Hydropower is derived from the potential energy available from water due to the height difference between its storage level and the tail water to which it is discharged. Power is generated by mechanical conversion of the energy into electricity through a turbine, at a usually high efficiency rate. Depending on the volume of water discharged and height of fall (or head), hydropower can be large or small.
Although, there may not be any international consensus on the definition of small hydropower, an upper limit of 30 Megawatts (MW) has been considered. Thus, 30 MW has been adopted as the maximum rating under this dispensation. Small hydro can further be subdivided into mini hydro (<1 MW) and micro hydro (<100 kW). Thus, both mini and micro hydro schemes are subunits of the Small Hydro Power (SHP) classification (Raghunath, 1986).
HYDRO RESOURCE SITUATION
Globally, hydropower is a very significant contributor to energy systems. Nigeria is endowed with abundant water resources. Annual rainfall decreases from a high of 3400 mm depth in the south central shores of the Niger Delta to 500 mm over the northern boundaries of the country, with a perched increase to 1400 mm over central Jos Plateau region. Similarly, the eastern ranges of Adamawa and Cameroon boundaries experience elevated precipitation as high as 2,000 mm relative to contiguous low areas of the country.
Rainfall duration is longest in the south and decreases progressively northwards. In the southern areas, precipitation lasts over 8 months of the year, whereas, at the extreme north annual rainfall duration can be <3 months.
It is clear that the country is blessed with a huge hydropower potential (Okoro, 2006). The most attractive areas would be the southern, Plateau and southeastern regions of the country, where rainfall is highest and of long duration and local topography provides appropriate drops and necessary hydraulic heads. It is also evident that the run-of-the-river SHP is unlikely to operate year round, except in the south and south-eastern areas where, river and stream flows are perennial. In the northern and Jos Plateau regions where stream flows are substantially ephemeral, the SHP would require flow regulation via storages and reservoirs. All the same, small hydropower can essentially be developed in virtually all parts of the country.
ESTIMATED RESOURCE BASE
From National Electric Power Authoritys (NEPA) most recent estimate, the countrys outstanding total exploitable hydro potential, are shown in Table 1 currently stands at 12,220 MW. Added to the 1930 MW (Kainji, Jebba and Shiroro), already developed the gross hydro potential for the country would be approximately 14,750 MW. Current hydropower generation is about 14% of the nations hydropower potential and represents some 30% of total installed grid connected electricity generation capacity of the country.
From a 1980 survey of 12 of the old states of the federation, namely; Sokoto, Katsina, Niger, Kaduna, Kwara, Kano, Borno, Bauchi, Gongola, Plateau, Benue and Cross River, it was established (Table 2), that some 734 MW of SHP can be harnessed from 277 sites. The potential would of course increase when the rest of the country is surveyed. It is presently estimated by the Inter-Ministerial Committee on Available Energy Resources (Technical Committee on Quantification of Energy Resources, 2004) that the total SHP potential could reach 3,500 MW representing 23% of the countrys total hydropower potential.
estimate of current exploitable hydro power sites in Nigeria installed
Small hydro schemes under operation in the country are shown in Table 3. As indicated, the projects are developed only in 3 states of the federation, namely; Plateau, Sokoto and Kano. Of the total 30 MW installed capacity, 21 MW (or 70%) is generated from 6 sites in Plateau State by the Nigerian Electricity Supply Corporation Ltd. (NESCO).
As indicated in Table 4, NESCO projects were completed between 1923 and 1964 and have continued to provide virtually uninterrupted power to not only supply the Jos metropolis and meet local consumption, but also feed into the national grid. NESCO operations are a clear example of a very successful Independent Power Production (IPP) that should be replicated in other parts of the country.
hydro potential in surveyed states of Nigeria
small hydro schemes in Nigeria
small hydro projects in plateau state
|Nigerian Electricity Supply Corporation Ltd. (NESCO), Jos
STATUS OF DATABASE
The database on small hydro in Nigeria is quite limited, incomplete and substantially obsolete. Only 12 sites were surveyed some 20 years ago and to date no new surveys have been conducted to either confirm/verify earlier data or extend the work over the uncovered states, which, incidentally, occupy the most promising south-western and southeastern regions of the country where, precipitation is high and most streams and rivers are perennial.
