Assesment of Solar Photovoltaic Water Pumping of Wasa Tube Wells for Quetta Valley Aquifer

Abstract

The unplanned use of ground water resources has led to the deterioration of water quality and quantity in Quetta valley. Water shortage in the region was further aggravated by the drought that hit the area during 1998-2004, thereby forcing people to migrate from rural to urban areas. Influx of refugees caused rapid increase in population of Quetta valley that rose from 0.26 million in 1975 to 2.2 million in 2017. Due to increase in urban water demand and agricultural activities, the aquifer of Quetta Valley is under tremendous stress and water table is declining at an alarming rate. The Water and Sanitation Agency of Quetta (WASA) is monitoring groundwater levels since 1989. There are 423 tube wells in operation installed by WASA in addition to PHE, Irrigation and MES, which covers 60 % of the city’s water demand. This study aimed to assess the impacts of WASA tube wells on total discharge & water table in the valley aquifer and conducted cost benefit analysis of running these wells on SPVWP (solar photovoltaic water pumping) system. Study revealed that Quetta is geographically divided in two zones, Zarghoon and Chiltan. Water table decline rate in the Zarghoon zone was observed 2 to 5 m/yr and discharge have been reduced from 4 to 19 %, while the water table decline rate in the Chiltan zone was observed between 2 to 8 m/year and discharge have been reduced from 5 to 20 %. Quetta receives the highest average solar radiation (data from RETScreen), due to which solar photovoltaic pumping is potentially efficient and economical. The solar photovoltaic viability and cost benefit (C:B) analysis for these tube wells has been carried out using RETScreen software. Using data of these tube wells C:B ratio for different pumps have been analyzed and it was noted that for five different pumps with power capacities of 5.5 KW, 11 KW. 15 KW, 18.5 KW, 30 KW, The C:B is 2.05, 3.52, 2.92, 2.52 and 2.97 respectively, while their payback period is 3 – 5 years. Based on 30-tube wells data analysis, it is recommended that two pumps having capacities of 18.5 KW to be installed for shallow depth and 30 KW for deeper depth depending on their discharge.