Science

  • Issue 63 / May - June 2008



    The Future of Solar Energy in the Energy Market and Why We Need It More Than Ever

    Muhammet Erkan Kose

    Renewable energy resources
    Our current source of energy is mostly fossil fuels such as oil, coal, and natural gas. Fossil fuels are nonrenewable. In other words, they are finite resources and they will diminish significantly in future; hence, they will be very expensive to use and environmentally harmful to recover. In contrast, solar, wind, biomass, hydrogen, geothermal, ocean, and hydro power are renewable energy resources, that is, they are constantly replenished and will not run out. Renewable energy is not only important for our energy needs but also has significant advantages over fossil-based energy resources in the protection of the environment. Besides, the environmental aspect of renewable energy also has a religious dimension, since preservation of the earth and its inhabitants is regarded as a duty for humankind.



    Among these energy resources, solar energy is generally used for electricity generation or for hot water heating. It also finds uses in solar cooling, and in direct heating and lighting of buildings and homes. Solar panels are made of photovoltaic (PV) cells. The term “photovoltaic” means “converting light into electricity.” Solar energy technology has been around since the late nineteenth century. Yet, its share in energy production constitutes a very small fraction (less than 0.1%) of production around the world. This stems from the higher cost of electricity generation with solar panels in comparison to use of fossil fuels. In the US, electricity generated from PV cells costs $0.30 to $0.40 per kilowatt-hour while consumers pay only $0.10 per kilowatt-hour to the electric utility companies. Nonetheless, with recent advances in this technology, it will be possible in the near future to decrease the cost and make this technology viable for our energy needs as we face shrinkage in fossil fuels around the globe.

    One of the factors that increases cost is the low power-conversion efficiency of current PV cells. The PV cells used in the market are mostly fabricated from silicon crystals and these cells show a power conversion efficiency of 15%. That means, 85% of photons go to waste when harvesting energy from sunlight. In fact, the theoretical limit of light harvesting in silicon-based solar panels is only 31% because of the low band gap of silicon, which only partially absorbs sunlight to form charge carriers in the device. To solve this problem, scientists have utilized three different crystals in a single PV cell to absorb more sunlight, and these studies have yielded a device efficiency of 37%. Just recently, scientists at the National Renewable Energy Laboratory (Golden, Colorado) and Boeing-Spectrolab have achieved a world-record conversion efficiency of 41% by using the same idea, establishing a new milestone in sunlight-to-electricity performance. Although such studies are very promising in this field, when it comes to production cost, these inorganic PV cells are still an expensive technology for power generation compared to fossil fuels.

    Organic photovoltaics
    An alternative solution to decrease the cost is to use devices with lower power efficiency but a very low cost of production. Organic-based PV materials offer such an alternative with easy and fast production techniques such as solution processing and printing. Conjugated polymers (polymers with alternating single and double bonds in their polymeric backbone) are especially important in this regard, since they exhibit semiconductor properties. The best organic PV cell efficiencies reported in recent years are around 5%. This number must double in order for the cells to be used in solar panels, assuming that the cell displays high photostability and conductivity. Many research groups are now focusing on organic-based solar systems as an alternative technology to their inorganic counterpart.

    Although we are all familiar with solar energy, most of us do not know how electricity is produced from sunlight. To show the mechanism for photovoltaic activity, one first should look into an anatomy of a typical organic PV cell which is shown in Figure 1. This cell is based on an organic PV cell. The organic layer is sandwiched in between two electrodes where light absorption and charge separation occurs. Typically, glass is used for support but plastic materials can also be used as alternatives. The anode is usually indium tin oxide (ITO) and the cathode can be aluminum, calcium, gold, or magnesium. The electrodes must be semi-transparent to facilitate light absorption. Specifically designed conjugated polymers are utilized for sunlight absorption, where the wavelength range of absorbed light may vary from ultraviolet-visible to near infrared depending on the material used in the device. The efficiency of the device is determined by the extent of light absorption, efficiency of charge separation, and charge diffusion to the electrodes. The morphology of the organic layer has been found to be very important for device characteristics and cell efficiency. In an organic PV, an electron is promoted from the highest occupied molecular orbital (HOMO) level to the lowest unoccupied molecular orbital (LUMO) level upon light absorption (Figure 2). This transition results in an electron-hole pair which is then separated by the electric field formed by the different ionization energy of electrodes (Φ). Therefore, the electron moves to the cathode and the hole moves to the opposite side. This process causes charge flow between the electrodes and hence electricity is generated in the process.





