# Performance Evaluation of Photovoltaic Solar System with Different Cooling Methods and a Bi-Reflector PV System (BRPVS): An Experimental Study and Comparative Analysis

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## Abstract

**:**

## 1. Introduction

## 2. Materials and Methods

#### 2.1. Electrical Modeling

_{L}with a p-n junction diode connected in parallel. This also has a parallel resistance, ${R}_{sh}$, and series resistance, ${R}_{s}$, as shown in Figure 2.

#### 2.2. Optical Modeling

_{module}). Irradiance (W/m

^{2}) on the surface of the module due to reflection (${G}_{m}^{i}$) can be calculated using relation [31]:

#### 2.3. Proposed Cooling Techniques

_{oc}) decreases. At the same time, a lower band gap allows more incident energy to be absorbed because a larger percentage of incident light has sufficient energy to raise charge carriers from the valence band to the conduction band; a larger photocurrent results. As the temperature is raised, however, the internal resistance of the material increases and the electrical conductivity decreases. The current increase for a given temperature rise is proportionally lower than the voltage decrease. Hence, the cell efficiency is reduced. Cooling systems are needed to reduce the temperature and increase the efficiency of solar PV modules. Based on a literature survey and previous work, the following four cooling techniques were compared to achieve the most effective cooling system for a solar PV system.

#### 2.3.1. Passive Air Cooled System

#### 2.3.2. Closed Loop Water Loop System

#### 2.3.3. Air Cooled System

#### 2.3.4. Water Sprinkling System

## 3. Experimental Setup

^{2}area was used. The convex mirror scatters light so two convex mirrors, 15 cm in diameter each, were fixed together and used as a reflector, as shown in the figure. Three different size aluminum foil reflectors were used to obtain a normalized value for the effect of the reflectors on solar panel output. The size of the first, second, and third reflector was 0.0648 m

^{2}(one-third of panel size), 0.1296 m

^{2}, and 0.1944 m

^{2}, respectively.

## 4. Results and Discussion

^{2}that was then converted to kW/m

^{2}to make the data compatible, easily understandable, and comparable to the existing published data. Maximum, minimum and mean temperatures of Busan and Arusha are given in Figure 6a,b, respectively.

^{2}(1000 W/m

^{2}), which is a standard solar PV designed parameter, was obtained. During December, January, and February the solar irradiance in the morning (7:00 am to 10:00 am) and evening (3:00 pm to 6:00 pm) was no more than 0.54 kW/m

^{2}. At the afternoon (11:00 to 2:00 pm) it was 0.63 kW/m

^{2}. Similarly, during a moderate weather period from March to May, the maximum solar irradiance was 0.70 kWh/m

^{2}, which is still less than the peak solar irradiance defined for the solar panel. In summer (June-July-Aug and Sept), this value increased to 0.95 kWh/m

^{2}but the problem is the temperature that also increases for solar panel and hence again solar PV system cannot generate electricity to its full capacity. Figure 7 shows that the solar irradiance for Busan at morning and evening varies throughout the year; however, these values are much less than the standard test conditions (STC) and there is always a chance to enhance the output power of PV modules using reflectors by increasing the amount of incident light on solar panel.

^{2}in morning (7:00 to 10:00) and evening (3:00 to 6:00). A reflector can show its effectiveness in increasing output power of PV module during these time intervals. At afternoon the values of irradiance are nearly equal to STC values. These dates and their corresponding solar irradiance data are as shown in Figure 8. It is very clear from the solar irradiance and temperature data of both sites that a reflector and cooling system are always needed to increase the solar radiations on PV module and control the temperature of solar PV module.

#### 4.1. Investigating Effective Reflector Material/Structure

_{oc}, I

_{sh}, and Power) of the solar panel with no reflector were then compared with outcomes of solar panels with plane using silvered mirrors, Al foil sheets and convex spherical mirrors as reflectors. The open circuit voltage (V

_{oc}) and short circuit current, I

_{sh}, for the plane, spherical mirror, and Al foil reflector were calculated from 8:00 am to 4:30 pm. A significant enhancement in output power using the reflector was noticed. As three different types of reflectors were used, the effects of each reflector material and structure were different. Maximum power delivered by the solar panel with no reflector was 16.84 W. Maximum power delivered by the convex spherical mirror, silvered coated plane glass and Al foil reflector were 17.44 W, 18.91 W and 20.31 W, respectively. The spherical mirror has a much less of an effect and Al foil showed a comparatively large effect from the plane mirror. Short circuit current and power curve showed this effect. Moreover, the reflector systems are more effective in the morning and evening and comparative less effective at noon.

