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Energy crisis and environmental safety has become a thing of global concern, Nigeria inclusive. This is due to the increasing energy prices and environmental impact. Energy generated from the non-renewable energy sources has been linked up with this energy crisis and non-friendly environment. Research is therefore been geared towards harnessing renewable energy resources as alternative sources of energy generation. Renewable energy sources such as hydropower, wind, geothermal and solar just to mention a few are environmentally friendly. This study therefore aims at exploring renewable energy sources and thus designing a small hydropower plant using Ikere gorge Dam as case study. A survey was conducted through personal interview and probing of previous records of the site. Basic parameters such as flow rate of 31.8 m
^{3}/s and a head of 30 m were obtained. These parameters were used together with the standard equations for the design of the small hydropower plant. Costing analysis of the plant was carried out in other to estimate the cost of the plant. The comparative analysis of the renewable and non-renewable energy sources was also carried out. The theoretical power obtained for small hydropower project is 9.36 MW. The initial cost of the project is estimated at N63,343,970 with an estimated annual maintenance cost of N500,000. The annual energy output is 3.6 × 10
^{7} kWh and the project has estimated annual revenue of N579,960,000. When compared with other renewable energy sources, the cost of small hydropower plant is low and when compared with dwindling oil prices and environmental effects of non-renewable energy sources, small hydropower stands second to none. The study established that Ikere gorge Dam is a feasible site for a small hydropower plant and a small hydropower plant has also been designed; hence small hydropower plant is therefore recommended.

Energy conversion and power generation has been a paramount and ever-evolving activity of man for several centuries. From simple wind-powered threshing mills, to coal-powered steam engines, power generation from natural gas, oil, renewable energy sources, and in recent time nuclear energy, man has constantly tried to improve. For developed countries, emphasis is laid on transition from non-renewable sources of energy to renewable sources with the aim of taming greenhouse effect and depletion of the ozone layer. For developing countries, such as Nigeria, it is a different ball game all together. Enough power is not being generated, let alone talks of transition. According to the Presidential Task Force on Power, “Nigerians are among the people most deprived of grid-based electricity in the world with a per capital consumption that is far lower than many other African countries”. Nigeria currently has the capacity to generate about 6000 megawatts of electricity of which only 3600 is being generated for a populace of over 160 million.

What this means is that about 22.8 Watts of electricity is produced for each Nigerian per capita. For all things being equal, Nigeria has the capacity to generate enough power to meet the power consumption needs of the populace. Small hydropower (SHP) is a proven technology that can stand-alone, being connected to an isolated grid, or the national grid. In most cases, it is often combined with irrigation systems. One of the major industrial problems in Nigeria is power generation. Sufficient power is not being generated to cater for industry needs, as well as the needs of the populace. Nigeria has the capacity to produce enough power to cater for the needs to industries and the populace at large. Aside being blessed with crude oil, solid minerals, and workforce, Nigeria is blessed with sufficient water bodies. While power from gas, steam, and coal is prevalent, the adverse effect of their usage cannot be overruled. Hydropower can contribute immensely in tackling the power situation in Nigeria. The bottom line is that SHP can adequately contribute to the electricity needs of Nigeria. Statistics prove that Nigeria is blessed with enough water bodies that can contribute substantially to power generation output. The exploitable hydropower potential in Nigeria is conservatively estimated to be about 10,000 MW [^{th} century with the coupling of waterwheels with electrical generators. As at the dawn of the 20^{th} century, many towns, industries, and cities located near rivers had harnessed hydropower. In a country like the United States, as at 1920, about 40% of the power produced was from hydropower. This wide spread popularity gave hydropower the nickname “white coal” [

The definition of small hydropower varies from country to country, as there is no internationally accepted value. In a country like Sweden, the limit is 1.5 MW, in India 15 MW, and in China, small hydropower encompasses capacities up to 25 MW. However, 10 MW is generally accepted as the threshold for small hydropower by European Small Hydropower Association, European Commission, and International Union of Producers and Distributors of Electricity [

The 30 MW limit for small hydropower was because all the projects in the considered region were added up (ECREEE, 2012).

[

Terms | Small Scale Hydropower “SSHP” | Power Output |
---|---|---|

Pico Hydropower | <5 kW | |

Micro Hydropower | 5 kW - 100 kW | |

Mini Hydropower “MHP” | 100 kW - 1000 kW (1 MW) | |

Small Hydropower “SHP” | 1 MW - 30 MW | |

Medium Hydropower | 30 MW - 100 MW | |

Large Hydropower “LHP” | >100 MW |

Small hydropower contributes immensely to the worlds’ renewable energy sources because it is cheap and provides clean energy.

