Sustainable water pumping using hybrid renewable energy sources

Namibia University of Science and Technology (NUST), Windhoek, Namibia

Abstract

The water-energy nexus indicates today's intricate interdependence of water and energy and holds the key to human well-being and national development. It is particularly significant in countries with arid climatic conditions, such as is the case with Namibia, where water scarcity is coupled with a huge gap between electricity supply and demand. In this paper, we assessed the viability of using Hybrid Renewable Energy Systems (HRES) to sustainably power borehole schemes in Namibia. As a case study, grid-connected photovoltaic (PV), onshore wind, and battery storage technologies were used to meet the electric energy demands at the Berg Aukas borehole scheme, which consumes an average of 7,820 kWh/day with a peak demand of 1,162.5 kW. HOMER Grid software was used to model the utility grid tariff and net metering structures and determine optimal system configurations. For the sensitivity analysis, the discount rate (interest rate) was used as a sensitivity variable. The results show that at Namibia's average discount rate of 6.7%, the proposed optimal HRES had a levelized cost of energy (LCOE) and payback period of USD 0.0929 /kWh and 4.17 years, respectively. At a discount rate of 10%, the optimal HRES had an LCOE of USD 0.105 /kWh with a projected payback period of 3.77 years. At a discount rate of 13%, the LCOE was USD 0.115 /kWh with a payback period of 3.43 years. For all the modelled instances, the proposed systems for the borehole scheme were found to be economically feasible as each had a LCOE that was lower than that of the utility company (CENORED), i.e., USD 0.283 /kWh.