Concentrator Photovoltaic (CPV): Structure and Functions
The Concentrator Photovoltaic, or CPV, is often viewed as the most efficient tool for retrieving solar energy to power various systems. The primary purpose of a CPV is to keep the solar radiation focused on the solar cells, therefore, accumulating the solar radiation. Creating the environment, in which the transformation of solar power into heat energy becomes a possibility, the device in question should be viewed as one of the means of introducing a policy of sustainable use of resources into the contemporary industry realm.
Structure
The primary structure of a CPV system is rather simple. The funnel lenses serve as the primary tool for capturing the solar energy and focusing it in the cells. The secondary optics allows magnifying the effect of the sun radiation, therefore, helping retrieve the necessary amount of energy. Finally, the cell assembly creates the environment, in which the process of receiving energy becomes a possibility. The cell assembly consists of a secondary concentrator and an electrical contact between the cell itself and its prismatic cover, the solder with a copper heat spreader, and a conductive adhesive supported by a module housing. The housing, in its turn, performs the function of a container for the cells and the optics.
Limitations
It should be noted, though, that the use of CPV is only possible in specific areas that can provide an environment favorable for the further accumulation of solar energy. Understandably enough, the tool in question is only applicable in the areas that provide exposure to large doses of solar radiation; particularly, it is required that the Direct Normal Irradiance (DNI) doses should reach 2,000 kWh/m2a at the very least [1]. Otherwise, the adoption of the CPV system is unlikely to be successful.
Taxonomy
Phillips et al. [1] specify two types of CPV, which are currently used as the primary means of collecting solar energy, based on their capacity. The High Concentration PV and the Low Concentration one differ primarily in the concentration ratio 300 to 1,000 and less than 100 correspondingly), the tracking type (solely two-axis one or the one inviting an opportunity for using either one- or two-axis approach), and the type of converter (III-V multi-junction solar cells or c-Si/other cells correspondingly). It should also be borne in mind that the above options allow for a significant reduction in the costs for the cells since the technology used to create the items in question has become quite popular and, therefore, reproducible.
Strengths
The application of CPV has a plethora of advantages as a tool for accumulating energy for its further use. First and most obvious, the high-efficiency rates that the specified tool displays, when applied in the environment of direct-normal radiance, need to be brought up [1]. Another essential outcome that sets the concept of CPV aside from the rest of the tools used for the same purpose concerns the adoption of the tools that can be viewed comparatively harmless to the environment, in general, and people’s health, in particular. In lieu of the tools that affect nature negatively, triggering a gradual extinction of species and the disintegration of unique habitats, the application of CPV seems rather reasonable.
In addition, the process of producing energy can be viewed as consistent when combined with the prospects for the double use of land, the opportunities that the adoption of the CPV technology implies rather positive outcomes. Finally, the fact that the framework of the system is modular and can be transformed from KW to GW deserves to be brought up. The flexibility in the usage of the system is especially important due to the need to apply it to a range of environments and, therefore, expose it to a wide variety of factors. Finally, the potential that the CPV tool has in terms of future energy production is truly ample and needs to be explored deeper.
Weaknesses
The current CPV structures, however, also have their problems, the expenses required to sustain the system in a working condition being the primary one. For instance, it is crucial that the tracking process should be carried out with outstanding accuracy; more importantly, the systems need to be cleaned on a regular basis as the slightest amount of dirt will hinder the process of accumulating light and, therefore, will result in a drop in efficacy.
In addition, the numerous restrictions in the use of the tools under analysis (the impossibility to install it on high rooftops and the need to locate it in the areas with high DNI rates) can be interpreted as the primary issue with the adoption of CPV as the means of generating electricity. Finally, the specified tool belongs to the new era of technology and has not been tested properly yet, which means that the use of CPV may trigger unforeseen difficulties.
Current Rates
As the study carried out by Du, Hu, and Kolhe [2] has shown, the performance rates of the CPV system are quite impressive. Specifically, the fact that the thermal efficiency of the construction peaks at 58% is rather impressive. The fact that the electrical efficiency of the structure is 11% might lower the expectations to a considerable extent; however, the combined efficiency of 69% allows for a rather positive prognosis.
It should also be borne in mind that the CPV system must be positioned appropriately so that its assets could be used to their full potential. Du et al. (2012) point specifically to the fact that the construction needs to be tilted at 35° so that it could capture all the light and produce as much energy as possible. As the experiment set by the authors of the article has shown, the solar intensity peaked at 1019 W/m2, which allowed the construction to retrieve an impressive amount of solar energy. With the difference between the temperature of the fixed solar cell and the ambient environment ranging from 20° C to 23° C, the cooling water extracted a large amount of heat from the cells.
In other words, the experiment has shown that the current preference for the use of solar cells with the cooling system to the fixed cells use is fully justified as the former provides a much better output. Therefore, the application of the CPV system requires the usage of cooling systems that create the environment, in which CPV can be used to its maximum capacity.
Stirling Engine: Structure and Functions
History
To compare the Stirling engine to the CPV tool, one must carry out a foray into the history of its creation first. Another innovative tool that allowed revolutionizing the very concept of generating power, the Stirling engine was supposed to provide has recently been renovated and upgraded to retrieve power from solar energy.
Stirling Engine: Structure
Because of its universal structure that permits its application in a variety of domains, the Stirling engine is used in rather specific domains such as submarines for generating the necessary amount of power. Nevertheless, the basic components of the engine remain basically the same. The system rests on a stump, which serves as the foundation for the crankcase. The latter contains the crankshaft, which is activated by the drive mechanism, and the connecting rod that makes the piston rod move.
