COMPARISON REVIEW BETWEEN MONOFACIAL AND BIFACIAL SOLAR MODULES

The objects of the study are solar modules. The world has witnessed a change in all aspects of life, especially in the last period, when the world witnessed an increase in the demand for energy and all regions. Here the imperfection appeared in meeting the energy needs, just as the traditional sources (oil, coal, and natural gas), for example, are no longer hope as they are non-renewable sources. In addition to these sources, to exploit the energy in them, we must burn, which pollutes the environment, in addition to the cost of transportation. Not long ago, solar energy began to produce electricity through photovoltaic modules, and competition began to make photovoltaic modules with higher efficiency. The main aim of this study is to clarify the concept of bifacial photovoltaic modules and show some differences between them and monofacial photovoltaic modules. The current report consists of the definition of bifacial photovoltaic modules and their most important specifications, comparing them with monofacial photovoltaic modules, which are the best, the factors affecting their energy production, and the type of radiation used in each type. In fact, the utilization of albedo radiation for monofacial photovoltaic modules does not exceed 2 %, while this percentage is exceeded in bifacial photovoltaic modules. So, it can be recommended here that the trend to use bifacial photovoltaic modules can be economical and space-saving space because it produces more amount of electricity for the same unit area, which in turn this spaces it available for other applications, and also, increase the amount of electricity due to the increase in the effective side size (two sides: one upwards and the other is downward) of the solar modules.


Introduction
A photovoltaic module is a device that converts solar energy directly into electrical energy by the Photovoltaic effect.It provides its current, voltage, and resistance, as well as a physical and chemical phenomenon [1][2][3].The radiation from the sun to the earth is divided into direct radiation that reaches directly to the earth's surface, called direct normal irradiance (DNI) [4][5][6].Scattered radiation usually happens due to two reasons Clouds and Negative Ozone Anomalies (NOA) [7][8][9].Albedo radiation definition is the ratio between the radiation coming from the sun and the radiation incident to the surface of the earth [9][10][11].The patent for a bifacial solar module was registered in 1979.This module is effective on both sides, meaning that both sides convert the radiation falling on it into direct electricity [12,13].The manufacture of a bifacial solar module is more expensive than the monofacial solar module due to the presence of additional mate rials such as (cells and glass) due to the presence of two effective sides in the cells and what requires glass and cells from both sides [14].It's important to study and differentiate between different technology of Photovoltaic cells to optimize and investigate their performance and the effect of weather conditions on power production in an actual system [15,16].
In Fig. 1, the upper left represents the structure of a monofaical solar cell and one layer of anti-reflection coating (ARC).The upper right represents the module of the same solar cell, the authors also see that there is one glass layer from the top of the cell, which is the part that is upward towards the sun.The bottom of all the cells is a back sheet layer to put the cells on top of, and there is an EVA layer for more protection.In Fig. 1, We also see in the lower left bifacial solar cells with two layers of (ARC), In the lower right, we see the module for bifacial solar cell, and we also see that there are two glass layers at the top and bottom of the cell.
It became known that albedo is the amount of solar radiation reflected from the earth's surface by water, trees, land, snow, etc., directly upwards or repeatedly bumping and reversing.
In monofacial solar cell systems, the utilization of albedo cells ranges from (1 to 2) percent [18].Recent studies have shown that bifacial solar cells' power gain ranges between 13-35 % in sunny weather and 40-70 % in cloudy conditions [19].We know that albedo is part of the sunlight falling on the earth's surface.And this radiation varies TECHNOLOGY AUDIT AND PRODUCTION RESERVES -№ 6/1(68), 2022 ISSN 2664-9969 based on the spectral distribution and the sun's angle of incidence.These differences are based on the change in the sun's position in the day, location (latitude), and clouds in the sky [18].
Table 1 provides the albedo value for the various surfaces, and the given albedo value is the annual mean.The author notes from the values given in the table and chart that there is a discrepancy in the albedo value based on the surface on which it fell.Hence, we can say that the amount of albedo will not be equal in all places, Since the most benefit from albedo is over pasture grass, and less albedo is over Semidesert grassland.
Fig. 2 explains and shows the difference between albedo values by location (surfaces).
After we learned that the bifacial solar module benefits from direct sunlight and albedo; this is one of the most important advantages.
Also, the sensitivity of the module for orientation to the south is lower, meaning that there is flexibility in choosing the orientation.When there are obstacles that do not allow the direction to the right south, it can be placed as close to the south as possible [20].
The power generated per unit area of the bifacial solar module is greater than that of the monofacial solar module.
This means we can save more space to generate the same amount of power [20].
Also, the bifacial solar cells are characterized by the effect of warping due to the small difference in thermal expansion between silicon and aluminum.It also reduces electrical losses due to aluminum absorption of spectral light [21].The biggest disadvantages of a bifacial solar cell are the high cost compared to monofacial solar cells due to the presence of additional materials, such as cells on both sides of the module [16].ISSN 2664-9969

