Comparative Performance of Grid Integrated SolarPhotovoltaic Systems Under the Tropical

Environment

Hamidah Ismail∗, Sathyajith Mathew∗, Aloka S†, Balakrishnan Narayanaswamy†, Lim Chee Ming∗,Saiful Azmi Hussain∗

∗ Universiti Brunei Darussalam, UBD|IBM Centre,

Jalan Tungku Link, Gadong BE 1410, Brunei Darussalam

hamidah.isma@gmail.com, {sathyajith.mathew, cheeming.lim, saiful.husain}@ubd.edu.bn†IBM Research Bangalore, KA, India

{alokas1, murali.balakrishnan}@in.ibm.com

Abstract—As the output from the solar PV systems variessignificantly with technologies, designs and prevailing weatherparameters, their evaluation under actual field conditions isimportant in identifying their real performance characteristics. Inthis paper, comparative performances of six different PV systemsconnected to a 1.2 MWp grid integrated solar farm are presented.The solar technologies considered are the single crystalline(sc-Si), poly crystalline (mc-Si), micro crystalline (nc-Si/a-Si),amorphous silicon (a-Si), Copper Indium Selenium (CIS) andHeterojunction with Intrinsic Thin Layer (HIT). Following theIEA guidelines, the array yield, capture losses, array efficiencyratio, and performance ratio were taken as the criteria for theperformance comparison. Among the six different module types,the systems based on amorphous silicon and HIT offer the bestperformance under the tropical environment considered.

Index Terms—renewable energy, solar insolation, photovoltaicsystem, tropical climate, reference yield, array yield, capture loss,performance ratio, efficiency ratio, poly crystalline silicon, singlecrystalline silicon, micro crystalline silicon, amorphous silicon,CIS, HIT

I. INTRODUCTION

With the rapid reduction in the system costs and promotional

policies for clean energy technologies, the solar photovoltaic

(PV) sector is growing at a fast rate. For example, with

the added capacity of 31.3 GW during the year, the global

cumulative installation of solar PV systems have reached

above 101 GW by the end of 2012 [1, 2]. Future projections

also show a steady growth in the global PV market and the

installed capacity may reach between 208 GW and 343 GW

by 2016, depending upon the support scenarios. Majority of

these installations are grid connected. Hence, the contribution

of solar PV generated electricity in the power sector is going

to be significant.

An estimate on the expected output from an existing solar

PV system is essential for its efficient grid integration and

smart power management. Such information is also vital in

the design of new PV power plants. Photovoltaic modules are

tested for their performances by the manufacturer/certifying

agencies. However, these tests are conducted at standard con-

ditions (STC) and under controlled environments. Apart from

the available solar insolation, performance of a PV system

is sensitive to various weather parameters such temperature,

humidity, wind speed and cloud cover. Hence, to understand

the real performance of a PV system at a given location and

environment, it has to be evaluated under the actual field

conditions.

Such field assessments are essential for the industry, as

the information generated can be used for bench marking the

quality of the products. Researchers and developers can use

the results in identifying the key areas to be focused for future

development. System integrators can use this information for

PV performance modeling which can further be extended

to solar power forecasts and dispatch decisions. For policy

makers, it gives the basic information for formulating the clean

energy policy frameworks - for example fixing the feed in tariff

and other production incentives.

The importance of field evaluation of PV systems has

been well identified by the industry, R&D institutions and

development agencies. For example, the International En-

ergy Agency (IEA), through its Photovoltaic Power Systems

(PVPS) project, has established standard monitoring tech-

niques and performance analysis methods for quantifying the

performance of PV systems under different weather conditions

[3]. Several studies were conducted on the performance of PV

systems at different locations and environmental conditions

[4-9]. These studies are based on small sized systems with

capacity less than 5 kWp. In [10-16], performances of larger

grid integrated systems, ranging from 36 kWp to 960 kWp

in size, have been reported. Useful information on solar

PV performance, under the respective regional conditions,

could be brought out through these initiatives. However,

only one type of solar cell has been evaluated under these

investigations and hence a comparison on different solar

technologies under the same environment is not available.

[18] tested three modules, namely the mc-Si, sc-Si and a-Si

under a similar tropical environment. Their findings indicate

that the crystalline silicon (c-Si) modules outperform the a-Si

modules, however, their performance decreased significantly

during cloudy days whereas the performance of a-Si modules

shows a slight increase. Though our study is also done under a

IEEE ISGT Asia 2013 1569815041

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Fig. 1. General layout of the 1.2 MWp grid-connected PV system.

tropical environment, local weather conditions also affect the

performance of PV modules, hence, our findings are not the

same.

