With the decline in price of the photovoltaic’s (PVs) and the increase in greenhouse gases due to the use of fossil fuels the use of photovoltaic as a power source for water pumping is becoming the more attractive solution instead of using diesel/gasoline generators. This paper deal with the optimal sizing of the water pumping system instead of gasoline generator for the irrigation of the onion farms in Cameroon it also discusses a share of greenhouse gas emitted from the cultivation of onions. The study uses the data generated from a survey carried out between 2014 and 2015 of consumption gasoline/lubrificant and water production from generators on the duration of the culture in the main production Area ''10°35’N, 14°18’E''. The results of the analysis indicates that the Life Cycle Cost, 'LCC' of the photovoltaic water pumping system depends on its capital costs (67 % of LCC) while the LCC of gasoline pumping system depends largely on recurring costs (79 % of LCC). The CO2 emissions depend not only on the type of land but on the stage of plant growth. This research work also demonstrates that using the PV water pumping system can improve living conditions of farmers.