Optimization of Hybrid Solar and Wind Power Generation

RESULTS AND DISCUSSION

Experiment results on performance of tracking system: Experiments are carried out to compare the performance of the solar tracker with one axis tracking system, two-axis tracking system and a fixed solar panel as a control. Each tracking system is installed with a 6 V, 3 W solar panels. Comparison between the generations of power of the three systems are made by measuring the short circuit current of the solar panels using a current sensor collected by an electronic data acquisition system. The difference between the generations of the systems are needed as in the sizing software developed, there are options for solar tracking system to be selected by the user. The experiment to compare the performance of one-axis tracking system, two-axis tracking system and a fixed solar panel as the experiment control was done on a typical cloudy day in Universiti Teknologi PETRONAS (UTP). The experiment was done from 8.00 a.m. till 6.00 p.m. Figure 3 shows the short circuit current generated by the fixed solar panel which acts as the control of the experiment, one-axis tracker and two-axis tracker. The control in the experiment starts to generate about 0.025 A of current at the moment the experiment was started at 8.00 a.m. whereas both the solar trackers start at current generation of about 0.05 A. It can be observed that the current for all three systems gradually rises until about 10.00 a.m. and decreases gradually after that period. The highest value of current generated by the fixed solar panel at that period is about 0.052 A whereas the highest value of current generated by the one-axis tracker and two-axis tracker are 0.13 and 0.21 A, respectively. Current generation reduces gradually at that period due to decrease in the solar irradiance at the earth’s surface due to passing clouds. The peak current for all the systems at the day was at about 12.00 p.m.

Fig. 3:	Short circuit current generated by the 3W, 6V solar panels attached to the two-axis tracker, one-axis tracker and fixed solar panel

Fig. 4:	Angle of incidence, θ of solar radiation (Mousazadeh, 2009)

The control of the experiment peaks at about 0.072 A whereas the one-axis tracker and two-axis trackers peaks at about 0.21 and 0.32 A. The current generated for all the systems at this period is the highest because the sun is at the highest elevation in the sky and the sun rays have the shortest path to reach the earth’s surface through the atmosphere. After noon, the current generation reduces and rises again at about 3.00 p.m.

The apparent trajectory of the sun which varies with position and time makes sun tracking an essential method to increase power gain from solar power generating systems. The incidence angle between the incident solar insolation and PV module are minimized by sun tracking systems resulting in higher solar power gain (Singh et al., 2012; Poulek and Libra, 1998) Figure 4 shows the angle of incidence, θ of solar radiation and the higher the angle, the lower is the solar power gain. In a two-axis solar tracker, the angle of incidence θ are maintained at an optimum perpendicular angle to the solar radiation at all times which maximizes the power gain (Mousazadeh et al., 2009). The two-axis tracker has a power gain of about 18 to 25% higher compared to the one-axis tracker. The location of Malaysia at the equator at about 4°N makes a two-axis tracking system not suitable for large scale electricity generation and the best would be a one-axis tracking system.

Sizing software descriptions: The sizing software is developed using Visual Basic 2010 Software Development Tool. The software developed needs the user to input the following data to perform the sizing analysis:

The analysis performed by the sizing software will output the following:

Figure 5 shows the main input window for the sizing analysis software where the resource type are selected and system details are input by the user and Fig. 6 shows the final output window where system details will be shown after the sizing analysis have been performed by the software.

Hybrid generator assembly and testing: The software developed was used to size a hybrid solar and wind generator with a 12 V configuration to power an AC load of 85 Wh and DC load of 45 Wh incorporated with a one axis solar tracker. Table 2 shows the specifications of the components used for the hybrid solar and wind generating system. The hybrid generating system consists of a 50 W solar based generation system and a 50 W wind based generation system.

Table 2:	Hybrid solar and wind generating system specification of the system that was built and tested

Fig. 5:	Main input window for the sizing analysis software where the user selects the resource type and the component details of the hybrid generating system

Fig. 6:	Final output window where the size of all the components to be used in the hybrid generating system are shown to the user after completion of the analysis

Table 3:	Performance of the hybrid generating system at different solar insolation and wind speed

The system built has a storage capacity of 100 Ah at 50% battery DOD for 3 days of storage, thus the system was able to sustain the load for 3 days if there is no any sun light or wind without deep discharging the deep cycle battery. The wind turbine used was a horizontal axis wind turbine with a swept area of 0.6 m². The solar and wind charge controllers have current rating of 5 A.

Table 3 shows the hybrid generating system performance at different wind speed and solar insolation. The charge controllers holds the battery charging voltage constant at about 13.4 A to prevent the battery from being overcharged. The average voltage and average current generated by the solar generation system increases with solar insolation value. The highest solar insolation value the system was tested is at 700 W m^-2. The wind for the testing was produced from a 160 W blower. The wind generator was tested at maximum wind speed of about 3.5 m sec^-1 and minimum wind speed at about 2.5 m sec^-1. Average voltage and average current generated by the wind generator increases with wind speed.

Sizing analysis for the hybrid solar and wind generator are performed using resource data collected on hourly basis for 7 days to obtain the weekly average value in the location where the generator will be developed. Hourly solar radiation data and wind speed data used in sizing analysis will produce the most optimum size of components to be used in the design. An optimally sized solar and wind hybrid generating system would be the best generation system in Malaysia as generating systems with single energy source has disadvantages. Sunlight is only available in the day and average wind speed in Malaysia which is at about 3-5 m sec^-1 are not sufficient for a wind generation system alone (Shafie et al., 2011; Hasan et al., 2011).

CONCLUSION

Proper sizing analysis can eliminate the intermittent nature of wind and solar resource. The hybrid generating system sizing software development explained in this study will be able to make solar and wind electricity more sustainable. The software developed for the sizing analysis uses an iterative method where daily average sun insolation and wind speed on hourly basis makes a reliable sizing calculation for the components to be used in the hybrid generation system. The hybrid solar and wind generating system developed is able to sustain an AC load of 85 Wh and DC load of 45 Wh with 3 days of storage and 50% battery depth of discharge. The recommended future work for the software developed would be incorporating the sizing analysis software together with a real time hybrid PV and wind generation system performance monitoring system. The user interactive system will be able to assist home users and industry based users to set up and monitor their hybrid PV and wind generation system.

ACKNOWLEDGMENT

The authors are grateful to Universiti Teknologi PETRONAS for the support given in completing this research project.