In this paper, the comparative field performance of six

different types of solar PV systems - consisting of both the

first and second generation solar cells is reported. This study

also serve to create a better understanding of the behaviour of

solar PV systems under a tropical environment. These systems

are installed at a 1.2 MWp grid connected experimental solar

farm in Brunei Darussalam.

II. THE EXPERIMENTAL SYSTEM

The experimental site is located in Seria, Belait District,

Brunei Darussalam. The farm consists of six different types

of solar cells. They are (1) Single crystalline (sc-Si), (2)

Poly crystalline (mc-Si), (3) Micro crystalline (nc-Si/a-Si), (4)

Amorphous silicon (a-Si), (5) Copper Indium Selenium (CIS)

and (6) Heterojunction with Intrinsic Thin Layer (HIT). The

specifications for these systems are given in Table 1. As we

can see, these modules have different conversion efficiencies

and hence, the number of modules and the panel area for 200

kWp rated capacity are different.

The layout of the solar farm and the data acquisition system

are shown in Fig. 1. Every two types of the solar module are

grouped together and connected to a converter and every two

converters are connected to an inverter. The data monitoring at

the solar farm consists of sensors and data loggers to measure

the weather parameters such as horizontal and inclined solar

insolation, wind speed at the panel height, ambient temper-

ature, relative humidity and precipitation. Outputs from the

panels, both DC and AC, are sensed at one second interval,

which are then averaged into hourly values for this study.

Performance data from the solar farm during 2012 was used

for the study.

A. First generation PV modules

The mono crystalline or single crystalline silicon (sc-Si)

and polycrystalline or multi crystalline silicon (mc-Si) solar

modules are known as the first generation PV modules as

they are the more mature technology and more dominant. Due

to extensive research and development over the years, these

generation of modules are now able to achieve very high effi-

ciency; typically in the range of 13% to 19%. As pure silicon

is needed, thus requiring energy intensive processes, overall

production cost are relatively higher than other technologies

[19].

1) Single crystalline silicon PV modules: Single crystalline

silicon cells are made from single large silicon crystals.

Compared to other PV cells, they exhibit higher efficiency but

tend to lose efficiency at high temperatures. The production

costs are highest, since it involves a complex, energy intensive

process. They have high longevity and durability.

2) Poly crystalline silicon PV modules: Poly crystalline sil-

icon cells are composed of multiple silicon crystals. Since the

TABLE ISPECIFICATION OF THE SOLAR MODULES

PV module type Po (W) ηSTC No. of Area(%) modules (m2)

Single crystalline 180 14.1 1,116 1,462Polycrystalline 185 13.4 1,098 1,518Microcrystalline 130 8.2 1,540 2,426Amorphous Silicon 100 6.3 2,000 3,150CIS 80 8.9 2,500 1,979HIT 205 16 980 1,257

2

Fig. 2. Monthly averaged daily array yields.

production process is relatively simpler than single crystalline

silicon cells, the costs are comparatively lower. The poly

crystalline silicon modules are slightly less efficient than the

single crystalline. The durability and longevity are comparable

to single crystalline PV modules. As they come at a lower

price and a comparable performance, poly crystalline silicon

PV modules are the more popular choice in the market.

B. Second generation PV modules

This generation of PV modules refer to the emerging thin

film technologies such as the amorphous (a-Si), CIS, the

hybrid micro crystalline (nc-Si/a-Si) and HIT solar modules.

Amorphous silicon (a-Si) is a non-crystalline form of silicon.

The panels are formed by depositing a thin layer of silicon on a

substrate material. The micro crystalline module here refers to

a hybrid technology combining the micro crystalline cells (nc-

Si) with an a-Si cell. HIT consist of a thin sc-Si surrounded

by ultra-thin a-Si while CIS is a solid state semi conductor

copper indium selenide (CuInSe2).

Although material and production costs are lower than the

former generation as they require less or no silicon, their lower

efficiencies create a setback resulting in lower demand and

modest productions, hence retails prices are more expensive.

Their degradation characteristics are also less understood.

Among its advantages are its flexibility and light-weight;

suitable for residential or building integration (i.e., BIPV).

Thin film technologies are also less affected by shading as

different materials with different absorption properties are

layered atop one another to enable absorption of multiple light

spectrums (both long and short wavelengths) [19].

