The performance of DualAxis Solar Tracker (DAST) and Static Solar System (SSS) with respect to clearness index in Malaysia is presented. An attempt to investigate the correlation between clearness index with energy gain and efficiency of DAST over SSS is being done experimentally. A good correlation could not be found out from the daily clearness index. It is due to the more profound advantage of DAST in the morning and evening compared to midday as it is able to follow the sun’s position. Hence, the daily clearness index is divided into three segments which are morning, midday, and evening to interpret the energy gain and efficiency better. A clearer correlation with low standard deviation can be observed on the segmented clearness index analysis. The energy gain and efficiency of seven cities in Malaysia is being estimated with the segmented clearness index and compared to the result generated from anisotropic radiation model. A similar trend is obtained and it has shown that the segmented clearness index could be utilized as a graphical method for estimation of energy gain and efficiency of DAST over SSS.
Solar energy has gained tremendous attention in recent years due to various reasons such as the fluctuating of the price of crude oil, awareness of public on environment issues, supporting policies and subsidies taken by local government to boost renewable energy sectors, and price reduction of photovoltaic (PV) panels. Many largescale solar farms were commissioned in USA, Europe, and China as the global PV price is dropping rapidly in recent years which agrees with the Swanson’s law [
From the literature, various tracking methods have been proposed and validated around the world in previous works and each of them has its pros and cons in terms of efficiency, complexity, and cost. Figure
Efficiency of solar tracker works reported around the world.
Malaysia as a country which lies at 1° to 7° north of equator has an equatorial climate and long hours of sunshine throughout the year. There are enormous potential for solar energy to be successful at this land. However, the potential for the DAST is rarely reported and investigated in this region. Hence, a quantitative advantage of DAST over SSS in this country still remains unknown although the consistently long sun hours suggested a promising outcome. Thus, it would be one of the endeavors for this study to carry out an investigation on some of the cities in Malaysia regarding their performance enhancement for installation of DAST over SSS. The advantage on the financial perspective would also be analyzed and a comparison can be made on the suitability for DAST installation on seven cities in Peninsular Malaysia.
While having better efficiency over SSS, the additional costs for the DAST could not be overlooked. The tracking mechanism requires extra mechanical structure and motors to rotate the PV panels according to the sun’s position. Operational and maintenance cost of the DAST will also be higher than SSS. Hence, estimation of the efficiency/energy gain of DAST over SSS is essential, and need to be part of the site evaluation criteria. As a rule of thumb, the gain from the DAST over SSS would have to surpass the additional costs whereby the profitability and sustainability of the DAST especially in large scale solar power plant are guaranteed. However, as shown in Figure
So far, comparison of efficiency and energy gain of DAST over SSS has been done by physically installing both systems on the site of interest. This method is not only expensive but also time consuming, since data over a sufficiently long period of time is needed to facilitate a meaningful comparison between the two systems. Moreover, the results obtained are not directly applicable onto other sites. Hence, there is a need for a method to estimate the gain of DAST over SSS in a more cost and timeeffective manner such that the site evaluation can be made more straightforward.
CruzPeragón et al. quantify the extra solar gain of DAST over SSS with respect to latitude of the cities in Spain based on the Reindl anisotropic model and Liu & Jordan isotropic model [
In this paper, an attempt is made to correlate the performance enhancement of DAST based on the clearness index of the sites in Malaysia. Subsequently, this correlation is used to estimate the performance boost of DAST at seven cities in Malaysia.
Clearness index is chosen as the sole variable in this work as it is derived from solar irradiance, the most fundamental factor that influences the performance of a PV system. Clearness index represents the ratio of the average global solar irradiation
For daily:
For hourly:
The data of global solar radiation over a day and over an hour,
The parameters in the equations can be found in the nomenclature.
The three components of global solar radiation.
The clearness index is higher in a sunny day as the solar radiation is dominated by beam radiation and less energy loss through diffusion and reflection. A higher clearness index will lead to a higher energy generated and efficiency for DAST. Hence, the relationship of clearness index with energy gain and efficiency of DAST is quantified and investigated experimentally. With the knowledge of the correlation, it is able to offer an alternative guideline for evaluating the performance enhancement of DAST to a specific site.
Diffuse radiation model is useful for evaluating the global irradiation over tilted surface by using the global solar radiation over horizontal surface. Liu and Jordan isotropic model [
Meanwhile, the horizon brightening component is concentrated near the horizon and is most profound in clear skies [
Circumsolar and horizon brightening components added to the isotropic component in diffusion model [
In order to have better estimation on the diffuse radiation, anisotropic models has to be adopted as larger diffuse components such as circumsolar diffuse radiation and horizontal brightening are taken into account. By analyzing various methodologies of anisotropic models, HDKR anisotropic model (Hay, Davies, Klucher, Reindl model) [
Anisotropic model considers that the radiation on the tilted surface is contributed by three components which are beam, anisotropic diffuse, and solar radiation diffusely reflected form the ground as in
Erbs et al. correlation [
Geometric factor
Equation (
In addition, the albedo
A DualAxis Solar Tracker (DAST) and a Static Solar System (SSS) with horizontal orientation are used in this experiment. The solar tracker has two axis of rotation which enable it to rotate along the eastwest and northsouth axis. The type of DualAxis Tracking System that is used in this research falls into the category of equatorial as categorized by Alexandru [
The hardware prototype of the DAST and its rotational axes.
The reference (“zero”) positions for the angular fields of the two rotational axes.
Indeed, the energy consumption is an essential part in calculating the energy gain (
The maximum power obtained by DAST in a low clearness index day and high clearness index day has substantial difference. Figures
The efficiency (
Clearness index, 
Efficiency, 
Energy generated, (Whr/m^{2})  Energy consumption, (Whr/m^{2}) 

