An outdoor PV lighting system will provide lighting for a walkway to be lighted

Question

An outdoor PV lighting system will provide lighting for a walkway to be lighted at dark. Suppose the longest winter night is 15 hours, 35 futures each containing a 6 watt LED is selected. A 12 volt system is considered and 3 days of storage are required. The winter peak sun is 4 hours Determine the PV module size and the battery requirement tor this system. Consider wiring efficiency 0.98, 0.9 battery charge discharge efficiency, 80% depth of charge for batteries and, 9 degradation factor for PVs due to temperature.

Explanation / Answer

Energy Consumed by the 35 fixtures each containing 6 W LED on for 15 hours a day is equal to

E = 6*15*35 = 3150 Wh /day in winter season;

Battery system required which should store energy sufficient for 3 days is

Eb = 3150 *3 = 9450 Wh

Considering loss and dicharge percentage EbT = 9450/(0.98*0.9*0.8) = 13392.85 Wh

Ampere hour rating of battery is Ah = EbT/Vb = 13392.85/12 = 1116.07 Ah battery system is required.

Solar Photovoltaic panels required is considering Watt rating of each panel of 200 W.

Given degradation factor for PVs is 0.9 , Power delivered per each panel at instant of peak sun is

P = 200*0.9 = 180 W

Given each winter day has peak sun for 4 hours.

Each PV will generate energy of Epv = 180*4 = 720 Wh.

Required energy to be stored is EbT = 13392.85 Wh

No,of solar panels required is N = EbT/Epv = 13392.85/720 = 18.6 = 19 Photovoltaic panels.

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