Abstract

Solar power recently has been found as environmentally friendly if used where electrical energy is required. While many researchers have been conducted continuously, the generation of electrical energy has been achieved by using Photovoltaic (PV) modular technology. Today’s solar system has been introduced in a number of systems including, Solar Home System (SHS), industrial, and agricultural activities, but within agribusiness there are some issues which are not yet solved due to the cost of buying a solar system for related activities. By reviewing most of nowadays agribusiness especially crop irrigation, solar system, number of visits, research, designing and questioning have been done to be aware of what is missing to make the irrigation solar system more effective. While the number of people in the case study was answering different question from questionnaires, deep research has led us to be aware of designing a pump by mean of SOLIDWORKS with power ranging between 450W-500W for irrigating crops under 1ha. The number of calculations for sizing a pump has been done to generate a flow rate of 5.2l/s in order to be able for irrigating crops under 1ha. This approach is intended to make a solar system more effective in irrigation system by introducing some features in existing solar pumping system at relatively low cost and maximum efficient. The results show that the designed system leads to Higher efficient compared to the pumps in current use and thus will make it to be useful and profitable at large scale in case the implementation took place. Therefore, practically efficiency will be increased in terms of shorter time consumption during the irrigation process, pump availability and cost optimization, use of solar energy as a power source and output discharge.

1. Introduction

Irrigation is the method in which water is supplied to plants at regular intervals for agriculture. It is used to assist in the growing of agricultural crops, maintenance of landscapes, and re-vegetation of distributed soil in dry areas and during the period of inadequate rainfall ¹. Low production of agriculture in the country of Rwanda is one of the major problems due to its geographical location and seasonal change. Worldwide almost 90% of the water consumption is used for irrigation purpose. With a rapidly increasing population, it can be questioned whether enough water will be available to increase the food production accordingly. For this reason, the current distribution of irrigated land was modelled first. As there was not enough information available on what crops are grown under irrigated conditions where and when, the cropping patterns and the growing seasons were also simulated by the model, based on soil suitability and climate. This shows that to optimize crop production there are most of studies undertaken with the aim of introducing new and improving existing methodology based on irrigation processes ².

Motor pump is commonly used diesel to power generators in irrigation process. While these systems can provide power where needed. There are some significant drawbacks, including: Fuel must be transported to the generator’s location, which may be quite a distance over some challenging roads and landscape. Their noise and fumes can disturb livestock, Fuel costs add up and spills can contaminate the land.

Generators require a significant amount of maintenance and, like all mechanical systems; they break down and need replacement parts that are not always available. For many agricultural needs, the alternative is solar energy. Modern, well-designed, and simple to maintain. Solar systems can provide the energy that is needed where it is needed, and when it is needed. Numbers of systems that have been tested and proven around the world are cost-effective and reliable, and they are already raising levels of agricultural productivity worldwide ³. However, most of the solar system has been modelled for large scale farmers at relatively high cost, the agriculture production would increase if the systems are modeled for both small and large scale farmers as smaller scale farmers are the ones who use traditional tools for irrigating their crops including a watering can, buckets, diesel motor pump which are not effective to crop growth. From research conducted we are aiming to model solar pumping system which will be available at affordable cost, reliable, portable and efficient for both small and large-scale farmers.

Nowadays, Rwanda has a problem in agriculture due to seasonal period and regions where in some areas they face a long period of the summer season and became challenge in the agricultural field because it results into poor productivity. Consequently, these affect people’s wealth, health, country, economic and environmental degradation. With available irrigation tools and system, including: Watering with bucket, Vegetable irrigation by watering can, Irrigation by use of motor pump, Irrigation with solar panels, pumps, Irrigation with Photovoltaic water pumping, Brick masonry lining of irrigation, Canal erosion at motorized pump, it has been found that some of these methods are not reliable to crops however, some of available ones which would lead to the increase in agricultural production efficiencies are relatively expensive, fixed system, and difficult to maintain. This paper is aimed to design a mechanical pump for irrigation, which has adjustable pipe, end pipe cover of varying mesh size, motor and shaft powered by Solar energy, metal fans for water pressurization, water container with inlet at the top and the outlet at the bottom so that the desired output will be optimized.

2. Material and Methods

Having Kinyinya swamp which was the case study in this project, collected data from farmers who do agriculture in this region located in GASABO district had indicated local methods which are used in their irrigation, their difficulties, suggestions and recommendation. Consequently, their influences had played a great role in the project by leading feasible and applicable design system for irrigation. The important data which are applied in the project design were collected as follows: Interview with farmers who use buckets, watering can and diesel motor pump at KINYINYA swamp the site, GASABO district., Interview with local dealers of diesel motor pumps, plumbing equipment, solar cells to get information on material selection and observation of irrigation system which employs a diesel motor pump on different areas.