0.34  24.91  108  0.30 
0.62  82.12  603  0.30 
Electrical power generation in an overcast day.
Electrical power generation in a sunny day.
Difference of instantaneous power of DAST and SSS along the sunny day and cloudy day.
Figure
Measured and modeled (anisotropic diffuse model) instantaneous irradiance of DAST and measured irradiance of horizontally positioned SSS.
There are two noticeable findings that can be interpreted from it. The first finding is that the anisotropic has demonstrated an inspiring result for estimating the irradiance of the DAST as both measured and modeled irradiance have very similar value. The experimental and modeled DAST would track the sun on a similar path in order to have the similar result shown. Hence, HDKR anisotropic diffused model can be reliably used to infer the instantaneous irradiances of DAST. The second finding is that the irradiances captured by both DAST and SSS are not far off from each other during the midday. It means the incidence angle of sun ray falling on both does not differ much at this period compared to other periods of the day. It agrees with the result from Figure
For the proposed DAST, the energy consumed is marginal compared to the additional energy gain from tracking. Thus, the energy consumption (
The voltage of the tracking system,
The DAST tracking is done within fifteen seconds duration for consecutive fifteen minutes. The tracking time is short as the sun movement does not vary much in fifteen minutes. The DAST tracks the sun from 7 am to 7 pm which is equivalent to twelve hours. The approximate energy consumption used for tracking in a day can be calculated as follows:
The energy consumption (
Figure
The daily energy captured by DAST and SSS for a month.
Hence, the underlying factor that determines the amount of advantage of DAST over SSS has to be found out. As a result, it leads to the investigation of the energy gain of both DAST and SSS with respect to clearness index. The clearness index is imperative for the performance evaluation of a PV system. It indicates the clarity of a day and the potential amount of sunlight for converting the solar energy into electrical energy by the PV system. The availability of abundant direct sunlight in a day has a profound impact on the energy generated by a PV system.
Generally, a direct proportional relationship could be hypothesized for both DAST and SSS with respect to clearness index. Based on the performance of both clear and overcast days reported on previous section, it could be deduced that DAST responds to clearness index on a more sensitive manner compared to a SSS. This is due to its ability to track the position of the sun and captured maximum sunlight from sunrise to sunset.
Figure
The energy captured by DAST and SSS against clearness index for a month.
On the other side of the clearness index, the energy captured by DAST increases in a steeper slope compared to SSS as the clearness index climbs from medium (0.4) to high (0.6) level. Thus, it fortifies the inference that greater amount of energy will be captured by DAST compared to SSS as the clearness index increase. In other words, the application of DAST ensures a performance boost of a PV system and the outcome is exceptionally well as the clearness index increases. In addition, the trends of both DAST and SSS with respect to clearness index show that a clearness index offers a good estimation for energy generation on different weather.
An endeavor to discover the relationship between clearness index and tracking advantage of DAST is made by plotting both efficiency and additional electrical energy gained over the clearness index for one month duration. There are different kinds of weather within the period which includes sunny, overcast, partial cloudy, and rainy days. Figures
Efficiency of DAST over SSS versus daily clearness index.
Energy gain of DAST over SSS versus daily clearness index.
The advantage of DAST over SSS is more remarkable at sunny day with high
It is necessary to divide the clearness index into three segments period which are morning (0700–1100), midday (1101–1500), and evening (1501–1900) for a better visualization of the influence of clearness index. Nevertheless, the splitting of the day into three segments is not without a tradeoff. Since the clearness index is split into three periods, the efficiency of DAST over SSS for a single day could not be established as the portion contributed by efficiency for three periods and could not be summed into a total amount as energy gain. Thus, the total efficiency of a single day could not be obtained although the total energy gain of DAST can be summed from the three segments. The tradeoff is justified as a more accurate energy gain of DAST over SSS resulted from the segmented analysis. An accurate energy gain is extremely handy for estimating the additional profit generated by DAST as the FeedIn Tariff (FID) is based on the energy generated (kWhr) instead of efficiency. Figure
Energy gain of DAST over SSS on 3 segments period.
The energy gain versus segmented clearness index graph is used to estimate the energy gain of other cities in Peninsular Malaysia based on the segmented clearness index of the cities, respectively. The performance improvement of DAST over SSS in seven cities of Peninsular Malaysia including Bayan Lepas, Ipoh, Kuantan, Muadzam Shah, Langkawi, Senai, and Subang are being estimated by the segmented clearness index graph method as shown in Figure
Energy gain of DAST over SSS for 7 cities developed by anisotropic model on 3 segments clearness index.
The average efficiency and energy gain of DAST over SSS in three segments of a day by using anisotropic model are plotted on the segmented clearness index graphs. It is observed that there are some similarities on the response of efficiency and energy gain of DAST over SSS with respect to the segmented clearness index in both anisotropic model and segmented clearness index curve from experimental. The slopes of both anisotropic model and experimental generally agree with each other albeit some discrepancies appearing due to some reasons. The value generated from anisotropic model tends to be slightly higher due to the horizon brightening component that may be estimated on a higher level than the actual level [
Energy gain based on experimental curve and isotropic model on morning segment.
Cities 

