COMPLETE SCHOOL PROJECT TOPICS & MATERIALS :
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CHAPTER ONE
INTRODUCTION
- Background of the Study
All living things depend on energy for survival, and modern civilizations will continue to thrive only if existing sources of energy can be developed to meet the growing demands, hence Energy is “Life” Energy is “Existence”, it is the dividing line between the rich and the poor, between the developed, developing and the underdeveloped (Ohunakins et al., 2011). For a country to grow beyond its subsistence economy, tackle the problem of poverty, the country will need to have minimum access to energy services for the larger proportion of its population (Ohunakins et al., 2011). However, in Nigeria energy supply has been epileptic in nature, causing the socio-economic status of the country to be downgraded (Ohunakins et al., 2011).
Nigeria’s energy demand increases with an increase in population, but power supply has remained unreliable and insufficient with a country generation capacity of about 3500 MW as at 2011 (Okeke, 2011). Nigeria as a nation has started feeling the impact of adverse climate change, that may be attributed to the overdependence on fossil fuel fired power plants which is the main source of greenhouse gas emissions (GHG), coupled with activities of manufacturing industries, oil prospecting firms and deforestation, to mention but a few.
Renewable energy (RE) has been identified as the only alternative of addressing these problems. RE is energy derived from an energy source that can generate itself through natural processes within a relatively short period; unlike fossil type resources that take millions of years to form and which is not regenerative. Examples of such energy
sources include: Hydropower, wind, solar, tidal, biomass, wave, ocean thermal and
geothermal (RETscreen, 2012). Hydropower amongst other renewable sources mentioned offers a clean and sustainable source for rural power, 24hours a day and even all through the year, provided there is water to power the turbines, causing little or no emissions to the ecosystem (RETScreen, 2005).
Inspite of abundance water resources that abound in all states and local government areas in Nigeria, hydropower remains an underutilized resources for electric power generation in Nigeria.
Hydropower
Hydropower is the power generated by using the potential energy stored in flowing water. It is a renewable energy source suitable for rural electrification in developing countries like ours. It is a proven technology that can be connected to the main grid, used as a stand- alone/ off-grid mode. When integrated with irrigation systems and community water supply scheme, the cost sharing effect reduces the cost of electricity production. Hydro power plants are robust and long lasting, easier to install and manage (compared to large hydro power installations) and may not require high investments in transmission lines, when connected in off-grid/decentralized modes, since end users are quite close to the source of generation. In China, the use of small scale hydropower to achieve rural electrification, started in the 1950s, with a strong lead from the government; presently, there are over 600 counties (accounting for 30% of all china counties) that rely mainly on small scale hydropower for electricity,serving over 300 million people (NASENI, 2010).
To overcome the increasing demand for electricity, new energy facilities are under construction all around the world. Fossil fuel fired power plants are the main source of greenhouse gas emissions which increase the threat of climate change. The countries all
around the world are trying to supply their increasing demands for electricity with clean energy technologies. Hydropower as sustainable and renewable resource is one of the major sources of power, which the country looks forward to in the nearby future, though a significant portion of the economically viable hydropower potential of Nigeria has not been harnessed, thus very few hydropower plants are under construction and in program to harness this economically viable potential (NASENI,2010).
Small hydro project development
The development of small hydro power (SHP) projects typically takes from 1 to 5 years to complete, from conception to final commissioning (ESHA, 1998). This time is required to undertake studies and design work, to receive the necessary approvals and to construct the project. Once constructed, small hydro plants require little maintenance over their useful life, which can be well over 50 years (ESHA, 1998). Normally, one part-time operator can easily handle operation and routine maintenance of a small hydro plant, with periodic maintenance of the largercomponents of a plant usually requiring help from outside contractors.The technical and financial viability of each potential small hydro project are very site specific. Power output dependson the available water (flow) and head(drop in elevation). The amount of energy that can be generated depends on the quantity of water available and the variability of flow throughout the year. The economics of a site depends on the power (capacity) and the energy that a project can produce, whether or not theenergy can be sold, and the price paid for the energy. In an isolated area (off-grid and isolated-grid applications) the value of energy generated for consumption is generally significantly more than for systems that are connected to a central-grid. However, isolated areas may not be able to use all the available energy from the small hydro plant and, may be unable to use the energy when it is available
because of seasonal variations in water flow and energy consumption. A conservative,
“rule-of-thumb” relationship is that power for a hydro project is equal to seven times the product of the flow (Q) and gross head (H) at the site (P = 7QH)(RetScreen, 2012). Producing 1 kW of power at a site with 100 m of head will require one-tenth the flow of water that a site with 10 m of head would require. The hydro turbine size depends primarily on the flow of water it has to accommodate. Thus, the generating equipment for higher-head, lower-flow installations is generally less expensive than for lower-head, higher-flow plants. The same cannot necessarily be said for the civil works components of a project which arerelated much more to the local topography and physical nature of a site.
