Page 99 - A Comprehensive Guide to Solar Energy Systems

94 A COMPrEHENSIVE GUIdE TO SOlAr ENErGy SySTEMS

FIGURE 5.9 Photographs of the build in Mutende, Lulamba, Zambia 12 months after installation, demonstrating the
problem dust can cause on PV systems in challenging climates. Dust accumulation on PV modules (left) and batteries
and inverters, even in enclosed spaces (right), is a major problem.
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65 kW h month ). Battery technology is developing rapidly; here we will concentrate on
commercially available technologies which could be put in place immediately.
Operation conditions have a strong influence on battery performance and lifetime.
South Africa, and SSA as a whole, is a less than ideal environment for batteries due to
high ambient temperature variations, both day-to-day and across the year, and dust
(Fig. 5.9). To mitigate this, we propose that batteries be buried at a depth of ∼1.5 m, where
we expect the insulation and thermal lag from soil cover to limit temperature variations
to an acceptable ∼12–25°C, thus removing the need for a cooling fan, which will almost
certainly be required for most land-surface mounted batteries [34]. We also advocate
periodic cleaning of PV panels to ensure power conversion efficiencies are maintained.
To give some idea of what is required in an off-grid solar home system for rural Africa,
we have modeled these battery and PV requirements using the Photovoltaic Geographical
Information System [35] with durban as an example location, and estimated the cost of
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a system capable of generating a minimum of 50 kW h month . A 600 Wp photovoltaic
system (optimized in terms of orientation and angle) coupled with a 12 V, 250 A h (250
amp-hour) lead-acid battery, with a minimum state of charge cut-off limit of 40% and
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a daily power consumption of 2 kW h, would yield an average of 56.5 kW h month
and 678 kW h year . We have used a value of r1.3928 (kW h) [€0.096 (kW h) ] as the
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consumer cost of electricity in durban, giving a yearly value of €65.09 for the 678 kW h. To
provide an indicative cost of this system, we have used a price of €0.34 W for a multi-Si
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