During the survey, lots of recognitions visits were done. The gross waterfall height is the altitude difference between the upstream and downstream water levels of the waterfall. A topographic datum can be measured and confirmed thanks to a map for high falls. The gross fall height was measured on this step using an electronic laser level with a suitable accuracy.

The demand for electrical power is based on the number of inhabitants and their activities. The population demand at the end of the maturity is determined by the following formula [5]:

D n = D m P 0 ( 1 + α ) n m (1)

D_n: Population demand in kW, n: Project duration, D_m: Needs per household in kW, P_o: current population, α: annual growth rate of the population and m: average number of persons per household.

For the evaluation, if data about discharge are not available, it will be possible to use a rainfall-runoff model. In case of Cameroon there is a rainfall-runoff model developed and proposed by local experts for equatorial region. This model was developed based on an artificial neural network method. It allows simulating some discharge on waterfall of one year from rainfall data [10]. Then, the next step is to plot the curve of the classified discharges [11]. After that, the power generated from hydraulic turbines could be determined using the following formula:

P = η ⋅ ρ ⋅ g ⋅ Q ⋅ H (2)

where P is installed power of plant in kW, H is net head of water in meter, Q is discharged in m³/s, g is gravity acceleration constant (=9.81 m/s²) and η is turbine efficiency (=80% - 90%) [5] [7].

The main technical components of MHP are: The Weir, The water intake, the feeder canal the fore bay, the penstock and power house dimensions [6]. There lots of software as RETSCREEN which can help to design these technical components. In case of Cameroon, new efficiency software called Mass_Hydro was developed with success. This software allows taking into account local advantages and constraints [12].

The choice of the turbine and generator 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 [4], as shown in the following Figure 4.

To set up a MHP, the costs of different elements depend on environment constraints and vary from a site to another. Local materials are much recommended to reduce costs. A MHP can usually operate around 60% to 80% of time per year, and the operating costs represent 30% of the cash-flow [5].

The net actual value (NAV) of the project is given by the following formula:

N A V = ∑ i = 1 N C F i − C i ( 1 + x ) i − I 0 (3)

where the initial investment cost is I₀; discount rate is “x”; for years 1, 2,…,N, Cash-flows and Operating costs can be respectively represented by: F₁, F₂, ∙∙∙, F_N; C₁, C₂, ∙∙∙, C_N; The net actual value (NAV) of the project is given by the following equation:

The project is profitable if NAV ≥ 0.

The gross fall height was measured on this step using an electronic laser level with a suitable accuracy. After many measurements, the gross head obtained is 2.9 m. Since that river does not have hydrological data, we have used a rainfall-runoff model proposed for equatorial area in Cameroon for the design of MHP [8]. Using average daily rainfall data of the year 2015 in the watershed concerned, collected from the meteorological office in the Kadey division of ministry of transport, we simulated average daily flows rate which allows plotting the flow duration curve (Figure 5).

The inhabitants sometimes use generators based on fossil fuel sources that not only, have higher production costs but are also highly polluting. Nearly, 150 houses were recorded. There are on average 5 peoples per household. The average annual rate of population growth in Cameroon was estimated at 3% at 2010 [13]. Considering the fact that it is a mining area, potentially the need for electricity is more important there than in other simple regions. Then, the power requirement is, according to equation (1) and integrated in our software, Bn = 162 kW. But the real demand in the village is more important globally. An interconnection to the national network allows us to look this demand more increased in a near future.

The local population must play a central role in the decisions to be taken in the

development and implementation of the MHP. A local committee to participate in the project and to manage the operation will be set up. As recommended in a recent study concerning the development of MHP in Cameroon [4], this committee will have skills such as: religious, agents of the municipality, farmers, breeders and fishermen, small traders and other representatives of the community according to cultural varieties... etc.

Our software proposed the flow rate of equipment equals 3.6 m³/s corresponding to the 70% of time equaled or exceeded per year in the flow duration curve and the installed power is 87 kW. This is done applying formula (2). P = 87 kW. So the producible or the annual Energy is:

P E = 87 × 8760 = 762 , 120   kWh

Characteristics of technical components for that MHP are proposed by our software Mass_hydro. The interface of results presented trough that software can be seen in the following screen [12] (Figure 6).

· The feeding canal: The section is 1.308 m² corresponding to a diameter ≈ 1.2 m;

· The fore bay: A section of fore bay proposed is 7.2 m²;

· The penstock: The length of the penstock can be around 10 m. Then for the PVC material, D_p = 0.842 m. The diameter of the pipe of 0.80 m available on the market can be considered. Then the minimum thickness of penstock t_p = 2.5 mm;

· Power house: The length is L = 14 m;

· The turbine and generator: According to the Sulzer-Escher Wyss diagram the corresponding turbine is Kaplan turbine. The nominal power of the turbine is 87 kW. A generator synchronous of frequency 50 Hz;

The technical characteristics of that MHP projection, obtained from our study, are summarized in the following (Table 1).

For the exploitation of the MHP of Koubou in Tikondi, that synoptic is proposed in Figure 7.

According to the law n˚ 022/2011 [14], for the MHP of Koubou (Tikondi), whose installed capacity is 87 kW, the legal regime is the authorization and the competent institution is the Electricity Sector Regulatory Board (ARSEL). Also, the generation especially from hydroelectric plants with an installed capacity equals or less than 5 MW, no special requirements for tender notices or advertisement shall be imposed. An environmental management plan is required as part of this project.

· Investment cost

A recent other assessment done in the other studies concerning the local blacksmith activity gives lots of orientations [5] [15]. The investment cost of MHP varies from a site to another. The following Table 2 shows the cost investment estimation of MHP of Koubou.

· Operating forecasts

In Cameroon, the prize of electricity in social range is 50 FCFA per kWh [5]. In that locality, which is a rural area, the consumption of each household will be in social range. The producible is equal to 762 MWh. Let’s consider 70% as the utilization rate of the MHP for our evaluation. Then, the annual Cash-flow is CF = 26,674,200 FCFA.

· Operating expenses

There are local blacksmiths who were manufacturing micro turbines and some spare parts for MHP in the West Region of Cameroon [15]. Then, maintenance will be at a low cost. In that case, let’s consider a running cost of 35% of the cash-flow. The rate of inflation in Cameroon in 2016 was about 3%. The discount rate in Cameroon is about 12.5% [7].

1 Euro = 656 FCFA.

· Estimated profitability

- Net present value NAV

Considering all the information about the operating cost, if the deadline of project is 20 years, then the NPV of that project is equal to: NAV = 32,685,938 FCFA.

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

- The project payback period (PBP)

The calculation of the payback period is: PBP ≈ 7 years + 3 months.