Comparing the Performance of Pivotless Tracking and Fixed-Type Floating Solar Power Systems

Abstract

Floating solar power has a higher power generation efficiency than existing solar power generation methods. It is easier to secure in an installation area as well as to connect to other renewable energy sources. Floating solar power is considered an essential component for achieving carbon neutrality because it compensates for the shortcomings of existing solar power systems and maximizes their advantages. In this study, a performance comparison was conducted between pivotless tracking-type and fixed-type solar power systems. These systems were installed at the Irwol Reservoir in Suwon, South Korea, and monitored for comparison between May 2019 and June 2020. The tracking-type system generated approximately 14% more energy than the fixed-type system; the performance was maximized in May, which showed 25.63% more output power, and the performance was minimized in winter, with 3% more generated power. Owing to its pivotless structure, this system can be used in the solar industry.

1. Introduction

Recently, environmental issues, such as floods and droughts, destruction of ecosystems, and sea level rising, have increased significantly owing to global warming; renewable energy is attracting great attention as an energy alternative to solve these problems [1,2,3,4,5]. This is because renewable energy is essential to prevent climate change, through the reduction of greenhouse gas generation, the root cause of global warming [6,7,8,9,10]. Solar power generation is one of the most promising technologies for renewable energy sources, and photovoltaic (PV) systems are a common application of solar energy [11,12,13,14,15]. Each PV module consists of several solar cells and is sealed with various layers to protect the solar cells from the external environment [16,17,18,19,20,21]. These PV modules generate electricity directly from sunlight; therefore, they do not generate waste or noise. The structure is simple and eco-friendly, and the power generation scale can be varied to respond to demand from small houses to large-scale industrial complexes, and it does not require additional machinery for operation [22,23,24]. Generally, solar power generation systems are installed on the ground, such as farmland and forests; however, avoiding ecological damage, such as destruction of farmland or forest, limits the number of installation locations, and land use issues have been an obstacle to the supply of solar power generation [25,26,27]. In recent years, hundreds of global companies have decided to participate in RE100, which will increase the demand for PV energy in the near future, and the burden of installing PV systems on the ground will increase greatly [28,29,30].

In a floating solar power generation system, the power system is installed on the water surface, and hence this does not require existing farmlands or forests. It uses an idle water area that is available in various parts of the land and can save not only the usage of land but also the operating cost for power generation [31]. Because it is installed on a water surface, the floating solar power generation system has additional advantages compared to conventional solar power systems. First, the amount of power generation increases because of the cooling effect on the module when the water temperature is lower than the outdoor temperature as well as light reflected from the water surface, which provides an additional amount of light to the power system [32,33]. In addition, it inhibits the occurrence of green algae in water by blocking sunlight and creating a suitable environment for spawning and breeding of fish [34]. Figure 1 shows a typical floating solar-power system. As shown, it consists of a photovoltaic module for power generation, pontoons or floats for floating PV modules on the water, a weight, an anchor for mooring, and power cables to deliver the electricity generated from the water to the ground.

Generally, PV modules of solar power systems fixed on the ground with a specific angle have been used; however, recently, more efficient solar power systems that track the position of the sun in accordance with the time of day and generate more electricity than a fixed-type system have attracted interest. For the tracking operation, PV modules are installed on long horizontal supports with bearing-mounted pylons or frames; however, because of the weight of the modules, only a few modules can be installed on each pylon; hence, the economic burden of installing PV modules on a large scale is large [35,36,37,38]. However, the installation of the tracking-type solar power system on the water can be a more effective method because of the distinct characteristics of the installation environment. The conventional rotary-floating solar power system rotates around the axis of rotation, and the pile must be fixed at the bottom of the reservoir, which increases the construction cost. In this study, a pivotless tracking-type floating solar power system was demonstrated. Unlike a conventional tracking-type PV system, it does not have a pylon to rotate the system and consequently, it can reduce the cost of construction and prevent any collision from floating objects. To compare the performance of the system, the conventional fixed-type floating PV system was also installed and analyzed. The pivotless tracking-type system generated approximately 14% more energy; the performance was maximized in May, with 25.63% more output power than the conventional fixed-type floating solar systems.

2. Materials and Methods

Floating photovoltaic power generation facilities are located on the water surface of reservoirs and dams; thus, they need to be stably positioned and oriented so that the floating structures do not shake, even in the event of frequent water level fluctuations; general natural phenomena such as wind, waves, and currents; and adverse weather conditions such as typhoons. Therefore, the floating body should be able to move freely according to water level fluctuations, and be simultaneously fixed to minimize the left and right movements of the floating body due to the wind. Figure 2 shows the layout of the pivotless tracking-type floating solar power system, which consisted of a pontoon to float the floating body on the water and a mooring system device to fix the floating body in response to changes in the water level. The mooring system is connected by forming an inclination with the floating body to prevent the floating body from deviating from the set position.

