Risk mitigation of lightning incursion into network equipment via PhotoVoltaic systems It’s not easy being “green”

Says Kermit the Frog, "It's not easy being green." Becoming "Green isn't cheap either. Forward-thinking telcos and data centers are considering photovoltaic (P.V.) panels as a way to save energy and exploit the very real public relations kudos to be had building "Green" facilities and features into their networks. Until recently P.V. systems were used only for very small installations typically less than a kilowatt. Such installations were used for sites that lacked available commercial power such as emergency roadside phones. Now, large array panels and systems are available with significant power capability and companies are considering placing P.V. systems in parallel with their commercial electric feeds or their d.c. systems. With price tags in the tens of thousands of dollars per kilowatt of capacity, it might take awhile for a facility to realize a significant payback despite grants and financial incentives. Still, that lure of P.R. sees companies considering these relatively large P.V. systems. While it's great to build new systems, it's critical to protect telecommunications central offices, data centers and smaller facilities such as cell or microwave sites from lightning. There are several design considerations that can make the difference between a safe, sound P.V. system or one that is a virtual bayonet in wait of an opportunity to stab your company's network systems squarely in the power bus. Typically, P.V. systems are installed as rooftop installations or in ground arrays mounted to frameworks. Each of these installations bears specific hazards of lightning or induced surge currents that could enter the network via the conduits or conductors that connect the P.V. system into the facility infrastructure. The lightning "hit" might be a direct stroke to the site or currents induced from strikes within a mile or more of the facility. A system-level approach to lightning and surge protection is prudent in order to protect the facility from damage. Most electrical engineers and contractors are well trained in ac distribution systems and to a lesser extent, dc systems. Lightning and lightning related surges, however, behave in ways that are very different from dc or low-frequency ac. Therefore, different skill sets and training are needed to approach P.V. systems from a lightning protection and surge suppression point of view. This paper will identify the finer points of bonding grounding (Earthing) and electrical protection as they apply to P.V. systems used in telecom network applications.