In order to properly conduct our research, we adopted the following methodology:

Site Visit

The visit is organized to reconnaissance the site and collect data for the design of an irrigation system and the choice of crops on the perimeter.

Field Work

Technical Works

This is the technical part of the study. It involves:

Data processing consisted of exploiting the data collected. This data is processed with appropriate software.

There already exists a topo survey of the perimeter carried out by the Irhazer-Tamesna project [7] and which we have used.

The site is characterized by clay-loamy-sandy soil, which presents cracks with a fine texture.

The study area has a semi-desert climate, and the recorded temperatures are characterized by very strong annual and daily variations. Two (2) periods of maximum temperatures were observed: one from April to June and the other from September to October. The average minimum temperature is recorded in December and January, and the monthly average temperature ranges from 17˚C to 37˚C. ( Table 1 )

The average daily wind speed in the area is around 3 m/s. Higher speeds are reached in January-February and December but never reach 4 m/s. It is in September that the weakest winds are observed, with an average of 2.4 m/s throughout the portion that has been monitored.

The monthly averages of the daily speed of the Agadez stations are presented in Table 2 .

Located in the desert part of Niger, the Agadez region, more particularly the study area, records fairly low precipitation, very poorly distributed in time and space. ( Figure 1 )

The first very light precipitation appears in April in our study area.

The rainy season mainly occurs between June and August, and the majority of rains are recorded during these three (3) month periods.

The site pumping station is a mini borehole with a very powerful Grundfos pump of model esp 60 - 17 of 30 kW, ensuring water drainage connected to a solar pumping system of 54.4 KWC and a 66 KVA emergency generator set, J66 model.

We are sizing the solar-powered photovoltaic pumping system for water supply for irrigation of the future irrigated area.

The following data characterizes the system:

The total head (HMT) of a pump is the pressure difference in the water column meters between the suction and discharge ports. It is given by:

HMT = Hg + Pc

Hg: geometric height between the pumped water table (dynamic level) and the use plan (see Figure 3 ).

For its determination, we used the following formula:

Hg = A + B + C

Topographic studies made it possible to determine A, B, and thus, we have: A = 3.20 m; B = 11.4 m and C = 5.60 m.

The diameter of the suction pipe must be calculated so that the pressure losses correspond to a maximum of 10% of the total geometric height.

HMT = A + B + C + Pc = 3.20 m + 11.4 m + 5.60 m + 2 m = 22.20 m

Ec = CH × Q × HMT/Rp

where Ec (electrical energy) is usually expressed in kWh.

Q: Flow [m³/day].

HMT is the total head.

CH is the hydraulic constant depending on terrestrial gravity and water density:

CH = g∙δ = 9.81.103/3600 = 2.725 (Kg∙s∙h/m²) and Rp the efficiency of the pump set (generally from 30% to 45%).

Pumping group efficiency: Motor efficiency x pump efficiency.

Engine efficiency from 75% to 85%, we will take the average which is 80%.

Pump efficiency from 45% to 65%, here too we will take the average of 55%.

Either Rp = 0.8 × 0.55 = 0.44 or 44%

$Ec=CH\times Q\times HMT/Rp=2.725\times 1400\times 22.20/0.44=192484\text{Wh}/\text{j}$

where Ec or Eelec (electrical energy).

The energy supplied by the solar panels in one day must be equal to the daily energy consumed by the pump

$\underset{\text{Wh}/\text{j}}{Eelec}=\underset{\text{W}}{Pc}\times \underset{\text{h}/\text{j}}{EI}\times K$

EI: Irradiation here equal to 5.8.

K: Efficiency of the power system (solar panels, heat, dust, line voltage drop, etc.) from 0.7 to 0.9.

We will take K = 0.8.

$Pc=Eelec/EI\times K=192484/5.8\times 0.8=41482\text{W}$

41482/320 = 129.63, so the need will be 130 panels.

Pump choice

We choose the pump according to the flow rate and the total head, and we calculate the hourly flow rate using the following formula: Qh = Q m³/h.

With: h: number of hours of maximum sunshine (Approximately 7 hours). Q: desired flow rate (1400 m³/day). This gives an hourly flow of approximately 140 m³/h. Knowing that the total head is 22.20 m, then we chose the 30 kW submersible pump ( Table 3 ).

For pumps with direct current motors, the electronic converter makes it possible to constantly obtain the best operating point of the pump (maximum flow rate) despite variations in sunlight. In most cases, it also makes it possible to manage the pump’s operation in the event of a lack of water in the borehole or well and maximize the filling of the water retention tank. The characteristics of the latter are summarized in Table 4 .

The pump requires at least twice its power to start. For 30 kW, the power required for the generator will be 60 kW. The 66 kW generator which is on the perimeter is well indicated ( Table 5 ).

We carried out flow measurements in the field at the borehole meter.

The measurements are obtained as follows:

On seven occasions (dry season and rainy season), readings were taken at the meter for an hour.

