Artigo Energia Solar

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PV Systems in Warm and Sunny Climates: Performance Assessment of 
Commercially Available Solar Photovoltaic Technologies under 
Different Climatic Conditions in the Brazilian Energy Mix 
Lucas Rafael do Nascimento, Marília Braga, Ruany Dolla, Rafael Antunes Campos and Ricardo Rüther 
Universidade Federal de Santa Catarina (UFSC), Campus Universitário Trindade, Caixa Postal 476, 
Florianópolis – SC, 88040-900, Brazil 
 
Abstract — The performance assessment of seven different, 
commercially-available PV technologies was carried out at eight 
different climates in Brazil. The eight identical, fully-monitored 70 
kWp photovoltaic Evaluation Sites (ESs) have all electrical and 
environmental parameters measured at one-second intervals. The 
R&D project, funded by twelve Brazilian Electric Utilities in the 
scope of the Brazilian National Regulatory Agency’s R&D 
Program, aims at providing performance information for Utilities 
to make informed decisions on which PV technology to adopt in 
the forthcoming utility-scale solar energy auctions taking place in 
Brazil. The PV technologies evaluated are: thin-film amorphous 
silicon (a-Si), microcrystalline silicon (a-Si/μc-Si), cadmium 
telluride (CdTe), copper indium gallium diselenide (CIGS), and 
bulk mono and multi-crystalline silicon (c-Si and m-Si), all at 
fixed, latitude tilt, as well as double-axis tracking, concentrated PV 
(CPV) using InGap/GaAs/Ge at 820 suns concentration. 
Index Terms — cloud enhancement, PV performance, utility-
scale solar, O&M, PID. 
I. INTRODUCTION 
With the declining costs of photovoltaics (PV), and the 
excellent solar energy resource availability in the country, the 
Brazilian government and the electricity sector have started to 
evaluate and consider PV as a serious potential contributor to 
the national electricity mix. Since the late 1990’s, Brazilian 
electrical utilities are required by the National Electrical Energy 
Regulatory Agency (ANEEL) to invest 1% of their operational 
income on R&D. In 2011, ANEEL issued an R&D call 
dedicated to utility-scale PV. The solar energy research group 
at the Universidade Federal de Santa Catarina 
(www.fotovoltaica.ufsc.br) has been actively investigating and 
promoting PV in Brazil, and operates since 1997 the first grid-
connected, thin-film PV generator in the country [1]-[2]. 
This paper shows the results of this utility-scale R&D project 
with the PV assessment of six fixed, flat-plate PV technologies, 
as well as double-axis tracking concentrated PV (CPV) 
installed at eight different sites, with distinct Brazilian climatic 
conditions. The results also present some of the peculiarities 
observed during the continuous and high-temporal-resolution 
monitoring of PV generators at all these warm and sunny sites. 
Cloud-edge and cloud-enhancement effects of solar irradiance 
resulted in operational issues that were not previously described 
in the literature. This information is of great scientific and 
economic interest as the PV technology increases its 
penetration and is part of the strategic planning of the national 
electricity sector in Brazil. 
II. EXPERIMENTAL SETUP AND METHODOLOGY 
Eight identical fully-monitored 70 kWp PV Evaluation Sites 
(ESs), each using seven different, commercially-available PV 
technologies (single- and multi-crystalline silicon, two-axis-
tracking 820 suns concentrated PV, and the thin-film PV 
technologies CdTe, CIGS, a-Si and a-Si/μc-Si), were installed 
in different regions of Brazil between 2013 and 2014. Fig. 1 
shows the map of Brazil and the location of the eight ESs, while 
Fig. 2 shows an aerial view of one of the eight ES. The only 
difference between the eight ESs is the module tilt angle for the 
fixed-tilt arrays at each site, which is equal to the local latitude 
in each case. The ESs are constantly monitored, with irradiance, 
temperature (ambient and back-of-module) and electrical 
parameters measured and logged at one-second intervals. High-
quality, research-grade and state-of-the-art irradiance, electrical 
parameters and temperature measurement devices and 
dataloggers were used. A more detailed description of the eight 
locations, the experimental set up and equipment specifications 
were presented elsewhere [3]. 
 
