Hydroelectric power comes from flowing water winter and spring runoff hydroelectric plants supplied as much as 40 percent of the electric energy produced. PDF | INTRODUCTION Energy is a critical factor in developing countries for For efficient operation of hydropower plants, in order to meet the. A typical hydropower plant is a system with three parts: a power plant where Hydropower (from the Greek word hydor, meaning water) is energy that comes.
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documents of the World Bank Group, but instead is an effort to capture the additional rational utilization of small hydropower plants exist in all countries. Brief Norconsult introduction. • Hydro Power in a global energy source perspective. • Hydro Power plant types, definitions and description of major components. Download PDF Recommend Documents Optimal control of a hydroelectric power plant with unregulated spilling water.
Abstract Water level fluctuations in lakes lead to shoreline displacement. The seasonality of flooding or beaching of the littoral area affects nutrient cycling, redox gradients in sediments, and life cycles of aquatic organisms. Despite the ecological importance of water level fluctuations, we still lack a method that assesses water levels in the context of hydropower operations. Water levels in reservoirs are influenced by the operator of a hydropower plant, who discharges water through the turbines or stores water in the reservoir, in a fashion that maximizes profit.
This rationale governs the seasonal operation scheme and hence determines the water levels within the boundaries of the reservoir's water balance. For progress towards a sustainable development of hydropower, the benefits of this form of electricity generation have to be weighed against the possible detrimental effects of the anthropogenic water level fluctuations.
We developed a hydro-economic model that combines an economic optimization function with hydrological estimators of the water balance of a reservoir. Applying this model allowed us to accurately predict water level fluctuations in a reservoir. The hydro-economic model also allowed for scenario calculation of how water levels change with climate change scenarios and with a change in operating scheme of the reservoir increase in turbine capacity.
Further model development will enable the consideration of a variety of additional parameters, such as water withdrawal for irrigation, drinking water supply, or altered energy policies. This advances our ability to sustainably manage water resources that must meet both economic and environmental demands. Introduction The development of hydropower is a controversial issue.
New dams use water as a renewable energy source and can help to limit emissions. The storage of water in reservoirs also alleviates supply problems of drinking water, provides water for irrigation, and improves flood control .
But new dams also come with far-reaching ecological consequences. The damming of rivers has altered the biodiversity and functioning of fluvial ecosystems on a global scale . Dams impair the natural flow regime of rivers and decrease the longitudinal and latitudinal connectivity of aquatic ecosystems; altered nutrient cycling, caused by flow changes and impaired species movements, caused by blocked migration routes, are just two major consequences.
The creation of reservoirs also affects terrestrial ecosystems, e.
Despite the detrimental effect of a dammed lake's transformation into a reservoir, it continues to be an ecosystem. This reservoir ecosystem, albeit shaped by humans, hosts biota that respond to a hydropower operation. One predominant change caused by hydropower operation is the shift from natural to artificial water level regimes. The level of water has particularly profound influence on ecosystem processes in lakes, because it affects the littoral zone . The littoral zone, whose extent is governed by the lake level, is of disproportionate importance to the food web of lakes .
With global climate change, though globally the potential is stated to slightly increase, some countries will experience a decrease in potential with increased risks.
Adaptation measures are required to sustainably generate hydropower. These are also discussed in the paper.
Introduction 1. World Energy Scenario and Sustainable Energy In this era, concerns about environment and climate change management influence choices investors and international financing institutions make concerning energy projects [ 1 ].
The surroundings can be divided into nonliving and living components. The important point concerning environment, according to Gorshkov and Makarieva [ 2 ], is that it provides resources, such as energy, that support life on earth.
Since energy is sourced and processed into a usable form from the environment, activities pertaining to its extraction, transportation, conversion, and utilisation impact the environmental system. The impacts are pronounced in thermal energy systems. For fossil fuel energy systems, it is also not possible to totally avoid emissions and environmental setbacks because of combustion.
During the combustion process, energy is converted from chemical into heat and the gaseous products of combustion are ejected from the system at a higher temperature than the ambient as dictated by Second Law of Thermodynamics.