III. PERFORMANCE CRITERIA

Nomenclature

• P0 - Peak capacity (Wp)

• EDC - DC energy output (kWh/m2)

• G - Reference radiation taken as 1 kW/m2

• Hd - Daily in-plane radiation on the panel (kWh/m2)

• YA - Array yield (hours/day)

• YR - Reference yield (hours/day)

• LC - Capture loss (hours/day)

• PR - Performance ratio

• ηR - Efficiency ratio

The performance parameters and procedures, suggested by

the IEA under the PVPS project (IEA PVPS Task 2 [3,17]) has

been adopted for the analysis. Based on this, the array yield,

capture losses, array efficiency ratio, and performance ratio

were calculated for the six different types of solar modules.

These parameters are defined in brief in the following sections.

A. Array Yield

Array yield YA (h/day) is the array DC energy output

(kWh/m2) per installed capacity per unit area of the PV array

(kWp/m2) which is given by

YA =EDC

P0(1)

B. Reference Yield

Reference yield, represented by YR (h/day) is the ratio of

total daily in plane radiation Hd (kWh/m2) on the panels to

the reference in plane radiation G (1 kW/m2). Hence,

YR =Hd

G(2)

C. Capture Loss

Array capture loss LC is the difference between the refer-

ence yield and the array yield. Thus,

LC = YR − YA (3)

D. Performance Ratio

Performance ratio, PR is the ratio of array yield and

reference yield.

PR =YA

YR(4)

Fig. 3. Annual averaged daily array yield and capture losses.

3

E. Efficiency Ratio

Array efficiency ratio, ηR which reflects the systems field

efficiency, is the ratio between the energy output (DC) per

in-plane irradiation on the array and the arrays efficiency at

standard test conditions.

ηR =EDC

H

ηSTC(5)

IV. RESULTS AND DISCUSSION

Variations in monthly averaged daily array yield and capture

loses are shown in Figs. 2 and 3 respectively. The array

yield normalizes individual module size and efficiency, and

represents the number of hours the module would have to

operate at its rated capacity to yield the same energy that it

has produced in a day. It can be noted that the array yield

varies accordingly with the variation of local solar radiation

in Fig. 7.

Comparing the different types of PV systems, the a-Si

modules showed the highest average array yield in most of

the months. The annual averaged daily array yield for a-Si

modules was 4.45 h/day, which was followed by HIT modules

(4.38 h/day). The lowest annual averaged daily array yield of

3.99 h/day was observed in case of sc-Si PV system (Fig. 3).

The capture losses in different PV modules are displayed

in Fig. 3. The major factors contributing to the capture

losses are thermal capture losses and miscellaneous capture

losses. Thermal capture losses reflect the reduction in cell

efficiency with the rise in cell temperature (higher than 25◦C).

Miscellaneous capture losses can be caused by low irradiance,

shadowing effect, spectral reflectivity, and dirt accumulation.

Following the same trend as in array yield, capture losses

were minimum in case of a-Si modules (18.2 %), followed

by HIT (19.5 %). The highest losses, at a level of 26.7 %,

were observed in case of sc-Si modules.

The monthly averaged daily performance ratios for the mod-

ules are shown in Fig. 4. The performance ratio compares the

actual performance of the module with the theoretical lossless

ideal condition while eliminating the effect of the variation

of in-plane solar radiation. It quantifies how effectively a

particular technology could interact with the solar resource

available at a given location, which may be affected by the

reflectivity of the modules’ surface and reduced efficiency due

to increase in ambient temperature. The amorphous silicon

and HIT modules showed the highest performance ratios

throughout the year. As expected, the performance ratios were

highest in months when the ambient temperature (and there

by cell temperature) is relatively lower.

The monthly averaged daily efficiency ratios of different

modules are compared in Fig. 5. This indicates how well the

PV modules could perform in real environment in comparison

to its laboratory performance under ideal conditions. From

the figure, it can be seen that field performance of the CIS

modules was close enough to its rated performance throughout

the year. The annual average efficiency ratio for these modules

Fig. 4. Monthly averaged daily performance ratios.

was 0.88, followed by a-Si (0.82) and HIT (0.8) modules. The

lowest performance ratio (0.71) was shown by sc-Si cells.

Fig. 6 shows the hourly variations of solar insolation levels

and the efficiency ratio of the cells averaged over the one

year period. It can be seen that the second generation modules

such as the Micro crystalline and amorphous silicon modules

reach their highest efficiency ratios at an earlier time, hence

at lower insolation levels. The Amorphous silicon and HIT

modules consistently maintained higher efficiency ratios even

at lower insolation levels, followed by the CIS modules.

Although the maximum efficiency ratio of micro crystalline

(nc-Si/a-Si) at high insolation levels are lower compared to

the other second generation PV technologies, it has the second

highest efficiency ratio, just below the amorphous modules

during hours when insolation levels are lower. Thus, second

generation thin film technologies could operate at higher

levels for a wider range of solar spectra. This is a desirable

characteristic, especially while operating at locations like in

Brunei Darussalam, where it is cloudy and the solar insolation

levels fluctuate significantly [17].