Energy gain (kWhr/m^{2})  

Experiment  Anisotropic  
Bayan Lepas  0.458  0.083  0.071 
Ipoh  0.476  0.091  0.088 
Kuantan  0.515  0.112  0.119 
Langkawi  0.619  0.175  0.183 
Muadzam Shah  0.455  0.081  0.074 
Senai  0.417  0.064  0.055 
Subang  0.492  0.099  0.095 
Energy gain based on experimental curve and isotropic model on midday segment.
Cities 

Energy gain (kWhr/m^{2})  

Experiment  Anisotropic  
Bayan Lepas  0.561  0.071  0.075 
Ipoh  0.564  0.071  0.073 
Kuantan  0.494  0.060  0.062 
Langkawi  0.529  0.066  0.073 
Muadzam Shah  0.495  0.060  0.062 
Senai  0.418  0.049  0.053 
Subang  0.570  0.072  0.074 
Energy gain based on experimental curve and isotropic model on evening segment.
Cities 

Energy gain (kWhr/m^{2})  

Experiment  Anisotropic  
Bayan Lepas  0.490  0.105  0.101 
Ipoh  0.370  0.048  0.052 
Kuantan  0.391  0.056  0.046 
Langkawi  0.420  0.069  0.064 
Muadzam Shah  0.354  0.041  0.035 
Senai  0.262  0.015  0.020 
Subang  0.401  0.061  0.071 
Technical characteristics of PV panel.
Sanyo HIP210NKHB5  

