## 1 Introduction
### Studies Related to Photovoltaic (PV) Tracking Techniques
In [58] techno-economic optimization of the hybrid energy system (PV/battery) for powered rural healthcare building, in south India is studied. Fixed tilt, annual optimal tilt (AOT), and six sun-tracking techniques were investigated using Homer software. The objective function wanted to arrive at the lowest investment cost, represented by NPC, LCOE. The result indicated that AOT with fixed installation could be achieved optimum configuration and attain an objective goal. Different major types of PV tracking system were reviewed in the study [59]. In this review, the study confirmed that the azimuth and dual-axis tracker were more efficient than other solar tracking technology. However, in terms of flexibility and economics, the single-axis tracker was more feasible than two-axis tracker. An off-grid hybrid energy system (PV/battery/Diesel) is compared with excluded diesel from the hybrid system, for supplying households in Urumqi. The fixed title, one-axis tracker, and two-axis tracker were examined their effect on technical and economic factors of the system. The result demonstrated that the PV system produced approximately 3.68 MWh, 3.79 MWh, and 3.83 MWh, for the fixed title, one-axis tracker, and two-axis tracker, respectively. The hybrid power system (PV/battery/diesel) was economically superior, whereas, the diesel-based power system was more expensive. The greenhouse gas emissions (GHG) reduced 5.5 t, 5.6 t for fixed-tilt, single or two-axis tracker. The off-grid hybrid energy system (PV/battery) with a single or two-axis tracker could demonstrate better performance regarding GHG reduction [60]. The PV tracking technology has been considered for the grid-connected PV system in Makkah, Saudi Arabia. The fixed-tilt, horizontal-axis (continuous, daily, weekly, and monthly adjustment), vertical continuous adjustment, and dual-axis tracker were examined. The result indicated that, in the dual-axis tracker, vertical-axis continuous adjustment gained up of 35%, 20%, more power than the fixed-tilt system, respectively. In addition, the horizontal adjustment shows the highest NPC, and LCOE. The study recommended that the vertical continuous adjustment was the best choice, as it achieved the best NPC, LCOE. Also, high solar energy penetration to the grid [14]. Three major PV trackers, fixed-tilt, one-axis trackers, and two-axis trackers were examined for a grid-connected PV system. A result of analysis indicated that implementation of dual-axis tracker could gain 35% more output power compared to static axis solar panels. Moreover, the project also reduced CO\({}_{2}\) emission by 606 t [61]. A 10 MW PV power plant in Al-Anbar, Iraq has been assessed under effect of three major PV tracker namely: fixed-tilt, single-axis tracker and two-axis tracker. The study aimed to evaluate the project from an economic and environmental perspective. The result illustrated that the two-axis tracker could enhance the economic feasibility of the project. Also, the reduction of GHG emissions was ensured [62]. Fixed and dual-axis tracking PV system has been installed in the US upper Midwest. The cost of energy produced by the fixed and dual-axis tracker were calculated to be $0.31 and $0.37 for each kWh [63]. In conclusion, the different PV trackers have different advantages and disadvantages. For tracking the solar energy and generating power, the dual-axis tracker is the best choice owing to its ability tracking the sun at different angles. However, it has extra investment cost on the tracking system. The fixed-tilt solar panel is the cheapest, but it has the worst ability of harvesting solar energy. For the horizontal single-axis tracker (HSAT) and the vertical single-axis tracker (VSAT), their costs and abilities of harvesting solar energy are similar. Furthermore, for the NPC, LCOE and GHG, the common conclusions cannot be got because the conditions, such as weather, geographic position and load demand, are different.