#### 4.2. Finding Optimal Reflector Size and Angle

#### 4.3. Investigating Appropriate Cooling Technique

_{oc}), short circuit current (I

_{sh}), and output power of different cooling system were compared. Figure 14a shows that the open circuit voltage decreases with increasing temperature. The values for V

_{oc}are higher at 11:00 am and decreased with increasing temperature; the lowest values for V

_{oc}were observed between 1:00 pm to 2:00 pm, which then increased with decreasing temperature. Moreover, the values of V

_{oc}for water sprinkling and air cooled method were higher (20.9 V to 21.82 V) than V

_{oc}for the system with no cooling and system with heat sink (19.75 V to 21.18 V). V

_{oc}for the closed loop method was in the range of 20.51 V to 21.32 V.

_{sh}) curves for all the systems are shown in Figure 14b. The short circuit values for the solar panel with no cooling ranged from 6.56 A to 7.96 A between 11:00 am to 3:00 pm with maximum values between 12:30 pm to 1:30 pm. The short circuit values for the solar panels with heat sinks for heat dissipation were within the range of 6.66 A to 8.13 A between 11:00 am to 3:00 pm. The I

_{sh}values for the solar panel cooled with the water sprinkling method ranged from 7.05 A to 8.44 A between 11:00 am and 3:00 pm. The I

_{sh}values for solar panel with the closed looped system ranged from 6.73 A to 7.94 A between 11:00 am and 3:00 pm. I

_{sh}for forced air by fans ranged from 7.13 A to 8.21 A. The I

_{sh}values for the water sprinkling system were the highest, whereas the values for the heat sink method were the lowest.

#### 4.4. Combined Effect of Cooling System and Reflectors

#### 4.5. Cost Effective Solution, Optimal Control and Implementation Plan

_{th}) of 50 °C was decided and an algorithm that can provide for the optimal operation of the cooling system was developed and can be implemented easily on an Arduino controlled program with some basic electronics components. This algorithm describes the turn on the cooling system when T

_{th}= 50 °C and turn off the system when the solar PV module (T

_{PV}) = T

_{L}or when P

_{n}> P

_{n−}

_{1}, i.e., no improvement in output power using cooling system. An algorithm for the optimal control of BRPVS system is shown by the flowchart in Figure 18. Enhanced solar PV output power requires optimal BRPVS. The results in Section 4 show that the movement of reflectors varies with time and the optimal angle between the reflector and solar panel is required. Figure 18 shows an algorithm for the timed-based optimal control BRPVS system. If time t = t

_{n}, turn both reflectors on; if t < t

_{n}, move the right reflector described in the algorithm; if t > t

_{n}, move the left reflector to an angle given in the algorithm. The algorithm shown in the figure summarizes only the movement of the reflector based on the experimental studies in this research; an algorithm for hardware implementation may require a proper explanation of the system using a LDR/CDS sensor.

## 5. Conclusions

## Acknowledgments

## Author Contributions

## Conflicts of Interest

## References

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**Figure 7.**Solar irradiance of Busan (35°10′0″ N, 129°4′0″ E). (

**a**) Morning (7:00 to 10:00); (

**b**) afternoon (11:00 to 14:00) and (

**c**) evening (15:00 to 18:00).

**Figure 8.**Solar irradiance of Arusha (3°23′58″ S, 36°47′48″ E). (

**a**) Morning (7:00 to 10:00); (

**b**) afternoon (11:00 to 14:00) and (

**c**) evening (15:00 to 18:00).

**Figure 9.**(

**a**) Solar Panel open circuit voltage (V

_{oc}); short circuit current (I

_{sh}) and output power without any reflector; comparative analysis of the (

**b**) short circuit current (Ish); (

**c**) open circuit voltage (V

_{oc}) and (

**d**) output power of silvered glass plane mirror, convex spherical mirror and Aluminum (Al) foil.

**Figure 10.**Effect of reflector on temperature of solar panel: (

**a**) without reflector; (

**b**) convex spherical mirror; (

**c**) silvered glass plane mirror and (

**d**) Al foil sheet.

**Figure 11.**(

**a**) Output power using different Al foil reflector size and (

**b**) percentage increase with different sizes.

**Figure 12.**Output power of PV (

**a**) south 0°; (

**b**) south east (30° from south towards east) and (

**c**) south west (30° from south towards west).

**Figure 13.**Infrared thermal images of different cooling system (

**a**) no cooling; (

**b**) passive heat sink method; (

**c**) water sprinkling system; (

**d**) closed loop system and (

**e**) active air fans cooling system.

**Figure 14.**Comparative analysis of proposed cooling systems (

**a**) open circuit voltage (V

_{oc}); (

**b**) Short circuit current (I

_{sh}) and (

**c**) output power.

**Figure 15.**Combined effect of different cooling system with reflector on output power (

**a**) no cooling/Natural cooling; (

**b**) passive heat sink method; (

**c**) active air fans cooling system; (

**d**) closed loop system; and (

**e**) cooling by water sprinkling.

**Figure 16.**Comparative analysis of output power by heat sink method with natural cooling (no cooling) when other cooling systems are not operating i.e., Morning (9:30 to 11:00) and Evening (15:30 to 17:00).

