^{1}

^{*}

^{2}

^{2}

^{3}

All serious projects over the world should respect the objectives of sustainable development. The contribution of every country against the climate change is request applied. The development of renewable energies is an effective contribution to solutions for this relevant question. Hydropower energy is one of most promising clean energy technologies. However, Micro Hydro Power Plants (MHPP) will be more promising than large hydro power stations. Cameroon has a great hydroelectric potential, but the access rate to electricity is still very low in rural areas of this country. The objective of this work is to do the technical and economic assessment of a MHPP in BAKASSA, which is a remote village in the West Region of Cameroon, in the intention to contribute to its sustainable development. The results of this study show that this MHPP project can be developed with installed power of 97 kW, where the Francis turbine is recommended. The investment cost evaluated at
**88,440,068 FCFA**. It is a profitable project with a maximum payback period of 9 years.

One of the reasons that greenhouse gas emissions were increasing is fossil fuels consumption. To reduce fossil fuel consumption, many countries have developed renewable energy technologies. Cameroon also intends to develop and integrate lots of renewable energies for the efficiency of its energy system.

The rate of access to electricity in Cameroon was 49% in 2012, which less than 20% in the rural area [

However, that country has significant hydroelectric potential. But only large power plants are often developed, leaving out many other sites favorable to the implantation of MHPP, able to satisfy the needs of electrification in the remote rural areas and thus contribute to their sustainable development. The aim of this study is to develop the feasibility studies of a MHPP project in the West Region of Cameroon, on a fall river of BAKASSA.

The hydropower plant is a system of power generating based on the principle that flowing and falling water has a certain amount of kinetic energy potential associated with it. Hydropower comes from converting the energy in flowing water, by means of a water wheel or a turbine, into useful mechanical energy. This energy can then be converted into electricity through means of an electric generator. The energy from the flowing/falling water can also be used directly by suitable machines to avoid the efficiency loses of the generator. Actually in the world MHPP receive a public interest as a promising, renewable source of electrical power for homes, farms, and remote communities. There is not yet a universal classification of hydro power plant according to the power generating. This classification varies from a country to another [

The MHPP system includes a water turbine that converts the energy of flowing water into mechanical energy. This mechanical energy drives a generator which produces electrical power. The efficiency of the overall system, given the pipe friction loses and turbine deficiencies, is generally on the range of 50% of theoretical power associated with the energy of the flowing water. Micro-hydro has been in use for many years in many applications. The turbine varies from site to site according to the given pressure head and design flow at each site [

Water flow in upstream will be diverted in intake weir and it will flow into the channel. The channel transports the water to fore bay tank before going to penstock pipe. In the tank, debris will be filtered and prevented from being drown to the turbine by means of penstock. Power conversion is done inside the power house, and turbine will transfer mechanic energy to generator, then generator produces electric energy.

BAKASSA is a river in Bansoa District, Menoua Division and West Region of Cameroon. Located in between 5˚26'54"North, 10˚18'49"East [

Software of feasibility studies of MHPP developed for local need, electronic laser level with Global Positioning Systems (GPS), questionnaire series, length meters, hydrological data and several other documents were used.

The gross waterfall height is the altitude difference between the upstream and downstream water levels of the waterfall. Lots of recognitions visits were done. The gross fall height was measured using an electronic laser level with a suitable accuracy. It is a topographic datum which can also be measured thanks to a map for high falls.

In the intention to do a good design of MHPP, it is necessary to collect (or simulate with a suitable model) some discharge on waterfall of one year. For an isolate system, the flow rate of equipment used to design the turbine is that which is exceeded 250 days per year [

A Software, called MASS-Hydro, developed by some local experts was used to calculate and determine technical elements of that micro-Hydro. This software was developed considering conventional calculation of formulas of MHPP characteristics shown below [

1) Installed power generation

The power generated from hydraulic turbines is a function of the available net head, the flow rate, and the efficiency of the turbine. It can be estimated by:

P = η ⋅ ρ ⋅ g ⋅ Q ⋅ H (1)

where P is hydro power generation capacity of plant in kW, H is net head of water in meter, Q is discharge in m^{3}/s, g is gravity acceleration constant (= 9.81 m/s^{2}), H_{n} = net head (m) and η is turbine efficiency (= 80% - 90%).

2) Weir

Several types of notch can be used such as rectangular, Vee or trapezoidal. The material may be metal plate, concrete or hard wood with sharp edges. A simple linear measurement of the difference in level between the up-stream water surface and the bottom of the notch is sufficient to quantify the flow rate. The height takes into account the point of entry of water into the supply pipe.