Two 310 W inverters were connected [39] to transmit the generated power and connect it to the power grid, and a solar radiation meter [40] was installed to measure and collect the amount of solar radiation. Also, collected energy output was automatically calculated by computer. To compare the output of the pivotless tracking-type and fixed-type solar power systems proposed in this study, a typical floating solar power system was installed in the same place; each system was equipped with five 310 W crystalline silicon photovoltaic modules [41] with an inclination angle of 27°. Each system has five modules, all connected in series to generate power.

3. Results and Discussion

Figure 3 shows a three-dimensional rendering image of the pivotless tracking-type floating solar power system and installed PV system, respectively. The pontoon was used as a floating body and 5 PV modules were installed on a pontoon to float the panels on the water. The floating body, which consisted of panels and a pontoon, was connected by the winding system and the position of the floating body was adjusted by increasing or decreasing the length of the wire. Besides, the floating body was surrounded by four mooring systems to stabilize and rotate the PV system, and each mooring system was connected to a buoy, sinker, and anchor to settle the mooring system on the water. For generation quantity comparison, the fixed and tracking types of the solar power system were installed in the Irwol reservoir, which is located in Suwon, Republic of Korea, at a latitude and altitude of 37.2880° N and 126.9726° E, respectively. The system was 50 m off the land and the length of the connected power cable was about 70 m. The setups of the two systems were almost same, such as the location of the systems and the inclination angle of the panels. However, the tracking-type had an additional winding system to rotate 270° of the overall floating body for tracking. This tracking-type system does not have a pylon, the cost of construction is reduced, and maintenance is easy because there is no collision between the pylon and structure. In addition, in the event of a typhoon, it is fixed with a mooring system to strengthen its resilience; thus, it is safe, even in strong winds, and the power generation facilities can be protected from floating objects resulting from floods. Figure 4, Figure 5, Figure 6, Figure 7, Figure 8, Figure 9 and Figure 10 shows the produced energy output of each system from May 2019 to June 2020. As the figures show, the tracking-type solar system generates more energy than the fixed-type system. The tracking-type solar system showed much better performance between March and September compared to other months. In addition, during winter, not only was the energy output small, but the difference between the two systems was small. These results correspond to the amount of solar radiation and the sun-path of the period [42]. Figure 11 shows the energy output of the two systems and amount of solar radiation from May 2019 to June 2020. This result clearly shows that in 2019, the tracking-type system had maximum output in May 2019 with 25.63% higher energy than fixed type solar systems. Besides, the minimum energy output occurred during winter, from November to January; however, the tracking-type system showed approximately 3–5% higher energy than the fixed type.

As shown, the tracking-type system worked more efficiently during certain periods of exposure to high insolation, such as in spring and summer. The tracking-type system rotates 270° along the horizontal axis to track the sun. As the amount of insolation increases, the amount of electricity produced by solar power generation also increases. Previously reported comparison between the fixed and tracking-type PV system on the ground showed that a tracking-type has 30% more energy output than a fixed-type [43]. The performance of our floating system is close to the previous results and considering characteristics of floating PV system, the pivotless tracking-type floating system has advantages.

Table 1. Comparison of the fixed and tracking-type system for total energy output and increased rate from May 2019 to June 2020.

Type	Fixed (kWh)	Tracking (kWh)	Increased Rate (%)
Total energy output	2313.30	2684.69	13.83

presents the total energy output during the entire monitoring period from May 2019 to June 2020.

As shown in the table, the tracking-type generated 371.39 kWh more than the fixed-type solar system, which had 13.83% better performance during the period.

4. Conclusions

In this study, we installed a pivotless tracking-type floating solar power system and compared it to a conventional fixed-type floating system. The pivotless tracking-type system rotates the floating body through the day so it can produce more energy than fixed-type. With the increased amount of exposed daily insolation, the suggested pivotless tracking-type system generated approximately 14% more energy production during the monitored 16 months. The performance of the tracking-type system was maximized in May, which showed 25.63% more energy output than the fixed-type solar system, and the performance was minimized during the winter with only 3% more energy output. Because of its pivotless structure, this system can be applied to large-scale floating solar power systems with reduced construction costs, simpler maintenance to prevent collisions between the pylon and structure, and safer operation in strong winds. These advantages are essential for large-scale power generation facilities, and this pivotless tracking-type solar power system can be used in the solar industry. For further work, it is necessary collecting more long-term period and versatile data to analyze in more detail.