Towards the Optimal Sizing of Solar-Powered Pump-Pipe-Storage Systems
Abstract
In this paper, a method for optimal sizing and performance prediction of a solar pump-pipe-storage system is proposed. The solar-pumping-system components namely, the pump; solar photovoltaic array; pumping mains and the water storage are sized in an integrated approach. The method develops a flow-power function, which comprehensively takes into account the time-step variation of solar irradiance and its effect on the pump system flow-rate and total dynamic head. The flow-power function expresses the flow output of the solar pumping system as a function of the time-step variation of the photovoltaic array power output, for a given pump and pipe size. Especially for long pumping mains, the PV array power required to deliver a specified daily volume of water reduces significantly as the pumping main pipe diameter is increased. Depending on the relative specific costs of PV array and pipe, an economically optimum combination of these two system components, which delivers the desired daily volume of water at the least cost of pumping, can be arrived at. Applying a time-step balance of the hourly pump flow output with the hourly water demand, also enables a more exact estimation of the required balancing storage, through the mass-balance-curve approach. The method proves to be a significant improvement to the traditional simplified approach of sizing solar pumping systems. It can result in significantly reduced unit cost of pumping and reduced cost of storage. In the present case study, the required PV array power was reduced by 20% and the required water storage capacity reduced by 50% when compared to their respective values prescribed by the traditional sizing method. Keywords:- solar pumping system; optimal sizing; dynamic variation; flow-power function; least cost of pumping