 
Fig. 1. General location in the Brazilian territory of the eight 
identical R&D ESs, located between 3°S and 28°S, each with 70 kWp 
of PV installed power evenly distributed among seven different 
commercially-available PV technologies. 
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Measuring environmental and operational PV electrical 
parameters at the individual PV string level, and at one-second 
time resolution at all these sites leads to very large amounts of 
data, which have to be verified and qualified every day. This 
high time-resolution was chosen in order to enable the detection 
and evaluation of fast-changing environmental conditions 
(particularly irradiance, which was measured with Kipp and 
Zonen SMP11 pyranometers and IMT reference cells), and 
their influence on the response and performance of PV devices 
operating in a utility-scale PV power plant environment. The 
decision of measuring all parameters at the one-second time 
resolution was made in the context of our previous experience 
with solar irradiance variations in a sunbelt region, in contrast 
with that in higher latitude climates [4]-[6], and the effects of a 
larger fraction of solar energy availability at higher irradiances 
on PV generator inverter sizing [7]-[9]. 
 
 
Fig. 2. Aerial view of one of the eight identical R&D ESs, with 70 
kWp of PV using seven different commercially-available PV 
technologies. 
IV. RESULTS AND DISCUSSION: PV PERFORMANCE 
ASSESSMENT 
In a warm and sunny environment, temperature is the main 
cause of energy losses in a PV system. Table I shows the 
temperature coefficient of maximum power point for the PV 
module technologies used in this study and Table II presents the 
irradiance-weighted back-of-module average temperature of 
the six fixed PV module technologies at each of the eight ESs 
during the analyzed period. 
The AC Performance Ratio (PR) assessment of the PV 
technologies installed in the ESs is presented in Fig. 3. The 
analyzed period includes only simultaneous valid data for all 
the PV technologies on each ES; this is the reason why some 
sites have only a few months of available data. 
 
 
TABLE I 
TEMPERATURE COEFFICIENT OF MAXIMUM POWER POINT FOR 
THE PV MODULE TECHNOLOGIES USED IN THIS STUDY, SORTED 
FROM LOWEST TO HIGHEST. 
 
 


 
 
 
 
 
 
 
 
TABLE II 
IRRADIANCE-WEIGHTED BACK-OF-MODULE TEMPERATURE 
AVERAGE OF THE SIX FIXED PV MODULE TECHNOLOGIES AT 
EACH OF THE EIGHT ESS DURING THE ANALYZED PERIOD. 
 
 
 
 
 
 
 
 
 
 
 
For the presented data it can be observed that the thin-film a-
Si technology resulted in a superior PR than the other 
technologies for most of the ESs. This behavior is due to the 
lower temperature coefficient of this technology, which results 
in good performance in warm climates [10]. A bluer spectral 
content of sunlight in the region might also have been beneficial 
for these blue-biased PV devices. The analyzed period was after 
stabilization of the Staebler-Wronski effect (SWE), which 
affectsthe output performance of thin-film a-Si PV modules 
strongly during the first year of outdoor operation and stabilizes 
after some 1000 kWh/m2 of sunlight exposure [11]. 
For c-Si and m-Si technologies, a good performance is 
observed in most of the ESs, with both technologies presenting 
very similar PR. However, a few ESs have presented a marked 
discrepancy between the two technologies. Field evaluations 
revealed intense PID degradation in coastal areas with high 
relative temperate and humidity at such sites. Fig. 4 shows the 
effect of PID in two p-type multicrystalline silicon strings from 
the Capivari de Baixo ES (28°S, 49°W), located on the coast of 
southern Brazil. 
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Fig. 3. AC Performance Ratio (PR) of the PV technologies installed 
at the eight ESs in different climates in Brazil. 
 