Some of the gaseous products of combustion are harmful to life and climate system, as will be discussed later in the paper. The increase in global energy demand as a result of population and economic growth in developing countries coupled with huge demand from developed countries is well documented. The contribution from other fuel sources is quite minimal. Figure 1: Global primary energy supply mixes in and , adapted from International Energy Agency [ 3 ].
The energy review study by the British Petroleum shows that in , the global primary energy consumption grew by 2. Coal alone growth by 5.
Coal in was accounted for Further, the overdependency on fossil fuels exerts pressure on the limited energy resources which may seriously affect global economy in the future due to shortage. Therefore, it is important to ensure that energy is extracted, converted, and utilised sustainably. The transition to sustainable energy resources provides an opportunity to address multiple environmental, economic, and development needs of the country and the world at large [ 6 , 7 ].
Currently, one of the issues confronting the world is the challenge of achieving a truly sustainable energy system [ 8 ]. The present path of economic development in most of the industrialised and emerging countries overrelies on energy from fossil fuel. Review of global fossil-fuel resources indicates that proven reserves for these resources are still abundant and are able to continue supporting the economy for the next several decades, as can be seen from Table 1 [ 6 ].
Coal reserves are more abundant than oil and natural gas. At the rate of coal consumption, present coal reserves are adequate to support another approximate years [ 6 ].
For oil and natural gas, the present reserves can support consumption of up to 40—65 years [ 6 ]. Despite the fact that new reserves of fossil fuels are being discovered in many countries and extraction capabilities are being improved, the key message from this paper is that these resources are finite and, therefore, at some time in future they will be depleted. Table 1: Data on fossil fuel types and their global consumption levels, amount of their proven reserves, and amount of lifetime reserves basing on their consumption rates, adapted from InterAcademy Council [ 6 ].
The facts that currently fossil fuels dominate the global energy system and that there are still some decades to come for these resources to get depleted stress the need to put in place measures to ensure that energy is generated sustainably. Some of these measures are finding alternatives for oil in the transport sector, using low carbon technologies for generating electricity and embarking on energy efficiency programs.
It must also be stated that, geographically, fossil fuel resources are not evenly distributed. Nations without fossil fuels and capabilities to refine them depend on imports. The volatility in international energy prices for the fossil fuel and the need to secure foreign currency to import the fuel, especially oil, can exert national economic challenges that sometimes can contribute towards economic meltdown.
As stated already, these fossil fuel resources are getting depleted while the demand is increasing; thus, it can be expected that prices will be higher in the future than it is currently due to shortage of supply. The conflicts can disrupt fuel production and supply. Energy security is one of the drivers for sustainable energy system because it calls for an expansion, diversification and localisation of energy sources.
The other drivers for sustainable energy include the call for increased access to modern forms of energy especially in the least developed countries to foster development and curb natural resource degradation. Before such a discussion on hydropower, issues of global environment and climate change are briefly discussed because they are argued as the main concerns for energy systems, as stated earlier. Environmental Degradation, Climate Change, and Energy Environmental degradation and climate change are stated to be among some of the challenges facing the world today [ 9 , 10 ].
Despite the fact that there are some natural processes causing environmental and climatic deviations, current research indicates that these processes are insignificant compared to the human-induced processes [ 11 ]. Processes such as those concerning unsustainable energy extraction, conversion, and utilisation have contributed to the worsening of these global changes.
Climate change is defined in many ways. It may be a change in the average weather conditions or a change in the distribution of weather events with respect to an average period of time. Carbon dioxide is the major greenhouse gas; others are methane, nitrous oxide, and carbon-fluorinated gases [ 15 ]. All GHGs have different capacities of trapping heat global warming potential but when it comes to analysing their potentials, these GHGs are weighted relative to the global warming potential of carbon dioxide.
The IPCC further states that the largest growth in global GHG emissions between and had come from the energy supply sector that is dominated by fossil fuels. Some recent studies agree with IPCC projections. The human response to challenges of global climate change is basically twofold: to reduce greenhouse gas emissions into the atmosphere mitigation and to adapt to the impacts of climate change adaptation.
