Powering Cellular Base Stations – A QUANTITATIVE ANALYSIS OF ENERGY OPTIONS Solar PV, Diesel Generators, Batteries and Electrical Grid by Ashok Jhunjhunwala, Bhaskar Ramamurthi, Sriram Narayanamurthy, Janani Rangarajan, Sneha Raj

Powering Cellular Base Stations A Quantitative Analysis of Energy Options- Prof. Ashok Jhunjhunwala, RITCOE- IIT Madras

at the Telecom Center of Excellence (RiTCOE) Indian Institute of Technology, Madras

Telecommunications networks are critical infrastructure that needs assured power supply 24×7. Before the advent of cellular wireless telecommunications, wired telecom infrastructure used to be largely confined to telephone exchanges. Even if there were remote units with electronics on the streets, these units required modest levels of power, and this power was supplied from the exchange using the cable infrastructure. With cellular systems replacing wired systems in a big way, and with coverage becoming ubiquitous, the number of base stations in the country has grown enormously. Currently, the number of sites hosting base stations is in excess of 4 lakhs. These base stations are on rooftops of buildings in the cities, and at the bases of remotely located towers in rural areas. They need grid power supply and autonomous power backup.

The amount of power needed at each base station is also much higher, exceeding a couple of kilowatts, depending on the size and age of the systems deployed. Often, the electronics needs cooling as well. The locations, at which these base stations are present, lack reliable power supply and some have no grid availability in the first place. Thus there arises a need to provide power backup in the form of generators and storage batteries. These backup systems were implemented in a bandaid fashion over the years, since (a) they were not required in many other geographies before the large Indian deployment started, and thus no well engineered solution was readily available, and (b) the scale of the backup needed in India too kept increasing as power supply became more erratic and cellular coverage began penetrating rural areas.

The consequence is that we have today back of the envelope solutions that are not optimally engineered, that are often over designed in order to meet unknown future needs without heeding efficiency, and that ignore the benefits that could accrue from renewable sources such as solar photovoltaics (PV). If the financial and environmental costs of such sub optimal designs were negligible, one could ignore the issue. However, the high operational expenditure on account of backup power supply, and the environmental cost of DG sets and backup batteries, has forced us to look afresh at the entire problem.

This report is a comprehensive effort to grapple with the issue of providing power backup for telecom base stations. It makes no prior assumptions neither about the suitability or otherwise of batteries, DG sets, or solar PV, the availability of grid power nor the power consumption of the base stations. The key aspect of the approach taken is that the optimal backFup solution is found through simulations, given the set of assumptions. A sophisticated simulator has been developed into which one can input the parameters, and obtain the optimal mix of battery backup, solar PV capacity, and DG set capacity. The required power level, the temperature profile, grid availability profile, relative costs of DG power, solar PV, and battery storage can be fed into the simulator to arrive at the optimal solution. One can also consider retrofitting older base stations to reduce power requirements (mainly cooling requirements) and changing the optimal mix. One can perform “whatif” analysis to determine how the optimal mix will change if grid availability changes, and plan a more robust solution if such is needed. When grid availability improves at a location, one can change the backup arrangements at the next available opportunity, or increase the electronics at the site if needed.

Thus, the methodology espoused by this report yields a location specific solution,which optimizes capital and operational expenditure. Operators can dynamically track the optimality of their implementations in a location specific manner as the POWERING CELLULAR BASE STATIONS: A QUANTITATIVE ANALYSIS OF ENERGY OPTIONS assumptions change, and either fortify the power backup, remove excess capacity, or add to the base station electronics as needed. The simulator and system dimensioning tool is very useful both for abinitio design of new sites, and for tracking the performance and upgradation of existing sites.
Several hundred examples of typical base stations configurations, power backup capacities, and grid availability assumptions have been considered and the cost of the backup power evaluated, with realistic models for the cost of finance. While these serve as examples for the way in which the methodology and simulator is to be used, they also enable us to arrive at some broad recommendations for the way forward with regard to the use of solar PV, DG sets, and batteries in the right mix to achieve a cost and energyFefficient power backup solution. We are also able to point out the critical areas where further research will lead to significant improvements.
We hope the user community telecom manufacturers, tower infrastructure companies, power backup system providers, operators, regulator, and policy making government agencies find this report and the simulator/tool useful. We believe it is a first, and important step, in addressing these pressing issues of cost effectiveness, energy efficiency and carbon footprint of our telecom infrastructure. The Reliance IIT Madras, Telecom Centre of Excellence (RITCoE) was set up, among six others in sister institutions, with a specific mandate for conducting research on energy related issues. With the release of this report, RITCoE has made its first major contribution in this regard.
The problem of energy efficiency in the Indian context has only begun to be addressed. Much more remains to be uncovered, and much remains to be accomplished. We hope that the utility of this work will serve to emphasize the need for strong research efforts within the country as the only way to properly address our specific technological challenges. We also hope that this work also demonstrates the effectiveness and value of academia industry collaboration, which was pioneered in an institutional framework through the TCoEs. We look forward to critiques of this report, as well as feedback from the use of the simulator. We are committed to continue our work in this area, and to improve the simulator and the approach itself in subsequent releases.

The authors would like to thank Reliance Communications, Department of Telecommunications, and IIT Madras for the support and encouragement provided to RITCoE.

Bhaskar Ramamurthi
Chairman, Governing Council, RiTCOE, IIT Madras

About Ritesh Pothan

Ritesh Pothan, is an accomplished speaker and visionary in the Solar Energy space in India. Ritesh is from an Engineering Background with a Master’s Degree in Technology and had spent more than a decade as the Infrastructure Head for a public limited company with the last 9 years dedicated to Solar and Renewable Energy. He also runs the 2 largest India focused renewable energy groups on LinkedIn - Solar - India and Renewables - India
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