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As data demands increase, so does energy consumption from high-density data and communications equipment on cell towers. This leads to the need for increased efficiency in power systems, especially in places with unreliable power grids. The push into rural areas and underdeveloped countries is another driving force causing tower owners to look for more energy efficient options for their macro sites.
On this week’s episode of Cell Tower News, Brian McCrea, National Accounts Manager for OEMs and DAS at Alpha Technologies, talked about the problem of power efficiency in cell towers and offered a few possible solutions.
“You’ve got to get more out of what you’ve deployed. You can’t just keep deploying new infrastructure every two to three years,” he explained. “They get down to the 600 frequencies…you’re going to want more power at the top and you’re going to want to reuse what you already have there.”
Currently, most macro site power systems use rectifiers to convert AC energy into DC energy. DC power systems are made up of many complex parts including frameworks, infrastructure in the frameworks, input/outputs, distribution and management systems and controllers and converters. A 2011 study predicted “some generator set manufacturers will start developing DC or variable-speed generators to meet increased fuel-efficiency requirements of cell tower sites.”
One possible solution McCrea has studied in the past is DC to DC converters. “What that allows them to do is allows them to put more power up at the top of the towers, re-utilizing existing or smaller cables, so if you could do something that would allow you to get the efficiency up or built into the rectifier or its a variable voltage and overcome the i squared r losses going to the top of the tower,” he said of the possible solution. “What that allows you to do is you can get more out of your battery. Problem is, how often do you use your battery?”
He says lack of battery usage might not make it worth the investment. Generally backup batteries are only used 15-30 minutes every two years unless you’re in a bad grid area. Deployment costs are a big issue.
McCrea studied the DC to DC possibility a few years back. “One of the things we kicked around with one of the OEM tower companies a couple years ago was DC to DC converters and does the inefficiency of the conversions offset the capital deployment? Initially no,” he said. “The DC to DC converters are too inefficient..Right now they’re probably at 90%. They need to be higher.”
“I did a business case on that two or three years ago, the payback operationally didn’t make sense at that time because it was two pieces of equipment, it was additional capital, but if you could do the replacement…and also get more distribution points, which every carrier is looking for in a macro site, it might make sense,” he added. “I think we’re on the cusp of it. I don’t think we’re truly there yet, but I think within a year or so someone will get there.”
However McCrea says perhaps the best solution is improving RF effiencieny. “It’s not very efficient right now. That would help out more so than putting a DC to DC converter or something to get higher voltages to the top.”