In this regard, in , several countries signed a treaty known as Kyoto Protocol. The treaty legally mandates developed nations to limit greenhouse gas emissions according to the set targets.
These nations can attain their emission reduction targets elsewhere by investing or downloading carbon credits from a project that has been proven to reduce greenhouse gases, through the Clean Development Mechanism CDM.
Developing countries are not mandated to reduce emissions; however, they are encouraged to do so, so that they can participate in the fight against the global climate change as well as sustainable development [ 13 ].
Fossil fuel, especially coal, remains the largest source of electricity generation in the near future, considering the fact that the current proven coal reserve is able to take more than a century to get depleted, as stated before. Figure 2: Fuel shares of global electricity generation in , adapted from International Energy Agency [ 3 ]. Because most of the GHGs are contributed from the energy and land-use sectors, most of the climate change mitigations measures are geared at reducing emissions from the energy sector and enhancing the capacity of carbon sinks in the forests [ 11 ].
This is where development of clean energy sources such as renewables is needed so as to reduce the GHG emissions. Fossil fuel substitution to renewable energy sources has high potential to mitigate climate change because they are associated with very little GHG emission levels. The lifecycle emissions from renewable energy are mainly from the process of component manufacturing and system installation of renewable energy generation plants.
Renewable energy is defined as any form of energy from solar, geophysical, or biological sources that is replenished by natural processes at a rate that equals or exceeds its rate of use [ 20 ]; therefore, it can play a key role in ensuring national energy security. Renewable energy sources have the potential to provide energy to meet or exceed the global energy requirements [ 21 ]. Further, because renewable energy is generally associated with nil or minimal gaseous emissions to cause damage to the atmospheric air composition, its importance is not only in climate change mitigation but also in air pollution control.
Developing countries such as those found in sub-Saharan African SSA region are well positioned for the application of renewable energy systems because of the relatively huge demand of sustainable energy for development. In developed and emerging countries, renewable energy can help end the present relationship that correlates economic development with carbon emission. Further, investments in renewable energy technologies can help create jobs and attract extra income from international carbon trading schemes such as the CDM.
The next section of the paper discusses hydropower as one of the most important renewable energy sources, especially in electricity generation. Issues of hydropower technology, global potential, GHG emissions from hydropower projects, environmental consequences of a hydropower project, environment degradation, and climate change impacts on hydropower generation are discussed.
Hydropower Technology In engineering, power is the rate with respect to time of doing work. The work may be in form of mechanical, electrical, or hydraulic. In any work process, forces are involved on or by a system whereby a system is defined as a quantity of matter that is bounded. Hydropower is the rate at which hydraulic energy is extracted from a specific amount of falling water as a result of its velocity or position or both.
The rate of change of angular momentum of falling water or its pressure or both on the turbine blade surfaces creates a differential force on the turbine runner thereby causing rotary motion. As a working fluid, water in a hydropower system is not consumed, it is thus available for other uses. Hydropower can be used to power machinery or to generate electricity or both at the same time.
The mechanical application is mainly true for small-scale hydropower plants where the power generated is used to power small-scale mechanical tools and machines for pressing, milling, grinding, and sawing applications.
In some instances, the output shaft from the small-scale hydropower turbine is extended in both directions to provide space for both mechanical power provision and electricity generation. Large-scale hydropower plants are normally used for electricity generation.
The basic schematic diagram for hydroelectric power generation system is shown in Figure 3. To produce electricity, the turbine output shaft is coupled to the generator. The generator is principally made up of electromagnetic rotor that is located inside a cylinder known as stator containing a winding of electric wires known as conductor.
During operation, the rotor in the stator turns and generates electricity by the principle of electromagnetic induction. The generated electricity is transmitted to load points through a transmission system that consists of components such as switch yard, transformers, and transmission lines.
Figure 3: Schematic view of a hydropower station and its basic parts, adapted from International Energy Agency [ 32 ]. For a well-planned and -operated hydropower project, hydropower electricity generation technology is stated as one of the cheapest in terms of electricity generation costs [ 33 ], possibly because the fuel falling water is available without direct costs associated with fuel download. The levelised cost of electricity generation for large-scale projects ranges from 0.
