Photovoltaic systems have a wide range of applicability and also include public or privately owned solar-powered lighting systems or solar powered water pumps  . Solar pumps offer a clean and simple alternative to fuel-burning engines and generators for domestic water, livestock and irrigation  . They are most effective during dry and sunny seasons. They require no fuel deliveries, and very little maintenance. Solar-powered lighting is an effective way to implement illumination solutions in terms of technology and consumption  . Global pressures were made to protect the environment, which has become a priority. In meeting these types of problems, various systems have been developed to replace traditional lighting with energy efficient lighting. The most common method is the LED (Light Emitting Diode) technology.
Various system simulations and dimensioning were developed for specific regions and applications, but using only one type of PV technology. In the paper “Performance analysis of a 190 kWp grid interactive solar photovoltaic power plant in India”, V. Sharma and S. S. Chandel have used polycrystalline modules to assess the performance of a power plant installed in India  .
In the paper called “Simulation and performance analysis of 110 kWp grid- connected photovoltaic system for residential building in India: A comparative analysis of various PV technology”, a similar approach is considered for a system to be implemented in a residential building in India. Four types of PV technologies were simulated to determine performance ratios and energy yield  .
The purpose of the present paper is to identify the best solar cell technology that offers the highest system performances in a specific location. In order to define the most efficient solution that could be implemented in a given location, simulations were developed using monocrystalline, polycrystalline and CIS photovoltaic modules  .
2. Real-Life Usage
Solar-powered lighting is an effective way to implement illumination solutions in terms of technology and consumption. Global pressures were made to protect the environment, which has become a priority. In meeting these types of problems, various systems have been developed to replace traditional lighting with energy efficient lighting. The most common method is the LED technology (Light Emitting Diode).
The design and simulation also provides general information and guidelines on planning and designing of small solar powered water pump system for use in irrigation and livestock feeding operations. One benefit of using solar energy to power water pump systems is that increased water requirements tend to coincide with the seasonal increase of incoming solar energy. When properly designed, these systems can also result in significant long-term cost savings. Aside irrigation and livestock feeding operations, these systems can and are being used for potable water supply in underdeveloped countries. As more and more groundwater sources become unsafe for drinking purposes, potable water often needs to be drawn from depths that require pumping. A Solar-Powered Water Pumping System uses solar energy to power a pump to supply a village with potable water. Solar pumping systems are also commonly being used where it is too far to walk to a well or where the well only provides seasonally usable water.
3. About PVSyst Simulation Software
The PVSyst software used in our study is one of the most comprehensive programs used for sizing and simulations of various PV systems. The software manages various types of photovoltaic system analysis like stand-alone PV systems, grid connected of hybrid systems. PVSyst uses meteorological data from international databases as well as detailed information about the component technical specifications  .
4. Sizing and Simulations for PV LED Lighting System
We have chosen the PVSyst software application for comparing various solar cell technologies that could power a photovoltaic lighting system. In order to obtain conclusive results, we varied only the solar cell technologies, but the other components of the system remained unchanged. The sizing for this type of system will be as a stand-alone type, meaning that connection to the local energy grid is not required. Most of this type of systems require means for energy storage, therefore our system will use a solar battery. The PV application must be dimensioned to fully charge the batteries when exposed to maximum intensity for the given application. To avoid the possibility of damaging the system because of solar radiation fluctuations or battery overload, the system will be equipped with a charge controller.
One of the main components of the system is the lighting fixture (Figure 1). This is an ELMA 80-12 component provided by Electromagnetica SA, a company that specialized in manufacturing LED system components for lighting fixtures, and provides the following advantages: easy configuration and install, ecologic product, very high energy efficiency, low heat emissions, high reliability coefficient, low maintenance costs. The main technical parameters provided by Electromagnetica SA in the product technical sheet for the lighting fixture are presented in Table 1, as follows  .
