The objective of this work is to analyze and evaluate the impact of cooling systems on photovoltaic modules (for electricity generation), applied at a pilot Testing Facility. The results obtained during this step are used as input in order to determine the best model to be applied at a real-scale Photovoltaic Power Plant (PVPP). This methodology is based on the monitoring and supervision of the operating temperature of commercial photovoltaic modules (PV), both with and without cooling systems, as well as on the study of the water supply design of the cooling system applied on a micro photovoltaic power plant which is connected to the commercial network. Through the analysis of the data, we observed that photovoltaic modules with cooling systems always operate at lower temperatures than the ones without cooling systems. During the testing period, the operating temperatures of the photovoltaic modules without cooling systems were above 60 oC (with a maximum temperature equaling 68.06 oC), whereas the maximum temperatures registered on the sensors of the model “A” were 43.55 oC and 44.75 oC, and the ones registered on the sensors of the model “B” were 46.76 and 48.33 oC. Therefore, we conclude that the photovoltaic module with the cooling system model “A” is the most suitable for large-scale application, since it was the only model to present temperatures lower than the nominal operating condition temperature (NOCT) of the cell (47 oC ± 2 oC).
Research and Development (R & D) entail a methodology and/or a scientific method which provides the guidelines for reaching a certain goal. Moreover, it entails an infinite number of tests, reproductions, and validations, guaranteeing the validity of the research. The empirical method, which is based on experiment and observation, generates knowledge that enables the evaluation of specific phenomena, providing a solid basis for the process of decision-making. Therefore, it is a tool that enables the observer to conclude his experiment and/or theory based on facts [
The Testing Facility (TF) (see
In terms of physical architecture, the TF has a metallic structure to support the modules which consist of zinc-coated steel beams connected to two horizontal concrete columns on the building terrace. Furthermore, the metallic beams present several holes along their length where a power box is installed in order to regulate the energy input of the water pumps [
Thus, the aim of this work is to systematically study and analyze the performance of the models of Modular Cooling Units (MCU) applied at an on-grid micro PVPP in order to select the model with the best thermal performance.
This methodology is based on a detailed description of the procedures and empirical methods applied on the operational tests used at the testing facility (TF) which was designed as a model for the monitoring and supervision of such procedures.
Since the following are subject to weather conditions, the operational tests on the TF’s comprise of measurements of temperature, energy production, and water-use; evaluation of the process of installation of the cooling system, and the resistance and lifetime of the materials during the operation. The operation of the cooling system is described in
At point 1, supply line. The water circulates permanently in order to reduce the operating temperature on the PV modules. This line is filled by two reservoirs of 10.0 m³ each, providing water to the MCU, which are connected in a series;
Point 2, discharge line, conducts the cooling fluid from the exit of the cooling system to the reservoir. Thus, all the water used in the system is returned to the reservoir, avoiding extra costs regarding water withdraws;
The module PV-2, PVa (with cooling system), receives the model B of the MCU;
The module PV-3 receives the model A of the MCU;
The module PV-5 receives no MCU and is used for comparison purposes.
The system that measures the temperatures consists of six thermal resistances,
type PT-100 [
PV | Code PV | Cooling Model | Sensor PT-100 | Code PT-100 |
---|---|---|---|---|
1 | PV | - | - | - |
2 | PVa | Model B (140.0 mm) | SM SP | Meio_B Ponta_B |
3 | PVa | Model A (85.0 mm) | SM SP | Meio_A Ponta_A |
4 | PV | - | - | - |
5 | PV | - | SM SP | Meio_Sem Ponta_Sem |
During the testing period the water supply did not present any problem related to interruptions or leakages. Initially, the water supply operated at a turbulent flow of 4.83 × 10−4 m³/s and Reynolds (Re) equaling 32,257 (see
The daily period of electricity production, which was registered by the inverter during the 61 days of measurements, starts at 06:10 am and finishes at 07:00 pm on the longest day. The mean daily period of electricity production is 11 h:13 min, the maximum is 12 h:10 min (on the 05/03/2015) and the minimum is 10 h:10 min (on the 06/03/2015).