The relatively low electricity generation cost may be one of the reasons why hydroelectricity is recommended as base load for most of the power utility companies. Hydroelectric power plants are able to respond to power demand fluctuations much faster than other electricity generation systems such as thermal electric power stations [ 35 , 36 ].
This makes hydropower a flexible energy conversion technology and also explains why hydroelectric power stations are sometimes used for peaking purposes. Further, hydroelectric power technology is a high efficient energy conversion process because it converts directly mechanical work into electricity, both of which are high forms of energy.
Classification of Hydropower Projects Hydropower projects are unique, in the sense that the installations, though having the same installed capacity, may not be identical because the design of hydropower plant is site-specific. This uniqueness of hydropower projects makes their classification important especially in matters concerning technology and application. Hydropower projects or schemes are usually classified according to size, head, and whether water for power generation is significantly impounded or not.
Hydropower classification according to size has led to projects being classified as small-scale and large-scale hydropower systems, based on the level of the installed electricity capacity.
Various countries or groups of countries and organizations define hydropower schemes based on size differently, as can be seen in Table 2. Many countries, especially in Europe, consider 10 MW as the limits for small hydropower, and above this limit, the hydropower system is considered a large-scale project.
The classification based on installed electrical capacity is important because of its being used in legal documents such as rural electrification acts and power supply contracts agreements. This difference in categorization has created a debate on the size of hydropower system to be considered on the CDM as a small hydropower system [ 38 ]. Table 2: Small-scale hydropower classification by installed capacity MW as defined by various countries and organizations.
A classification by head refers to a difference in level between inlet headrace and outlet tailrace of a hydropower installation. Head is one of the important parameters in the design because it determines the water pressure hence the force acting on the turbines and hence power output. There is again no consensus concerning classification of hydropower projects according to head. In India, a high head hydropower project is above 40 m, low head one is less than 40 m, and ultralow is less than 3 m [ 39 ].
When categorizing hydropower basing on levels of water impoundment, there are three main types of projects namely: run-of-river, reservoir storage hydro and pumped storage.
These types are described in the following subsections. Run-of-River Type A run-of-river hydropower project RoR HP , as shown schematically in Figure 4 , generates electricity from the river flow without significant impoundment. Water flow in the river depends on precipitation, groundwater flow and runoff: these parameters may have substantial daily, monthly, or seasonal variations. Therefore, ideally for a variable flow river, a RoR hydropower system will have a variable power generation that mimics the river flow profile.
To ensure some limited degree of adaptation to the electricity demand profile, the RoR HP includes some short-term storage known as pondage , to provide extra electricity demand limited peak demand when required. Without significant storage system, RoR HP schemes are vulnerable to changes in the river system that affect amount of flow and its water quality, for example, droughts, floods, and water abstractions. Figure 4: Schematic diagram of a typical run-of-river hydropower system [ 4 ].
RoR HP scheme is stated to be suitable for a river that has minimum flow variation or a river that is regulated by a large natural reservoir e. The RoR HP projects are not associated with a lot of construction activities, and because of this, RoR HP projects possess economic as well as environmental advantages over other hydroelectricity generating systems of the same installed capacity [ 41 , 42 ].
RoR hydropower generation technology is used in many countries of the world. For example, in Malawi, almost all of the hydropower electricity generation projects are RoR HP plants cascaded along the Shire River, an outlet from Lake Malawi [ 43 ].
Further, because of their economic advantage, RoR HP plants are the commonly used in small-scale hydropower systems [ 43 ]. Run-of-river hydropower plants can be divided into two different types, according to how the flow diversion system is arranged. The diversion system can be either of in-stream or cross-watershed.
In-stream diversion system, which is quite common in RoR HP projects refer to Figure 4 , diverts a portion of water from the river bed to take advantage of the local topography so as to have an improved head. This is to optimize hydropower generation from the site.
