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Wireless+Networking+in+the+Developing+World_Part17

Wireless+Networking+in+the+Developing+World_Part17 -...

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The solar system has been designed to provide 12 and 24 V DC output in order to match the input voltage of all low power servers and workstations for NOC infrastructure and training classrooms. The solar panels used are Suntech STP080S-12/Bb-1 with the following speci fi cations: Open-circuit Voltage (V OC ): 21.6 V Optimum operating voltage (V MP ): 17.2 V Short-circuit current (I SC ): 5 A Optimum operating current (I MP ): 4.65 A Maximum power at STC (P MAX ): 80 W (Peak) The minimum 6 KWh/day that feeds the NOC is used to power the following equipment: Device Hours/Day Units Power (W) Wh Access points 24 3 15 1080 Low power servers 24 4 10 960 LCD screens 2 4 20 160 Laptops 10 2 75 1500 Lamps 8 4 15 480 VSAT modem 24 1 60 1440 Total 5620 The power consumption for servers and LCD screens is based on Inveneo's Low Power Computing Station, http://www.inveneo.org/?q=Computingstation . The total estimated power consumption of the NOC is 5.6 kWh/day which is less than the daily power generated from the solar panels in the worst month. Chapter 11: Case Studies 311
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Figure 11.2: The NOC is built by locally made laterite brick stones, produced and laid by youths in Kafanchan. Network Operating Center (NOC) A new Network Operating Center was established to host the power backup sys- tem and server room facilities. The NOC was designed to provide a place safe from dust, with good cooling capabilities for the batteries and the inverters. The NOC uses natural methods and is made from locally available materials. The building is comprised of four rooms: a battery storage room, a server room, a working space and a room for equipment storage. The battery storage room hosts seventy 200 Ah deep cycle batteries, as well as fi ve inverters (one of them pure sine wave), two solar regulators, power stabilizers and DC and AC disconnects. The batteries are stacked vertically on a metal shelf structure for better cooling. The server space accommodates a rack unit for servers and a fan. The room has no regular windows, to avoid dust and overheating. The server room and battery room face south to improve natural cooling and to help keep the room at an appropriate temperature. 312 Chapter 11: Case Studies
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The server room and the battery space require effective low cost/low energy cooling as they need to operate 24x7. To achieve this goal, natural cooling techniques have been introduced in the NOC design: small fans and extrac- tors and thick walls of bricks (double width) in the direction of the sunset. The south side of the building hosts 24 solar panels in a shadow-free area on its metal roof. The roof was designed with an inclination of 20 degrees to host the panels and limit corrosion and dust. Extra efforts have been made to keep the panels easily reachable for cleaning and maintenance. The roof has also been strengthened in order to carry the extra load of 150-200 kg.
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