Data | Unit | Beginning | End |
---|---|---|---|
Flow | Q (m³/s) | 4.83 × 10−4 | 6.6 × 10−5 |
Speed | u (m/s) | 1.69 | 0.23 |
Diameter | D (m) | 1.91 × 10−2 | 1.91 × 10−2 |
Kinematic Viscositya | n (m²/s) | 1.00 × 10−6 | 1.00 × 10−6 |
Reynolds | Re | 32,257 | 4,415 |
Flow type | - | Turbulent (Re > 10.000) | Transition (2.000 < Re < 10.000) |
aKinematic Viscosity (n (T, P)) calculated in Normal Temperature and Pressure (NTP) Conditions.
Date (dd/mm/aaaa) | Time (hh:min) | Ti (˚C) | To (˚C) | Ta (˚C) |
---|---|---|---|---|
05/03/2015 | 10:09 | 21.0 | 21.0 | 28.9 |
16/03/2015 | 10:00 | 20.5 | 20.5 | 26.2 |
31/03/2015 | 10:00 | 21.0 | 21.0 | (a) |
14/04/2015 | 11:04 | 21.5 | 21.5 | 28.6 |
31/04/2015 | 10:29 | 20.5 | 20.5 | (a) |
(a)No ambient temperature available.
The analysis of the maximum and the minimum values, which occurred on consecutive days, reveals that climate factors have a strong influence on the production of electricity. This fact is more evident in
An important analysis of energy systems is given through the energy Yield (Y), here meant as the ratio between net energy output and the systems installed capacity (kWh/kWp). The energy yield provides a relative measure that allows inter-comparison among different projects, dimensions, and technologies [
correspond to the testing period, and the consecutive months (5, 6, 7, 8, 9, 10 and 11), reveal that these present a more oscillating behaviour. The overall energy yield is equal to 1659.97 kWh/kWp.
The analysis of the graphs on
The temperatures measured on the modules PV-2 (TPV-2), PV-3 (TPV-3) and PV-5 (TPV-5), with and without MCU, vary daily. By analyzing the data shown on
tively good performance for the period, presenting a REDP equaling 13.62 and an electricity output equaling 6.81 kWh/day―both above the mean value for the testing period.
On the 16/03/2015 the system presented a rather low performance since both the REDP (10.22) and the electricity output (4.72 kWh/day) lied below the average. By comparing the
Through the analysis of
highest difference among the minimum and the maximum temperatures during the testing period. By analyzing the temperature difference within the same PV module (ΔTPV), PV-3 presents ΔTPV-3 = 2.06˚C, PV-2 has ΔTPV-2 = 2.26˚C, and PV-5 ΔTPV-5 = 0.67˚C. Furthermore, both temperatures registered on the PV-3 show that it operates below the Nominal Operating Cell Temperature (NOCT) de 47˚C ± 2˚C [
The highest electricity production occurred on the 02/04/2015, 7.82 kWh/day, presenting the second highest REDP equaling 16.31.
output shows the highest score for the testing period, the maximum temperature registered on this day was 10.75˚C lower than the one registered on the 16/03/ 2015. Moreover, the Tmax registered on the 02/04/2015 occurred at the sensor “Meio_sem”, whereas the one registered on the 16/03/2015 occurred on the sensor “Ponta_Sem”.
During the testing period, 235 measurements of temperature were higher than 60˚C and they were observed on 21 days, representing 34.4% of the period. These measurements presented a mean value (Tmean) equaling 62.01˚C, the minimum equaling 60.01˚C, and the maximum equaling 68.06˚C. The observations occurred exclusively on the PV-5 module, from which 77.0% occurred on the sensor “Meio_Sem”. At the same time, the minimum temperatures were registered on the PV-3 module, from which 97.4% occurred in the sensor “Meio_A” (see
In terms of the temperature difference among the same PV module (see
equaling 5.12˚C (the highest maximum value observed). Moreover, the temperatures registered on the PV-3 module show that it operated once more below the NOCT, with maximum temperatures equaling 43.55˚C and 44.75˚C, respectively on the sensors “Meio_A” and “Ponta_A” (see
Several photos were taken on the 04/03/2015 at three different times (10:00 am, 12:00 pm and 03:00 pm). The focus was to cover the region where the sensors PT-100 were applied on the inferior surfaces, and the superior surfaces of the PV modules.