Materials and Methods
The subtitles will be discussed here, is the performance in energy production, temperature effect in both types, and bifacial solar cell datasheet.
2.1.Performance in energy production.The performance of solar cells in terms of electricity production varies according to the intensity of the radiation falling on them, and this is what we will discuss in this section.
As shown in Fig. 3, a, the electricity production in both types increases at sunrise and reaches its peak at approximately noon since there are no clouds in the sky.That is, there does not impede the arrival of sunlight to the surface of the solar cell and the surface of the earth, meaning that albedo is present and can be exploited.
In Fig. 3, b as for here, in the presence of clouds in the sky, the production of electricity is greatly affected by the decrease in value.
2.2.Temperature effect in both types.The performance of solar cells varies depending on temperature (ambient air temperature) as well as solar radiation and wind cooling processes [23], the increase in the temperature of the solar cell reduces the voltage that given [24].
Fig. 4 shows the effect of a monofacial solar cell on radiation and temperature.As shown in Fig. 4 IV curve for the same solar cell at different radiation intensity and operating temperatures, the radiation intensity ranged from 0-100 mw/cm 2 , and the operating temperature ranged 20-50 °C.We note well that the higher the temperature, the lower the voltage, which leads to a decrease in the power coming out of the solar cell.We also note that the increase in the radiation value increases the current coming out of the solar cell.
Fig. 5 shows the IV curve for the bifacial solar cell under different temperatures for the front and rear sides.Also, it shows the voltage and current at two ranges of temperatures 25 °C and 50 °C for two modules (B and D) at the same power density of 1000 W/m 2 .As the case in the polycrystalline solar cell, the increase in the temperature of the solar cell leads to a decrease in the value of the voltage.Here the voltage output from the front and rear sides are both affected by temperature.2.3.Bifacial solar cell datasheet.From the literature review, the bifacial cells are producing more power.When looking at Table 2 and Fig. 6, we see the characteristic (thermal and electrical), and can compare them with any data sheet for monofaial module.
The result can be that the bifacial module gives more power value if the cell in module is in the same characteristic.ISSN 2664-9969

Results and Discussion
The comparison between monofacial and bifacial solar cell are shown in Table 3 and Fig. 7.It became clear from Table 1 that solar cells depend on their production for power, effective surface area, radiation intensity, and operating temperatures, the use of bifacial solar cells is better in terms of the value of the output of electricity.Still, it is more expensive.On the other hand, the electrical losses are more in monofacial solar cells, the utilization of albedo in bifacial solar cells is better, and the power generated per unit area is better in bifacial.The ability of warping is large in monofacial compared to bifacial.The need for the right orientation is more significant in monofacial than bifacial, the performance of bifacial in cloudy time is better than the monofacial, increasing in temperature effect in both types as reducing the output voltage.Fig. 7 below explain the difference between monofacial and bifacial solar cell in different parameter.The use of bifacial photovoltaic modules is available for work in all areas, and the quality of this work lies in areas where the reflection of solar radiation increases, as well as it is suitable to work in areas where the concentration of solar radiation is low.
For example areas with a floor of Semidesert grassland (20.4 % of reflection for incident radiation), it is considered the least suitable land for the use of this application of solar modules because there is the area with the least reflection of the sun's rays, compared with the Pasture grass areas (26.2 % of reflection for incident radiation), it is considered the best suitable land for the use of this application of solar modules because there is the area with the most reflection of the sun's rays.Can be understood from this research that the use of bifacial modules may be the future of electricity production from solar modules.As well as saving space, installation, and transportation costs.This is due to the need for fewer modules from bifacial to produce the same amount of electricity in comparison with monofacial modules.In addition, it concluded from the current research that the use of bifacial cells in the best case is in Pasture grass areas, with the highest maximum power of modules to obtain the highest possible cell efficiency.
It should be taken into account that the cleaning of bifacial modules, it is harder than monofacial modules because the upper and lower sides must be cleaned to obtain the maximum power, likewise cleaning the lower part added cost, effort and time.On the other hand, the cleaning of bifacial modules need special technique.As well as the cooling technics for bifacial module is difficult than the monofacial modules to reduce the temperature of solar cell to enhance the PV module performance.

Conclusions
This study concludes from the previous research that changing to the use of bifacial solar cells can produce a greater amount of electrical energy, if we take into account that the price of bifacial solar cells is higher than the monofacial solar cell, what motivates people to use bifacial cells is their greater production of electricity, and these cells are exploited for that albedo radiation, which varies from place to place and from one surface to another.It may not be feasible on some surfaces, such as Tallgrass prairie.The best design for bifacial cells is to have pasture grass underneath because it reflects 26.2 % of the radiation falling on it.If cleaning is a defect of solar cells in general, the use of bifacial may constitute an additional burden for cleaning matters.The presence of glass on both sides requires more consideration in transportation and installation.To reduce the areas used in producing electricity with solar energy, the use of bifacial may be feasible, and the purchase of land may be expensive; this is also a saving.

Fig. 2 .
Fig.2.The difference value of albedo for some surfaces

Table 1
Albedo reflected from some surfaces

Table 2
Electrical and Thermal characteristics of bifacial solar module [26]s: the table is based on data from[26]; * STC: means Air Mass AM 1.5, Irradiance 1000 W/m 2 , Cell Temperature 25 °C

Table 3
Some points of comparison between monofacial and bifacial solar cell