As of May 2021, according to government data, at least 500,000 households in Indonesia lacked access to electricity. Most of these households were located in remote villages [1]. PT Perusahaan Listrik Negara (Pesero), the national electricity provider, reported that approximately 4,700 villages in the outermost, frontier, and underdeveloped regions (3T areas) have yet to experience electricity [2]. Currently, most energy production relies heavily on fossil fuels, such as coal, oil, and gas. With the depletion of global oil reserves and the negative environmental impacts associated with these sources, a more sustainable and environmentally friendly approach is urgently needed [3]. As a country located along the equator, Indonesia has significant potential for renewable energy, particularly through the use of hydroelectric power plants that, harness water as the primary source of energy [4]. These plants offer cleaner and more sustainable solutions to the country’s growing energy needs.

Hydrokinetic energy refers to the conversion of kinetic energy from flowing water into electrical power, without the need for large infrastructure such as dams [5]. Unlike traditional hydropower systems, that rely on damming rivers to create reservoirs and utilize the potential energy difference between high and low water levels, hydrokinetic systems harness the natural flow of rivers, tides, and ocean currents to generate electricity [6]. The basic principle of hydrokinetic energy generation involves positioning turbines along the path of the water flow [7]. As water moves past or through the turbine blades, it causes them to rotate, driving a connected generator to produce electricity. The harnessed energy is directly proportional to the velocity of the water flow and the area swept by the turbine blades. This process makes hydrokinetic systems particularly suitable for regions with consistent water flow that lack the topographical conditions necessary for dambased hydropower [8].

Hydrokinetic turbines can be deployed in riverbeds or near the outflow of conventional hydroelectric power plants, where the residual energy from released water can be captured and reused [9]. One of the primary advantages of hydrokinetic systems is their minimal environmental footprint [10]. Because they do not require the large-scale modification of ecosystems associated with damming, such as the disruption of aquatic habitats and local communities, they are considered a more sustainable alternative to traditional hydropower projects [11]. Additionally, these systems can be implemented in remote areas providing an effective means of delivering power to isolated communities that are often excluded from the national grid [12].

Hydrokinetic systems are particularly well-suited for Indonesia, given its extensive river networks and the geographical challenges of electrifying remote areas [4]. The deployment of hydrokinetic turbines in rivers with moderate to swift flows can help generate a continuous supply of renewable energy, particularly in regions where the construction of large dams is impractical or environmentally challenging [13]. Furthermore, the use of hydrokinetic technology downstream of existing hydropower plants can further enhance energy efficiency by capturing the residual energy from water that has already passed through dam turbines [14].

This study focused on calculating the power generated by the designed water turbine and measuring the water flow speed, water discharge, and cross-sectional area of the river. In addition, the efficiency of the designed hydrokinetic system is analyzed and recommendations for future efficiency improvements are provided. The primary motivation for this study is the abundance of water resources in Indonesia, which presents great potential for small-scale hydropower development. Although considerable research has been conducted on hydrokinetic technology, there is still limited focus on its application to small rivers with low flow velocities. Therefore, this study aims to address these challenges, particularly in rural areas. The main contribution of this study lies in the design and performance analysis of a hydrokinetic power plant suited for low-velocity rivers while offering an economical and easily implementable solution for remote communities in need of access to renewable energy. The remainder of this paper is organized as follows; The methodology explaining the design and testing process, The results and discussion that detail the system's performance, and conclusions with recommendations for further development.

2.1. Material

Before assembling a hydrokinetic turbine, thorough planning is essential to minimize errors. The components of the hydrokinetic river technology used in this study are shown in Figs. 1–5. Figure 1 shows the blade support structure made from strip iron, which serves as a connector between the blade and wheel axle. Figure 2 shows the blade itself, made from 4-inch polyvinyl chloride (PVC) pipes, which were designed to harness the water flow and rotate the turbine. Figure 3 shows a the connection plate, attaching the blades to the turbine shaft. Figure 4 shows the transmission system, designed to stabilize the turbine rotation in response to fluctuating water speeds. Figure 5 shows the generator, which is an essential component responsible for converting mechanical energy into electrical energy. The generator contains two key parts: a rotor (rotating component) and a stator (stationary component). A permanent magnet generator was used, to generate the alternating current voltage. Figure 6 shows a schematic of the river hydrokinetic system, illustrating the integration of the turbine, transmission system, and generator within a complete setup.

Figure 1. Strip iron for blades design.

Figure 2. PVC pipe as blade design.

Figure 3. Contact plate blades design.

Figure 4. Transmission system design.

