E.3 Component Selection

In order to be able to build prototypes, a certain system setup must be chosen and each system component must be dimensioned. The following section addresses the selection of an adequate battery and PV type, solar cell incorporation, and charge controller options.

E.3.1 Battery Unit

First, typical battery parameters such as energy density (Wh/kg and Wh/cm3), cycle life, charging time, cell voltage, discharge rate, operation temperature, and so on were evaluated. This narrowed the possible choices down to the following battery types: nickel–cadmium (NiCd), nickel metal hydride (NiMH), lithium-ion (Li-ion), sealed lead–acid (SLA), and rechargeable alkaline manganese (RAM).

Each technology was assessed on five aspects: cost, efficiency, design, durability, and environmental aspects. The performance of specific battery technologies was categorized as very bad (−−), bad (−), good (+), and very good (++) in the SPM product case (Figure E.3.1). Categorization took into account information from handbooks as well as the particular expertise of the involved PV and industrial product designs experts. From this, only two types of batteries were considered further, the NiMH and the Li-ion, as these did not have a very negative score in any category (NiMH) or fell short only on cost and durability grounds (Li-ion). Finally, the choice was made for NiMH batteries for various reasons. NiMH batteries are available in different shapes and capacities, and voltages are multiples ...

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