Every effort should be made to complete the survey over the entire country developing new data and verifying existing information. Data can be assembled through the River Basin Development Authorities, State and Local Governments, NEPA, State Rural Electrification Boards and relevant Non Governmental Organizations (NGO) under the responsibility of the Energy Commission of Nigeria (ECN, 2004). Data thus, generated should be organized in appropriate reports and stored in other suitable formats for easy retrieval and application. For each potential small hydro site, data to be assembled should cover, among other items: rainfall depths and duration; river and stream systems including flow rates and duration; seasonal and long-term variation of flows; local topographical features; suitability of site for reservoir development; geology; demographic characteristics; community trades and employment; land use; status of power supply in the area; developable small hydro capacities; cost of schemes; project feasibility and requirements for hydro system implementation.
RESULTS AND DISCUSSION
Overview of technology: A relatively simple technology, SHP depends on the
availability of water flow or discharge and a drop in level over the river course.
For the run-of-the-river scheme, where there is no impoundment, computation
of the hydropower only requires a determination of the magnitude of the discharge
and the head or vertical distance of the waterfall (Jack, 1984). The flow can
be measured by the bucket method, which simply determines the time taken to
fill a bucket of a known volume. Discharge can also be determined by the velocity
method, where a weighted float is timed over a longitudinal flow path and stream
depths are measured across the flow section to determine the cross-sectional
Where, the topography permits the hydro yield is firmed up by the construction of a small dam, which creates a reservoir. The storage provides additional head and flow regulation, thereby increasing power output and extending power generation over low-flow periods. Other components of the small hydro include the penstock, a turbine which transforms the energy of flowing water into rotational energy, an alternator which converts rotational energy into electricity, a regulator which controls the generators and wiring which delivers the electricity to the end users. In many systems, an inverter is incorporated to convert the resulting low-voltage Direct Current (DC) into 220 or 240 V Alternating Current (AC) compatible with existing national power systems.
Sometimes excess power is stored in batteries for use during periods of low flow or water scarcity. While, the bulk of small-hydro requirement and accessories are import-based during early stages of development, it is believed that with appropriate government incentives and support, virtually all basic components of the systems can be manufactured locally. This would also facilitate system maintenance and repairs.
To date, small hydro technology is still at its infancy in Nigeria. As shown in Table 2, the schemes are operated in only three of the 36 States of the Federation and only the NESCO complex in Plateau State, whose first unit went on stream some 80 years ago, has developed some form of local technology in its facility operation and maintenance.
Technical characteristics: Power output from the small hydro plant is dependent on the characteristics of its key components namely: the penstock, turbine, generator, regulator, inverter and cabling. Penstock piping should be selected to reduce flow friction and hydraulic losses by using smooth piping materials and limiting the number of joints, bends and transitions.
Turbines are preferred over waterwheels, because they are more compact have fewer gears and require less material for construction. As shown in Table 5, several types of turbines are available for the small hydro. The impulse turbines, which have the least complex design and rely on flow velocity to move the wheel or runner are the most commonly used for the high head SHP systems. The most common types of impulse turbines are the Pelton and Turgo wheels.
With the Pelton wheel, water is funneled into a pressurized pipeline via a jet existing from a nozzle and striking double buckets attached to the wheel. The resulting impact creates a force that rotates the wheel at a high efficiency rate of 70-90%. The system is particularly suited for low-flow high-head conditions.
The Turgo impulse wheel is an upgrade of the Pelton. Using the same spray concept,
the Turgo jet is about half the size of the Pelton, but its spray hits three
buckets simultaneously. Thus, the Turgo wheel is less bulky and moves almost
twice as fast the Pelton version. It also, needs few or no gears and generally
operates trouble free under low-flow conditions, requiring medium or high head.