The analysis of the images revealed the temperatures ordered as TPV-3 < TPV-2 < TPV-5, corroborating the observations obtained from the sensor PT100 (see
PV | Cooling Model | Sensor PT-100 | Tmean (˚C) | Tmin (˚C) | Tmax (˚C) |
---|---|---|---|---|---|
2 | Model B | Meio_B | 44.21 | 42.49 | 46.76 |
Ponta_B | 45.90 | 43.84 | 48.33 | ||
3 | Model A | Meio_A | 41.48 | 39.40 | 43.55 |
Ponta_A | 42.61 | 40.24 | 44.75 | ||
5 | - | Meio_Sem | 61.86 | 58.86 | 67.39 |
Ponta_Sem | 60.73 | 56.06 | 68.06 |
Period (hh:min) | PV | Cooling Model | Sensor PT-100 | T (˚C) |
---|---|---|---|---|
10:00 am | 2 | Model B | Meio_B | 40.9 |
Ponta_B | 39.2 | |||
3 | Model A | Meio_A | 36.6 | |
Ponta_A | 37.1 | |||
5 | - | Meio_Sem | 56.6 | |
Ponta_Sem | 55.4 | |||
12:00 pm | 2 | Model B | Meio_B | 41.9 |
Ponta_B | 40.0 | |||
3 | Model A | Meio_A | 36.1 | |
Ponta_A | 35.5 | |||
5 | - | Meio_Sem | 55.2 | |
Ponta_Sem | 54.0 | |||
03:00 pm | 2 | Model B | Meio_B | 35.7 |
Ponta_B | 35.3 | |||
3 | Model A | Meio_A | 32.3 | |
Ponta_A | 33.5 | |||
5 | - | Meio_Sem | 44.1 | |
Ponta_Sem | 43.7 |
region near the junction box, specifically the lower right corner, where the energy transmission takes place.
The supervision and monitoring of the PV modules (as the models A and B) were not trivial tasks, since the technology is new, lacking a solid theoretical background, and challenging the interpretation of its real operation. In order to overcome such limitations, the previous elaboration of the methodology produced satisfactory results.
The water supply system operated permanently and without leakages to the ducts and junctions. The operation of the system had no influence on the amount of water stored in the reservoirs. The temperature of the water at the entrance and at the exit remained equal. The only issue regarding the water supply system was the difference in the water flow if compared to the beginning and the end of the testing period, varying by 86%.
The results show that the PV-2 and the PV-3, both with a cooling system, operated at lower temperatures than the PV-5, without a cooling system. The daily maximum temperatures occurred exclusively in the PV-5 module, with Tmean, Tmín and Tmax equaling 62.01˚C, 60.01˚C and 68.06˚C, respectively. The difference between these temperatures and the minimum ones is 20.53˚C higher than the average, with a minimum difference equaling 17.7˚C, and a maximum equaling 25.61˚C. All minimum temperatures were registered on the sensor PT-100 in the PV-3 with cooling system model A.
The comparison between PV-2 and PV-3 reveals that PV-3 always operates at temperatures below 45˚C. Thus, the cooling system model A allows the the PV modules to operate at a temperature below the NOCT, since the maximum temperatures observed in the PV-3 were 43.55˚C and 44.75˚C, in the sensors Meio_A and Ponta_A, respectively. Moreover, the differences between the temperatures registered in the same module are lower in the PV module with the cooling system model A (the average value equaling 1.13˚C), than the ones registered in the PV module with the cooling system model B (the average value equaling 1.69˚C).
The analysis of the performance factors (Y and FC) indicates that the TF presented lower monthly oscillations when the cooling system operates (Ymin and Ymean 0.01 and 0.1, respectively).
Therefore, the model of MCU selected for a large-scale application that is to be installed as the prototype of the PVPP is the model A.
To CAPES, for the scholarship, to CESP for funding the R & D ANEEL PE-0061-0037/2012 which enabled the conclusion of this article. To the team of GEPEA/EPUSP researchers and collaborators who helped direct and indirectly on the accomplishment of this R & D project.
da Silva, V.O., Udaeta, M.E.M., Gimenes, A.L.V. and Linhares, A.L. (2017) Improving the Performance of Photovoltaic Power Plants with Determinative Module for the Cooling System. Energy and Power Engineering, 9, 309-323. https://doi.org/10.4236/epe.2017.95021