Year-wise Innovations and Developments

Solar photovoltaic (SPV) cells convert the sun’s energy into electricity. Sunlight is composed of miniscule particles called photons, which radiate energy from the sun. As these hit the silicon atoms of the solar cell, they transfer their energy to loose electrons. Hence, the flow of electrons produces electricity. Although harnessing of energy through solar cells is no more than 60 years old, the photovoltaic (PV) effect was discovered about 200 years ago. This article describes the history of PV cell and gives a comparative view of the current scenario.

Discovery of PV effect

French scientist Edmond Becquerel first discovered the PV effect (Figure 1) in 1839. This process occurs when light is absorbed by a material and creates electrical voltage. Most modern solar cells use silicon crystals to attain this effect.

Discovery of Selenium’s Photoconductivity

English electrical engineer Willoughby Smith discovered the photoconductivity of selenium in year 1873. This means that selenium becomes electrically conductive when it absorbs light. Three years later, in 1876, William Grylls Adams and Richard Evans Day learned that selenium could produce electricity from light without heat or moving parts that could easily break down. This discovery proved that solar power was easy to harvest and maintain, requiring fewer parts than other energy sources—such as coal-fired plants.

Solar Cell

The first solar cell was created in the year 1883 by New York inventor Charles Fritts. The solar cell was coated with selenium and a thin layer of gold. This cell achieved an energy conversion rate of 1–2 per cent. Most modern solar cells work at an efficiency of 15–20 per cent.

Observation of the Photoelectric Effect

German physicist Heinrich Hertz first observed the photoelectric effect in the year 1887, where light is used to free electrons from a solid surface (usually metal) to create power. Contrary to expected results, Hertz found that this process produced more power when exposed to ultraviolet light, rather than more intense visible light. Albert Einstein later received the Nobel Prize for further explaining the effect. Modern-day solar cells rely on the photoelectric effect to convert sunlight into power.

Commercial Production of Silicon Solar Cells

In the year 1953, physicists at Bell Laboratories discovered that silicon is more efficient than selenium. Between 1953 and 1956, they created the first practical solar cell that had 6 per cent efficiency. This discovery led to solar cells capable of powering electrical equipment. In 1956, Western Electric began selling commercial licenses for its silicon PV technologies, but the prohibitive costs of silicon solar cells kept them from widespread market saturation.

Solar Energy for Spaceship

After years of experiments to improve the efficiency and commercialization of solar power, solar energy gained support when the governments around the world first used it to power space exploration equipment in 1958. The first solar-powered satellite, Vanguard 1, has travelled more than 197,000 revolutions around the Earth in the 50 years that it has been in orbit (Figure 2). This application paved the way for more research to decrease costs and increase production.

Cost Cutting Years

As oil prices rose in the 1970s, demand for solar power increased. Exxon Corporation financed research to create solar cells made from lowgrade silicon and cheaper materials, pushing costs from $100 per watt to only $20–$40 per watt in those years. The federal government of the USA also passed several solar-friendly bills and initiatives and created the National Renewable Energy Laboratory (NREL) in 1977.

Application of Solar PV in Agriculture

PV technology is a cheaper option than new electric lines for providing power to remote locations on farms, ranches, orchards, and other agricultural operations. As it requires no fuel and no maintenance, it is more convenient to operate and maintain than diesel or gasoline generators. PV systems are a highly reliable and low-maintenance option for electric Figure 3: Isolated high tech communication satellite with solar cells fences, home lightening, and water pumping, either for livestock watering or crop irrigation. Current prices for solar panels and continuous hike in prices of conventional fuel makes PV technology economical for agriculture. In addition, the cost of PV panel is projected to decline significantly over time, which will make more applications costeffective. Skill development course on technology repair maintenance can make it better in operation.

Future of Solar Cells

Presently, silicon-based solar panels are widely use in solar power plants. These weigh about 15–20 kg and are heated at hundreds of degrees Celsius during the manufacturing process, which actually results in greenhouse gas (GHG) emissions. Developing technologies, such as dye-sensitized solar cells (DSSCs), organic PV, perovskite PV, and inorganic quantum dot solar cells, will take the place of silicon solar panels in the near future.

Organic solar cells are made by thinly coating the polymers on various materials, such as plastic. The cells are crafted at temperatures of less than 100°C, making them more environmentally friendly. Organic cells are flexible in nature, so these can be stacked vertically on weak structures such as vinyl greenhouses.

DSSCs feature a porous network of disordered titanium dioxide (TiO2) nanoparticles that are coated with light-harvesting dye molecules and are typically surrounded by a liquid-phase electrolyte. Photons captured by the dye—generally a ruthenium complex—generate pairs of negatively charged electrons and positively charged electron vacancies called holes. The charges separate at the surface of the nanoparticles. Electrons are injected into and transported through the TiO2 layer to one electrode, and positive charges migrate via the electrolyte to the opposite side of the cell.

Perovskite solar cells have attracted more attention in the past few years than all other types of emerging PV technologies because they are proceeding on an unprecedented trajectory. These devices use compounds with the perovskite crystal structure and stoichiometry to absorb light. In quantum dot solar cells, nanocrystals of semiconducting metal chalcogenides—including CdS, CdSe, PbS, and PbSe—and other materials function as the lightabsorbing material in the device. These new technologies in solar cell are therefore expected to play a vital role in the future.

CONCLUSION

Solar power has come a long way in the past 200 years, from observing the properties of light to finding new ways to convert it into power. This technology shows no signs of slowing down. Recent boom in the demand for PV modules has created shortage in supply of silicon. It provides an opportunity for technological advancement in nanotechnologybased thin-film solar cell modules. It is clear that improvements and innovations are needed for further market scale-up. The cost comparison of PV technology with various technologies for agriculture showed that PV technologies are suitable for any location in the world.

article courtesy : Er Kapil K Samar, Project Manager, Biogas Development and Training Center, MPUAT Udaipur, Rajasthan, India. Email: kapilsamar18@gmail.com.