The Turgo wheel therefore, achieves even higher efficiency than the Pelton wheel.
of turbines and parameters for small hydro schemes
|National energy plan vision 2010 for small hydropower technology
In reverse action, conventional pumps, which are mass produced and relatively
less expensive, can operate as turbines. Reasonable pump performance, however,
requires generally constant head and flow, not usually achievable under the
small hydro concept. Pumps are also less efficient and more prone to damage
The generator, regulator and inverter are generally standard equipment with fixed but lower than turbine efficiencies. Thus, whereas the turbine efficiency can be as high as 90%, overall efficiency of the small hydro composite unit is in the range of 53%. Achievement of this level of efficiency requires regular and proper system maintenance.
Since, the hydro plant has only few moving parts and operates at ambient temperatures, its life span can be quite long. While, thermal power plants require very large operation and maintenance costs and must be replaced every 5-7 years, the hydropower system can operate for as long as 20 years under generally inexpensive operation and maintenance requirements before there is need for major rehabilitation. As shown in Table 6, the lifetime of the small hydro facilities is 20-30 years, compared with 8-10 years for diesel engine generators. Long service life is therefore, another important attraction of the small hydro system.
Parts of SHP plants are readily available in the economy. Other than the turbine, which may be import based, other components of the system can be purchased virtually anywhere in the general market. Development and support of the small hydro can thus, be easily achieved within the Nigerian economy.
Economic competitiveness: Although, the small hydro may require a moderately
high capital cost (Table 7), its low operation and maintenance
(O and M) requirements (Table 8) coupled with long life spans
are its major advantage over other prospective sources of power to small and
medium sized local communities and settlements. The petrol/diesel generators
which may be installed at a relatively moderate cost are prone to such serious
limitations as unreliability of fuel supply, frequent breakdown, high O and
M requirements, short service lives, noisy operation and environmental pollution.
of off-grid renewable energy technologies
capital costs of electricity generating systems
Costs are as of 1990, national energy plan vision
2010 small hydropower technology (March, 2004)
and Maintenance (O and M) and fuel costs for different technologies
The economic value of small hydro schemes would be further enhanced when more
units come on stream, local service areas are established and system components
are predominantly locally sourced. Training facilities would need to be set
up in different states, particularly in areas of high SHP potential and/or development.
Prospective operators and managers can also, be trained in higher institutions
throughout the country. Economic competitiveness of the SHP would increase with
more use and improvements.
Benefits and limitations: Several benefits are derived from the small hydro development, among which are provision of a basic tool for rural development, very low operation and maintenance costs, no fuel costs, kick-starting and support for cottage industries, access to remote and often neglected communities, competitive economic and supply advantage over other power systems, environmentally friendly and emission free power generation (Table 9), poverty alleviation, general upliftment of the social structure of the community, provision of rural employment, economic empowerment of the community, reduction of rural-urban migration and opportunity to tap substantial unutilized energy resources of the country.
of environmental effects of power generating plants
|National energy plan vision 2010 small hydropower technology
Despite its obvious benefits, the small hydro has its limitations. Power can
usually be generated only during the rainy season when sufficient flow would
be available. Even where, a reservoir is integrated as a component of the scheme,
it is still unlikely that power is produced over an appreciable period of the
dry season or drought. Small hydro plants are usually sited in remote, sometimes
rugged and virtually inaccessible locations from where, it is difficult at times
to bring the power to populated areas and load centers. Other SHP limitations
include: long project development periods and high in situ investment
costs; administrative bottlenecks relating to organization, awarding the contract
and construction of projects involving complex coordination of tendering, construction
and supervision; water right problems where water is diverted from areas with
prior rights; the absence of technical standards, which leads to utilization
of substandard equipment, resulting in low efficiency and poor system reliability;
insufficient financial resources for necessary O and M for sustained operation
of SHP, the bulk of which is produced for consumptive residential use; there
are no real models for companies to finance and operate SHP on a private development
basis; financial institutions may be reluctant to finance non-traditional (power)
projects and land acquisition could lead to social and cultural controversies.
