Water Supply in Rwanda. Use of photovoltaic systems for irrigation

Abstract

The current energy situation in the world where most of the energy needed is generated from non-renewable sources such as fossil fuels is no longer sustainable. During few years, nonrenewable sources have become an interesting solution to provide energy to areas with small needs of electricity, rather than using non-renewable sources. Therefore, this project has pursued to implement photovoltaics panels to supply energy in a rural region in central Africa, contributing to the development of the area and proving that this technology is viable to pump water for irrigation instead of the conventional electric grid. A rural area between Kidogo Lake and Rilima town, in Bugesera district of Rwanda, has been chosen as target. This analysis has focused on typical plantations of the country, being the main crops banana, cassava and maize, each one with very similar maximum water needs; 71 m3/ha_day, 70 m3/ha_day and 67 m3/ha_day, respectively. The eastern province of Rwanda is formed by seven districts. A preliminary study was developed in order to find the target area in terms of weather conditions, high temperature and low rainfall. Therefore, parameters such as precipitation, solar irradiance and evapotranspiration, among others, have been crucial for deciding the driest zone. Indeed, the Bugesera district is an ideal candidate due to the reception of a large amount of solar irradiation, with an annual average of 5,28 kWh/m2_day. In order to dimension the photovoltaic and water-pumping system, a preliminary research including a large amount of background was required to determine the best structure. Indeed, knowing the water demand, we decided the water should be pumped up into a tank, letting it irrigate the field via gravitation only. A sample irrigation layout was then designed to ensure that with a number of pipes, water was conveyed to every plant. The use of a tank not only for storing water, but also as a source of system’s pressure lead us to calculate the minimum distance from the ground to the bottom. The height obtained of 2,2 meters provides the necessary pressure to distribute water and irrigate the field. With the energy needed for the water supply, a photovoltaic pumping system, consisting of a PV generator, inverter and pump, was selected. Our main findings was that the photovoltaic system must have a rated power of 1,73 kW in order to guarantee proper functioning. For the photovoltaic system, six STP290 - 24/Vd solar modules from Suntech were chosen, for the water pumping system, a B50 Electric Drive from the company BBA Pumps. Moreover, and regarding the inverter system, model Galvo 1.5-1 from company Fronius with a nominal output power capacity of 1.500 watts was chosen.