Going by the definition of small hydropower being between 1 MW - 10 MW, as at 2004, the total globally installed small hydropower plants produced about 48 Gigawatts (GW), as shown in

As stated in preceding sections, economic development of a country is closely tied to its ability to provide enough power to cater for the domestic and industrial needs of the populace. In Nigeria however, the demand for power far

Energy Source | Percentage |
---|---|

Large hydro (>10 MW) | 86% |

Small hydro (<10 MW) | 8.3% |

Wind and solar | 0.6% |

Geothermal | 1.6% |

Biomass | 3.5% |

Region | Capacity (MW) | Percentage (%) |
---|---|---|

Asia | 32,641 | 68.0 |

Europe | 10,723 | 22.3 |

North America | 2929 | 6.1 |

South America | 1280 | 2.7 |

Africa | 228 | 0.5 |

Australasia | 198 | 0.4 |

outstrips the power being generated and supplied. Nigeria has numerous potential sites for SHP. Harnessing these options will go a long way in changing the power production level in Nigeria. Between 2003 and 2007, Nigeria experienced a growth in hydropower of 9.7% [

Results were obtained using the standard hydropower equations with the data obtained from the site (Ikere gorge Dam) coupled with some other fundamental fluid property values [

State | Potential Sites | Estimated output |
---|---|---|

Adamawa | 3 | 28.600 |

Akwa Ibom | 13 | |

Bauchi | 1 | 0.150 |

Benue | 10 | 1.306 (one site) |

Cross River | 5 | 3.0 |

Delta | 1 | 1.0 |

Ebonyi | 5 | 1.3999 |

Edo | 5 | 3.828 |

Ekiti | 6 | 1.2472 |

Enugu | 1 | |

FCT | 6 | |

Gombe | 2 | 35.099 |

Imo | 71 | |

Kaduna | 15 | 25.0 |

Kano | 2 | 14.0 |

Katsina | 11 | 234.34 |

Kebbi | 1 | |

Kogi | 2 | 1.055 |

Kwara | 4 | 5.2 |

Nassarawa | 3 | 0.454 |

Niger | 11 | 110.580 |

Ogun | 13 | 115.610 |

Ondo | 1 | 1.3 |

Osun | 8 | 2.622 |

Oyo | 3 | 1.062 |

Plateau | 14 | 89.1 |

Sokoto | 1 | |

Taraba | 9 | 134.720 |

Yobe | 5 | |

Zamfara | 16 |

Theoretical Power (P_{th})

The theoretical power is the maximum power that can be generated from the hydropower project. The assumption is that the efficiency of the system is 100%, as well as no head losses.

The theoretical power is calculated using equation below

P_{th} = ηρgQH

η = 1

ρ = 1000 kg/m^{3}

g = 9.81 m/s^{2}

Q = 31.8 m^{3}/s

H = 30 m

Therefore,

P t h = 1 × 1000 × 9.81 × 31.8 × 30 = 9.36 MW

Penstock

Penstock Diameter (D)

Selection of the diameter size of a penstock is interplay between limiting head losses and reducing the cost of the penstock. The head losses decrease as the penstock diameter increases. On the contrary, the cost of penstock increases with an increase in diameter.

The penstock diameter is calculated such that the overall head loss is limited to 4%. This is given by Equation (3.3) as.

D = 2.69 ( n 2 Q 2 L H g r o s s ) 0.1875

n = 0.009 for PVC

Q = 31.8 m^{3}/s

L = 100 m

H_{gross} = 30 m

D = 2.69 ( 0.009 2 × 31.8 2 × 100 30 ) 0.1875 = 2.1 m

When the head losses―loss at intake, loss at trash rack, frictional losses, losses through bends, and loss at gate valve were calculated using this value (2.1 m), it was discovered that the total head losses exceeding the acceptable range limit of 4%. Different values of D were computed―2.1 m, 2.2 m, 2.3 m, 2.4 m, 2.5 m, and 2.6 m. At 2.6 m, the total head loss was within the limit of 4%.

Hence, D = 2.6 m

Minimum Thickness (t_{min})

t min = 2.5 D + 1.2 = 2.5 × 2.6 + 1.2 = 7.7 mm

A supplier recommended 15mm, hence the choice for a penstock thickness of 15 mm.