3) The water intake

Placed at the inlet of the supply line, the water intake avoids turbulence, stops heavy or light debris with the screen, threshold and chicane. The inlet water level must be below the water level to prevent air from entering the line. The flow rate through it can be given as [

Q = 1.8 × ( w − 0.2 h ) × h 1.5 (2)

where, Q is discharge in m^{3}/s w = weir width (m), h = Weir height (m). If w ≥ 3 h, then weir dimensions can be calculated.

4) The supply channel

Not only, for its stability channel must be a rigid structure and do not permit deformations, but also Channel does not support thrust or up lift pressure. It is recommended to consider that the minimum permissible speeds in the channel are limited to reduce sedimentation, to avoid the erosion of the walls or the bed. These speeds are: 2.49 m/s for the steel lining and 3.66 m/s for the concrete lining [

5) Fore bay

For a good decantation of water before entering the penstock, it is recommended to equip it with a 20 cm high concrete sill which retains the creeping particles, a screen which overcomes the threshold and stops the other particles, and a deflector which stops the floating debris. The depth of the fore bay varies from 1.50 to 2.50 m [

6) The penstock

The economic diameter in (m) is calculated using several methods, including the following equation:

D p = 2.69 × ( n p 2 × Q 2 × L P / H g ) 0.1875 (3)

where, n_{p} is Manning’s coefficient (= 0.009 − 0.011) for PVC in example), Q is turbine water flow rate (m^{3}/s), L_{p} is penstock length (m), H_{g} = gross head (m).

The minimum wall thickness recommended is:

t p = D p + 508 400 + 1.2 (4)

where, D_{p} is penstock diameter (mm), t_{p} = minimum penstock thickness (mm) [

7) Electromechanical equipment

The turbine and generator depend on the characteristics of the Fall River (net head and flow rates). The choice of the turbine is made as a function of the nominal flow rate Q_{n} and the net head H_{n} according to the Sulzer-Escher Wyss diagram [

8) The power house

The turbo-generator equipment and control elements are installed in power house. The dimension can be calculated using the following equations.

L = n ( 5 d + 2.5 ) + e (5)

l > 5 d + 2.5 (6)

2.5 > h > 2 (7)

where, L is the length (m), l is width (m), height h (m), n is the number of turbo-generator sets, d is the turbine outlet diameter (m), e is the length of the loading dock equivalent to the maximum right-of-way of one unit (m) [

9) The distribution network

Grid voltage: For low power and short distances. The experts recommend that, the distribution can be done directly in low voltage, 380/220 Volts with a frequency of 50 Hz.

To set up a MHPP, the costs of different element depend on environment constraints and vary from a site to another. Local materials are much recommended to reduce costs. A MHPP can usually operate during around 60% of time per year, and the operating costs represent 30% of the cash-flow [

1) The net present value (NPV)

Considering that the initial investment cost is I_{0}; discount rate is “a”; for years 1, 2, ⋯ , N, Cash-flows and Operating costs can be respectively represent by: CF_{1}, CF_{2}, ⋯ , CF_{N}_{,}; C_{1}, C_{2}, ⋯ , C_{N} ; the net present value (NPV) of the project is given by the following equation:

The project is profitable if NPV ≥ 0.

N P V = ∑ I = 1 N C F i − C i ( 1 + a ) i − I 0 (8)

2) The pay-back period

It is the time takes for the net present value to be zero.

After many measurements, the gross head obtained is 3, 4 m. At less than 1 km from the BAKASSA waterfall, that river has been gauged by a hydrological station belonging to the Hydrological Research Center of the Institute of Geological and Mining Research in 1985. We obtained the means daily discharges of one year from this institute [

This project will be more efficient for the feeding of a decentralized network. Then, considering the ^{3}/s. Then, P = 96,727, W ≈ 97 kW.

So the producible is: P_{E} = 97 × 8760 = 849,720 kWh ≈ 850 MWh.

The weir: Can be built stone and concrete beam. We recommended a trapezoidal type because of the shape of environment. Developers (those working in

engineering) will give more precision to the dam structure, fore bay and tailrace and power house dimensions in a timely manner.

The penstock: The length of the penstock can be between 10 to 15 m. then for the PVC material, D_{p} = 0.38 m. The diameter of the pipe of 0.40 m available on the market can be considered. Then the minimum thickness of penstock t_{p} = 2, 47 mm.