Figure 5. Stator and rotor design.

Figure 6. Schematic of the river hydrokinetic system.

Turbine assembly involves pairing all the components based on a preliminary design. Iron strips were connected to PVC pipe pieces and metal plates to form the turbine system. The two turbines were mounted on a single axis to maximize the effectiveness of turbine wheel. Each turbine included 16 blades positioned 45° relative to each other, with a total blade curvature of 8 cm. The blades were designed to rotate at optimal angles to harness the water flow. Figure 7 shows the turbine design.

Figure 7. Actual turbine design.

2.2. Design parameters and methodology

Planning is required before assembling the device to minimize error during the assembly process. Considering the various types of previously built hydrokinetic turbines, the authors designed and created a turbine whose principle is similar to that of a cross-flow turbine with an in-plane axis. However, in this case, the functions and principles are identical. This study attempted to innovate the turbine by creating a hinge on each blade. The hinge is intended to be a turbine wheel that can spin by splitting when the water flows. The working principle of this turbine is as follows. When the turbine rotates with the hinge upward, both sides of the blade shut down; therefore the opening of the blade becomes lighter, and the rotation can be maximized. The most important aspect of the design of water turbines is the determination of their outer diameters. The design was based on the distance between the upper side of the turbine and the end of the waterways, as well as within the bottom of the turbine with drains. The diameter is designed based on the volume of water provided by the blade. The formula used to calculate the volume of water (V) that drives a turbine blade can be calculated as follows (the blade size is half of the tube):

where r and l denote the radius and length of the pipe, respectively. The torque (T) of the turbine was calculated as follows:

where F is the force and d is the distance. The peripheral speed or angular velocity (ω) of the turbine is expressed as follows:

where n is rotational speed of the turbine (rpm). The power produced by the turbine (P_t) is the product of torque and angular velocity. It can be calculated as follows [15]:

The efficiency of the turbine (η_t) can be calculated as follows:

where P_w is the power produced by water and can be calculated as follows [16]:

with

The cross-sectional area (A) channel used can be calculated as follows:

where w and h are the width and depth of the river at the cross, respectively, and Q, v, and ρ_w are the debit, velocity, and density of the water.

To help maximize the results in terms of the design and manufacture of hydrokinetic river hydropower, the authors designed a method to connect the turbine and turbine generator so that they could be reproduced. Correspondingly, as it was previously known that the speed of the water flow is not completely fixed and even tends to be heavy, especially without the initial damming process, each generator has a number of rounds to produce stable electricity.

A turbine that harnesses the flow of the river alone cannot meet the number of rounds required to become a standard generator because the normal rotation of a generator ranges from 500 to 2,200 rpm or higher. A turbine or windmill encounters difficulties in reaching the same number of rounds. A pulley is an element of a functioning machine that is used to transmit power from the motor to the shaft through a belt. Pulleys can be made from cast iron and can be steelprinted. Pulleys are generally made of cast iron because of their low cost. The diameter of the driven pulley, defined by the pulley speed ratio equation is expressed as follows:

where n₁ and n₂ are rotation speed of the driving pulley (rpm), and D₁ and D₂ are diameter of the driving pulley (m).

The freewheel and sprocket were set as transmission gears consisting of gears and chains. In this study, the authors used bicycle transmission based on certain considerations and experiments they conducted. The bicycle transmission is suitable for use in this hydrokinetic system because its rotation is lighter than that of motor transmission systems. The following equation is used calculate the ratio of these transmissions:

where N_i and N_o are the input and output of the gear rotation number, respectively, and Z_i and Z_o are the input and output of the gear number, respectively.

In this study, a generator was built with a permanent magnet as the rotor because such a generator using a permanent magnet is suitable for use in power plants based on water flow. The authors used a permanent-magnet generator because generators of this type are easy to create and design. In addition, they have the capacity of a certain power and voltage by changing certain parameters, such as the magnetic flux, coil diameter, number of coils, and number of magnets used.

The generator can also operate at low rpm. Given that this ability has become an advantage of permanent-magnet generators, this type of generator was used. The following equation was used to calculate the output induction permanent magnet generator (GMP). The GMP frequency can be calculated as follows:

where Pis the number of coils and n is the round mover. The magnet area was calculated as follows:

The magnetic field and magnetic flux were calculated according to the obtained data as follows:

where l_m and w_m are the length and width of the magnet, d is the distance between magnets, M is the magnet number, δ is the distance between the rotor and the stator, and ρ_m is the density of the magnet.

