transported to the photosystem II primary donor in photosystem II and to the photosystem I primary donor in photosystem I [5]. When photosystem II absorbs one photon of light, this causes the eradication of an electron from the photosystem II primary donor [6]. The consequent positive charge causes the photosystem II primary donor to eradicate an electron from a water molecule [1].

Next, photosystem II releases hydrogen ions which stimulates the generation of ATP. Electrons are transported to the cytochrome b6/f complex which transports electrons amid the two photosystem's and is involved in creating the proton gradient [7]. Stimulation of the photosystem I primary donor causes it to collect the electrons from the complex and increase them to a position with a greater redox potential so that following their progression through ferredoxin which transfers electrons, they are able to cause the reduction of NADP+ [8]. Finally, the generated ATP and NADPH are utilised for the reduction of carbon dioxide into glucose and this is why they are crucial compounds produced during the light reactions of photosynthesis. This phase is independent of light and is also known as the Calvin cycle, additionally, it takes place in the chloroplast's stroma. The process is as follows; two molecules of glycerate-3-phosphate are produced when carbon dioxide reacts with ribulose 1,5-bisphosphate [9] in the stroma. The conversion of glycerate-3-phosphate into two triose phosphates [9] is carried out by ATP and NADPH. Lastly, the conversion of the triose phosphates into glucose occurs with the help of fructose bisphosphate and fructose-6-phosphate [9].

Photosynthesis does not produce hydrogen and without a doubt for biohydrogen energy to be generated, hydrogen needs to be produced therefore, cyanobacteria and microalgae can be used because they are able to carry out oxygenic photosynthesis. In photosynthesis, solar energy is converted into biochemical energy and carbon dioxide is reduced to carbohydrates however; microalgae and cyanobacteria consist of enzymes which utilise the energy to generate hydrogen rather than causing the reduction of carbon dioxide.

Approaches and problems for biohydrogen production technologies using solar power energy

There are locations of the world which receive a lower intensity of luminescence from the sun yet this is still an adequate amount to make biohydrogen production technologies using solar power energy highly beneficial. However, to utilise solar energy there needs to be more efficient solar energy technologies developed at a lower cost which have an advanced photon conversion [1] capability but are also able to transform the solar energy into hydrogen. With these advantages come disadvantages which include the high price of setting up great scale technologies and these expenses are much greater than utilising fossil fuels. Solar energy is expensive hence why it is not used enough but if low cost, highly effectual solar energy systems were produced then demand would increase. In my opinion, as fossil fuel resources diminish further, their price will increase and there will be a large investment made which will lead to a decrease in the cost of solar energy systems and a rise in their effectiveness.

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However, a number of microorganisms, such as microalgae and cyanobacteria are able to generate hydrogen naturally from water using sunlight. These biological procedures utilise nitrogenase and hydrogenase enzymes, which control the metabolism of hydrogen. The presence of an enzyme which produces hydrogen is crucial [18] for biohydrogen production technologies using solar power energy. Nitrogenase generates hydrogen as a result of nitrogen fixation and hydrogenase is the enzyme of major importance in the metabolism of hydrogen [11]. It acts as a catalyst in the oxidation of hydrogen. The procedures of generating hydrogen using sunlight consist of light dependant mechanisms which include direct biophotolysis and indirect biophotolysis. Biophotolysis is the breakdown of water by light and occurs in both microalgae and cyanobacteria [3]. Direct biophotolysis involves green algae whilst indirect biophotolysis involves cyanobacteria. These photosynthetic organisms are capable of transforming light energy from reactants into hydrogen. Biophotolysis of water using algae and cyanobacteria produces hydrogen. When there is sunlight, cyanobacteria breakdown water and produce hydrogen and oxygen by photosynthesis [2]. However, they are unable to generate great amounts of hydrogen. The challenge is to raise the amount of hydrogen generated to approximately 85% [3]. In continuance, direct biophotolysis and indirect biophotolysis have their advantages; direct biophotolysis is able to generate hydrogen from light and water; additionally, indirect biophotolysis can also generate hydrogen from water but is capable of fixing nitrogen [3] aswel.

Cyanobacteria are photosynthetic bacteria that consist of photosynthetic pigments, such as carotenoids [19] and they utilise nitrogenase and hydrogenase to produce hydrogen. When they are in a nitrogen limiting environment, nitrogenase can be located in the heterocysts [12] and when nitrogen is fixed into ammonia using ATP, hydrogen is generated as a result. Nitrogenase includes dinitrogenase and dinitrogenase reductase [12] moreover, nitrogenase consists of different forms of dinitrogenase and dinitrogenase reductase brings about the movement of electrons from the ferredoxin to the dinitrogenase [12]. On the other hand, hydrogenases appear as two forms [12], one form oxidises hydrogen and the second form is reversible hydrogenase or bidirectional hydrogenase and it is able to generate hydrogen [12]. Nitrogenase and hydrogenase are very sensitive to oxygen so carry out their actions in an anaerobic environment as oxygen inhibits these enzymes. There needs to be a development of more ways to remove oxygen in order to result in greater yields of hydrogen. For a great generation of hydrogen, photobioreactors are crucial [12]. Photobioreactors need to receive enough sun light as cyanobacteria require sun light to grow, hence for biohydrogen production. Photobioreactors are confined to prevent any generated hydrogen from escaping. There needs to be an increase in the rate of growth of cyanobacteria and the amount of hydrogen generated. This can be achieved by improving the design of the photobioreactor so that there is a greater amount of light falling on to the surface. With these improvements, biohydrogen will become a competitor amongst the other approaches to production. There are also limitations to studying cyanobacteria because they form toxins which target important procedures in cells hence influence many organisms.