In large-scale hydropower projects, the diverted portion of the river may be dammed and diverted through tunnels in the mountain side to the powerhouse and then discharged further downstream back in its riverbed [ 32 ]. In cross-watershed diversion, the aim is to increase volume of water flow in the river where the power plant is located. Flow from another river is diverted across the catchment area into the river where the power plant is located. The increased flow in the river will again improve the energy generation [ 32 ].
It is possible to combine the two diversion systems to optimise energy generation on the site. The most widely used scheme for in-stream RoR HP plant consists of an open channel, a forsite, and a generally relatively short penstock [ 41 ]. Storage Hydropower A storage hydropower project has a reservoir behind a dam to store water for later power generation and other purposes , as shown schematically in Figure 5.
The reservoir regulates the flow and, thus, storage hydropower plants have more power reliability than RoR HP plants. The generating stations may be located just at the dam toe or further downstream connected to the reservoir through tunnels or pipelines.
Figure 5: Schematic diagram of a typical hydropower plant with reservoir [ 4 ]. Storage HP projects are typically used for highly variable flows in the middle reaches of a river system [ 32 ]. The opportunities offered by the topography influence the design and type of reservoir that can be constructed on the river. Storage HP schemes constructed on gorges and canyons are associated with high output and efficiency [ 32 ]. Storage hydropower schemes are superior in terms of offering energy benefits as compared to pure run-of-river schemes.
One of the fundamental advantages of storage hydropower is the storage of energy in form of potential energy in water behind a dam. This potential energy can be released to generate hydroelectricity when needed and, thus, the storage hydropower system can be used for supplying both base load and peaking load. Beside the advantage of energy storage, storage hydropower projects have the ability to regulate flow in the river downstream of the dam.
In this case, a reservoir may increase the reliability of power generation from the sites located downstream, as the regulated river will typically flow more evenly throughout the year. Thus, multiple run-of-river power plants may be installed downstream in cascade form, using the same water to produce additional hydropower of constant output.
Further, because of regulated flow into the powerhouse, control of power and efficiency of generation for a storage hydropower system is enhanced. Efficient but flow-sensitive turbines like Kaplan and Francis are able to be operated at best efficiency point with a high degree of performance reliability. Pumped Storage Pumped storage plants, shown schematically in Figure 6 , are not energy sources, but are simply hydraulic energy storage devices [ 44 ].
Practically, in terms of both design and economics, pumped storage technology is stated to be the only large form of grid-based electric energy storage currently available to the power utility [ 45 , 46 ]. In pumped storage system, water is given hydraulic energy by a pump. Water is pumped from a lower reservoir into an upper reservoir, using excess electricity generated by the hydropower plant during off-peak hours or at any other times when demand is reduced. During the peak load times or at other times when extra electricity is needed, extra electricity is generated from water stored in the upper reservoir as it is released back to the lower reservoir via a turbine.
It is possible to employ a turbomachine that can be operated both as a pump and a turbine in this case, for example, a reversible pump-turbine machine like a Reversible Francis Turbine.
Figure 6: Schematic diagram of a typical pumped storage system [ 4 ]. The lower reservoir can be a river, a lake or an existing reservoir for hydropower generation or other purposes and ideally, any electric generating station can use pumped storage technology.
Although the energy losses incurred during the pumping process make the pumped storage a net energy consumer, the system is able to provide large-scale energy storage with flexibility at low operating costs [ 32 ].
For a hydropower system incorporating pumped storage technology, the point of concern is the high investment cost relative to other hydropower generating systems of the same installed capacity. The pumped storage technology installation requires special sites. Mountainous areas are ideal for the technology in order to make use of the topography for potential energy storage.
The distance between the reservoirs also matters in the design of the pumped storage because long distances increase the investment costs and the pumping losses; making the system unattractive economically and technically. The pumped storage technology is not only ideal in managing peak power demands, but it also ensures that process of governing the electricity production is efficient.
The latter advantage comes about because the hydropower plant with pumped storage generates electricity at nearly constant output, thus fixing load available on the generators.
This condition is necessary for a smooth governing process. Hydropower as a Renewable Energy and Its Global Resource Potential and Generation Hydraulic energy in the water is derived from a hydrological cycle as shown in Figure 7. In the hydrological cycle, water constantly flows through a cycle in different phases; evaporating from lakes and oceans, forming clouds, precipitating as rain or snow, then flowing back down to the ocean, seas, dams, rivers, and other water bodies.