The PV system is intended to provide two days autonomy, in order to compensate for days with high cloudiness. This feature will result in a slightly oversized PV generator and battery. The types of PV technologies used in the simulations are monocrystalline silicon, polycrystalline silicon and CIS solar cells. In order to choose the most suited solar battery for the system, important factors are considered, like daily energy consumption (27 W), number of days for system autonomy (2 days), battery voltage (12 V) and discharge coefficient (0.4). To obtain the battery capacity, the following equation was used  :
Figure 1. ELBI lighting fixtures.
Table 1. Main technical characteristics of ELMA LED.
Taking this result in consideration, for all the different types of PV technologies used in the simulations, we have considered a Deka battery of 12 V/90 Ah. The solar radiation data for the photovoltaic generators were required from Meteonorm database for Bucharest site and is presented in Table 2  , as monthly daily values [kWh/m2/day].
The simulation results of the photovoltaic system using monocrystalline silicon shows that for January, November and December months, the system fails to provide 3068 kWh of energy needed. A quantity of 75.68 kWh is lost due to the battery capacity. This problem could be adjusted by lowering the power of the PV modules.
Results using polycrystalline silicon, as well as the monocrystalline silicon indicate that in January, November and December, the system cannot fulfill the total system energy needs, by a quantity of 2546 kWh. Battery losses are also present in the quantity of 80.19 kWh. This could also be adjusted by using smaller PV modules but, it is important to take into consideration the solar resources in the months that with low solar radiation.
In Table 5, numerical simulation results for the PV LED system using CIS (Copper, Indium and Selenium) cells are presented, while Figure 4 shows the normalized energy and the performance ratio of the system.
Simulation results for CIS technology shows that a total of 2717 kWh is missing in order for the system to operate at maximum capacity. A total of 80.06 kWh are lost due to full battery.
Table 2. Mean daily values for Bucharest location.
Table 3. Monthly numerical simulation results for PV LED system using monocrystalline silicon modules.
where: -GlobHor represents Horizontal global irradiation; -GlobEff represents Effective global irradiation corrected for IAM and shadings, where IAM is the Incidence Angle Modifier; -EAvail represents the produced solar energy; -EUnused represents losses due to unused energy; -EMiss represents the missing energy in order for the system to function; -EUser represents the energy supplied to the user; -ELoad represents the energy needed of the user; -SolFrac represents the Solar Fraction, which is calculated as EUser/ELoad  .
Figure 2. Normalized energy productions, system performance ratio and solar fraction for monocrystalline silicon modules.
Table 4. Monthly numerical simulation results for PV LED system using polycrystalline silicon modules.
Figure 3. Normalized energy productions, system performance ratio and solar fraction for PV LED system using polycrystalline silicon modules.
Taking into account the obtained results, in this study the polycrystalline silicon offers the best yield. This is highlighted by the annual solar fraction between the energy supplied and the energy needed of the system. However, the overall energy loss caused by the full battery situations is 80.19 kWh, which is the highest of the analyzed situations. During the simulations, the modules used are almost identical in means of power and voltage, the main differences are the type of cells used. The simulation program estimates the module losses reported to the power tolerance, namely to a value of half of the inferior tolerance. This value is given by the manufacturers. During simulations, because of different manufacturers and power tolerance values, it could explain the fact that the polycrystalline silicon is more efficient than monocrystallinne silicon.
Table 5. Monthly numerical simulation results for PV LED system using modules with CIS cells.
Figure 4. Normalized energy productions, system performance ratio and solar fraction for PV LED system using modules with CIS solar cells.
5. Sizing and Simulations for PV Water Pumping System
The PV pumping systems are able to deliver water both for irrigation and local water supply. These pumps are usually using direct current for operation that means that the power could be delivered straight from the PV modules. The pumps that use alternative current are also used but have some disadvantages, for example the system components are more complex and the yield drops when the type of current is changed by inverter.