Fig. 4 (a) shows the mapping of the two strings: string M 
outlined in blue, and string P outlined in orange, with 13 and 16 
modules, respectively. In the image, modules in green belong 
to the positive end of the string, while modules in red belong to 
the negative end. Fig. 4 (b) shows the electroluminescence (EL) 
images made for the same two strings. Finally, Fig. 4 (c) shows 
the measured power relative to the healthiest module on the 
string, obtained from individually measured I-V curves. The 
modules marked in black on images (a) and (c), and shaded and 
outlined in red on image (b), are modules that were blown away 
from the metallic structure during an extreme meteorological 
event that hit the region on October 16th, 2016 with strong 
winds (up to 200 km/h gusts), prior to the EL imaging and the 
measuring of the modules I-V curves. Many modules were 
severely damaged, but not all of them could be replaced, and 
therefore were put back on the structure but not connected back 
to the strings they belonged to, hence should be disregarded in 
this analysis. In Fig. 4 (b), it can be easily seen that the modules 
located towards the negative end of the strings present more 
darkened cells on the EL image and, therefore, presented a 
lower peak power when measured with the I-V curve tracer, as 
seen in Fig. 4 (c). 
Fig. 5 shows the individually measured I-V curves for each 
of the modules on the two strings shown in Fig. 4. A reduction 
in shunt resistance can be seen, as well as a decrease in Voc, 
reflecting the junction to be less capable of separating holes and 
electrons [12]. 
For the a-Si/μc-Si and CIGS technologies, a slight negative 
discrepancy between the measured power and the power 
declared by the manufacturer was observed at the 
commissioning of these technologies. 
(a) 
(b) 
(c) 
Fig. 4. PID effect on two p-type multicrystalline strings from the 
Capivari de Baixo ES (28°S, 49°W), located on the coast of Southern 
Brazil. (a) Shows the mapping of the two strings connected to 
independent MPPT channels: string M (outlined in blue, with 13 
modules) and string P (outlined in orange, with 16 modules), with 
positive modules in green and negative modules in red. (b) Shows the 
EL images made for all the m-Si modules within the two strings. (c) 
Shows the measured power, obtained using an I-V curve tracer, 
relative to the healthiest module on the string. The modules shaded in 
red and black in the pictures are modules that were damaged and were 
thus disregarded in the study. 
 
For the CdTe technology, important advances have been 
made by the manufacturer First Solar since the installation of 
these systems [13], and the output characteristics of Series 2 
modules installed at our eight ESs were considerably improved 
in the current Series 4 product. AC performance ratios 2-3% 
higher than multicrystalline silicon have been reported in the 
literature for Northern Brazil in a similar R&D project using 
CdTe Series 3 modules from the same manufacturer [14]. 
At the end of the project, all installed double-axis tracking 
concentrated PV (CPV) were inoperative or intermittent. In 
view of the faced problems, it was not possible to assess the 
long-term evaluation of this PV technology. Despite the state of 
maturity of CPV systems, until the deployment of this project 
(2013-2016) no such system had been installed in Brazil. The 
equipment was supplied by the company for the first time to the 
Southern hemisphere, which required changes in system 
control and hardware, which were not sufficient for the 
acceptable operation of the systems. 
A detailed energy loss analysis was also carried out through 
simulations regarding the Itiquira ES (17°S, 54°W), using PV 
sizing software PVsyst 6.72 with default parameters values, 
with exception of soiling losses, which were assessed on site 
through the measurement of I-V curves before and after 
cleaning the PV modules. The simulation was performed using 
on-site measured GHI (secondary standard pyranometer) and 
ambient temperature. The total measured loss and the simulated 
losses are presented in Fig. 6 and in Table III a summary of the 
results obtained in this part of the study is shown. 
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(a) 
(b) 
Fig. 5. Individually measured I-V curves for each of the PV 
modules on the two strings shown in Fig. 5. Fig. 6 (a) displays the I-V 
curves measured for the modules on string M, while Fig. 6 (b) displays 
the same for string P. 
 