Present demand and supply situation: From a projection of overall energy
demand for the Country, electricity demand for households and industry, the
principal consumers of the SHP are projected to grow at annual rates between
8 and 9% under the high growth scenario and between 3 and 5% for a low growth
pattern. It is projected that the demand for SHP will grow at a faster pace
and could reach an annual rate of 10%. Based on year 2000 Nigerian population
of some 110 million and per capita power requirement of about 30 W, the 2000
year demand for the small hydropower is estimated to be 190 MW. Corresponding
future demands, as set out in Fig. 1, are projected to reach
approximately 490 MW in year 2010, 1280 MW in 2020 and 3315 MW by 2030.
Sufficient SHP potential exists to meet the national demand over the next 30
years. There is a need for government to be fully committed to developing these
Nigerian small hydro power demand
Overall national power requirements indicate substantial deficiency in supply
relative to demand. In year 2000, for example, only 30 MW of the 190 MW demand
was generated leaving a supply shortfall of 160 MW or some 84%. Without additional
developments, the supply gap would increase further over time and could exceed
90% in the next 20 years. At the estimated demand of 3315 MW, the year 2030
requirement just about matches the estimated national potential of 3500 MW.
It means therefore that full realization of the nations small hydro potential
will be achieved in 30 years if available sites are developed in line with the
projected growth in national demand.
Key drivers for the SHP market: Population growth creates the demand and market for small hydropower development. Population pressure leads to demographic changes, which result in settlement over remote areas usually near sources of water. These settlers provide the demand and market for the SHP.
Such government sponsored programs as rural electrification, water resources development, cottage industries, rural enterprises, agriculture, poverty alleviation programs and health care services constitute important activities that can draw from the small hydro scheme.
Diversification of community trades and services would also provide ready markets. The high cost of fuel, O and M and related expenses associated with diesel based generator sets together with the unreliability of fuel supply promote a justification for the SHP option.
So, does the remoteness of the rural areas as well as the absence of national power grid. Improved community awareness through individual and general public education including interaction with other communities is also an important driver for the SHP market.
Gaps and barriers to small-hydro market development: As noted in Nigerias
Vision 2010 National Energy Plan, the following barriers face implementation
and marketing of renewable energy, including small hydro: implementation requires
significant initial investment with generally low rate of return while, there
is very limited level of consumer awareness on the benefits and opportunities
of SHP development. The economic and social system of energy services is based
on centralized development around conventional sources of energy, specifically
electricity generation, thus, making a level playing field impossible. Financial,
legal, regulatory and organizational barriers need to be overcome in order to
implement the projects and develop new energy markets. There is an absence of
a framework for power purchase agreement between owners of small hydro plants,
the grid and other users. There has also been a lack of assessment of the market
potential and the structure necessary to harness the SHP potential.
RECOMMENDATIONS AND CONCLUSION
Integration of renewable energy and systems: Different renewable energy technologies offer different services depending upon the availability of potential resources.
Therefore, there is need for adopting an integrated approach to overcome technical challenges related to fluctuations and intermittency of energy supply provided by different renewable energy systems.
Technology acquisition and development: Nigeria lacks manufacturing capacity for renewable energy technologies and so most of the technologies used in the country are imported. There is an urgent need to develop regional, sub regional and national strategies to develop requisite R and D capacity and skills for adaptation and strengthening of the manufacture base.
Human and regulatory development environment: The renewable energy markets
in Nigeria are seriously constrained by lack of coherent policy and regulatory
environment, which can create level playing field for renewable energy technologies.
Therefore, the country needs to establish policy and regulatory environment
that will facilitate the promotion of renewable energy technologies.
Financing options: New and additional mechanism of targeted investment need to be developed to finance both grid-connected and stand alone renewable energy projects.