**Figure 18.**(

**a**) Optimal control algorithm for cooling system and (

**b**) optimal control algorithm for Bi-reflector PV system (BRPVS).

**Table 1.**Technical properties of aluminum foil sheets [24].

Density | 2.7 g/cm³ |

Al Foil Specific Weight | 6.35 µm foil weighs 17.2 g/m^{2} |

Melting Point | 660 °C |

Electrical Conductivity | 64.94% IACS (IACS: International Annealed Copper Standard) |

Electrical Resistivity | 26.5 nΩm |

Thermal Conductivity | 235 W/m K |

Thickness | Foil is defined as measuring less than 0.2 mm (<200 µm) |

At Short Circuit | ${\left[dI/dV\right]}_{sc}=-1/{R}_{sh,ref}$ |

At Open Circuit Voltage | I = 0, V = Voc,ref |

At Short Circuit Current | I = Isc,ref, V = 0 |

At the Maximum Power Point | I = Imp,ref, V = Vmp,ref |

At the Maximum Power Point | ${[dI/dV]}_{sc}=$ 0 |

Model No. | SL-389 |

Voltage | 220–240 V |

Flow Rate | 500 L/H |

Frequency | 50 Hz |

Current | 0.07 A |

Head Max | 1.6 m |

Dimensions | 64 mm × 45 mm × 56 mm |

Power | 10 W |

Outlet | 13 mm diameter |

Dimensions (L × h × w) | 120 mm× 120 mm× 25 mm |

Voltage (V) | 12 VDC |

Safety Current (A) | 0.16 A + 10% |

Rated Current (A) | 0.15 A + 10% |

Power (watts) | 1.92 W + 10% |

Speed (R.P.M) | 1200 R.P.M + 10% |

Air Flow (CFM) | 44.73 CFM |

Air Pressure (mmH_{2}O) | 1.65 |

Noise (dB) | 19.1 dB |

Weight (g) | 120 g |

Color | black |

Bearing Type | Sleeve |

Life (h) | 30,000 h |

Cable Length | 300 mm |

Short Circuit Current | 1.38 A |

At Open Circuit Voltage | 21.5 V |

Maximum Power Voltage | 17.5 W |

Maximum Power Current | 1.15 A |

Maximum Power | 20 W |

Test Conditions | AM 1.5 25 °C 1000 W/m^{2} |

Time | No Cooling System (°C) | Heat Sink (°C) | Water Sprinkling Method (°C) | Closed Loop (°C) | Active Air Cooled (°C) |
---|---|---|---|---|---|

8:00 | 26.3 | 24.2 | OFF | OFF | OFF |

9:00 | 36.5 | 33.2 | OFF | OFF | OFF |

10:45 | 50.1 | 47.9 | Just turned ON | Just turned ON | Just turned ON |

11:00 | 54.8 | 51.7 | 35.1 | 46.1 | 39.2 |

11:15 | - | - | 37.2 | - | - |

12:00 | 61.1 | 58.3 | 35.7 | 55.2 | 39.7 |

12:15 | - | - | 38.2 | - | - |

13:00 | 66.9 | 62.1 | 37.1 | 57.1 | 39.9 |

13:15 | - | - | 38.9 | - | - |

14:00 | 65.1 | 61.3 | 36.1 | 56.1 | 39.1 |

15:00 | 58.1 | 55.1 | 35.1 | 49.9 | 37.1 |

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## Share and Cite

**MDPI and ACS Style**

Khan, M.A.; Ko, B.; Alois Nyari, E.; Park, S.E.; Kim, H.-J.
Performance Evaluation of Photovoltaic Solar System with Different Cooling Methods and a Bi-Reflector PV System (BRPVS): An Experimental Study and Comparative Analysis. *Energies* **2017**, *10*, 826.
https://doi.org/10.3390/en10060826

**AMA Style**

Khan MA, Ko B, Alois Nyari E, Park SE, Kim H-J.
Performance Evaluation of Photovoltaic Solar System with Different Cooling Methods and a Bi-Reflector PV System (BRPVS): An Experimental Study and Comparative Analysis. *Energies*. 2017; 10(6):826.
https://doi.org/10.3390/en10060826

**Chicago/Turabian Style**

Khan, Muhammad Adil, Byeonghun Ko, Esebi Alois Nyari, S. Eugene Park, and Hee-Je Kim.
2017. "Performance Evaluation of Photovoltaic Solar System with Different Cooling Methods and a Bi-Reflector PV System (BRPVS): An Experimental Study and Comparative Analysis" *Energies* 10, no. 6: 826.
https://doi.org/10.3390/en10060826