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Battery Back-Up: Powering the telecom sector

October 31, 2011
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C. Niranjan, Deputy General Manager,   Engineering, Amara Raja Batteries

Energy architecture in the telecom sector has undergone a significant transformation. Starting from an air-conditioned single base transceiver station (BTS) platform with a no-sharing model, it has moved to a fully air-conditioned multiple BTS-infrastructure-sharing model. Both these models are purely indoor based. Recently, they have been followed by an architecture that allows outdoor batteries to be used in indoor sites. The concept of outdoor sites (grid/off-grid) with diesel genset (DG) batteries evolved much later and has finally given way to the current hybrid-site model including solar energy, wind energy, battery, etc.

Batteries are a critical back-up resource. They are today powering telecom infrastructure to a great extent. However, there have been instances when batteries have failed to support the load in exigencies, primarily due to the presence of gaps in technology, make, design and usage. Further, there are typical failure modes such as low back-up, long charge duration, low current acceptance, high charge voltages and premature failures that result in poor functioning and lower the efficiency of batteries. These contribute significantly to increasing energy costs, which, in turn, increase the operational expenditure (opex) and capital expenditure (capex) borne by users.

The other obstacles that prevent the efficient usage of batteries include unfavourable installation locations, which leave batteries exposed to rain and dust; loose-fitting terminations; incorrect location of temperature sensors; and improper voltage settings. These add to existing installation prices, thus increasing overall energy costs. Moreover, the infrastructure required for charging these batteries is generally not sufficient because of the low efficiency of DG sets and insufficient DG runtimes. Factors like improper battery size and lack of visibility in the battery usage pattern at a site also create gaps in battery usage.

Moreover, the features of a battery play a crucial role in influencing the opex of a user. Poor recharge efficiency, resulting from long DG run- hours and undersized DG sets, impacts energy costs. Most of the batteries today have low recharge efficiency and are unable to accept high charging current. Further, these are unsuitable for partial state-of-charge (PSOC) and outdoor operations because of their increased sensitivity to high temperature. Soaring diesel prices, too, add to the user’s opex. The best solution, thus, is to have a battery model that gets recharged quickly, does not require high maintenance and is suitable for outdoor applications.

Amara Raja Batteries Limited has provided an optimal solution for railways using valve-regulated lead acid (VRLA) batteries. These have a higher life of four-five years and are highly suitable for extreme outdoor charging conditions. These give a significant haulage benefit (25 kWh per 1,000 kg per 1,000 km) and require very low maintenance. Another initiative by the company has been in the solar energy space, where it has introduced the absorbed glass mat (AGM) VRLA battery for ONGC’s offshore platforms. This has resulted in improved PSOC capability and enabled huge savings in energy requirements.

Different technology options

There are different battery technology options available to users, that help in arresting these additional energy costs. These include Na-metal halide, Pb-carbon, blue battery, vanadium (flow battery), lithium and AGM VRLA batteries. The performance of these battery solutions varies across different performance parameters. In terms of specific energy, measured in Wh per kg, Na-metal halide, Pb-carbon and lithium batteries give excellent performance. As far as safety is concerned, lithium batteries are considered the least safe. Charge recovery after deep discharge is one parameter on which none of the battery options delivers an above-average performance. Further, Na-metal halide, vanadium and lithium batteries have a high recharge capability of 0-100 per cent at 2.30 V.

Understanding the value proposition of each technology is important to arrive at an optimal battery solution. Merits like life cycle, kilowatt hours delivered, cost per unit, capex and opex requirements, and savings per annum are also deciding factors for choosing an appropriate product.

Recent advances in battery technology

Some of the recent advances in battery optimisation are as follows:

Remote monitoring

Integration of information and technology with power sources through GPRS enables cost-effective and reliable monitoring of batteries. This leads to healthy and effective maintenance. Remote monitoring creates a platform for easy collection of data, on the basis of which the condition of a battery can be estimated. This is done by analysing the parameters, external to the battery, by using a sensor network. With this, users have benefits such as timely notice of failures, lesser downtime and reduction in opex. It also eliminates the need for an expert to monitor the batteries on a continuous basis.

Green shelter

Green shelter is an arrangement by which no external heat is allowed to enter the battery compartment. This reduces the effect of heat caused by direct solar radiation and reduces the operating temperature by 4-5 °C, when compared to normal outdoor cabinets. The reduction of operating temperature increases the life of batteries by at least 20-25 per cent.

Conclusion

Batteries are an important means of meeting the energy needs of the telecom sector. Going forward, optimal use of the existing battery solutions and continuous innovation in technology will empower telecom infrastructure, resulting in efficient battery options and lower energy costs for users.

 
 
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