1. Introduction
Even though fossil fuels and coal mines are still in adequate quantity according to some industrial experts, the earth is experiencing drastic climate change which is commonly believed as the outcomes of mining, tapping, and using coals and fossil fuels to provide electricity to homes and industries all over the world since the Industrial Revolution [7]. Therefore, one of the greatest concerns today is how to efficiently and cost-effectively utilize renewable energy, particularly solar energy, for domestic use. Solar energy is intense heat and light from the sun utilized through an array of different technologies like solar thermal energy and photovoltaics [3]. It is one of the most promising sources of renewable energy at present. Unfortunately, the solar panel industry has been affected by economic recessions and financial crunches during this period. In order to sustain the fast-paced development thrust of harnessing solar energy, there should be continuous research on the new methods of converting solar energy to electric power with reduced cost and greater efficiency.
Numerous methods have been researched and suggested to lower the cost and enhance the efficiency of solar panels for domestic use. One evident method of enhancing the absorptive capacity of solar panels is utilizing various materials like organic resources, cadmium telluride (CdTe), amorphous silicon (a-Si), and crystalline silicon (c-Si), among others [7]. Another key method to enhance the efficiency of solar panels is utilizing light trapping structures to boost the capacity of solar cell components to absorb light. Light trapping structures are used to raise the amount of photons or light absorbed by the solar cell components which can produce the electron-hole pair [7]. The use of economical solar cell materials and low-cost substrate for light trapping structures to attain greater absorptive capacity can lessen the cost. Hence, thin film solar cells would benefit significantly from improved light trapping structures [6]. These light trapping structures can expand the optical path distance, which would then result in the reduction of material utilization in solar panels.
2. Trends
Majority of researches on photovoltaic (PV) solar energy for domestic use is presently focused on a reduction in cost per watt of electric power generated. With the aim of attaining this goal, numerous technologies using various materials are continuously studied. Nonetheless, c-Si is still the prevailing technology because c-Si PV has a large number of advantages to facilitate extensive distribution [6]. The growth of extremely efficient silicon PV mechanisms and associated advances in the production of module and power electronics resulted in expectations that PV electricity can be distributed to households at a minimal rate of $0.10 per kilowatt-hour (kWh) [5]. This finding has been proven. Certain researchers have experimented with different methods and technologies to further substantiate this prediction.
Guo and colleagues [2], using meticulous coupled-wave analysis technique, have created double-side grating light trapping structures for ultrathin silicon solar panels. They draw upon the fact that thin layers normally lead to low absorption because of reduced optical length. Thus the thin-film solar cells’ photoelectric conversion efficiency is unsatisfactory. In order to solve this problem, an important light trapping method is carried out in the design of thin-film solar cells with greater absorptive capacity. The idea of light trapping is currently focused on a combination of a back reflector and randomly textured interfaces [2]. This material has to expand the optical paths and produce systematic, cost-effective diffusion at big gradients of the deflected light, hence absorptive capacity can be significantly enhanced. The researchers find out that the application of double gratings in ultrathin solar cell is definitely better than a single grating (either bottom or top grating) [2]. The double gratings create a possibility of generating bigger optical absorption over the whole operational solar scale.
Abdulgafar and associates [1] conduct a more inexpensive method of enhancing the efficiency of solar panels for domestic use, particularly for domestic heating purposes. They perform a distillated water immersion method to enhance the electrical productivity and outcome of polycrystalline silicon panel.
Figure 1. Behavior of polycrystalline photovoltaic cell in different depths of water [1]
The performance of PV panel immersed in water is examined. The efficiency of the PV panel increased when it was submerged in cold water. A significant rise in electricity output is reported for low distillated water [1].
Trompoukis and colleagues [6] claim that reducing the quantity of crystalline silicon material usage could lower the cost. They incorporated a 1 μm c-Si solar cell system based on thin film technology into 2D periodic photonic nanostructures. They find out that nanopatterning enhanced the optical quality of the solar cell and it does not greatly affect the material and electrical quality [6]. Integrating nanopattern parameters into a more complex solar cell structure and optimizing it will enable greater improvement of the efficiency of solar panels. This could be an inexpensive PV technology made possible by photonic-supported thin-film solar cells [6]. Yu and colleagues [8] also report that 2D gratings offer greater improvement than one dimensional grating. The below image illustrates the impact of the balance of the grating contour on the absorption enhancement parameters.
Figure 2. A high absorption enhancement over the whole wavelength scale is attained through the grating structure. Identifying the whole absorption bandwidth of a certain material and the upper absorption enhancement parameters in nanophotonic system is definitely a crucial development in the production of efficient solar panels for domestic use [8].
These are promising advances in the field of solar energy research and development, specifically with regard to the goal of enhancing solar panel efficiency for domestic use.