Furthermore, green algae are the focus of research targeted at the development of technology systems for the generation of hydrogen. Green algae are highly efficient at transforming light into chemical energy [16]. Also, they are committed to producing a renewable fuel from the sources, light and water [17] which are in abundant supply. Increasing attraction to the production of hydrogen by algae will cause the creation of advanced systems. Photosynthesis in green algae is able to generate hydrogen with a photon transformation performance of approximately 80% [13]. In the 1940's, Gaffron [14] found that algae are able to utilise hydrogen to donate electrons or generate hydrogen when the sun is out and even when it is not. Green algae can generate hydrogen once they have been incubated under anaerobic conditions without light [14] because this stimulates reversible hydrogenase [14] to allow the production of hydrogen. The reversible hydrogenase joins the hydrogen ions and the electrons to produce hydrogen.

Following on, when algae undergo photosynthesis, they oxidise water and produce oxygen [19]. The sun light that photosystem II absorbs produces electrons which are transported to ferredoxin by the solar energy seized by photosystem I [19]. Next, reversible hydrogenase obtains electrons from the reduced ferredoxin [19] in order to produce hydrogen. There is a two stage photosynthesis procedure for the generation of hydrogen in green algae [14]. The first stage is the fixation of carbon dioxide into reactants loaded with hydrogen. The second stage is the incubation of microalgae in an anaerobic environment whilst the production of hydrogen is brought about by sun light. The oxygen produced in photosynthesis is able to prevent reversible hydrogenase from functioning. The conflict amongst the generation of oxygen and hydrogen can be solved by dividing these different reactions and this can be accomplished via the incubation of green algae without the presence of sulphur [14]. Sulphur deprivation causes certain green algae to reduce the amount of oxygen generated. However, a great deal more of research on the generation of hydrogen by sulphur deprivation [13] needs to be carried out. It is thought that sulphur deprivation causes green algae to produce hydrogen and not oxygen [13].

The study of algae has resulted in effective transgenes expression [15] and a method for regulating genes with the use of riboswitches [15]. Recent research has enabled advances to be made in efficient gene expression [15] of algae. Development of algal transgenics [15] has led to further knowledge being acquired however; more sequencing of the genome is required to help develop the technologies generating hydrogen. In continuance, development of the two stage photosynthesis procedure and generation of hydrogen in green algae is important because sun light and water produce great amounts of hydrogen [13]. This technique does not produce substances which would cause harm to the environment although, there are various issues which need to be conquered in order for this technology which holds much potential to become something that truly exists. The science behind this technology and research on the way hydrogen is generated needs to be thoroughly analysed in order for it to be fully understood. An increase in the production of hydrogen will ultimately diminish effects of global warming as it will result in less fossil fuels being used.

Photosynthesis technologies are unable to generate hydrogen at a rate which is enough to reach the target of supplying the energy demand. Direct biophotolysis using microalgae to generate hydrogen is restricted by the design and price of the photosynthetic bioreactor but also the effectiveness of the solar energy transformation. This means, this technique needs to be improved and one way of accomplishing this is by increasing the amount of light reaching the photosynthetic bioreactors. Likewise, to increase the amount of hydrogen generated via the photosynthesis of algae, other types of algae should be studied and the procedure of hydrogen production in the absence of sulphur should be interpreted.

In my opinion, the energy crisis will be solved once it has been understood how hydrogen can be produced more easily from solar energy and it could also help stop global warming. It has been confirmed that the population of the UK alone is set to increase a great deal and this further stresses the point across; that it is critical we prevent further damage to the environment and one way of doing this is by utilising solar power energy as it is crucial we stabilise our climate. Of all the renewable energy sources, solar energy is the most able at supplying the world's energy demand and I believe solar power energy is the way forward. Biohydrogen production technologies that are dependant on light, so including direct and indirect biophotolysis are currently being studied in order to enhance the rate hydrogen is generated and also the amount produced. Direct biophotolysis using green algae to generate hydrogen is restricted by a number of factors including, the effectiveness of light transformation photosynthetic apparatus [19]. However, hydrogen production can be enhanced by the genetic engineering [19] of the antenna systems and by altering the two stage photosynthesis procedure in green algae [19]. Indirect biophotolysis using cyanobacteria to generate hydrogen can be enhanced by altering the environment for cultivation such as changing the temperature [19]. The generation of hydrogen by cyanobacteria provides a great assurance however, there needs to be more studies carried out in order for it to be used efficiently. Furthermore, hydrogen production could be increased by utilising appropriate microbial strains [3], or by making more economic photobioreactors. The perception of having a future of hydrogen is dependant on thorough research to enable the improvement and expansion of hydrogen production processes. I conclude that hydrogen is the gas of the future and its significance will increase [20] because carbon dioxide is not generated as a result of combustion and it can be transformed without too much difficulty into electricity so will help stop global warming and overcome the worldwide energy crisis. Also the price of natural gas and petrol is rising [21] so demand for hydrogen will increase. For biohydrogen production technologies using solar power energy to become a competitor in the economy, more research needs to be done in order for the rate of production and overall yield generated to increase.