Measured losses were calculated using the Performance 
Ratios for each technology in this specific ES using GTI data 
measured with secondary standard pyranometers, and energy 
data obtained through high-quality, research-grade energy 
meters. 
 
 
Fig. 6. Measured loss (left bars in orange) and simulated losses 
(stacked bars on the right) for the Itiquira ES (17°S, 54°W). 
 
Most of the differences between simulation and measured 
results, as presented, are a consequence of PID problems, 
marked initial degradation and not necessarily only due to 
simulation uncertainties. 
 
TABLE III 
SUMMARY OF RESULTS FOR MEASURED LOSSES AND TOTAL 
SIMULATED LOSSES FOR THE ITIQUIRA ES (17°S, 54°W). 
 







   
   
   
   
   
   
III. RESULTS AND DISCUSSIONS: OVERIRRADIANCE EVENTS 
The highest irradiance measurement reported in the literature 
so far was 1891 W/m2 [15], measured at a 1829 m altitude site 
in Colorado - USA. The highest irradiance peak measured in 
Brazil (Itiquira ES 17°S, 54°W), at 522 m altitude, and where 
large-scale PV power plants are currently being installed, was 
1823 W/m². While this extreme overirradiance event only 
lasted a few seconds, other overirradiance events lasting several 
minutes have also been recorded, as detailed in Table IV, and 
which can lead to deleterious consequences to the operation and 
maintenance of PV power plants, as will be further discussed. 
Overirradiance events can only be detected if solar irradiance is 
measured at a high time resolution with high-quality, fast 
pyranometers, and the suspicion is that such events might go 
unnoticed in many other low-latitude sites throughout the 
globe. 
When overloaded, inverters limit the output power to 
nominal power. This is done by the inverter’s MPPT 
(Maximum Power Point Tracking) increasing the DC voltage 
from maximum power point voltage towards open circuit 
voltage. Assuming this inverter strategy and considering that 
most of utility-scale projects use undersized inverters, one 
might be lead to the conclusion that, in the occurrence of an 
overirradianceevent, inverters will sweep MPPT and all the 
strings will operate with a higher voltage and a lower string 
current than during normal MPPT operation. However, infield 
measurements in this R&D project support what has already 
been suggested in the literature: overirradiance events have 
only a small spatial footprint, because of their direct 
dependence on the suncloud edge-surface geometry [15]. This 
implies that depending on cloud geometry, inverter maximum 
power and Inverter Loading Ratio (ILR), during an 
overirradiance event part of the array could be operating with 
currents proportional to overirradiance magnitudes, while the 
other part of the array could be in the cloud shadows, resulting 
in an instantaneous inverter output power below inverter 
nominal power. In this case, the inverter will not limit the 
output power using the strategy described above, which will 
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result in high currents, which associated with high fuse 
operating temperatures might cause string fuses to blow. 
 
TABLE IV 
OVERIRRADIANCE EVENTS AND EVENT DURATION FOR 
IRRADIANCE PEAKS AT OR ABOVE THE EXTRATERRESTRIAL 
IRRADIANCE OF 1367 W/M2 REGISTERED IN BRAZIL (ITIQUIRA 
ES 17°S, 54°W) BETWEEN JANUARY 2015 AND MARCH 2017. 
 