    Despite all the improvements in organic PV technology, current cell efficiencies are still low for electricity generation. The stability of organic PV materials must be improved as most of them are prone to degradation by oxygen and humidity in the air. The large-scale production of organic solar panels is possible, and yet the feasibility of current methods has not been investigated extensively so far.

    Solar energy is a clean, renewable resource of energy and is projected to have significant role in the energy market in near future. Funding in the field of solar energy has been increasing in recent years due to the increasing need for energy and the likely reduction of fossil fuels towards the end of this century. Yet, our research efforts are still not sufficient for the advancement of this technology.

    Importance of renewable energy for the environment: an Islamic perspective
    Solar energy, like other renewable energy resources, is environmentally friendly. Its use should be promoted, as fossil fuels play a dominant role in the increase in greenhouse gases, which are believed to be responsible for the increased rate of global warming and hence climate change. Global warming may cause rises in sea level and changes in the amount and pattern of precipitation. These changes may in turn increase the frequency and intensity of extreme weather events, such as floods, droughts, heat waves, hurricanes, and tornados. Other consequences may include higher or lower agricultural yields, glacial retreat, reduced summer stream flows, and species extinctions. Warming is expected to affect the number and magnitude of the events mentioned above; however, it is difficult to connect particular occurrences to global warming.

    In any case, focusing on renewable energy and energy-efficient technologies is one of the best options to secure the future of our planet and all existing forms of life on it. Our effort should not only be due to the expected shortage of fossil fuels in future. Rather, it must be seen as a duty and moral act to save the environment since use of renewable energy resources has little or no negative impact on nature. Religious awareness and guidance in this area is necessary so that each individual may take active part in the protection and development of the environment. Much environmental degradation is due to our ignorance of what our Creator requires of us. People should be educated to realize that the conservation of the environment is a religious duty demanded by God. This fact is expressed in Qur’an in a number of places such as, “Do good, even as God has done you good, and do not pursue corruption in the earth. Verily God does not love corrupters” (Qasas 28:77), “And do not follow the bidding of the excessive, who cause corruption in the earth and do not work good” (Shu’ara 26:151–152), “And do not cause corruption in the earth, when it has been set in order” (A’raf 7:56). Any deliberate damage to the natural environment and its resources is a kind of corruption which is forbidden by Islam.

    As Muslims, we should protect and preserve the environment because by doing so we protect the creatures which pray to God and praise Him. Although we do not know how they praise God, the Qur’an clearly points this out: “The seven heavens and the earth, and all beings therein, declare His glory: There is not a thing but celebrates His praise, and yet you understand not how they declare His Glory!” (Isra 17:44). Islam is established on the concept of good (khayr). Since it is scientifically proven that protecting the environment is of great significance for all animals and plants on earth, Muslims should see it as khayr. In the last two verses of chapter Zalzalah (99:7–8), God says, “And whoever does good an atom’s weight will see it then. And whoever does ill an atom’s weight will see it then.”

    Protecting God’s creatures and the environment is a duty of humankind because human beings are the “agents” of God on earth. This task cannot be performed by other creatures. Therefore, as the Muslim community we should all commit ourselves to the preservation and to the protection of the environment. Surely, investing in and promoting improvement of the technologies based on renewable energy is one way to go.


    References

    http://www.nrel.gov/learning/re_basics.html

    http://www.islamonline.net

    http://lfw.pennnet.com/Articles/Article_Display.cfm?Section=ARTCL&ARTICLE_ID=257239&VERSION_NUM=3&p=12 (PHOTOVOLTAICS: Research targets more-efficient photovoltaics)

    http://lucy.mrs.org/publications/jmr/jmra/2005/dec/0407.html (Organic and nano-structured composite photovoltaics: An overview)

    http://www.orgchem.science.ru.nl/molmat/mm-web/education/caput-college/SolEnergMatCells-2004-83-125.pdf (A brief history of the development of organic and polymeric photovoltaics)

    http://en.wikipedia.org/wiki/Global_warming

    http://www.islamset.com/env/index.html

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