The crankshaft and the piston rod are activated by the drive shaft. The piston rod seal, which is a specimen of a hydraulic seal, connects the driveshaft to the cylinder block, therefore, activating the latter as the former starts the motion. The volume of the gas in the cylinder increases as the preheater is activated, or drops as the cooler are set into motion. Therefore, once the fuel injector supplies the fuel, and the fuel lighter triggers the creation of gas, the Stirling engine is started [3]. The structure described above allows for retrieving the maximum energy possible from the amount of fuel supplied to the engine.
Solar Stirling Engine: Structure
While the transfer from obtaining energy from the traditional sources to the extraction of solar energy has altered some of the elements of the Stirling engine, the general structure and properties remain in their places. Among the primary changes that occurred to the structure, the addition of the solar receiver needs to be brought up. According to the description provided, the receiver contains an insulated cavity; the latter, in its turn, has the aperture needed for the sunlight to enter [3]. It should be noted, though, that focused solar energy is not acceptable in the specified case; herein lies the need for the slew shield. The latter serves as the means of protecting the PCU. As soon as the hydrogen in the heater heads reaches the temperature of 600° C, the engine is set into motion.
PDSSPP System
Talking about the Sterling engine and its application as the tool for extracting solar power to turn it into usable energy, one must mention the PDSSPP system. the above construction consists of a parabolic dish concentrator or PDC. At this point, the fact that the Stirling engine represents a closed cycle system needs to be brought up. The PDSSPP framework, in its turn, incorporates a parabolic mirror that serves as the means of concentrating solar radiation and transforming it into heat energy, which, in its turn, is absorbed into the pipe. Thus, the energy cycle is created within the system, allowing for its accumulation.
Strengths
A more detailed analysis of the device carried out by Reddi, Akashi, and Tyagi [4] has shown the adoption of the solar Sterling engine as the tool for extracting solar power and using it as the source of energy has delivered rather impressive results.
The adoption of an improved system is likely to cause a subsequent increase in the efficacy of the system to the impressive rate of 26.95%. As the research states, the performance results of a solar Stirling engine located in the area favorable for retrieving the necessary amount of sunlight showed a stunning result of 95.77 x 103 MWeh. Although the annual amount of solar radiation was very high (384.064 x 103 MWh) and the percentage of energy retrieved was comparatively small, the outcome is, nevertheless, rather convincing as proof of the significance of the Stirling engine as a tool for extracting solar-power-based energy.
Finally, the fact that the peak amount of energy accumulated while using the device was 29.18% shows that the solar Stirling engine should be considered as one of the primary devices for retrieving solar-powered energy.
Weaknesses
Unfortunately, there are some dents in the current framework of the device. Although the report prepared by Reddi et al. [4] has shown that the Stirling engine has the capacity of extracting 29.18% of solar-powered energy, the lowest energetic efficiency value was 16.83%. Therefore, the mean thereof lands at the mark of 23.005%, which is slightly lower than the bar set by the CPV tool. The inconsistency in the amount of solar power accumulated and the energy produced, therefore, can be viewed as the primary weakness of the device. One must note the similarity with the CPV tool, which is also excessively dependent on the area that it is located in and the time of the year that it is used at. Unless the appropriate setting is selected and the required environment is provided, the device does not permit retrieving the necessary amount of solar power; consequently, the energy output becomes very low.
Current Rates
When considering the efficacy of the Stirling engine, one must mention that the current efficacy rates land at the mark of 31.25% [3]. The given characteristics of the tool show that the adoption of the Stirling engine is unlikely to return positive effects at a reasonable rate of expense. The amount of energy that is lost in the course of the process is far too big to apply Stirling engines to solve energy-related problems.
However, the design of the tool commonly known as the SunCatcher can be deemed as a rather efficient means of addressing the problem above. A comparative analysis of the performance delivered by a SunCatcher compared to other tools such as the rooftop PV, the parabolic trough, and the power tower, has shown that the use of the SunCatcher triggers an immediate increase in the productivity of the tool. Moreover, the SunCatcher makes the Stirling engine unsurpassed compared to other instruments. For instance, the device does not have any fuel needs; it has a rather good predictability rate; it is very reliable as a source of energy; its peak efficiency is the highest among the devices selected (24%), just as its annual efficiency (22-24%) is [3]. Therefore, the application of the above device is a supplementary tool for enhancing the performance of the solar Stirling engine should be viewed as a necessity.
Based on the above indicators, it is possible to assume that the use of CPV triggers better results at present. However, the Sterling engine clearly has much more potential in terms of its further transformation and upgrade. Therefore, both technologies need to be sustained and incorporated into the framework of modem industries.
Reference List
S. P. Phillips, K. W. Bett, A. Horowitz, and S., Cruz, Current Status of Concentrator Photovoltaic (CPV) Technology. Springfield, VA: U.S. Department of Commerce, 2013.
B. Du, E. Hu, and M. Kolhe. ”Performance Analysis of Water Cooled Concentrated Photovoltaic (CPV) System,” Renewable and Sustainable Energy Reviews, vol. 16, no. 9, pp. 6732-6736, 2016.
“Appendix B: Solar Stirling Engine,” California Energy Commission, n. d. Web.
V. S. Reddi, S. C. Akashi, & S. K. Tyagi. “Exergetic Analysis and Performance Evaluation of Parabolic Dish Stirling Engine Solar Power Plant.” International Journal of Energy Research, vol. 37, no. 11, pp. 1287-1301, 2013.