To examine the effect of inclination angle on the output power of the PV panel, three PV panels have been installed at 30O, 40O & 45O angle of inclination. The values of the open circuit voltage Voc and short circuit current Isc were measured on hourly basis for twelve months in the year 2014. The observations have been analyzed for finding the optimum angle of inclination of PV panel. It is concluded that, for Chandigarh, from January to March the inclination angle of PV panel can be 45Oas this inclination gives highest power output among the three PV panels. From April to September optimum inclination angle of PV panel is 30Oas the sun is overhead during this period and higher power output is obtained. The better performance of PV panel can be obtained by changing the inclination angle twice in a year i.e. in mid April and in mid September.
In the view of shortage of fossil fuels and rising pollution concerns, more and more focus has been given to the renew-able energy sources. Solar energy is most promising form of renewable energy. It has many advantages:
- It is one of the least destructive of all the sources of energy.
- It is capable of satisfying the world’s major energy demand.
- It can power almost everything with proper modification and set up.
The solar energy can be converted into electricity by a photovoltaic cell or into thermal energy by a PV panel to heat water and air. The amount of solar radiations received on a PV panel depends on the latitude, time of the day, day of the year, slope or tilt angle, surface azimuth angle, & the angle of incident radiation.
The efficiency of PV panel can be increased if the panel is placed in such a manner that incidence angle (angle between the sun rays and the perpendicular line on PV panel) is null or almost small. Such a condition can be obtained in two ways, firstly a tracking system is used so that sun can be followed throughout the day and secondly, the panels are fixed in such a manner that angle of incidence is relatively small for most of time in day. In first case, the efficiency of PV panel increases significantly as a proper tracking system make incidence angle almost null throughout the day. However, it is linked to major disadvantage of energy requirement of tracking system which includes motor drives to move the bulky system. The maintenance is another big issue. Hence, generally such a system is not viable for small power panels. Fixed panels are most commonly adopted PV panel structures. When the PV panels are fixed, it is not possible to obtain the minimum incidence angle throughout the day. However, for achieving the reduced incidence angle for maximum duration the PV panels have to be installed with proper orientation and angle of inclination (also called tilt angle). The paper thus contributes towards an extensive analysis of the solar PV panels’ data and presents an alter-native to continuous sun tracking system by changing the angle of inclination biannually.
Sun Earth Geometry & Inclination Angle of PV Panel
The angle of inclination of PV panels depends upon the location of panels (i.e. latitude) and sun-earth geometry. The sun-earth geometry involves the study of earth’s rotation and revolution as well as the tilt angle of earth’s axis. Earth’s rotation refers to the spinning of our planet on is axis, because of rotation, the earth’s surface moves at the equator at a speed of about 467 m/s. The earth’s revolution refers to the orbiting of the earth around the Sun. This celestial motion takes 305.26 days to complete one cycle. As the earth rotates and orbits around the Sun, there are significant seasonal and hourly positional changes of the Sun (and length of daylight). The relative position of the Sun is a major factor in the performance of the PV panels.
Fig. 1: Sun-Earth geometry
Duffle and Beckman gives “rules of thumb” that to give maximum annual energy availability, a surface slope to latitude is optimal and the surface should face the equator. It means, a solar collector in southern hemisphere should face to the North with slope equal to its latitude to get maximum solar radiation. Number of studies have been carried out in different countries of the world to obtain the optimum tilt angle of the PV panels. However, it is found that no study has been done in India particularly in North India and the estimation of tilt angle of PV panels were obtained through global data. In this paper, the optimum tilt angle to maximize output power is estimated by PV panels installed in Panjab University Chandigarh, India which has latitude of 30O44.
Studied Photovoltaic System
To overcome the energy shortage in country, Government of India has started Jawaharlal Nehru Solar Mission and under this many cities have been declared Model Solar cities. Under this scheme, Chandigarh has also been declared as the “Model Solar City”. The latitude of Chandigarh is 30O44’N. PV panels have been installed on many buildings in Chandigarh to harness the solar energy to meet its energy requirements.
Power generation of a PV system depends on various factors such as, solar irradiation, time of day, day of year, power conversion efficiency, PV panel tilt, weather conditions and many more. Among the above parameters the direct solar irradiation is the most significant factor for calculating the power generated by a PV panel. The power generated in a day is a function of power efficiency (η), sunlight intensity (Ga, W/m2), incident angle (θ), no. of PV panels (n), area of a PV panel (A, m2.)
To obtain the optimum angle of inclination of PV panels at Chandigarh experimental set up consisting of 3 solar panels has been installed at UIET, Panjab University, Chandigarh as shown in Fig. 2. These PV panels of 100W each have been installed at an inclination angle of 30O, 40Oand 45Oas shown in Fig.3.
Fig 2: Installed Photovoltaic panels at UIET, Panjab University
Fig 3: Inclination of the PV panels installed at UIET, Panjab University
In this research, a yearlong recorded data is recorded and analyzed to reveal the PV performance from January 1st, 2014 to December 31st, 2014. There are 3 panels installed which are facing south and tilted at an angle of 30O, 40Oand 45O with the horizontal. Each panel is connected to a charge controller unit (CCU) which charges a 150Ah, 12V tubular battery. The battery is connected to an inverter through which a load of 40W tube light and a 60W fan is connected in 3 rooms. Block diagram for the experimental setup consisting of different ammeters, voltmeters, battery and inverter is shown in Fig. 4 and a photograph for the setup is shown in Fig. 5.