Velocity in Penstock (V)

V = Q/A

Q = 31.8 m^{3}/s

A = 3.142 × 2.6^{2}/4 = 5.31 m^{2}

V = 31.8 5.31 = 5.99 m − s

Head Loss at Intake (h_{i})

h i = k V 2 2 g

K is a constant and is given as 0.04 for this design

V = 5.99 m/s

g = 9.81 m/s^{2}

h i = 0.04 × 5.99 2 2 × 9.81 = 0.073 m

Frictional Loss (h_{f})

The frictional loss is given by equation

h f L = 10.3 n 2 Q 2 D 5.333

L = 100 m

n = 0.009

Q = 31.8 m^{3}/s

D = 2.6 m

h f = 10.3 0.009 2 × 31.8 2 × 100 2.6 5.333 = 0.517 m

Head Loss at Bend (h_{b})

h b = K b V 2 2 g

K_{b} is a constant and is given as 0.085 for this design

V = 5.99 m/s

g = 9.81 m/s^{2}

h b = 0.085 × 5.99 2 2 × 9.81 = 0.155 m

Loss at Gate Valve (h_{v})

h v = K v V 2 2 g

K_{v} is a constant and is given as 0.15 for fully opened gate valve

h v = 0.15 × 5.99 2 2 × 9.81 = 0.274 m

Pressure Wave Velocity (c)

The surge pressure wave velocity is given by Equation (3.8)

c = 10 − 3 K 1 + K D E t

K = 2.1 × 10^{9} N/s^{2 }

E = 2.75 × 10^{9} N/m^{2}

D = 2600 mm

t = 15 mm

c = 2.1 × 10 6 1 + 2.1 × 10 9 × 2600 2.75 × 10 9 × 15 = 125.49 m / s

Critical Time (T)

T = 2 L c

P s = 2 × 100 125.49 = 1.59 seconds

Surge Pressure in Penstock (p_{s})

The surge pressure is given as:

P s = 4 c 9.8

P s = 4 × 125.49 9.8 = 51.22 m

Trash Rack

Surface Area (S)

The surface area of the trash rack is as given below:

S = 1 K 1 ( b + a a ) Q V 0 1 sin α

K_{1} = 0.85 for an automatic raker

b = 70 mm

a = 60 mm

The approach velocity, V_{0} is limited to 1.5 m/s since there are plans to make use of mechanical raking system.

α = 60˚

S = 1 0.85 ( 70 + 60 60 ) 31.8 1.5 1 sin 60 = 62 m 2 ^{ }

Head Loss through Trash Rack (h_{t})

h t = K s [ t b b ] 4 3 × v 0 2 2 g sin α

K_{s} = 1.67 for flat bar with rounded ends as seen in

t_{b} = 12 mm

h t = 1.67 × [ 12 60 ] 4 3 × 1.5 2 2 x 9.81 sin 60 = 0.019 m

Turbine

NetHead = GrossHead − Losses = 30 − ( 0.073 + 0.517 + 0.155 + 0.274 + 0.019 ) = 28.96 m

Power Output (p)

The power output the turbine is given as (P)

P = ηρgQH_{n}_{ }

η = 0.9

ρ = 1000 kg/m^{3}

g = 9.81 m/s^{2}

Q = 31.8 m^{3}/s

H_{n} = 28.86 m

P = 0.9 × 1000 × 9.81 × 31.8 × 28.96 = 8.13 MW

Specific Speed (n_{QE})

The rotational speed of a Kaplan turbine is given by equation

n Q E = 2.294 H n 0.486

n Q E = 2.294 28.86 0.486 = 0.5 s − 1

Rotational Speed (n)

The rotational speed is calculated from equation below

n Q E = n Q E 3 4

E = H n × g = 28.96 × 9.81 = 284.09 m 2 / s 2 ^{ }

n = n Q E E 3 4 Q = 0.5 × 284.09 3 4 31.8 = 6.1 s − 1 ^{ }

Runway Maximum Speed

The runway maximum speed for a Kaplan turbine is given as:

3.2 × n = 3.2 × 6.1 = 19.52 s − 1

Runner diameter (D_{e})

D e = 84.5 ( 0.79 + 1.602 n Q E ) H n 60 n

D e = 84.5 ( 0.79 + 1.602 × 0.5 ) 28.96 60 × 6.1 = 1.98 m

Hub diameter (D_{i})

D i = ( 0.25 + 0.0951 n Q E ) D e

D i = ( 0.25 + 0.0951 0.5 ) × 1.98 = 0.87 m

Cavitation coefficient (σ)

σ = 1.541 × n Q E 1.46 + v 2 2 g H n

σ = 1.541 × 0.5 1.46 + 5.99 2 2 × 9.81 × 28.96 = 0.623

Suction head (H_{s})

H s = P a t m − P v ρ g + v 2 2 g − σ H n

P_{atm} = 98,000 Pa

P_{v} = 3493.04 Pa

H s = 98000 − 3493.04 1000 × 9.81 + 5.99 2 2 × 9.81 − 0.623 × 28.96 = − 6.577 m

Cost analysis was carried out using the fundamental equations [

The annual energy output is given as a function of

E = f ( Q median , H n , η turbine , η generator , η gearbox , η transformer , γ , h )

where;

Q_{median} = flow in m^{3}/s for incremental steps on the flow duration curve

H_{n} = Specific net head

η_{turbine} = turbine efficiency

η_{generator} = generator efficiency

η_{gearbox} = gearbox efficiency

η_{transformer} = transformer efficiency

γ = specific weight of water

h = number of hours in a year

Annual Energy GenerationThe annual energy generation is given as:

Annual Energy Yield (kWh) = capacity factor × Power (kW) × Hours in a day × Days in a year

Annual Energy Yield (kWh) = 0.5 × 8130 kW × 24 hours × 365 days = 3.6 × 10^{7} kWh

The current rate of electricity in Nigeria is ₦ 16.11 per kWh.

