This study aims to assess the reservoir data of a hydroelectric power plant for effective energy production. The evaluation involves an in-depth analysis of various parameters, including water level fluctuations, sedimentation rates, and environmental impacts. By examining these reservoir-related factors, the research aims to optimize energy generation and contribute to sustainable hydropower practices. The findings of this assessment can potentially guide decision-makers in enhancing the efficiency and environmental sustainability of hydroelectric power plants.
Hydraulic energy stands out among renewable energy sources due to its widespread use in energy production. Its renewable nature contributes significantly to its environmental importance. Moreover, the absence of raw material consumption in hydroelectric energy results in considerably lower operational expenses compared to fossil fuel-based thermal power plants. Additionally, hydroelectric power generation is cleaner compared to plants that emit substantial amounts of harmful pollutants into the atmosphere. When compared to other energy production systems, hydroelectric power plants exhibit minimal operational costs, the longest operational lifespan, and the highest efficiency. Storage-type hydroelectric power plants offer numerous advantages, including flood prevention, facilitation of irrigation works, improvement of fisheries, support for afforestation, contributions to tourism, and enhancement of transportation facilities. Electricity has become an indispensable necessity in today’s world, driven by ease of use, global prevalence, convertibility to other energy types when needed, and widespread daily applications. The amount of electricity consumed is a crucial indicator of economic development and social welfare within a society. Globally, electricity is sourced from various outlets, and hydroelectric energy is one such extensively utilized resource.
Hydroelectric Power Plants
Hydroelectric power plants (HPPs) are facilities that harness the potential and kinetic energy of water to generate electrical energy. In hydraulic power plants, this energy is converted from mechanical energy to electrical energy through hydraulic turbines and generators driven by these turbines. The head and flow rate of water significantly influence the power that can be obtained from the turbine. The head is the difference between the upper and lower water surfaces. Both the head and flow rate have a considerable impact on the power that can be obtained from the turbine.
Hydroelectric Power Plants Classification
Hydroelectric power plants (HPPs) are commonly classified based on their heads, installed capacity, storage conditions, dam type, and the location of the power plant building.
Installed Capacity Classification
There is no universally accepted classification for installed capacity globally. Many countries define large and small hydroelectric power plants differently based on their installed capacity. Generally, plants with a capacity of less than 100 kW are termed micro, those between 101-1000 kW are mini, those between 1001-10000 kW are small, and those with capacities exceeding 10000 kW are referred to as large hydroelectric power plants.
Head Classification
Based on head, hydroelectric power plants are categorized as low head (head less than 10 meters), medium head (head between 10-50 meters), and high head (head greater than 50 meters) hydroelectric power plants. Storage Conditions Classification: Hydroelectric power plants are generally classified as reservoir-based (with dam or natural lake), run-of-river (without reservoir), and pumped storage based on their storage conditions. Reservoir-based hydroelectric power plants, also known as dammed plants, involve closing the water flow with a dam to create a reservoir behind it. This stored water reduces dependence on precipitation patterns, ensuring a steady supply even during dry seasons. Additionally, the reservoir created by the dam increases the head height, enhancing the potential energy of water. This approach results in an increased amount of electricity generated by the hydroelectric power plant.
Run-of-river hydroelectric power plants, in contrast to reservoir-based ones, rely on the natural flow of the river without flow regulation. The reliable production of electrical energy is limited by the minimum flow of the river, typically resulting in lower energy output. Ideally, these plants are constructed on rivers that do not experience dry seasons or on rivers where reservoir-based hydroelectric power plants are already present in the basin. This way, they can benefit from the regulated flow provided by the reservoir-based hydroelectric power plant. In these plants, a diversion weir diverts water from the river to a channel, and excess water in the loading chamber is managed through an overflow weir. Water is then directed to the turbine through a penstock, where hydraulic energy is converted into mechanical energy.
Pumped storage hydroelectric power plants consist of two reservoirs, upper and lower. These plants play a crucial role in increasing energy efficiency. During times of high energy demand or when electricity is expensive, water stored in the upper reservoir is released to generate electricity. Conversely, during times of low demand or when electricity is inexpensive, pumps are used to lift water from the lower reservoir to the upper reservoir, providing energy storage. Pumped storage plants are utilized as base load power plants, responding quickly to changes in demand. While thermal power plants struggle to adapt to demand fluctuations, hydroelectric power plants can easily be started or stopped, making them suitable for meeting peak demand. Pumped storage plants can also be operated as hybrid systems to mitigate the adverse effects of intermittent energy sources such as wind turbines, making the energy generated from wind turbines more reliable.
Hydroelectric power plants are further classified based on dam type into primarily concrete dam, concrete arch dam, rock-fill dam, and earth-fill dam. Additionally, based on the location of the power plant building, they can be classified as surface, underground, or semi-submerged or submerged hydroelectric power plants. These facilities can take various forms depending on the topography of the location where they will be established. A hydroelectric power plant may encompass all or some of the sections such as the dam structure and reservoir, water intake facility, waterway facilities, power plant building, power plant outlet canal, switchyard, bottom spillway facilities, and top spillway facilities.
Hydraulic Turbines
Turbines are hydraulic machines used to convert the free mechanical energy present in a fluid, typically by utilizing rotating blades on a shaft, into useful mechanical energy. The structure of the turbine is determined by the fluid it operates in. The working principle of a hydraulic turbine is as follows: the fluid strikes the blades of the turbine, causing the turbine shaft to rotate and generate mechanical energy; this mechanical energy is then transmitted to a generator where it is converted into electrical energy. Hydraulic power plants operate on this principle, and the turbines used in these plants are called hydraulic turbines.
