Solar cells are considered as one of the key factors towards a sustainable energy supply. In ancient times, solar cells have been used in situations when there is an absence of power supply from grid, such as in remote area power systems, Earth orbiting satellites and consumer systems. Due to the advancement in technology coupled with the environmental concerns such climate change, global warming and non-biodegradable waste led to the installation of grid interfaced solar PV system and standalone solar system. Private investments along with favourable government tariff policy regimes aim to generate competitively priced Solar Thermal and Solar Photovoltaic Power. According to the recent reports of Ministry of New and Renewable Energy (MNRE) solar capacity increased by 370 per cent in the last three years from 2. 6 GW to more than 12.2 GW. World’s largest renewable energy expansion program will be an installed capacity of 175 GW till 2022. Between 2014-2017 approximately 1.1 lac solar pumps have been installed for the green electricity expansion. A record low solar tariff of Rs. 2.44 per unit is achieved by Bhadla Solar Park of Jodhpur district. Photovoltaic cells are electronic devices that transform the sun’s energy into electricity. In recent years, PV cells have become one of the fastest growing nonconventional technologies which are going to play a significant role in the future global green energy generation. Solar PV is utilised to power the mini and micro grids to bring electricity access to people who do not live near power transmission lines, particularly, in developing countries with abundance of solar energy resources. Manufacturing cost of solar panels has declined remarkably in the last decade, making them more affordable for domestic and commercial usage. Solar panels have a lifespan of roughly 30 years, and available in variety of shades depending on the type of material used in manufacturing. The graph shown in figure 1 provides a comparative overview on prices of solar PV modules in European market from year December 2017-2018. The classification is based on the type of materials used for fabrication and it also depicts the significant reduction in the prices till end of year 2018.
The cost of electricity has declined by three quarters from 2010-2017. Focusing on the global weighted average trends for utility scale PV projects by year, the levelised of cost of electricity (LCOE) reduced by 73 per cent from 2010-2017. The given graph in figure 2 provides an overview on latest global trends in renewable energy costs.
Recent Solar PV Cells Inventions
As per the latest reports of American Technion Society, researchers at the Israel Institute of Technology have developed a technology that could improve the efficiency of photovoltaic cells by nearly 70 per cent. Photovoltaic cells optimally utilise a very narrow range of the solar spectrum. Radiations cannot warm these cells effectively thereby, reducing the efficiency modules by 30 per cent. A recent American research described an intermediate process that happens between sunlight and the photovoltaic cell. The photoluminescence material is created to absorb the radiation from the sun, and converts the heat and light from the sun into an ideal radiation, which illuminates the photovoltaic cell and enhances the conversion efficiency from 30 per cent to 50 per cent. The inspiration for the technology comes from optical refrigeration, where the absorbed light is re-emitted at higher energy, thereby, cooling the emitter.
A George Washington University researcher designed a prototype for a new solar cell as shown in figure 3 that combines multiple cells stacked into a single device capable of capturing nearly all of the energy in the solar spectrum with an efficiency of 44.5 per cent. The new device uses concentrator photovoltaic (CPV) panels that use lenses to concentrate sunlight onto micro-scale solar cells.
Solar Cell Technologies
The mismatch of radiations between the solar cells and sun rays is the key factor for restricting their efficiencies. Various materials exist in the nature which can enhance the incident sunlight properties to optimise the absorption process of cells. The spectral modification to solar cells put high impact on solar PV devices. Figure 4 shows the percentage of solar spectrum represented as energy loss that occurs in silicon cell. Solar cell efficiency is fundamentally hampered by non-absorption of low-energy photons, thermal losses from the absorption of high-energy photons and extraction losses due to unavoidable charge carrier recombination.
The maximum theoretical efficiency of a 1.1 eV band gap silicon solar cell was calculated to be approximately 30 per cent. Today, there are a range of solar technologies which use new materials apart from silicon wafer based modules. These include second generation thin film and third generation nano structured devices whose efficiencies are much more than that of traditional solar cells. Despite promising progress, if the efficiencies could be further enhanced in a non-expensive manner, then the price of solar electricity could be further reduced which would ease the transition to a sustainable global economy. The various technologies along with their efficiencies and cost per peak watt are shown in Table 1.
Perovskite solar cells are popular in solar cell research. Dye-sensitised solar (DSS) cells, thin film solar cell and silicon solar cell accounted for easy fabrication process but at lower efficiencies. Perovskite solar cells promise the enhanced output of about 21 per cent from about 9.7 per cent. The issue of degradation of perovskite and its stability should be addressed for good reproducibility and long-life time with high conversion efficiencies. Organic-inorganic hybrid perovskite solar cells have attracted unprecedented attention in recent years due to their high power conversion efficiency, ease of fabrication and potential to yield low cost photovoltaic modules.
Conclusion
A brief discussion on technological developments in solar PV system has been carried out here. The enormous potential of renewable energy sources coupled with the government subsidies in generating green power has led to growing research in maximising the efficiency of solar modules. The spectral modification is used to achieve greater solar cell efficiencies with the low cost, which is an important research area in the context of environmental issues and current engineering limitations.