3. Gap
The capacity of crystalline silicon and thin-film solar cells to enhance the efficiency of solar panels is already established and proven. However, these two materials still bear disadvantages that have to be addressed by another feasible solution—the use of photonic nanostructures. Crystalline silicon panels are still costly to produce, while thin-film solar cells have a low rate of conversion and are only able to absorb minimal amount of electrical power from the sun. Apparently, based on the studies reviewed, converting solar cells to module outcomes result in the reduction of efficacy for silicon cells and thin-film. Thin films can lower the costs of production uniformly as opposed to silicon in terms of cost per watt, but their low level of efficiency must be counterbalanced either with improved rate of deterioration or field outcome [4, 3]. The literature review demonstrates how researchers are still attempting to enhance the efficiency of solar panels for domestic use using crystalline silicon and thin-film solar cells.
4. Solution
Majority of the solar cells utilized for domestic purposes are bulk-type and made from a single or multiple crystalline silicon. Even though it is designed to lower the cost of solar cell module production, the substantial boost in conversion efficiency and decrease in the cost of solar cells are difficult, even impossible, to attain through traditional solar cell systems and materials [7]. For that reason, production of and research on solar cells with reduced feedstock depletion, high efficiency of conversion, and reduced cost of production are crucial. The biological, chemical, and physical trails of research and development on solar energy intersect in nanoscience. Creation of elaborate nanoscale structures facilitates accumulation and interlocking of active molecular components for the process of capturing, converting, and storing solar energy with accuracy and dependability not achievable in the past [4, 3]. The evolving mechanisms of nanoscale production, identification, and replication offer an important knowledge on the molecular processes of solar conversion and a vital direction for future research.
Therefore, a potential solution to the reduction of solar cell production cost and enhancement of solar panel efficiency for domestic purposes is photonic nanostructures. The consolidation of nanoscale physics, chemistry, and biology is a new development that forms potential interdisciplinary paths to efficient conversion of solar energy [3]. The intense demand for increasing energy output in the near future, the extraordinary value of sunlight as a sustainable green energy resource, and fast developments in the biology, chemistry, and physics of conversion of solar energy at the nanoscale are strong impetus for an organized research and development project on solar energy use.
Simply put, in order to solve this problem, nanostructured materials should be used instead of bulk-type materials. There are two compelling reasons why nanostructures are the most promising solution. As explained by Narasimhan and Cui [4], it enhances the functioning and outcome of traditional solar cells, and it facilitates high level of conversion efficiency from low-cost materials with reduced consumption of energy and reduced costs of production.
5. Conclusion
Enhancing the efficiency of solar panels and making it affordable for domestic use are a challenge that seems insurmountable before. However, with the advancement of technologies and research on potential methods to enhance the capture, conversion, and storage of solar energy, the ultimate solution to this problem seems to be within reach. Crystalline silicon and thin-film are currently the most studied materials in the field of solar energy utilization, including the water cooling method. However, as shown in the studies, the efficiency of these materials eventually deteriorates thus another solution must be created. Photonic nanostructures are another promising solution, with its capability to boost the efficiency of traditional solar cells and lower production costs.
References
[1] S. Abdulgafar, O. Omar, and K. Yousif, “Improving the efficiency of polycrystalline solar panel via water immersion method,” International Journal of Innovative Research in Science, Engineering and Technology, vol. 3, pp. 8127-8132, 2014.
[2] X. Guo, J. Liu, and S. Zhang, “Design of light trapping structures for ultrathin solar cells,” Photonics and Optoelectronics (P&O), vol. 3, pp. 66-69, 2014.
[3] N. Lewis, Argonne National Laboratory, and U.S. Department of Energy, Basic Research Needs for Solar Energy Utilization. Lemont, IL: Argonne National Laboratory, 2005.
[4] V.K. Narasimhan and Y. Cui, “Nanostructures for photon management in solar cells,” Nanophotonics, vol. 2, pp. 1-23, 2013.
[5] R. Singh, G.F. Alapatt, and A. Lakhtakia, “Making solar cells a reality in every home: Opportunities and challenges for photovoltaic device design,” IEEE Journal of the Electron Devices Society, vol. 1, pp. 129-144, 2013.
[6] C. Trompoukis et al., “Photonic assisted light trapping integrated in ultrathin crystalline silicon solar cells by nanoimprint lithography,” Applied Physics Letters, vol. 101, pp. 1-14, 2012.
[7] X. Wang and Z. Wang, High-Efficiency Solar Cells: Physics, Materials, and Devices. London: Springer Science & Business Media, 2013.
[8] Z. Yu, A. Raman, and S. Fan, “Fundamental limit of light trapping in grating structures,” Optics Express, vol. 18, pp. A366- A380, 2010.