Measurements taken during the dry season

Measurements carried out during the rainy season

From the measurements taken, we note a very large drop in flow which explains that during the rainy season.

The meteorological data recorded at the study site makes it possible to set the daily flow at 1070 m³/h. Thus, we obtain the flow rate of the borehole by taking the ratio of the daily flow rate to the maximum number of hours of irrigation per day 1070/10 = 107 m³/h rounded to 110 m³/h.

In conclusion, from the different results obtained and retained, the characteristics of the drilling are summarized in Table 6 .

The fact that solar energy is available right at the point of use frees the farmer from the problems of fuel supply, or the existence of easily accessible electricity transmission lines. Currently, the main obstacles hindering the use of solar pumps on a larger scale are their high cost and the too recent nature of this technology. The development of a sufficiently reliable and reasonably expensive solar pump—which would be very likely within a few years—could give a boost to agriculture in the Third World. Solar pumping systems allow water to be supplied from a source at any location, even if no energy source is present on site. The source can be a pond, a well, a borehole, a river, a stream, etc.

In my country, the solar pumping system is actually calculated at 44% and is very close to modern standards. The ineffectiveness of this system is observed during the rainy season when there is very little sunshine. The solutions envisaged are of two (2) types: we have a 5 m³ pool to store and use on days of low radiation. A thermal device is also used during low sunlight.

The sizing will be done from the irrigation terminals to the supply pipe.

The irrigation terminals or supply terminals are sized so as to deliver the flow rates they need to the plots. These are the main PVC pipes attached to the secondary pipes. Each irrigation terminal supplies two (2) plots. In this case, the design flow rate of a supply terminal is double a hand of water (10 l/s).

The pipe diameter is therefore obtained using the following formula:

$D\left(\text{m}\right)=2\sqrt{Q/\pi \times V}$

$V=\left(4\times Q\right)/\left(D\times D\times \pi \right)$

D: pipe diameter;

Q: flow rate in m³/s;

V: flow speed in the pipe in m/s Speed condition: 1 m/s ≤ V ≤ 3 m/s.

The speed in all tubes must be such that:

- For plastic tubes V ≤ 1.7 m/s;

- For others (steel, aluminum, cast iron, etc.) V tubes ≤ 2 m/s.

The secondary pipes are sized in the same way as the irrigation terminals. However, a secondary pipe simultaneously supplies six (06) irrigation terminals. Thus, the design flow of a secondary pipe is double that of an irrigation terminal, that is to say, 30 l/s.

As for the main pipe, it supplies the secondary pipes in turn. Since the flow rate passed through the main pipe is the same as that at the secondary pipe, the dimensions of these two pipes remain identical. The same goes for the supply pipes which feed the main pipe.

In conclusion, the secondary, main, and supply pipes are sized at the same flow rate. Therefore, their diameters are the same, but their speeds and diameters are different ( Table 7 ).

To evaluate the pressure losses in the pipes, it is technically accepted to consider the hydraulically most unfavorable pipes. However, in our case, the supply terminals, the secondary pipes, the primary pipes and the supply pipes have the same respective lengths; we will be interested in the longest circuit of the network to evaluate the load losses

The linear pressure losses inside the pipes are calculated by the following Colbrook, Calmon and Lechap formula:

$\Delta H_{rampe}=\frac{a{Q}^{n}L}{D^m}\times F$

Q: flow rate in m3/s is the flow rate of the ramp considered;

D: cataloged internal diameter of the ramp (m);

L: length of the pipe in m;

a, n and m are the coefficients according to Calmont-Lechapt.

a = 0.916 * 10⁻³, m = 1.78 and n = 4.78 for PVC 50 ≤ D (mm) ≤ 200.

F: reduction coefficient due to the distribution of water along the pipe F is a function of the number of distributors or outlets on the pipe (N).

if N = 0, F = 1, N = 2, F = 0.639 and if N > 100, F = 0.35.

This formula, which takes into account the number of openings, tends to reduce loss loads when the number of openings is large.

Here, we have 6 outlets, so F = 0.435 for the secondary pipes

The pressure losses at the pipe singularities are estimated at 10% of their linear pressure losses. The total loss is the sum of linear pressure losses and singular pressure losses ( Table 8 ).

BA: Power terminal; CS: Secondary pipes; CP: Primary pipes; CA: Feed pipes.

The Californian network minimizes water losses, and there are no measurements or calculations to support this assertion in the study. We could not include data quantifying the reduction in evaporation and infiltration because these data are very negligible.

Table 9 shows us the cost of development of 12ha in Californian network with solar pumping station

171,568,473FCFA = 272,794 USD

If we take a gravity irrigation system, the development of 12 ha with electricity supply, its cost is 12,000,000FCFA/haX12ha = 144,000,000 FCFA. So less expensive than the Californian system with power supply.

For the first system, apart from maintenance, there are maintenance costs, electricity and fuel costs for the pumping station. Meanwhile, for the device, maintenance costs are minimal.