In order to simulate a PV pumping system properly, we have used specific steps for choosing the right components of the system  . These steps are:
1-identification of the water needs,
2-identification of the water supply,
3-identification all necessary components and their location,
4-designing a water storage component,
6-identification of needed water flow,
7-identification of total dynamic head pump,
8-pump selection and nominal power,
9-PV system design.
The project simulates the need of water in a farm in Romania. The water need for the project is calculated for 100 cattle. The farm area is contained in 16 hectares of land. We need that the system will be able to supply water in the period of May-September from a water well, when the animals are grazing. A storage tank will also be used, to store the water in order for the system to function in periods with clouds or poor solar availability  . A comparison between the different types of PV cells is made and the results are presented in the following tables and figures.
Figure 5 represents the simulation of the PV water pumping system using polycrystalline cell technology.
Table 6 represents the numerical simulation results for polycrystalline cell technology on an average monthly basis.
The results show that from the annual needed water amount of 1460 m3, the system provided an amount of 1331 m3. Energy in the amount of 46 kWh was lost due to the system oversize and annual, the amount of 8.9 % of water was not provided. Months in which the system is unable to provide water are January, February and December. This is due to the low solar radiation availability needed to power the system.
Table 7 represents the numerical simulation results for the PV pumping system using CIS (Copper, Indium and Selenium) cells, while Figure 6 shows the normalized energy and the performance ratio of the system.
Figure 5. Normalized energy productions, system performance ratio and solar fraction for PV pumping system using polycrystalline silicon modules.
Table 6. Monthly numerical simulation results for PV pumping system using polycrystalline silicon modules.
where: -GlobEff represents Effective Global radiation correlated for IAM shadings; -EArrMpp represents Array virtual energy at MPP; -EPmpOp Pump represents the operating energy; -ETkFullis the unused energy (when the water tank is full); -WPumped represents the amount of water pumped; -WUsed represents the water drawn by the user; -WMiss represents the missing water  .
Table 7. Monthly numerical simulation results of PV pumping system using modules with CIS cells.
Figure 6. Normalized energy productions, system performance ratio and solar fraction for PV pumping system using modules with CIS solar cells.
The simulation results conclude that from an annual quantity of 1460 m3 of water, the system provided a quantity of 1309 m3. An overall energy of 18 kWh was lost due to oversizing the system. The annual missing water quantity is 10.3%.
Table 8 represents the numerical simulation results for the PV pumping system using modules with monocrystalline cells, while Figure 7 shows the normalized energy and the performance ratio of the system.
The results show that the system delivered 739 m3 of water. There were no energy losses due to oversizing the system and the overall missing water quantity is of 49.4%. The reason this simulation has a very low yield is due to the fact that the voltage of the PV module (16 V) resides below the converter working voltage (19 - 38 V). Another converter more suited for this system could be installed to obtain better results, however in the PVSyst database, such converter doesn’t exist.
Sizing and simulations of a photovoltaic system before installation are a very important step. Critical information could result in finding unknown errors in the system or, why not, enhancing the system overall yield.
This paper shows the results of systems using various solar cell technologies but with almost identical BOS components  . For the analyzed systems, our simulations show that polycrystalline solar cell technology offers the best results in terms of overall yield. However, we have to take into consideration that these results are dependent by a series of factors like emplacement, solar resources availability, type of application, operating period, etc., and could differ from other PV application projects in various regions.
Further studies could also take into consideration grid-connected photovoltaic systems, however, in order to improve results, data regarding implementation and simulations of additional system components like inverters and regulators
Table 8. Monthly numerical simulation results for PV pumping system using modules with monocrystalline silicon cells.
Figure 7. Normalized energy productions, system performance ratio and solar fraction for PV pumping system using monocrystalline silicon cells.
should be considered.
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 Diaconu, A., Moraru, A. and Fara, L. (2013) PV Pumping Systems. Case Study: Sheep Farm in South Romania. Proceedings of the International Conference on Energy Efficiency and Agricultural Engineering, Ruse, Bulgaria, 17-18 May 2013, 606-616.
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