Because the hydrological cycle is an endless process, hydropower is considered as a renewable energy resource, according to the definition. Due to engineering reasons concerning the integrity of properties of materials for constructing hydroelectric power plants, only freshwater resources are used to generate hydropower.
The main characteristics of hydropower potential are flow and head , as given by the following power equation: where is the hydropower coefficient, a constant. Figure 7: Hydrological cycle [ 48 ].
As can be seen from hydropower equation 1 , in practical sense, the flow parameter is the only variable since the head cannot be increased or improved upon at least for most of hydropower projects. The flow for hydropower generation can be regulated, thereby controlling power production. In some instances head can be modified, for example, by means of pumping water from other source s into a reservoir or regulating the water entrance and exit from the reservoir.
Hydropower plants utilizing flow and head as given in 1 are called conventional hydropower systems. The unconventional hydropower systems use only the kinetic energy in the water current to drive the turbine and generate power.
These systems are usually installed in-stream to the waterways such as high velocity rivers, irrigation canals, and water supply systems. The unconventional hydropower systems are also known as zero-head hydropower systems or hydrokinetic power systems. Hydropower is stated to be the largest renewable energy resource in the world; in it produced 3, TWh of electricity representing a share around It is the one of the most important source of power in many countries: according to World Energy Council Report, about countries in the world have hydropower in their national electricity generation mixes [ 47 ].
The first top four countries, namely, China, Brazil, Canada, and USA, contribute with about half of the total electricity production, as shown in Table 3.
Table 3: Electricity Production and share of world electricity production in top ten countries and the rest of the world in , adapted from World Energy Council [ 47 ]. Despite being used in many countries, hydropower contributes significantly less towards the worldwide total primary energy supply: in , it contributed only 2. If the hydropower potential from small-scale hydropower sites and from nonconventional sources are taken into account, then the world hydropower potential is very large considering numerous availability of small hydropower potential sites in many countries and potential of water current in rivers and canals such as water supply and irrigation canals.
Therefore, technically, with such a large share of undeveloped potential, hydropower fits very well in the context of providing sustainable electricity for development in Africa—the region of the world where electricity is needed most.
Challenges associated with lack of financing in other regions of the world such as Africa are stated to be some of the main reasons for the underdevelopment of hydropower in such regions [ 47 ]. Table 4: Regional hydropower generation potential, installed capacity, undeveloped potential, and capacity factor in , adapted from World Commission on Dams [ 49 ].
Figure 8: a Share of world hydropower technical generation potentail by region in , adapted from World Commission on Dams [ 49 ].
Capacity factor is the amount of actual electricity energy generated by a power station for a specified period of time e. For a hydropower system, capacity factor depends not only on the availability of water for power generation, but also on whether the power station is designed as a peaking or base load plant. A peaking plant has low capacity factor because the plant operates only during specific times while a base-load has a high capacity factor because the plant operates most of the times.
A conservative figure of GW was proposed by International Hydropower Association [ 50 ] as a fair reflection of the situation. The worldwide-installed capacity did not include pumped storage installations which were estimated to be around GW and GW [ 50 ].
If the annual generation is compared with the worldwide technical generation potential, it can be seen that the latter is over four times greater than the former, indicating a positive outlook for hydropower growth. Table 5: Top ten countries by installed hydropower capacity and generation share in , adapted from International Renewable Energy Agency [ 35 ].
The top ten hydropower producing countries as of are listed in Table 5 together with their installed capacity. From Table 5 , it can be seen that some of the developed and emerging countries, namely, Norway, Canada, Sweden, and Brazil rely heavily on hydropower for their electricity generation.
The IPCC states that the main reason for these developed countries to heavily invest in hydropower energy systems is to consolidate their electricity supply base so as to ensure energy security and trade [ 4 ]. The overdependence of hydropower for electricity generation in these nations demonstrates the capacity of renewable energy hydropower to be used for large scale industrial applications and for energy security.