Good Report About Review Of Solar Water Heating:
The journal article was written to provide an overview of solar water heating (SWH) technology which include the basic principle and theory of thermodynamics, applications of these principles and theories, effectiveness of SWH in providing energy, market potentials for
SWH technology and potential research questions to improve existing technology. Furthermore, the article also outlines the importance of SWH as one of the economical renewable energy scenarios.
The introduction section of this article presents the facts of fossil fuel as the primary source (80%-90% of energy usage) to date, and clearly discusses the potential setbacks and effects of fossil fuels (e.g. increased fuel price and greenhouse gas emission). The article then discusses the potential use of solar thermal technology as a clean, renewable and cost-effective energy source (Wang, Yang and Qiu 69). The article uses the description of the current fossil fuel usage as background information without specifying how much the solar thermal contributes to the reduction of existing fossil fuel consumption. The article does not make any attempt to estimate how much contribution of solar thermal will be considered as a significant contribution to the global energy needs.
Nevertheless, the article provides information on the current global market share of SWH in the context of solar thermal use for energy source worldwide. The article specifies that SWH comprises 80% of the global solar thermal market (Wang, Yang and Qiu 69), which implies that water heating is the most dominant sector in the solar thermal market. In the discussion about global market for solar thermal technolgy, the article does not provide any explanation or hypothesis on the reasons behind SWH market advantage. Instead, the article states that SWH technology have several identified problems that create constraints for promotion. This information seems to contradict with the fact that SWH already has a market advantage over other solar thermal applications.
The next section of the article provides a thorough description of the working principles behind the SWH technology. This technology relies on the absorption of energy and prevention of heat loss to ensure positive energy gain from the sunlight (Wang, Yang and Qiu 70). This process follows the first law of thermodynamics (where energy cannot be created or destroyed) and takes place in a solar collector, a main component in the SWH technology. Although there are many types of solar collector, the main principle for keeping the energy balance remains the same. The energy that comes from the heat of the sun radiation is transferred through convection in an insulated collector to provide available energy (useful energy) for heating. The mathematical equations presented in the article shows that the amount of the useful energy depends on the property of materials used in the collector (glass cover, insulator, etc.) and the area of the solar collector. The efficiency of a solar collector is defined as a ratio between useful energy collected and the radiation (Wang, Yang and Qiu 73). The efficiency is represented as a percentage where a maximum efficiency of 100% is never achieved within current SWH technology, as a small portion of sun’s energy is not collected as useful energy (the energy is reflected back or absorbed in the convection).
The useful energy is then used in energy balance within water storage where the energy is used to increase the water temperature in this container. This process follows the second law of thermodynamics where the energy balance is facilitated through transformation from the heat load to the increase of water temperature. Heat loss in the pipeline and the distribution should also be considered in this energy transformation, where effective pipeline and water distribution designs can minimize the energy loss and increase entropy (Wang, Yang and Qiu 74).
In theory, the net solar energy that the earth receives by far exceeds the currently available energy source. By this calculation, an hour of sun radiation should be able to supply a year of mankind’s energy demand (Wang, Yang and Qiu 74). Using this comparison the article shows the vast opportunity in global solar thermal market. The increase in solar collector installation worldwide shows that the global solar thermal market is growing. The article shows a degree of quantification where the solar thermal may contribute to about 15% of the heat demand by the year 2030 (Wang, Yang and Qiu 75). The expansion of the global solar thermal market depends on various aspects including the cost and efficiency in the solar heating mechanism. Both cost and efficiency of solar heating mechanism rely on the first and second laws of thermodynamics. The efficiency of solar collector in trapping the useful energy (first law) and the efficiency in tranferring the useful energy into heat to increase water temperature (second law) become the main factor affecting the cost effectiveness of solar heating. Additionally, the labour cost, materials and technology are also factors in determining the cost effectiveness.
Solar thermal technology has gone a long way since its first inception, but there are still aspects to improve such as optimizing structures; improving thermal performance; modeling and laboratory prediction; dynamics in real-time performance; energy, economic and environmental performances; and marketing strategies (Wang, Yang and Qiu 79). This article provides information on researches done to address the above aspects which can be linked to the laws of thermodynamics. Addressing the above aspects generally involve two main strategies namely improving the performance of solar collector and improving the performance of energy transfer system.
In relevance with the first law of thermodynamics, the main challenge of using solar energy is to capture optimal amount of energy by considering factors such as the size of the solar collector; the properties of materials used; and trends in weather and climatic conditions. Scientist consider all of these factors (and modify accordingly) to increase the efficiency (performance) of the solar collector in collecting the useful energy.
Knowing that there are several identified problems with the current SWH technology, the next strategy is aimed towards improving the technology. This strategy relates to the second law of thermodynamics that aim for optimal arrangement of components to reach a maximum entropy. This will allow transfer of the useful energy from the solar collector on to heat energy that can increase water temperature. An example of this strategy is the use of all-glass vacuum tube collector to ensure that energy balance from the collector can be optimally used in heat balance equation in water.
Research in improving the SWH technology involves prediction from laboratory experimentation and modeling. This strategy is done to simulate and predict the performance of a solar heating system and its associated heat and mass transfer processes (Wang, Yang and Qiu 81). There are two models (analytical and transient energy) used in the simulation to predict the best option of a solar heating system. Furthermore, the simulation (modeling) results can be compared with laboratory measurements to assess consistency of a particular option. In the end, the laboratory measurements will be compared to the actual real-time performance of the system to determine the efficiency of this particular system.
The implementations of the first and second laws of thermodynamics are seen in the physical manifestation (e.g., location, size of collectors, and angle), chemical composition (e.g., materials used and heat transfer components) and structural consideration (e.g., passive system, active system, and designs of tube collector) of a SWH technology. This article compiles mathematical equations, examples of researches to show the application of the basic thermos principles in developing and improving solar heating system. The basic thermos principles are also used in designing laboratory procedures and modeling to answer most of the research questions. All of these strategies and approaches are expected to help establish a clean, cost-effective renewable energy mechanism.
Wang, Zhangyuan, et al. "Solar water heating: From theory, application, marketing and research." Renewable and Sustainable Energy Reviews 41 (2015): 68-84. Print.
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