Minimum cost solution of photovoltaic–diesel–battery hybrid power systems for remote consumers

Abstract

Hybrid systems present a new dimension to the time correlation of intermittent renewable energy sources. The paper considers the daily energy consumption variations for winter and summer weekdays and weekends in order to compare the corresponding fuel costs and evaluate the operational efficiency of the hybrid system for a 24-h period. Previous studies have assumed a fixed load and uniform daily operational cost. A load following diesel dispatch strategy is employed in this work and the fuel costs and energy flows are analysed. The results show that the photovoltaic-diesel-battery model achieves 73% and 77% fuel savings in winter and 80.5% and 82% fuel savings in summer for days considered when compared to the case where the diesel generator satisfies the load on its own. The fuel costs obtained during both winter and summer seasons for weekdays and weekends show substantial variations which should not be neglected if accurate operation costs are to be achieved. The results indicate that the developed model can achieve a more practical estimate of the fuel costs reflecting variations of power consumption behavior patterns for any given system. Keywords: optimisation algorithm, hybrid system, control strategy, economic dispatch, energy efficiency, operation efficiency * Corresponding author. Tel.: +2712 420 2068.Email address: henerica.tazvinga@up.ac.za. (Henerica Tazvinga)Preprint submitted to Solar Energy August 8, 2013Nomenclature P 1 (t) control variable representing energy flow from the diesel generator to the load at any hour (kW ) P 2 (t) control variable representing energy flow from the PV array to the load at any hour (kW ) P 3 (t) control variable representing energy flow from the PV array to battery at any hour (kW ) P 4 (t) control variable representing energy flow from the battery to the load at any hour (kW ) P L (t) control variable representing the load at any hour (kW ) T A the ambient temperature ( 0 C) NT standard and nominal cell operating temperature conditions A c the PV array area (m 2 ) P pv the hourly energy output from a PV generator of a given array area (kW h/m 2 ) η R the PV generator efficiency at reference temperaturethe ratio of beam irradiance incident on a tilted plane to that incident on horizontal plane SOC the state of charge B C (t) the state of charge of the battery bank at any hour B C (t − 1) the state of charge of the battery bank at the previous hour η C the battery charging efficiency η D the battery discharging efficiency B C (0) the initial state of charge of the battery B min C the minimum allowable battery bank capacity (kW h) B max C maximum allowable battery bank capacity (kW h) DOD the depth of discharge a, b fuel cost coefficients P DG generator rated power output (kV A) 2

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