The data which detail weather conditions of Kinyinya have been founded on OpenStreetMap project. The city of Kinyinya has a tropical climate. In winter, there is much less rainfall in Kinyinya than in summer. The climate here is classified as Aw by the Köppen-Geiger system. In Kinyinya, the average annual temperature is 20.6°C. About 949 mm of precipitation falls annually. The least amount of rainfall occurs in July. The average in this month is 8 mm. With an average of 160 mm, the most precipitation falls in April. The variation in the precipitation between the driest and wettest months is 152 mm. During the year, the average temperatures vary by 1.1 °C. ⁴

A portable sprinkler irrigation system is a type of irrigation, which sprays water to the crops like rainfall. However, most of sprinkler irrigation system available in nowadays is likely to be fixed systems, the system to be designed is a portable sprinkler irrigation system which is much likely to the other closed pipe low pressure systems in its layout, hydraulic design and operations. The system is composed by pumping unit, pipes for water suction and delivery, couplers for joint connection in between pipes and pumping unit, valves and pressure gauge to control the water pressure, sprinkler/spray nozzle gun to spray suitable amount of water directly to the crops, storage tank or well accordingly for water storage ⁸.

This paper is aimed to design a system which will be able to produce total daily water requirement of 56300L in 3 hours. To avoid water loss during the day time, the system should be used to store water with appropriate tank according to the availability of farmers and field location even if we recommend storing water during the daytime when not irrigating. The Design of Mechanical Pump for Irrigation Power-Driven by Solar Energy Technology was carried out by considering the following considerations: Less and simple maintenance, Ease of installation, Ease of use and safety, Portability, Shape, size and efficiency adaptability which meet the demand, Longer life expectation and reliability, Use of solar energy and Environment friendly. Pump sizing involves matching the flow and pressure rating of a pump with the flow rate and pressure required for the process. Since the pump in case of this project will be used to pump cold water for crop irrigation, the flow velocity at Inlet piping should be in between 0.7 to 1.5 m/s, whereas that in the discharge piping is 1.0 to 2.0 m/s ⁵. The pump sizing in this project is considered to provide the efficiency of 90% and total daily water requirement of 5.2L/s and from the above parameters, the task is to find a pump operating pressure defined as total dynamic head (TDH) by considering both net positive suction head available (NPSHa) and power required to drive the pump (P) ⁶.

Within an interview with former employing their agricultural activities in the swamp of Kinyinya located in Gasabo district, farmers from which their data played a great role in the project have been collected from those who employ agriculture as company, cooperatives and individual farmers. To those who work as company and cooperatives sometimes use diesel motor pump costing in between 400,000 to 1,500,000rwf to irrigate one hectare in 3 hours, which cost them about 5,845rwf for daily fuel (4l) and another time by use of buckets and watering which cost them 24,000rwf to pay 24 manpower to irrigate one hectare. On the other hand, the farmer who works as an individual has suggested the price of 200, 000rwf for a pump which would help them due to the difficulties they face when employing watering can and bucket to irrigate crops. And for them, one farmer can irrigate one are in between 1 to 3 hours.

The Figure 3 above is showing the estimation of efficiency when using a bucket (blue line), watering can (orange line) and diesel motor pump (gray line) to irrigate crops for individual farmers, cooperatives and company and here production efficient increase depending on the tool used to irrigate crops. Maximum when using a pump and minimum when using a watering bucket. By considering life expectance of solar powered systems, the system has shown that in case farmers continue to employ a diesel motor pump it should cost them over 175,350rwf monthly which is more expensive compared to the solar system cost in case we consider a number of years even if most of solar system require high initial cost compared to diesel motor pump initial cost. As a conclusion, with solar insulation of 5.08 sun peak hour we are expecting to come up with solar system which can make an effective balance considering the hearings from farmers and the pump should meet the System should be able to supply water requirements in the months of June and July, Supply irrigation water need of 5.63m³ per day.

4. Design of System Components

There exists many software’s use in design and modelling, but SOLIDWORKS was selected due to its availability and the ease of use and it is compatible with most machines which use windows and its accessibility. SOLIDWORKS can produce a solid model of the product, its engineering drawings with different views. It is used to analyze the effect of load that should be applied to the material to decide whether the design should be repeated or improved. It is also used to optimize the design and makes it fulfill the requirements.

The pump is a device which converts a mechanical energy into hydraulic energy. A solar powered pump is a pump powered by solar energy and thus a solar powered irrigation pump can be of one or more solar panels also known as solar modules or solar plates. Initially, pump receives mechanical energy from prime mover which can be electrically motor or IC-engine. Considering the pumps which use electric motor the mechanical action of the shaft driven by this motor will help the pump to create a partial vacuum at the inlet. This causes the atmospheric pressure to force the fluid into the inlet of the pump which is then pushed to the desired location (outlet line) due to the internal design of the pump.

Conclusion

The choice of designing a solar powered pumping system used in irrigation is influenced by a number of factors, including: solar energy in Rwanda is abundant, free, and environmentally friendly. In order to meet the amount of water required to irrigate one hectare of crops in Kinyinya swamp, Gasabo district, the research project has found out that the solar system which can produce minimum power of 450W to power surface pump operating against the total head of 11.06m is required to make effective irrigation system in Kinyinya swamp with no more use of buckets, watering can or diesel motor pump. Looking at the technology of electrical power generation by mean of solar photovoltaic modules, we have decided to model the pump which could make effective change in society by ensuring an environment sustainably, country economics and agriculture production maximization for feeding people around the world. By considering life expectance of PV system and the ability of a surface pump in terms of use, maintenance and initial cost.

References