Comparative study of electricity storage batteries for Solar Photovoltaic home systems

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The installed capacity of solar PV systems in Ghana was about 1MWp in the year 2003. This capacity is expected to increase significantly as the Strategic National Energy Plan (SNEP) seeks to enhance the role of stand-alone solar photovoltaic systems for off-grid rural communities that could not be electrified economically through grid extension. For such systems, it is now widely acknowledged that the high replacement cost and environmental impacts of chemical storage batteries constitute the key challenges to deployment and sustainability particularly in poor rural settings. On a life cycle basis, the storage batteries normally contribute about 40-45% of system cost. This thesis undertakes a comparative assessment of the technical, economic and environmental characteristics of the currently available electricity storage batteries that could be utilized in stand-alone solar PV systems. The batteries considered are Lead Acid, Nickel Cadmium, Nickel Metal Hydride and Lithium-Ion. The technical assessment was based on cycle-life, discharge and charging characteristics and charge retention. Life-cycle cost was used as the economic performance indicator, while human safety risks and ecological impacts formed the basis of the environmental assessment. The cost and other data for the batteries were obtained from literature (print and online) and survey of the retail market in Ghana. The life cycle cost of electricity storage based on online retail pricing data and 12% discount rate ranged from an average of US$0.03 cents for lead acid to US$0.15 cents /Wh for Lithium-Ion batteries. Price data obtained from local suppliers yielded storage costs of 0.17- 0.42GHp/Wh for deep-cycle solar batteries and 0.93-1.0GHp/Wh for shallow-cycle automotive batteries on a life cycle cost basis.
A thesis presented to the School of Graduate Studies, Kwame Nkrumah University of Science And Technology Kumasi, in partial fulfillment of the requirements for the Degree of Master of Science in Mechanical Engineering.