ISSUES THREATENING THE EFFICIENCY OF SUSTAINABLE ENERGY AND ITS SOLUTIONS
Issues threatening the efficiency of sustainable energy and their solutions
There are many factors responsible for the reduced efficiency of sustainable energy sources like solar energy, wind energy, and biofuel. Various factors responsible for the low efficiency of sustainable energy sources and their solutions have been discussed.
First, let’s take a look at the various aspects of solar energy, since it is the most abundant form of sustainable energy source in nature. Also, solar energy is expected to play a major role in fulfilling the future energy needs of our planet.
The efficiency of a normal solar panel is about 14-18%, this is one of the major problems faced by the authorities, as to generate high amount of energy larger spaces are required. Let’s take a look at the equation of energy conversion efficiency to get a better perspective about this situation. The energy conversion efficiency is calculated by using the ration of maximum power point Pm and input irradiance & total surface area. Energy conversion efficiency η= Pm/E x Ac, where Pm is maximum power point, E is irradiance in W/m^2, and Ac is the surface area in m^2. As can be seen from the equation, in order to convert a large amount of energy a larger surface area is required. But there are various developments taking place in order to increase the efficiency of solar panels. With the increased efficiency, more energy will be created in less space.
The other major factor which reduces the efficiency of solar panels is the fluctuations in temperature. As a result of the increase in the temperature, the band gap of the given semiconductor decreases, and hence decreasing the open circuit voltage, Voc. The decrease in Voc and increase in the short circuit current Isc, directly impacts the maximum produced power in the solar cells. The relationship between the maximum power, short circuit current, and open circuit voltage is Pmax= Voc X Isc. This shows us that, the increased temperature has a negative effect on the overall efficiency and power of the solar cells. One new development that has taken place for increasing the efficiency of solar cells is the development of polymer photovoltaic cells. They are generally preferred due to their low cost and simple fabrication process. In this category, the Polymer bulk heterojunction (BHJ) photovoltaic cell is one of the best technology. The BHJ cell provides fluent separation and transportation of charge. As a result of these properties, high efficiency is gained. A further modification in this technology has been suggested by using an interlayer of cesium carbonate (Cs2Co3) in the polymer cell. This addition greatly helps in increasing the efficiency of inverted polymers, and even more when the addition of Cs2Co3 is done at a relatively lower temperature.
The directly affecting factor regarding the efficiency of the solar panels is shades. The solar panels are connected in a series connection, hence the overall current generated by them will be considered by the lowest performing cell. Now, when shade falls on one cell, this impacts the entire connected panel and eventually reduces the efficiency of the entire panel. In order to deal with this situation, the primary thing would be to install the panels at an appropriate place. Solar plants should always be located at the places where there is no risk of any shade. This compulsion of the open non-shaded place is one of the downsides of solar energy. Nevertheless, on the other side various developments have occurred to increase the efficiency of the solar panels. There are many new ideas that have been applied to further develop the scope of using sustainable sources of energy. Let’s take a look at some of these developments. The other development that has taken place in order to improve the existing solar technology is in the field of chemistry. The usage of solid state junction has been prominently done in the past, but there is an alternative available in the form of bulk junctions. These bulk junctions are primarily made from nano-crystalline inorganic oxides, polymer devices, and ionic liquids. The usage of these junctions can be used in the solar cells to increase the efficiency of the solar panels. Let’s take a look at how these cells functions. When the sunlight enters into this cell, it passes through various layers of the dye, and hence effectively increasing the amount of light in the structure. In some ways, it acts like thylakoid vessels of the trees, which helps in the process of photosynthesis. The final factor affecting the efficiency of solar energy systems that has to be looked at is the problem of orientation. The sun changes its path with the change of season, hence it becomes necessary with every changing season to reorient the panels in the direction of sun. In this way the amount of energy received and hence the efficiency of the solar energy plant can be increased. The good thing is that the technology for automatic reorientation of the panels is available. But the problem with this automatic reorientation technology is its high cost, this high cost makes it almost non-useful for small solar energy plants.
The wind energy is another form of the alternative energy source. Presently, it is one of the widest used sustainable source of energy and in future the use is of wind energy is expected to increase. It is assumed that by 2040, wind energy will provide up to 20% of the total energy consumption. Hence it becomes important to understand the issues regarding wind energy. The efficiency of the wind power greatly depend on the speed of the wind. The windmill turbine starts working when speed of the wind reaches 4 m/s and it keeps functioning until wind reaches 25 m/s. On an average a modern windmill is at work for about 80% of time. The overall annual efficiency of the windmill turbine is about 30% of its maximum assumed value.
The main issue with the efficiency of wind energy plants is the variation in wind speed. There are times, when the wind blows at an appropriate speed but at the other times, there is no wind at all. Due to this reason, the wind energy plants never functions at their full capacity. There is no way of controlling the wind, hence the only thing that can be done to increase the energy output is by installing more plants. This suggestion seems fine but various problems are involved in installing large numbers of wind energy plants. The primary problem is of the space, there are various other activities that can be done on a given space, which are economically more beneficial. Also, due to aesthetic reasons, people have opposed the installation of windmills at a countryside. In order to solve this problem of space, a suggestion of floating wind turbine has been given. According to the suggestion, the floating wind turbines should be based on the model of already existing offshore oil companies. The main problem that is stopping the implementation of this strategy is the cost. Hence, due to economic limitations this project is currently stalled, but various methods are being suggested to make this system less costly.
Due to the diverse speed of wind, the usage of varied speed wind turbine becomes essential to increase the overall efficiency. In order to effectively couple this varied speed turbine, a gearbox is used in many wind energy systems. Usage of gearbox is helpful but it leads to many faults and hence an increase in the maintenance cost. But this problem of low reliability of gearboxes can be dealt with by using the technology of permanent magnets. In the past years, the permanent magnets were not used due to high cost, but now as they have become economically affordable, it has become possible to use them in the wind energy plants on a large scale. The usage of permanent magnet is important as it allows the usage of relatively smaller pitch holes. This enables designers to design the generators to rotate at a speed of 20-200 rotations per minute. Also, multipolar permanent magnets have been used by several companies to further increase the efficiency of their system. Also, one thing that affects the efficiency of the wind energy generation is the size of the motor. This can be understood by the formula that the power generated (P) is directly proportional to the surface area of the rotor. Now, in this particular aspect much progress has been done. The size of the wind plant is constantly on a rise. In 1990, the size of the plant was around 40 meters and in 2010, it was around 150 meters. This figure is expected to rise and the size of the wind energy plant will reach 252 meters by 2050. As a result of the increasing size of the rotor surface area, the energy extraction has increased substantially.
Biofuels are another important sustainable energy forms. They have become very lucrative in past few years, as they have the potential to replace the conventional fuels. This increase can be seen clearly in Brazil. In 2007, the production of biofuels was about 4800 million gallons and in this is expected to go above 7500 million gallons by 2016. The biofuels have the advantage of low carbon emission, but on the other hand biofuels are less efficient. But in order to increase the efficiency of biofuels, technology such as artificially increasing the photosynthetic efficiency in algae is being introduced.
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