Fig. 5. Variation in monthly averaged daily efficiency.

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Fig. 6. Hourly variation of Solar Irradiance and Efficiency Ratio.

Fig. 7. Monthly variation of solar radiation.

Fig. 8. Frequency of Solar Radiation in Brunei.

V. CONCLUSIONS

Field performances of six different solar PV systems, with

a nominal power rating of 200 kWp each, were analyzed

and compared under this study. Following the IEA guidelines,

array yield, capture losses, efficiency ratio and performance

ratio are considered as the yardsticks for the performance

assessment. PV systems based on a-Si showed the highest

array yield and performance ratio under the study. Capture

losses were also the lowest for this type of modules. Perfor-

mance of HIT modules was also impressive under the given

conditions. However, the efficiency ratio was found to be the

highest for the CIS modules followed by the a-Si and HIT

systems. Based on these performance parameters, PV systems

with a-Si modules are found to be best suited for the tropical

environment of Brunei Darussalam. Sc-Si modules showed the

poorest field performance with regard to all the considered

measures. It should be noted that the assessment was purely

based on the technical performance while economic aspects

also play a major role in the final selection of the PV system

for a given location.

A study carried out under a similar climate in Malaysia

evaluated three types of PV modules such as a-Si, sc-Si and

mc-Si modules over a four day period covering two sunny days

and two cloudy days. Solar radiation of 369 and 402.24 W/m2

were considered for cloudy days, and 796.16 and 807.49

W/m2 for sunny days, both for a duration of 6 sunshine hours

[18]. The result shows a considerably lower PR (below 60%)

and ηR (below 45%) compared to that under Brunei condition.

Their comparison results are contrary to this paper where the

PR and ηR are highest for mc-Si modules, followed by sc-Si

and a-Si modules whereas under the Brunei condition, a-Si

modules gives the highest PR and ηR followed by mc-Si and

sc-Si.

Fig. 8 is the frequency of Brunei solar radiation where it

is divided into three categories based on its intensity such

as low, medium and high corresponding to the colours red,

blue and green. It can be seen that the solar radiation of

Brunei predominantly occurs in the medium region while

the study done in Malaysia has only considered radiation

values corresponding to the low and high intensity regions.

It that study, the sc-Si and mc-Si modules show very high

performances compared to a-Si under high solar radiation

while the a-Si performs almost on par with the sc-Si and mc-Si

modules during low solar radiation.

Based on these two studies, it may be concluded that a-Si

modules will perform worse than c-Si modules at high solar

radiation, on par with c-Si modules at low solar radiation

and better than c-Si modules at mid-range solar radiation.

Despite a-Si having the lowest efficiency under the study in

Malaysia, the efficiency was almost consistent for both sunny

and cloudy days whereas mc-Si and sc-Si modules suffer

from considerable drop in efficiency under cloudy condition.

This is consistent with the advantage associated with thin film

technologies.

Though this analysis is based on the field performance

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of the PV systems at a specific site, the results can give

useful implications on the expected performances of such

systems under similar climatic conditions. Further, the field

performances can be correlated with various environmental

parameters to develop PV performance models, which can

be used in conjunction with Numerical Whether Prediction

(NWP) models to come up with a power forecasting system

for the given solar farm.

ACKNOWLEDGMENT

The support extended by the Energy Department, the Prime

Ministers Office (EDPMO), Brunei Darussalam, during the

course of this study, is thank fully acknowledged.

REFERENCES

[1] IPEA, “Global market outlook for photovoltaics until 2016,” EuropeanPhotovoltaic Industry Association, Tech. Rep., 2012.

[2] (2013) Worlds solar photovoltaic capacity passes 100-gigawatt landmarkafter strong year. [Online]. Available: http://www.epia.org/news/press-releases//

[3] IEA, “Annual report 2011 of pvps programme,” International EnergyAgency, Tech. Rep., 2011.

[4] F. Karg, D. Kohake, T. Nierhoff, B. Kuhne, S. Grosser, and M. C.Lux-Steiner, “Performance of grid coupled pv-arrays based on cis solarmodules,” Presented at the 17th EC PVSEC, vol. 24, p. 26, 2001.