Maximum power ( 
210 
Max. power voltage ( 
41.3 
Max. power current ( 
5.09 
Open circuit voltage ( 
50.9 
Short circuit current ( 
5.57 
Dimension ( 

Weight [kg]  15 
Cell efficiency [%]  18.9 
Module efficiency [%]  16.4 
Consider a proposed 1 MW PV solar farm in Langkawi which is expected to produce 1310 MWhr from horizontal orientation system per year from 4800 solar panels. The additional profit by incorporating DAST onto this solar farm is calculated. The Malaysia feedintariffs (FIT) for gridconnected PV systems with 1 MW capacity are up to $0.35/kWhr as of year 2013. The additional energy gain of DAST in Langkawi is 0.31 kWhr/m^{2}. A 1 MW PV system with 210 W and an area of 1.283 m^{2} PV panels could generate an additional energy of 1909 kWhr per day. Assume a 10% inverter loss for converting the DC (Direct Current) power from PV into AC (Alternating Current) for feeding into grid, $601.34 daily extra profit can be obtained by using DAST. An annual additional profit of $219,499 is the advantage of DAST over SSS. Similar financial analyses on the other cities which are being done and the additional financial gain due to the advantage of DAST over SSS are shown in Figure
Estimated additional financial gain for seven cities with DAST.
This work demonstrates the correlation of clearness index with energy gain and efficiency of DAST over SSS based on experimental setup. Apparent advantage of DAST occurs in morning and evening sessions due to the ability of DAST to follow the sun’s position throughout the day as compared to the static position of SSS. A segmented clearness index graph for the experimental result is plotted and it shows a lower standard deviation and better correlation for clearness index with both energy gain and efficiency during morning, midday, and evening. This correlation has been used, respectively, to estimate the energy gain of seven cities in Peninsular Malaysia and compared with their value developed by anisotropic model. A similar trend for the response of energy gain and efficiency to clearness index is found. It shows that this correlation can offer an estimation of the energy gain of DAST over SSS while considering the potential of installing PV system on a site. Additional financial gain due to the advantage of DAST over SSS for seven cities is also calculated based on a 1 MW PV solar farm case study and Malaysia feedintariffs (FIT). Moreover, this work could be a starting point for further detailed economic analysis for DAST. More economical details included cost analysis of DAST; ground field price and payback period could be explored to validate the investment model of DAST solar farm in the future works.
Dual Axis Solar Tracker
Static Solar System
Photovoltaic
Clearness index for a day ()
Clearness index for an hour ()
Global solar radiation over a day (W/m^{2})
Extraterrestrial radiation over a day (W/m^{2})
Global solar radiation over an hour (W/m^{2})
Extraterrestrial radiation over an hour (W/m^{2})
Solar constant, 1367 (W/m^{2})
Julian day ()
Latitude (°)
Declination (°)
Sunset hour angle (°)
Hour angle for start of an hour (°)
Hour angle for end of an hour (°)
Energy gain of DAST over SSS (kWhr/m^{2})
Energy generated by DAST (kWhr/m^{2})
Energy generated by SSS (kWhr/m^{2})
Energy consumed by DAST (kWhr/m^{2})
The voltage of the tracking system (V)
The current drawn by the tracking system (A)
Maximum Power Point Tracking ()
Constant Voltage method for MPPT ()
Efficiency of DAST over SSS ()
Radiation received by tilted surface (W/m^{2})
Beam component of irradiance over horizontal surface (W/m^{2})
Geometric factor ()
Anisotropy index ()
Modulating factor account for cloudiness ()
Diffusive component of irradiance over horizontal surface (W/m^{2})
Slope of tilted surface (°)
Albedo ()
Radiation received by horizontal surface (W/m^{2})
Angle of incidence of beam radiation on tilted surface (°)
Solar zenith angle (°)
Solar azimuth angle (°).
The authors thank the technical and financial assistance of UM Power Energy Dedicated Advanced Centre (UMPEDAC) and the High Impact Research Grant (H1600100D000032).