 






    

    

    

    

    

    
 
Typically, technical specifications provided by PV module 
manufacturers include information on the “maximum series 
fuse rating”, and designing a PV array with a fuse rated above 
this maximum value will lead to voiding the PV module 
warranty. At most sites where PV plants in Brazil will operate, 
ambient temperatures and irradiation levels are high, and the 
string boxes where the above-mentioned fuses are installed can 
reach temperatures higher than 70°C [16], as has been routinely 
measured throughout this project. Fuse maximum currents are 
usually rated at 20°C operating temperatures, and at 70°C the 
typical derating factor is 0.7. This fact, associated with 
overirradiance values in excess of 1.4 to 1.6 suns for time spans 
in the minute-range, will result in conditions that will lead to 
the blowing of even slow-blow or time-delay fuses, if they are 
designed as per the PV module manufacturer’s maximum series 
fuse rating specifications. 
 No previous reports of such a combination of effects has 
been found in the literature. Based on these findings, it can be 
foreseen that a number of such events might take place in many 
of the large-scale PV power plants being installed in Brazil 
since 2017. It is therefore recommended that PV module 
manufacturers reassess their maximum series fuse ratings in the 
light of this information, and utility-scale projects could size 
string boxes in a manner to keep fuses from reaching such high 
temperatures. 
In Brazil, current guidelines require that a minimum of one-
year irradiance measurements in 10 minutes averaging intervals 
should be presented for a PV power plant to be eligible for the 
regulated market energy auctions. These requirements are made 
so that site-adaptation techniques between long term satellite-
derived data and ground measured solar radiation can be 
performed, aiming at the reduction of the uncertainty on the 
energy production estimation [17]-[18]. This 10-minute 
averaged data, however, prevents the better assessment of ILR 
losses. In Fig. 7, a cloudy day’s global horizontal irradiance 
measured at one-second (blue and orange spiky curve) and 10-
minute averages (light-orange shadow smooth curve) at the 
Cachoeira Dourada ES (18°S, 49°W) are presented. Averaging 
one-second measurements at 10-minute intervals hides 
valuable information on irradiance peaks, and leads to 
misleading conclusions on ILR losses and the true irradiation 
resource availability at a particular site. 
 
 
Fig. 7. One-second instant (blue and orange spiky curve) and 10-
minute averages (light-orange shadow smooth curve – Brazilian PV 
power plant standard data acquisition resolution) solar irradiance 
measurements at the Cachoeira Dourada ES (18°S, 49°W). The high 
irradiance peaks tend to disappear when data is averaged at 10-minute 
intervals. 
 
However, the use of one-second time resolution leads to very 
large amounts of data and requires high-performance 
computing. Data averaging of one minute is suggested to be an 
optimum resolution without requiring further improvements in 
computational capacity. 
V. CONCLUSIONS 
In this work, the performance assessment of seven different 
PV technologies for utility-scale applications in eight warm and 
sunny sites in Brazil has been described and evaluated on a 
long-term project. The results presented in this paper give a 
concise overview of the main aspects (cloud-enhancement 
effects, blowing fuses, PID, simulation uncertainties) that will 
have to be considered as utility-scale PV power plants start to 
emerge in large amounts in warm and sunny countries. 
The results also present the performance assessment of the 
PV technologies installed at each ES. Thin-film PV 
technologies with a low temperature coefficient of power 
presented superior output performance. Mono- and multi-
crystalline revealed intense PID degradation in coastal areas 
with high temperature and relative humidity. Extreme 
overirradiance events (which lasted from seconds to several 
minutes) were measured and shown, and it can be speculated 
that high time resolution irradiance measurements in many 
sunny sites with considerable cloud movement will reveal this 
aspect to be a common feature at such sites. 
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ACKNOWLEDGEMENTS 
The authors wish to acknowledge with thanks the Brazilian 
Electrical Energy Regulatory Agency ANEEL, as well as 
ENGIE Brasil Energia and the 11 other cooperating Electrical 
Utility companies involved in project PE-0403-0027/2011 for 
sponsoring this project. 
L. Nascimento acknowledges the Brazilian Post-Graduate 
council CAPES for a doctoral scholarship. 
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