The Many Considerations for Cell Site Backup Power

Mark Hendrix 5-28-13--compressed Mark Hendrix May 29, 2013

Editor’s Note: This is the sixth installment for our “Meet the RF Experts” series in which contributors to the Understanding the RF Path e-book elaborate on subjects in their areas of expertise.

Whether you notice them or not, cell sites are everywhere. Not all sites look the same—some have large standalone towers, others are deployed on rooftops, and some can be disguised within street furniture—but they share the critical requirement of an electrical infrastructure for power.

There are many things wireless engineers must consider in the design for powering these sites.
One of the most important considerations is the backup system to keep power—and communication—flowing in the event of a power outage.

Integrated into most standard power systems are backup batteries. Lead-acid batteries are one of the most commonly used power alternatives at cell sites. They are compact and are similar to the one under the hood of your car. While these batteries are charged by the cell site power system, it will not discharge until grid power is interrupted. When this occurs, the batteries seamlessly replace grid power. These batteries can last from two to eight hours, depending on their backup configuration design. CommScope provides several outdoor cabinets, which can accommodate power systems, batteries and combinations thereof.

In addition to backup batteries, generators are usually another line of defense against service interruption. Unlike batteries, generators require fuel and can supply the needed power for a longer period of time. There are different types and configurations for generators so factors like space, cost and service expectations must be considered. Diesel generators contribute to air and noise pollution, even when there is no actual power outage, due to periodic maintenance runs. Operators may need to find out what kind of noise restrictions or codes apply to the area where the cell site is located. Some operators can receive fines if the generators are too loud, or stay on for a certain period of time, contributing to the air and noise pollution in the area.

The latest backup power solution gaining favor with wireless operators is hydrogen fuel cell technology. Hydrogen fuel cells use proton electrolyte membrane technology to generate power. There are several key advantages to this technology: low cost, higher efficiency than typical diesel generators, the ability to operate in extreme temperatures, high density, silent operation and zero emissions.CommScope has a unique fuel cell solution, which unlike competing solutions doesn’t require monthly operation for hydration of the fuel cell membranes. This helps conserve the hydrogen fuel, which is used only when there is an actual outage.

These are some of the factors we want customers and wireless engineers to be aware of regarding selection of a cell site backup system. In addition to these factors, cell site power systems can have fairly sophisticated monitoring reporting software that communicate with the operator on the status of the site battery, site alarms, temperature and condition. It is important to know what can be monitored and reported in regards to the power and backup system.

You can learn more about powering wireless networks and other features of today’s cell sites in chapter 10 of CommScope’s Understanding the RF Path e-book, which I helped author. Use the link to view the online version or download it as a mobile application. And feel free to ask questions about powering wireless networks in the Comments section below.

About the Author

Mark Hendrix 5-28-13--compressed

Mark Hendrix

Mark is engineering director, Enclosure Solutions, responsible for directing innovation efforts in wireless communications enclosure systems for CommScope, with particular focus on thermal design, power systems and other efficiency drivers. He brings 30-plus years of expertise in electronic packaging, with backgrounds in both defense electronics and telecommunications for such names as Texas Instruments, Fujitsu and Xtera Communications. Mark holds 12 U.S. patents and is a registered professional engineer in the state of Texas. He holds a Bachelor of Science degree in mechanical engineering from  Clemson University, and a Master of Science degree in mechanical engineering from Southern Methodist University.