The turbine: According to the Sulzer-Escher Wyss diagram the corresponding turbine is Francis turbine. The nominal power of the turbine is 97 kW. Let’s consider a turbine of a nominal power of 100 kW.

The generator: A generator synchronous of frequency 50 Hz.

The technical characteristics of that MHPP projection, obtained from our study, are summarized in the following

According to the rules of safety, environmental and protection (Section 60: 1 of law n˚022/2011) [

1) Investment cost

A recent other assessment done in KEMKEN river gives lots of orientations [

2) Operating forecasts

In Cameroon, the prize of electricity in social range is 50 FCFA per kWh. In that locality, which is a rural area, the consumption of each household will be in social range. If the producible is equal to 850 MWh, as calculated previously, considering a MHPP’s utilization rate of 60% for our evaluation. Then, the annual Cash flow is CF_{i} = 25,491,600 FCFA.

3) Operating expenses

There are local blacksmiths whom were manufacturing micro turbines and some spare parts for MHPP in the West Region of Cameroon [

Sizes | Values |
---|---|

Site characteristics | |

Gross head | 4 m |

Mean flow rate | 9.72 m^{3}/s |

Minimum flow rate | 0.503 m^{3}/s |

Turbine | |

Type | Francis |

Rotation speed | 375 tr/min |

Net head | 4 m |

Nominal flow rate | 2.9 m3/s |

Nominal power | 100 kW |

Alternator | |

Type | Synchronal |

Tension | 380/220 V |

Frequency | 50 Hz |

Interconnection/distribution | |

Type of grid | Isolate |

Production of electricity | |

Producible | 850 MWh |

N˚ | Component of the MHPP | Total Price (FCFA) |
---|---|---|

1 | Civil engineering works: Total 1 = T1 | 43,125,062 |

2 | Metal construction: Total 2 = T2 | 1,700,000 |

3 | Turbo-generator group: Total 3 = T3 | 18,775,000 |

4 | Equipment for transmission and supply of electricity: Total 4 = T4 | 9,800,000 |

Others cost (administration and legal fees): Total 5 = T5 | 7,000,000 | |

Total = T1 + T2 + T3 + T4 + T5 | 80,400,062 | |

Contingences 10% = I | 8,040,006 | |

Grand Total | 88,440,068 |

1 Euro = 656 FCFA.

will be in low cost. In that case, let’s consider that the direct costs represent 30% of the cash-flow. The rate of inflation in Cameroon in 2016 was about 3%. The discount rate in Cameroon about is 12.5% [

4) Estimated profitability

a) Net present value NPV

Considering all these information about the operating cost, if the deadline of project is 20 years, then the NPV of that project is equal to: NPV = 29,441,430 FCFA.

Since the net present value is positive. So, the project is profitable with the hypothesis took in account.

b) The project payback period (PBP)

The calculation of the payback period is: PBP ≈ 8 years + 2 months.

It is important to say that 97 kW cannot solve all the electricity problem of that locality in long term. But actually, the population of BAKASSA mainly needs electricity for lighting, the charge of telephones, the supply of radios and televisions and some transformations of agricultural products (cassava, maize…). Let’s remind that, Lomé and Katmandou conferences in 1979 had presented the possibility to feed around one hundred households (in rural area) with 30 kW [

Solar energy for photovoltaic can also be studied and integrated gradually for a more effective coverage of the long term electricity demand. But at least for the next ten years after the implementation of that project, the population will not have any problem of electricity. The project is profitable but, the lack of funding can be a constraint.

The aim of this work was the technical and economic assessment of the project of MHPP in the waterfall of BAKASSA.

It emerges that the development of the BAKASSA MHPP will be an example of the contribution of renewable energies to the sustainable development of that locality. Considering the hydrological data of the river, the installed power is 97 kW for an isolate network. A Francis turbine is recommended for its equipment. The investment cost of this project is 88,440,068 FCFA. It is a profitable project and the maximum payback period is 9 years. The lack of funding in Cameroon can be the main constraint to the development of that MHPP.

Solar energy for photovoltaics can also be studied and integrated gradually for a more effective coverage of the long term electricity demand.

Kengne Signe, E.B., Hamandjoda, O., Nganhou, J. and Wegang, L. (2017) Technical and Economic Feasibility Studies of a Micro Hydropower Plant in Cameroon for a Sustainable Development. Journal of Power and Energy Engineering, 5, 64-73. https://doi.org/10.4236/jpee.2017.59006