Types of small hydro developments
Small hydro projects can generally be categorized as either “run-of-river developments” or“water storage (reservoir) developments,” which are described in more detail below.
- Run-of-river developments
“Run-of-river” refers to a mode of operation, in which the hydro plant uses only the water that is available in the natural flow of the river (ESHA, 1998), “Run- of-river” implies that there is no water storage and that power fluctuates withthe stream flow. The power output of run-of-river small hydro plants fluctuates with the hydrologic cycle, so they are often best suited to provide energy to a larger electricity system. Individually, they do not generally provide much firm capacity. Therefore, isolated areas that use small hydro resources often require supplemental power. A run-of-river plant can only supply all of the electrical needs of an isolated area or industry if the minimum flow in the river is sufficient to meet the load’s peak power requirements (RETscreen, 2012).
Run-of-river small hydro can involve diversion of the flow in a river. Diversion is often required to take advantage of the drop in elevation that occurs over a distance in the river. Diversion projects reduce the flow in the river between the intake and the powerhouse. A diversion weir or small dam is usually required to divert the flow into the intake, as shown in figure 2.1.
Figure 2.1Typical Arrangement of a Run-off – scheme Small Hydro Power Station (Source: NASENI SHP, 2010)
- Water storage (reservoir) developments
For a hydroelectric plant to provide power on demand, either to meet a fluctuating load or to provide peak power, water must be stored in one or more reservoirs. Unless a natural lake can be tapped, providing storage usually requires the construction of a dam or dams and the creation of new lakes. This impacts the local environment in both negative and positive ways, although the scale of development often magnifies the negative impacts. This often presents a conflict, as larger hydro projects are attractive because they can provide “stored” power during peak demand
periods. Due to the economies of scale and the complex approval process, storage
schemes tend to be relatively large in size. The creation of new storage reservoirs for small hydro plants is generally not financially viable except, possibly, at isolated locations where the value of energy is very high. Storage at a small hydro plant, if any, is generally limited to small volumes of water in a new head pond or existing lake upstream of an existing dam. Pondage is the termused to describe small volumes of water storage. Pondage can provide benefits to small hydro plants in the form of increased energy production and/or increased revenue. Another type of water storage development is “pumped storage” where water is “recycled”between downstream and upstream storage reservoirs. Water is passed through turbines to generate power during peak periods and pumped back to the upper reservoir during off-peak periods. The economics of pumped storage projects depends onthe difference between the values of peak and off-peak power. Due to the inefficiencies involved in pumping versus generating, the recycling of water results in a net consumption of energy. Energy used to pump water has to be generated by other sources. The environmental impacts that can be associated with small hydro developments can vary significantly depending on the location and configuration of the project. The effects on the environment of developing a run-of-river small hydro plant at an existingdam are generally minor and similar to those related to the expansion of an existing facility (RETscreen, 2012). Development of a run-of-river small hydro plant at an undeveloped site can pose additional environmental impacts. A small dam or diversion weir is usually required. The most economical development scheme might involve flooding some rapids upstream of the new small dam or weir. The environmental impacts that can be associated with hydroelectric developments that incorporate water storage (typically larger in size) are mainly related to the creation of a water storage reservoir. The creation of a reservoir
involves the construction of a relatively large dam, or the use of an existing lake to impound water. The creation of a new reservoir with a dam involves the flooding of land upstream of the dam. The use of water stored in
the reservoir behind a dam or in a lake results in the fluctuation of water levels and flows in the river downstream. A rigorous environmental assessment is typically required for any project involving water storage.
- Hydro projects engineering phases
According to Belvoir (2005), there are normally four phases for engineering work requiredto develop a hydro project. Note, however, that for small hydro, the engineering work isoften reduced to three phases in order to reduce costs. Generally, a preliminary investigationis undertaken that combines the work involved in the first two phases described below. The work, however, is completed to a lower level of detail in order to reduce costs. Whilereducing the engineering work increases the risk of the project not being financially viable,this can usually be justified due to the lower costs associated with smaller projects.