[5] A. Aristizbal and G. Gordillo, “Performance monitoring results ofthe first grid-connected {BIPV} system in colombia,” RenewableEnergy, vol. 33, no. 11, pp. 2475 – 2484, 2008. [Online]. Available:http://www.sciencedirect.com/science/article/pii/S0960148108000359

[6] B. Marion, J. Adelstein, K. Boyle, H. Hayden, B. Hammond, T. Fletcher,D. Narang, A. Kimber, L. Mitchell, G. Rich et al., “Performanceparameters for grid-connected pv systems,” in Photovoltaic SpecialistsConference, 2005. Conference Record of the Thirty-first IEEE. IEEE,2005, pp. 1601–1606.

[7] C. Boonmee, B. Plangklang, and N. Watjanatepin, “Systemperformance of a three-phase pv-grid-connected system installedin thailand: Data monitored analysis,” Renewable Energy, vol. 34,no. 2, pp. 384 – 389, 2009, renewable Energy for SustainableDevelopment in the Asia Pacific Region. [Online]. Available:http://www.sciencedirect.com/science/article/pii/S0960148108002097

[8] A. Elhodeiby, H. Metwally, and F. MA, “Performance analysis of 3.6 kwrooftop grid connected photovoltaic system in egypt,” Presented at theInternational Conference on Energy Systems and Technologies, Cairo,Egypt, 2011.

[9] J. H. So, Y. S. Jung, G. J. Yu, J. Y. Choi, and J. H. Choi, “Performanceresults and analysis of 3 kw grid-connected pv systems,” RenewableEnergy, vol. 32, no. 11, pp. 1858 – 1872, 2007. [Online]. Available:http://www.sciencedirect.com/science/article/pii/S0960148106002722

[10] A. M. Al-Sabounchi, S. A. Yalyali, and H. A. Al-Thani,“Design and performance evaluation of a photovoltaic grid-connected system in hot weather conditions,” Renewable Energy,vol. 53, no. 0, pp. 71 – 78, 2013. [Online]. Available:http://www.sciencedirect.com/science/article/pii/S0960148112006842

[11] A. Chimtavee, N. Ketjoy, K. Sriprapha, and S. Vaivudh, “Evaluationof pv generator performance and energy supplied fraction of the120 kwp pv microgrid system in thailand,” Energy Procedia,vol. 9, no. 0, pp. 117 – 127, 2011, 9th Eco-Energy andMaterials Science and Engineering Symposium. [Online]. Available:http://www.sciencedirect.com/science/article/pii/S1876610211017668

[12] “Performance of a 500 kwp grid connected photovoltaicsystem at mae hong son province, thailand: Chokmaviroj, s.renewable energy, 2006, 31, (1), 1928.” Fuel and EnergyAbstracts, vol. 47, no. 5, p. 334, 2006. [Online]. Available:http://www.sciencedirect.com/science/article/pii/S0140670106821855

[13] L. Clavadetscher and T. Nordmann, “Prediction and effectiveyield of a 100 kw grid-connected pv-installation,” Solar Energy,vol. 51, no. 2, pp. 101 – 107, 1993. [Online]. Available:http://www.sciencedirect.com/science/article/pii/0038092X9390072V

[14] P. Congedo, M. Malvoni, M. Mele, and M. D. Giorgi,“Performance measurements of monocrystalline silicon pv modulesin south-eastern italy,” Energy Conversion and Management,vol. 68, no. 0, pp. 1 – 10, 2013. [Online]. Available:http://www.sciencedirect.com/science/article/pii/S0196890413000022

[15] M. Drif, P. Prez, J. Aguilera, G. Almonacid, P. Gomez,J. de la Casa, and J. Aguilar, “Univer project. a gridconnected photovoltaic system of at jan university. overview andperformance analysis,” Solar Energy Materials and Solar Cells,vol. 91, no. 8, pp. 670 – 683, 2007. [Online]. Available:http://www.sciencedirect.com/science/article/pii/S0927024806004764

[16] S. Wittkopf, S. Valliappan, L. Liu, K. S. Ang, and S. C. J.Cheng, “Analytical performance monitoring of a 142.5 kwpgrid-connected rooftop bipv system in singapore,” RenewableEnergy, vol. 47, no. 0, pp. 9 – 20, 2012. [Online]. Available:http://www.sciencedirect.com/science/article/pii/S0960148112002352

[17] S. Mathew, C. Lim, and P. GS, “Exploring the feasibility of large scalesolar power plants in brunei darussalam,” in press.

[18] A. Ghazali and A. Abdul Malek, “The performance of three differentsolar panels for solar electricity applying solar tracking device under themalaysian climate condition,” Energy and Environment Research, 2012.

[19] IRENA, “Renewable energy technologies: Cost analysis series, solarphotovoltaics,” International Renewable Energy Agency, Tech. Rep.,2012.

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