The performance of Pico hydro turbines is governed by fundamental design parameters, which include hydraulic head, discharge rate, turbine efficiency, and mechanical losses. Optimizing these variables is essential for viable small-scale energy production. Turbine type and design parameters will be carefully selected based on the site conditions to optimize power generation efficiency.

The turbine components were fabricated using Polyethylene Terephthalate Glycol (PETG) through 3D printing, selected for its excellent durability, high impact resistance (Izod impact strength ~3.5 kJ/m²), and high tensile strength (~50 MPa) [13] . These properties ensure the runner can withstand the dynamic hydraulic forces and mechanical stress in a wet environment. Furthermore, PETG is a recyclable material, aligning with the sustainable ethos of the project. The turbine casing frame was constructed from low-carbon steel hollow sections, valued for their high strength-to-weight ratio, excellent weldability, and cost efficiency. Its high yield strength (~250 MPa) provides a rigid and stable support structure capable of damping vibrations during operation, which is crucial for maintaining alignment and protecting generator bearings in field deployments [14] .

The tools and equipment used in the project include computer-aided design (CAD) software for turbine design and modeling, engineering and measurement tools such as measuring tape and rulers for accurate measurements, electrical components such as generators and control systems, testing and measurement instruments like multimeters, wattmeters and tachometers for evaluating turbine performance. (see Table 1 ). Figure 1 shows the physical construction of the Pico hydro turbine casing.

Hydropower operates on the fundamental principle of utilizing water pressure to initiate the rotation of a mechanical shaft in a hydro turbine. This rotational motion is then harnessed to drive a generator that transforms the energy into electrical power. Both head and water flow rate are critical parameters in a hydropower system. Head refers to the measurement of falling water at the turbine, representing the vertical distance from the top of the penstock to the turbine at the bottom. On the other hand, water flow rate indicates the volume of water that passes through the system within one second. Consequently, precise measurement of the head becomes crucial since a higher head result in increased power and higher rotational speed of the turbine [15] .

The design of Pico hydro turbines is guided by fundamental fluid mechanics and energy conversion equations, including Euler’s turbine equation, continuity, and Bernoulli’s principle. These governing equations establish the relationship between hydraulic head, flow rate, and mechanical power output, ensuring optimal turbine performance, which is discussed in the following sub-section.

Water flow calculation involves determining the volume of water passing through a specific point per unit of time. It is a crucial aspect of hydropower system design, requiring consideration of factors such as the cross-sectional area of the penstock and the velocity of the water. The flow rate is a key parameter for optimizing power generation efficiency. Various methods can be used, including flow meters and mathematical formulas, to accurately calculate and control water flow within the hydropower system, ensuring that the turbine receives the necessary water volume to generate the desired electrical output. Equation (1) represents to determine the velocity of water and while Equation (2) is to determine the water flow rate [16] .

$v_2=\sqrt{2gH}$ (1)

$Q=v_{2}A$ (2)

where:

$v_2$ = velocity of water, m/s

$H$ = water head, m

$g$ = gravity, m/s²

$\mathcal{Q}$ = flowrate of water, m³/s

$A$ = area of penstock, m²

The number of Pelton buckets in a Pelton turbine is determined based on the specific characteristics of the hydropower site, including water flow, head, and desired turbine speed. These curved buckets, situated around the rotating wheel or runner, interact with a high-velocity water jet, converting kinetic energy into mechanical energy to drive a generator for electricity production. Higher number of buckets may enhance overall efficiency. The number of Pelton buckets or drive can be determined by Equation (3).

$n_b=15+\frac{D_r}{2d_j}$ (3)

where:

$n_b$ = number of Pelton bucket

$D_r$ = diameter of runner, m

$d_j$ = diameter of jet, m

The geometrical area of a penstock, (which is the pipeline conveying water from the source to the turbine in a hydropower system), is calculated based on factors such as the required flow rate and the desired velocity of the water. The cross-sectional area of the penstock is determined to ensure that sufficient water is delivered to the turbine to generate the desired power. Area of penstock can be determined by the Equation (4) below. Penstock mass calculation involves assessing the material and structural requirements of the penstock to withstand the pressure exerted by the flowing water. Factors such as the material’s tensile strength, wall thickness, and diameter contribute to the mass calculation which is using the Equation (5).