Fig 4: Block Diagram for the PV system.
Fig 5: Digital ammeter readings
As the voltage is measured at open circuit and current is measured at short circuit so the switching scheme is designed so that there is load cut off while taking the readings. After taking the readings, the load is re-connected to the CCU for the charging of the battery. From the battery, the supply is given to the inverter which is further supplying the AC load.
From the experimental setup various parameters for power calculations were recorded for each hour between 09:00 A.M. to 05:00 P.M. The readings were recorded for various days during different months of the year 2014. The open circuit voltage (Voc) and short circuit current (Isc) were measured and power is calculated on hourly basis for 12 months from January to December. The formula used for calculating power is,
The data recorded was for different seasons in varying weather conditions such as cloud, partially cloudy and clear day and this data is used to calculate the average power generated in a particular month of the year. However for comparison and analysis purpose the readings for a full bright sunny day have been shown in Fig. 5-9. The output power of PV panels with 30O, 40O, 45O of tilt angle have been shown as bar graphs fordifferent day in the month of January, April, July, September & December.
Fig 6: Power (watts) on 03-01-2014
Fig 7: Power (watts) on 25-04-2014
Fig 8: Power (watts) on 15-07-2014
Fig 9: Power (watts) on 16-09-2014
Fig 10: Power (watts) on 11-12-2014
It is observed that power output is highest for 45Oinclination in the month of January (Fig. 6). However in the month of April the power generated for 40Oand 45O are comparable (Fig. 7). In the month of July the power measured is higher for PV panel at 30Oas compared to 40Oand 45O(Fig. 8). The values of power at an angle of 30O becomes more in the month of September (Fig. 9). The power generated by the PV panel at an angle of 45O is highest among the three panels in the month of December (Fig. 10).
The measurements are also made for short circuit current (Isc) for the 3 PV panels during different months of the year as shown in the Fig. 10-12. For 30O it can be seen that the average short circuit current (Isc) is higher in the month of April and September whereas it is smaller during the month of July and December. The reason for such outcomes can be due to the impact of changing solar irradiations and climate conditions during these months as the month of April and September has quite even weather whereas July experiences heavy rainfall and December has extremely cold conditions and dew effect in Chandigarh.
Fig 11: Short Circuit Current (ISC) at 30o angle
Fig 12: Short Circuit Current (ISC) at 40o angle
Fig 13: Short Circuit Current (ISC) at 45o angle
Table 1. below shows the average power calculated during a full sunny day during different days of the year 2014. It is analyzed that the average power calculated during the month of January is more for 45O than 30O PV panel. The average power is more for 30O than 45O in the month of April and continued till the month of July. The average power is almost comparable for both 30O and 45Oin September. The average power again becomes more for 45O in the month of December.
In order to find the percentage power difference during different seasons of the year from different season of the year from different PV panels the calculations has been made. The percentage difference (PD) in power output is calculated using,
Fig.13-17 shows the percentage power difference (%PD) for 5 days in different seasons i.e., Fig. 13 for 03-01-2014, Fig. 14 for 25-04-2014, Fig.15 for 15-07-2014, Fig. 16 for 16-09-2014 and Fig. 17 for 11-12-2014.
Analysis of these plots shows that, the PD for the month of January as in Fig. 13 show a significant difference in output power throughout the day. There is a power difference of minimum 6% in morning and maximum 18% in evening which is quite significant. This indicates that, a PV panel with 45O inclination is good as compared to 30O inclination for the month of January.
Fig 14: Percentage Power Difference at 30o and 45o on 03-01-2014
From Fig. 14, it is seen that PD is negative for most of the day time with maximum negative value of 8%. This indicates 30O angle inclination gives better output as compared to 45O inclination angle in April.
From Fig. 15, it is seen that PD is again negative for most of the day time with maximum negative value of 13.81%. This indicates that 30Oangle inclination gives better output as compared to 45O inclination angle in July.
Fig 15: Percentage Power Difference at 30o and 45o on 25-04-2014
From Fig. 16, it is seen that PD is positive for most of the day time with maximum positive value of 5.88%. This indicates that 45O angle inclination gives better output as compared to 30O inclination angle.
Fig 16: Percentage Power Difference at 30o and 45o on 15-07-2014
From Fig. 17 it is seen that PD is positive for complete day with maximum positive value of 19.9%. This indicates that 45O angle inclination gives better power output as compared to 30º inclination angle in the month of December.
Therefore from Fig. 13-17 it can be observed that 45Oangle is good for months, January to mid April and 30Oinclination angle is better for months, mid April to September. The 45O angle is again better for months October to December.
Fig 17: Percentage Power Difference at 30o and 45o on 16-09-2014
Fig 18: Percentage Power Difference at 30o and 45o on 11-12-2014
The short circuit current (Isc) and output power vary with the change in position of the Sun from morning to evening. In all the three panels, the short circuit current (Isc) and power output has been observed to be higher for the PV panel with 30O inclination during month of April to September. However, the short circuit current (Isc) is higher for 45O inclined PV panel from January to March. It is concluded that, as per the location of Chandigarh (latitude 30º44’N) the Sun is overhead during summer season starting from April to September. The 30Oinclination is optimum, whereas for the rest of the year, the angle of the panel can be adjusted to 45O. So with biannual change the efficiency of the PV panel can be enhanced to great extent.