Reserve Power Hybrid Systems Deliver Cost Savings for Growing Demand in Telecommunication Applications

Mike Kulesky, Marketing Director for Telecommunications
EnerSys

In remote areas across the globe such as on the continent of Africa and in the Caribbean, the demand for wireless communications is growing faster than the telecommunications companies can update their obsolete infrastructures. Unlike their counterparts in well-developed areas, the companies have poor power grids that make expanding the networks difficult.

Fortunately, recent advancements in technology have opened the door for new hybrid applications that deliver off-grid power to households and telecom base transceiver stations (BTS), or cell sites where main grid network quality is poor or non-existent. These applications often rely on diesel generators to provide either the partial or entire power supply.

“It’s really a new frontier. We can connect people through reliable cell phone service in remote areas of the world; something that the rest of us take for granted,” said Bob Rader, director of sales for South America and the Caribbean at EnerSys.

Today’s technology has made it possible to deliver better performing batteries that support hybrid systems. In areas where the grid network is reliable, a hybrid application is characterized by a stationary battery that is working in parallel with another power source such as a diesel generator, PV panels or wind turbines. Stationary batteries by design are slightly overcharged and remain in the “float” charge mode. If an outage occurs, they can provide all of their stored energy.

In unreliable service areas, however, new stationary battery technologies that are designed to be discharged and recharged daily are a better choice for remote hybrid systems, according to John Gagge, senior director of Engineering and Quality Assurance at EnerSys. For remote off-grid telecom sites, hybrid systems that use high cycle batteries in conjunction with another power source can help reduce fuel consumption and save overall operating costs.

“With rising fuel costs, telecom companies are welcoming ways to cut down the amount of time they are running generators to achieve greater cost efficiencies,” said Gagge.

For example, a hybrid system using a quick-charge battery would alternate a 16-hour cycle of generator power with an eight-hour cycle of battery power. In the first cycle, the generator runs to supply the power load, which simultaneously recharges the battery. In the next eight-hour cycle, the battery supplies the load while the generator is shut down. In hybrid quick-charge applications, cyclic control is necessary to allow the battery to achieve its eight-hour discharge and fully recharge from the generator in 16 hours, so it is ready for the next discharge.

New Technology Permits Greater Control
Depending on the application, battery requirements can vary drastically. For instance, powering a stand-alone hybrid application system is a much different animal than supplying backup power with the traditional valve-regulated lead acid (VRLA) standby battery. For efficient systems, it’s important to select the battery and design the system carefully while considering the characteristics of each unique operating environment.

Through the latest technologies in manufacturing capabilities and process control, manufacturers can produce more cycles from every battery. Network engineers benefit from newer, more intelligent power equipment that gives them more accurate measurements and control of charging and discharging batteries through proprietary algorithms.

“Hybrid systems that offer quick-charge methods combined with our SBS EON technology for off-grid power are the best choice for supplying power to remote areas, which is typically not how traditional VRLA batteries have been used,” said Gagge. “When the batteries are built with enhancements like SBS EON technology, they can support quick-charging methods that are commonly used in motive power applications. It’s a new frontier in hybrid systems.”

Meeting Demand for Remote Applications
In the case of remote applications using a hybrid system, VRLA stationary standby batteries are actually used as one of the main sources of power. In stand-alone hybrid applications, the batteries work more like those in motive power lift trucks or handling trucks because the standby batteries are discharged daily. The charging method is the key to achieving the full life expectancy of the battery.

To meet the output demands and be available for any potential power failures, analyzing the unique requirements of the network is critical when choosing the battery. In many cases, remote off-grid telecom applications use two diesel generators to give constant power to the systems. Some applications have a battery for backup power when generators break down or run out of fuel, leaving the operator minimal time to react.

Hybrid Systems Generate Cost Savings
Site operators have found tremendous cost savings when the battery has a major role as an energy source. Rader noted that the major benefits cited by telecom operators are reduced generator run-time, lower fuel costs and less frequent maintenance for generators, especially since many sites only need one generator rather than two.

Site operators ideally would run exclusively on grid power with a back up solution of batteries and eliminate the costs of fuel and equipment. However, in many parts of the world, quality electric grid service is a luxury. Within these areas, there are several aspects to consider in order to achieve the battery’s expected lifetime and to meet the needs of the network. Here are the four major points to determine if the standby application will provide ample power.

1. Cycle Life, Effect of Deep Discharge
This is a key parameter to correctly size a system. VRLA battery cycle life depends on the amount of energy discharged at each cycle. While every battery design varies, as a general rule, a battery is capable of providing a finite amount of amp hours in its whole life. If a certain amount is discharged at every cycle, the battery can provide many cycles, whereas depleting the whole capacity at each cycle results in a shorter cycle life.

2. Time to Recharge, End of Charge Detection
The systems often use many battery elements or blocs in series. To achieve the expected cycle life, they have to be fully recharged and homogenous at each cycle. So using float charging voltages that are commonly used in stationary applications is not suitable. If a typical stationary battery that is on float charge has been discharged to 80 percent of its rated capacity, it needs 24 hours to fully recharge. Recharge time can be reduced even lower (two to three times) with alternative batteries using thin plate pure lead technology, if the available current is sufficient.

3. Available Charge Current
There is a minimum current to properly charge a battery at each cycle. To optimize the hybrid system, it’s ideal to use the generator for the minimum time to recharge the battery. The generator size is important yet in many cases, an oversized generator already exists at many sites and is being underutilized. When the generator is operating, it normally has excess power that ideally could be used for proper or quick-charge methods.

4. End of Discharge Detection
Overcharging affects the cycle life, so it’s important to detect the end of discharge by measuring the amount of amp hours the system used. This isn’t an option in older power generation systems, so the battery manufacturers often estimate the cut-off voltage to a given depth of discharge. The estimation method is not recommended for quick-charging since there is a risk of over- or under-charging the batteries.

The New Hybrid is a Success
Using hybrid systems in remote areas of the world is gaining traction. They provide a cost-effective and environmentally-conscious means for creating a renewable independent power source in areas that would otherwise have unreliable service or no power at all.

In one application in North Africa, the hybrid powered a wireless cell tower. By day, it ran on battery power for four to eight hours. At night, the generator ran to keep the cell tower in operation.

“The cost savings in fuel alone justified the site’s investment in the hybrid,” said Gagge. Another company reported an approximate 20 percent savings due to better fuel efficiencies. “The new hybrids are becoming popular tools to manage power loads, give extended runtime solutions and make positive green-minded decisions.”

A telecom business veteran of more than 10 years, Mike Kulesky is director of Marketing for Telecommunications at EnerSys. Previously, he worked at Lucent Technologies, supporting a wide range of power projects and products.

Contact EnerSys at www.enersys.com.

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