Hence, Annual generated revenue = Annual Energy Yield × Rate

=3.6 × 10^{7} × 16.11

=₦ 579,960,000

Design Head, H: 30 m

Flow Rate, Q: 31.8 m^{3}/s

Theoretical Power, P_{th}: 9.36 MW

Material: Polyvinyl Chloride Pipe

Length, L: 100 m

Diameter, D: 2.6 m

Minimum thickness, t_{min}: 7.7 mm

Penstock thickness, t: 15 mm

Velocity in Penstock, V: 5.99 m/s

Head loss at penstock inlet, h_{i}: 0.073 m

Frictional loss in penstock, h_{f}: 0.517 m

Head loss at bends, h_{b}: 0.155 m

Loss at gate valve, h_{v}: 0.274 m

Pressure wave velocity, c: 125.49 m/s

Critical time, T: 1.59 sec

Surge pressure in penstock, P_{s}: 51.22 m

Configuration: Type 1

Approach velocity to trash rack, V_{0}: 1.5 m/s

Inclination to the horizontal, α: 60˚

Bar Spacing, b: 70 mm

Bar thickness, t_{b}: 12 mm

Bar width, a: 60 mm

Total surface area, S: 62 m^{2 }

Head loss through trash rack, h_{t}: 0.015 m

Selected turbine: Kaplan

Power output: 8.13 MW

Rotational speed: 6.1 s^{−1 }

Specific speed: 0.5

Runway Maximum Speed: 19.52 s^{−1}

Runner diameter: 1.98 m

Hub diameter: 0.87 m

Cavitation coefficient: 0.623Suction head: −6.577 m

Preparation of Site: ₦ 2,000,000

Civil Works: 6,000,000

Penstock: ₦ 15,660,000

Control System: ₦ 500,000

Turbine: ₦ 8,439,000

Generator: ₦ 4,000,000

Exciter: ₦ 3,700,000

Protection System: ₦ 700,000

DC Emergency Supply: ₦ 1,000,000

Transformer: ₦ 15,000,000

Installation: ₦ 4,500,000

Total Cost: ₦ 61,499,000

Miscellaneous/Unforeseen expenses: 3%

= ₦ 1,844,970

Total Cost: ₦ 63,343,970

The annual revenue is defined as the gross average annual energy output multiplied by the estimated cost of energy per kilowatt (kw/hr) minus the cost incurred as a result of downtime. Downtime is any period the SHP is not functioning either due to maintenance reasons or shortage of water.

Annual Energy Output: 3.6 × 10^{7} Kilowatt hour

Estimated Annual Revenue: ₦ 579,960,000

Estimated Yearly Cost of Maintenance: ₦ 500,000

In conclusion, this work has been able to establish that Ikere gorge Dam in Nigeria is a feasible site for a small hydropower plant. Small hydropower plant capable of supplying electricity for a small community using the gorge as a case study has also been designed. Estimated power generation capacity of the designed SHP is 9.36 MW. While the estimated total cost of the plant is ₦ 63,343,970, the plant annual deliverable expected revenue estimated is ₦ 579,960,000 with annual power yield of 3.6 × 10^{7} kWh/yr.

Recommendations

It is clear that adoption of small hydropower schemes is a viable source towards increasing the power generation capacity of Nigeria. However, the underdevelopment in small hydropower is tilted towards certain governmental policies and their implementation than towards the unavailability of the technology. As a result, the following recommendations are made with regards to small hydropower. In order to reduce the overall cost of purchasing SHP components, local manufacturing capacity needs to be sorted after, encouraged and tested. Deregulation in the upstream and downstream sectors, such as private investors, are encouraged to invest in power generation.

The authors declare no conflicts of interest regarding the publication of this paper.

Odunfa, M.K., Saudu, T.C. and Oladimeji, T.E. (2019) Development of a Small Hydropower Plant: Case of Ikere Gorge Dam, Oyo State, Nigeria. Journal of Power and Energy Engineering, 7, 31-45. https://doi.org/10.4236/jpee.2019.73003