Turbines can be classified into two categories: volumetric and dynamic. Volumetric turbines are generally small machines used for measuring volumetric flow or flow rate rather than power generation. Dynamic turbines, on the other hand, come in various structures ranging from miniature to massive, and they are used both for flow measurement and power generation. Water turbines can be classified according to the way water acts on them: as impulse (action) or reaction turbines. The classification of water turbines is based on operational structure, design, hydraulic head, and flow direction.
In impulse turbines, the pressures at the inlet and outlet of the turbine are equal to atmospheric pressure. These turbines are referred to as equal pressure turbines because the inlet and outlet pressures are equal. In these turbines, water is passed through a nozzle to impart velocity to the water and create a jet. The water jet strikes the blades of the turbine, which are concave-shaped, causing the turbine to rotate. The energy transformation in these turbines is explained by Newton’s second law. Impulse turbines are preferred for high heads, and common types include Pelton, Turgo, and Crossflow (Michell-Banki) turbines.
For reaction turbines, such as Francis, Kaplan, Uskur, Propeller, Bulb, Tube, Straflo, and Water Wheel, the energy transformation is explained by Newton’s third law. In reaction-type water turbines, both the kinetic and potential energy of water are utilized. Typically, the pressure at the turbine outlet is much smaller than at the inlet. Hence, there is a requirement for water to flow through closed channels. The rotation of the turbine is facilitated by the reaction force generated due to the acceleration of water at the turbine outlet.
Hydraulic Turbine Selection in Hydroelectric Power Plants
The most decisive factors in the selection of turbines used in hydroelectric power plants are the hydraulic head and the volumetric flow rate of water passing through the turbine, known as the discharge. The speed of the turbine or generator is a significant criterion in turbine type selection. Another criterion is whether the turbine will operate under partial flow conditions. All turbines have a power-speed and efficiency-speed characteristic. The design of the turbine is determined by selecting a model turbine rotor geometrically similar to the main turbine rotor desired to be manufactured, with a useful hydroelectric head (H) of 1 m, a volumetric flow rate (Q) of 1 m³/s, and operating at the chosen operating speed (n). The specific speed (ns) of the model turbine rotor, which works under these conditions, is then determined. After determining the specific speed, the design of the turbine is carried out using specific empirical formulas based on ns. The specific speed can be calculated using the following equation.
Minimizing Speed Changes between Turbine and Generator
It is essential to minimize the speed changes between the turbine and the generator. For this purpose, different turbine types should be used for different hydraulic heads. The speed of a turbine decreases proportionally with the square root of the hydraulic head. Therefore, high-speed turbines are used in locations with small heads. Table 1 provides the range of turbine types according to hydraulic head, while Table 2 presents the specific speed values for various turbine types.
Turbine Types According to Hydraulic Head
- Kaplan and Propeller: 2 < H < 40
- Francis: 10 < H < 350
- Pelton: 50 < H < 1300
- Banki-Michell: 3 < H < 250
- Turgo: 50 < H < 250
(Note: H represents the hydraulic head in meters)
Specific Speed Values for Turbine Models
- Pelton: 12-30 (revolutions per minute per meter of hydraulic head)
- Turgo: 20-70 (revolutions per minute per meter of hydraulic head)
- Cross-flow: 20-80 (revolutions per minute per meter of hydraulic head)
- Francis: 80-400 (revolutions per minute per meter of hydraulic head)
- Kaplan: 340-1000 (revolutions per minute per meter of hydraulic head)
Hydraulic Energy
The kinetic energy obtained from the potential energy of water is referred to as hydraulic energy. The energy resulting from the descent of water from a higher to a lower level is converted into mechanical energy and, with the assistance of hydraulic turbines and generators, into electrical energy. Subsequently, electrical energy is transmitted to end-users through power transmission lines. Hydraulic potential is dependent on precipitation patterns. The potential of water in a region is determined by the amount of rainfall. Therefore, minor fluctuations in climatic conditions will affect hydroelectric energy production. Water vapor evaporates from rivers, seas, or lakes with solar energy, reaches the slopes of mountains in the form of rain or snow, and returns to rivers or lakes. Hence, hydraulic energy is a renewable energy source.
To harness energy in hydraulic turbines, water must have a specific head. The head of a hydropower plant is the height difference between the upper water surface and the lower water surface. The hydraulic head mentioned above is called gross hydraulic head or geometric head. In the water transmission sections of a hydropower plant (transmission channels, transmission tunnels, penstocks, turbine inlet valves, etc.), losses occur due to the friction of water molecules. The total of these losses is denoted by ΣΔH. Subtracting the total net losses from the gross hydraulic head yields the net hydraulic head. The mechanical power that can be generated from a hydraulic turbine is determined by the formula:
P mechanical = ρ x g x Q x H x η
where:
- P mechanical is the mechanical power (W),
- ρ is the density of water (kg/m3),
- g is the acceleration due to gravity (m/s2),
- Q is the volumetric flow rate of water (m3/s),
- H is the net hydraulic head (m),
- η is the efficiency of the hydraulic turbine.
This mechanical power is then converted into electrical power by the generator with an efficiency denoted by η generator :
P electrical = P mechanical x η generator