$A=\pi r^2$ (4)

$m=\rho \mathcal{Q}$ (5)

where:

$A$ = area of penstock, m²

$r$ = radius of penstock, m

$m$ = mass, kg

$\rho$ = density of water, kg/m³

$\mathcal{Q}$ = flowrate of water, m³/s

The theoretical power output of a Pelton turbine is determined by the potential energy of the water available at a given head. When water of density $\rho$ falls under gravity $g$ with a volumetric flow rate $Q$ and an effective head $H$, the maximum theoretical hydraulic power can be expressed as Equation (6):

$P_{th}=\rho gQH\eta$ (6)

where:

$P_{th}$ = theoretical power output, W

$\rho$ = density of water, kg/m³

$g$ = gravity, m/s²

$\mathcal{Q}$ = flowrate of water, m³/s

$H$ = water head, m

$\eta$ = efficiency of the Pico-hydro, %

Equation (7) provides a means to assess the turbine-only efficiency of the system, which measures how effectively the turbine converts the hydraulic power of water into mechanical shaft power. The generator’s efficiency is not accounted for in this calculation.

${\eta }_t=\frac{P_{act}}{P_{th}}\times 100\%$ (7)

where:

${\eta }_t$ = turbine-only efficiency, %

$P_{act}$ = actual power output from turbine, W

$P_{th}$ = theoretical hydraulic power, W

The design of a Pelton bucket for a pico-hydro system with a low head of 1 m requires careful consideration of geometry and control features to ensure efficiency and reliability. Key factors include the use of a cut-out mechanism for emergency flow stoppage and speed regulation, as well as the bucket’s shape. A sharp splitter enhances jet division, a shallower bucket depth suits compact low-head operation, and a smaller pitch circle diameter helps achieve higher rotational speeds. These features collectively improve energy conversion from the water jet into torque and rotation.

The bucket was modeled using CAD software ( Figure 2 ), with the integrated cut-out system as a central feature. This mechanism ensures stable operation and rapid flow interruption during emergencies, offering a safer and more efficient alternative to earlier designs that relied on external, less effective flow-control methods. Figure 3 shows the finished actual prototype of the turbine bucket. The inclusion of a splitter is a critical design feature for optimizing performance. The sharp edge of the splitter cleanly cleaves the water jet, directing it symmetrically across the bucket curvature to maximize momentum transfer. This efficiently accelerates the turbine, enhancing energy extraction and overall power production. In contrast, buckets without a splitter allow the jet to disperse more uniformly upon impact, resulting in less effective force application and a comparative reduction in efficiency.

The hydraulic performance of a Pelton bucket is strongly influenced by its depth. A deeper profile increases jet interaction time and energy capture, enhancing speed and power output. However, in this low-head (1 m) pico-hydro application, a shallower bucket depth was selected to achieve better efficiency under low-pressure flow, while maintaining a compact design. The pitch circle diameter (PCD) also plays a crucial role. Larger diameters favor torque and power but reduce rotational speed. For this project, a smaller PCD was chosen to deliver higher rotational speeds compatible with standard generators, while also reducing size and manufacturing cost. This choice accepts a controlled trade-off in peak torque in favor of practicality and efficiency.

Overall, the final design integrates key features tailored to the project’s constraints: a cut-out system for stability and emergency shutdown, a sharp splitter for effective jet division, a shallow bucket depth for low-head flow adaptation, and a small PCD for compactness and higher rotational speed. These combined design strategies ensure reliable, efficient, and cost-effective performance in low-head pico-hydro generation.

The design of the turbine casing, piping, and test rig are critical for transforming the Pelton runner’s theoretical performance into a functional, measurable pico-hydro system. This sub-chapter details the engineering of these supporting components, which ensure structural integrity, direct hydraulic flow, and provide a controlled environment for performance evaluation.

The turbine casing is made of Hollow mild steel and transparent acrylic sheet. This hollow steel offers a high strength-to-weight ratio and weldability for cost-effective frameworks. The acrylic provides optical clarity, UV resistance, and impact strength for glazing and displays. Both are valued for their durability, lightweight properties, and versatility in construction and fabrication. Finally, for the piping system, Polyvinyl chloride (PVC) components were selected due to their durability, corrosion resistance, and cost-effectiveness.

The piping system utilized 1-meter-long pipes with four diameters (15 mm, 20 mm, 25 mm, and 32 mm) to analyze the effect of conduit size under a 1-meter water head (See Figure 4 ). These pipes were interconnected using PVC reducing bushes—tapered fittings that create secure, leak-resistant transitions between different diameters—specifically sized at 40 mm-to-32 mm, 40 mm-to-25 mm, 40 mm-to-20 mm, and 40 mm-to-15 mm (See Figure 5 ). Flow to the entire apparatus was controlled by a 40 mm non-threaded PVC ball valve, which provides reliable on/off control via a 90-degree turn of its handle and is designed for permanent solvent-welded connections. Figure 6 shows the overall view of the fully assembled prototype Pico hydro turbine, casing and piping.

A constant water head (H) of 1.0 m was maintained by a gravity-fed reservoir. Head losses in the PVC penstock were minimized by eliminating unnecessary bends and fittings. The net head was verified by measuring the static pressure immediately upstream of the turbine nozzle to ensure accuracy in the theoretical power calculations.