The kinetic energy of an object depends on its mass and velocity. Numerous forms of kinetic energy exist, including vibration (vibration energy caused by movement), rotation (energy caused by rotational motion or spinning), and translation (energy resulting from displacement from one location to another). The equation for kinetic energy is as follows:

where m is the mass and v is the velocity. Electrical energy is generated when the turbine rotates its rotor, which also generates electricity. Electrical energy and power can be determined using the following equations:

where V is voltage (V), I is current (A) and t is operating time (s).

3.1. Results

The test site was measured prior to testing the hydrokinetic system. An associated measurement is the measurement of the channel’s crosssectional area, speed of water flow, water flow, and water power. After all the measurement results were obtained, the turbine parameters were calculated, including torque, angular velocity, turbine powers, and turbine efficiency. The research was conducted on the water flow of the Tapung River, Petapahan village, Tapung Hulu district, Kampar regency, Riau. Figure 8 shows the implementation of the hydrokinetic system in river flow. The cross-sectional area was measured using the three-point line. Table I summarizes the measurement results.

Figure 8. Implementation of hydrokinetic system in river flow.

Table I. Measurement results implementation of hydrokinetic system in river flow..

No.	Measurement	Value
1	Cross-sectional area	0.6 m2
2	Water flow velocity	1.03 m/s
3	Water discharge	0.61 m3/s
4	Water power	327 W
5	Volume per blade	0.0007 m3
6	Torque	32.34 N⋅m
7	Turbine power	67.38 W
8	Turbine efficiency	20.6 %

Based on the measurements of the important parameters and through Eq. (8), the sectional area for water flow is obtained as 0.6 m², where the width is 0.6 m and the depth is 1 m. River water flow velocity is measured through the floating method. Measurements were obtained wuisng this method with floating light objects, such as plastic balls, corks, or wood. Thereafter, the distance between the floating objects was measured. In this study, a three-point velocity measurement location for water was used, and the measurement was repeated up to ten times at any point to obtain accurate results. After measurements at the three points were taken, data were obtained to calculate the speed of the river water flowing under normal river conditions. Average velocity of 1.03 m/s was obtained. Equation (7) was used to obtain the river water debit, which was 0.61 m³/s. The power of water was 327 W, as obtained from Eq. (6). Equation (1) was used to obtain the volume of water provided by a blade, which is 0.0007 m³, with a radius of 0.06 m and a length of 0.13 m. The torque of the turbine can be calculated using Eq. (2). When d is parallel to F and the angle being 90o, the torque obtained is 32.34 N⋅m. The power and efficiency generated by the turbine were 67.38 W and 20.6 % respectively, which were obtained from Eqs. (4) and (5), respectively.

This study adopts three reducing transmission rates by the transmission system, which is a mixture of pulley-belting and freewheelsprocket. Both types of transmissions are used to increase the number of rounds because the pulley-belting dimensions are sufficiently large, such that the ratio is 5:1. However, obtaining this type of freewheel, which is quite large in comparision, is very difficult. The pulley-belting ratio can be calculated using Eqs. (9) and (10). The drive pulley was set to 100 rpm, as obtained using Eq. (9). The calculations for the first gear (freewheel and sprocket) is 150 rpm, as obtained from Eq. (10). Additionally, the second gear (directly linked to the generator) is 495 rpm, as obtained from Eq. (10). The generators used were three-phase generators having 12 coils with a diameter of 0.6 mm, and each coil consisted of 100 loops. The dimensions of the magnet were 3 cm × 1 cm. The stator has a diameter of 25 cm, and the rotor has a diameter of 15 cm. With the coil number at 12 and the round mover at 495 rpm, the GMP frequency is 49.5 Hz, as obtained from Eq. (11). With the length and width of the magnet at 0.03 and 0.01 m, the distance between the magnets at 0.003 m, and the number of magnets at 12, Eq. (12) yields a magnet area of 1.6 × 10-5 m². Equations (13) and (14) are used to obtain magnetic field and flux magnetic at 1.74 × 105 T and 2.78 Wb respectively. Therefore, the theoretical power is 0.21 W, as obtained from Eq. (18).

3.2. Discussion

The results of this study indicate that the hydrokinetic turbine system produces relatively low power output, ranging between 0.18 and 0.24 W. The measured efficiency of 20.6 % indicates potential areas of inefficiency in the current setup, which require improvement to achieve more viable power generation. Several factors contributed to the observed low-power output. First, the blade design and position can be optimized to better capture and convert energy from water flow. Improving the hydrodynamic performance of the blades can improve their ability to utilize energy effectively. In addition, the alignment of the transmission system with the turbine speed must to be refined to match the generator’s operational requirements, potentially resulting in an increased power output.

