By this moment, we are very familiar or have heard about solar as an alternative and greener source of power or energy. In fact, solar technology has been around for many decades now. Despite such fact, we can still ask why is it that solar power, notwithstanding its obvious advantages, was not able to completely replace the conventional sources of our energies like coal and gas. Almost every part of the world receives plenty of sunlight, but why are we still stuck for so long now after the development of solar power, to environmentally harmful energy sources? The answers lie on how efficient are the technologies use in harvesting energy coming from the sun nowadays.
Just recently, news was released about the development of new methods in harvesting the power of our sun by a group of scientist. According to the article, scientists at UC Santa Barbara’s Departments of Chemistry, Chemical Engineering, and Materials have developed a new way to convert sunlight into energy whit the use of a process based on metals that are more robust than many of the semiconductors used in conventional methods. Their findings were published in the latest issue of the journal Nature Nanotechnology.
Though the development of this new technology is on its early, an expert saw it as “radically new and potentially workable alternative to semiconductor-based solar conversion devices”. The current and basic technology being used for about several decades is not really that efficient and continues to face challenges in the successful harnessing solar energy.
Looking At the Current Solar Harvesting Technologies
So that we may fully understand the impact of this latest development in solar energy technology, let us first look at the conventional methods used in taking advantage of the sun’s seemingly limitless power.
In order to capture or collect solar radiation and convert them into energy, the use of photovoltaic (PV) effect is required. This process involves the interaction of light with certain materials in order to produce an electric current. It was during the 1950s that the first practical PV cells were developed using silicon based cells ‘doped’ making this traditional semiconducting material sensitive to light. One simple solar cell will be consists of a thin silicon wafer with two layers, one doped to be electron-rich and the other electron-poor, so that an electric field is set up across the layer junction.
There are conductors attached to the layers and these are connected to an electrical circuit. When sunlight hits the cell the negative electrons are released and these leave behind positively charged ‘holes’. Negative and positive charge carriers then travel through the circuit in opposite directions to create the electric current. In order for the light to be absorbed at the maximum levels, the cell is coated with an anti-reflective material and covered with a protective glass plate.
The current production of photovoltaic or PV units mostly uses silicon, making them occupy about 95 percent of its total supply. These cells have the capability to convert sunlight into electricity with an efficiency of up to 17 percent with maximum efficiency estimated at only about 25 percent. The reason for this is that only the light with more energy than that required to generate the charge carriers is absorbed. Silicon has its disadvantages including the current shortage of electronic-grade crystalline silicon, which is also fragile and expensive to make. The most widely used these days are photovoltaic cells made from cheaper though less efficient polycrystalline silicon.
Alternative Technologies Being Developed
There are other alternative technology being used apart from the silicon based PV cells and one involves the use of thin layer cells of semiconducting compounds estimated at about few micrometers thick. Examples are cadmium telluride combined with cadmium sulphide, which are capable absorbing sunlight well and right now considered the best-performing PV material to date in terms of cost effectiveness and efficiency, which can be put at 16.5 percent). The problem however is that cadmium is toxic.
One more technology used in PV cell uses the combination of copper indium diselenide, gallium and sulphur capable of giving an efficiency of nearly 20 percent based on laboratory test. The problem however for this technology is the high cost and limited supply of indium and gallium for large-scale use.
Another technology, which scientist and researchers have seen potential, is using nanocrystalline films, which combine the best attributes of the crystalline and amorphous forms. What this does to coat polyester sheets with silicon nanocrystals, which can then be integrated into roofs or used for awnings. Using luminescent dyes to concentrate the light and then transmit it through the plastic sheet to PV cells placed around the edges. The primary goal of the cell design is to trap light to maximized absorption.
Furthermore the higher energy conversion problem was addressed by using layers of materials with different bandgaps and each responding to a different light-energy range. This called the multijunction cell that could nearly reach 40 percent efficiency, although too expensive for more general use.
What Are The Future Technologies?
The future of efficient and affordable photovoltaic cells is constantly being tackled in many research laboratories in many countries. For example the Imperial College London is involve in the used of so called quantum wells, which are actually ultra-thin nanostructures which absorb light over a wide energy range, result in efficiencies as high as 27 percent. In order to reduce cost sunlight is concentrated using cheap lenses. Among the potential application being seen for this technology are smart window blinds capable of cutting out direct sunlight, generating electricity and diffusing light to brighten the interior room.
So what does the team of researchers from at UC Santa Barbara’s Departments of Chemistry, Chemical Engineering, and Materials have developed? In this new technology, it is not the semiconductor materials that will provide the electrons and venue for the conversion of solar energy. This will be undertaken by the nanostructured metals specifically gold nanorods according to the news. The gold nanorods when subjected to several processes during the experiments showed great capability in absorbing light.
However, the main problem in the current method use, which is considered less efficient and more costly than conventional photo processes. The researchers point out that this study is at the early stage and only with continued research will the result in the improvement on the cost and efficiency of this new method. The researchers also pointed out that they have already attained ‘respectable’ efficiencies and that they imagine achievable strategies for improving the efficiencies radically.