In this study, a tachometer was used to measure the turbine’s speed, while a multimeter was used to measure the voltage and current generated by the generator, in order to calculate the power generated. Each configuration (pipe size and bucket number combination) was tested three (3) times to ensure result consistency. The values presented in Tables 3-7 represent the average of these repeated runs. The measured parameters showed minimal variation, with standard deviations of ±2.1 RPM for speed and ±0.15 W for power output, indicating high measurement reliability.

A flowmeter was utilized to measure the water flow in PVC pipes of different sizes, which 15 mm, 20 mm, 25 mm, and 30 mm. The data collection involved variations in the number of buckets, specifically 6, 8, 12, 18, and 24 buckets. Following the measurements, the task involves computing the average flow rate for each pipe size. Table 2 displays the collected data on flow rate through different pipe sizes.

A tachometer is used to measure the turbine’s speed, while a multimeter was used to measure the voltage and current generated by the generator, in order to calculate the power generated by the generator. Furthermore, flow Rate, speed, voltage, current, and actual power generated by the generator are obtained based on different Pelton bucket numbers and pipe sizes on a 1m water head. The turbine efficiency is then calculated based on the theoretical power of the turbine. The complete results are shown from Tables 3-7 .

Turbine speed performance was evaluated at a constant 1 m head across various pipe sizes and bucket numbers (See Table 8 and Figure 7 ). Results demonstrate that rotational speed (RPM) is significantly influenced by both parameters. Smaller pipe diameters yielded higher RPM, with the 15 mm pipe achieving the maximum speed of 89.8 RPM (24 buckets). Conversely, the 32 mm pipe produced the lowest speeds, ranging from 51.4 RPM (6 buckets) to 68.8 RPM (24 buckets). This trend is attributed to the higher jet velocity generated by smaller pipes under low-head conditions, which increases the impulse force on the turbine buckets. Increasing the bucket count from 6 to 24 also enhanced turbine speed across all pipe sizes, with the most substantial gains occurring between 6 and 12 buckets. Performance improvements diminished beyond 18 buckets, likely due to increased flow interference and frictional losses. The 15 mm pipe showed the highest relative gain (34.8%), though all sizes exhibited significant improvements (20% - 35%).

The optimal configuration for maximizing RPM under low-head conditions was the 15 mm pipe with 18 - 24 buckets. Larger pipes underperformed due to reduced jet velocity and potential spreading losses, highlighting the critical role of nozzle optimization in pico-hydro Pelton turbine design.

The power output of a Pelton turbine-driven generator was measured across a range of pipe diameters and bucket numbers (See Table 9 and Figure 8 ). Results indicate that power output is highly sensitive to pipe size, with smaller diameters (e.g., 15 mm) yielding significantly higher output compared to larger diameters (e.g., 32 mm), across all bucket configurations. For instance, with 24 buckets, the 15 mm pipe produced 4.56 W, while the 32 mm pipe produced only 2.14 W—a reduction of over 53%. Additionally, increasing the number of buckets consistently improved performance, with the most substantial gains observed in smaller pipes. The 15 mm pipe exhibited a power increase of 2.48 W when moving from 6 to 24 buckets, compared to a gain of only 1.19 W for the 32 mm pipe. These findings underscore the importance of optimizing both hydraulic design (pipe diameter) and mechanical design (bucket count) to maximize energy extraction in micro-hydro systems.

The analysis for turbine efficiency is shown in Table 10 and Figure 9 . For a smaller pipe diameter, the 6-bucket impeller achieved a peak efficiency of 78%, outperforming the 24-bucket design, which registered only 62%, a 16% reduction attributed to excessive frictional losses and flow restriction in a constrained environment. Conversely, for the largest pipe diameter, this relationship inverted dramatically; the 24-bucket turbine achieved a maximum efficiency of 92%, substantially outperforming the 6-bucket variant’s efficiency of 75%, a 17% difference resulting from insufficient fluid guidance and energy capture in an unconstrained flow. The 12-bucket impeller frequently emerged as a robust compromise, maintaining efficiencies above 80% across most pipe sizes, yet the data conclusively shows that no single bucket count is universally optimal. This non-linear response surface underscores the necessity of a system-level design approach, where a 20% increase in efficiency is attainable solely by optimizing the bucket-to-conduit ratio, a finding with profound implications for the customization and energy output of micro-hydro and fluidic systems. With an efficiency of 88.14% under a 1 m head, this turbine’s performance is favorable compared to the typical range for pi-co-hydro installations [17] . It also suggests potential for efficiency gains in the ultra-low head category, building on the groundwork established by earlier specialized turbines, such as the Z-Blade design presented in reference [11] .