The turbine speed produces a consistent electrical frequency. With the current setup, the generator achieves an average frequency of 49.5 Hz, which is close to the target of 50 Hz but may require additional adjustment. With the number of coils at 12 and the circular drive at 495 rpm, the GMP frequency is 49.5 Hz, close to 50 Hz.

The calculated total system efficiency of approximately 15.9 % illustrates the cumulative impact of efficiency losses across each stage of the hydrokinetic system. Initially, the turbine demonstrated an efficiency of 20.6 %, demonstrating its ability to convert a portion of the kinetic energy of water into mechanical power. However, the inclusion of additional components, specifically three gear stages and a generator, results in further reductions in efficiency. Each gear stage operates at an efficiency of 95 %, resulting in approximately 5 % power loss at each stage owing to friction and mechanical dissipation. In addition, a generator, with an efficiency of 90 %, imposes further conversion losses during the transition from mechanical to electrical energy. Consequently, when the individual efficiencies were combined, the overall system efficiency declines to 15.9 %.

To calculate the turbine power output of 67.38 W, the torque and angular velocity of the turbine were considered. The torque, which is provided as 32.34 N⋅m, is multiplied by the angular velocity to determine the mechanical power produced. The angular velocity is calculated using the river water velocity of 1.03 m/s and the turbine radius of 0.06 m, resulting in an angular velocity of 17.17 rad/s. Multiplying the torque by the angular velocity gives the mechanical power of 555.23 W. However, with a turbine efficiency of 20.6 %, the actual output power is lower. After applying the efficiency factor, the output power is determined to be 67.38 W.

The electrical power produced by the generator in this study, which ranges from 0.18 to 0.24 W, was measured under full-load conditions. The generator’s performance when operating at full load indicated that the power output was relatively low, given the measured voltage (5.0 – 7.6 V) and current (0.012 – 0.026 A) (Table II). This result suggests that while the generator is function under full load, it may not reach its expected efficiency. This low output can be attributed to various factors, including mechanical losses in the transmission system or inefficiencies in the generator itself.

Table II. Voltage and current output.

No.	Measurement	Value
1	Voltage	5.0 – 7.6 V
2	Current	0.012 – 0.026 A

A comparative analysis with other studies supported these findings and underscored the commonality of low efficiency in hydrokinetic systems. For instance, [17] noted similar challenges in optimizing turbine designs for household applications, emphasizing the need for improved designs and efficiency. Similarly, [18] discussed the difficulties in enhancing the hydrodynamic performance of micro-hydrokinetic turbines, suggesting that advancements in blade and transmission technologies are essential for better performance. Subsequently, [19] also identified limitations in turbine efficiency, highlighting the ongoing challenges in improving hydrokinetic technology. These studies corroborate the need for targeted design improvements and provide a broader context for understanding the efficiency issues observed in this study.

The limitations of this study include difficulties in acquiring large freewheel components and constraints related to the generator design, such as the number of coils and the magnet configuration. These factors can affect the overall power output and efficiency of a hydrokinetic system. Additionally, variations in river flow conditions and potential inaccuracies in the measurements could have influenced the results. Addressing these limitations is crucial to improve the performance and practicality of hydrokinetic turbines.

Future research should focus on several key areas to enhance the turbine performance. Optimizing the blade design to improve the water flow capture and energy conversion is essential. Exploring alternative transmission systems that better align with generator requirements can also increase the power output. Additionally, refining the generator settings and configurations may further enhance efficiency. By addressing these issues, future studies can contribute to making hydrokinetic turbines more practical and effective for real world applications.

This study demonstrates that the designed hydrokinetic power plant is cost-effective and suitable for use in rivers with a flow rate of at least 5 m³/s and a minimum velocity of 0.8 m/s. The system yields a voltage output ranging from 5.0 to 7.6 V and a current ranging from 0.012 to 0.026 A. Although the power generated is relatively low, there is significant potential for enhancement through design modifications. To increase the power output, it is recommended to implement additional transmission mechanisms and increase the number of windings in the coil. These adjustments are expected to improve the efficiency of the system and optimize its performance. Future improvements should focus on upgrading the voltage transformer to better match the system’s output voltage and frequency, and further increase the number of coils and windings in the GMP.

The authors thank UIN Suska Riau for support and resources throughout this study. We also appreciate the guidance of faculty members, cooperation from local communities, and technical support provided by the university.

The authors declare no conflicts of interest.