Within just two decades, mobile telephony has changed the way we do business, the way people communicate, their leisure and pleasure pursuits and social relationships. Today, mobile telephony is truly global, having penetrated the world's highest density population areas. The future challenge for operators is now focused on reaching out to rural locations and remote communities. Diesel generators powered by fossil fuels have traditionally been the technology of choice for powering off-grid network infrastructure as well as providing back-up power generation in unreliable grid supply scenarios. In terms of operating efficiency and reliability, the diesel engine-powered generator continues to provide a low CapEx solution for the provision of both continuous and/or standby electricity supplies. However, with mobile network operators (MNOs) experiencing increasing OpEx as the price of fossil diesel fuel continues to escalate, much attention is being focused on development of power generation systems using sustainable energy resources. According to latest figures issued by the GSM Association, around 640,000 off-grid base stations (BTS) will be rolled out across emerging markets by 2012. The target is for 118,000 of these BTSs to be powered by renewable energy. It is perhaps naive to assume that some 500,000 diesel engine-generator sets (gensets) will therefore be installed over the next two years. But it is clear that rising fuel prices and environmental considerations such as emission control, noise, carbon footprint and environmental impact are all issues that will be influencing specification decisions. Outside the grid Globally, there are now more than five billion mobile phone subscribers (ITU figs) and this could increase by 50% over the next five years. The magnitude of the task set for MNOs planning further expansion into remote areas and for providers of off-grid power generation systems cannot be understated. It is estimated that 1.6 billion people live off-grid, and an additional 1 billion people reside in unreliable grid regions. South Asia has the largest off-grid population in the world: some 614 million people (40% of the region's population). Lack of a stable grid drives the deployment of vast numbers of diesel generators for primary and backup power. And with the cost of conventional mineral diesel fuel escalating, alternatives such as biodiesel, diesel hybrid (both wind and solar solutions) wind turbines, and solar power arrays are receiving much attention. In traditional GSM networks, an off-grid cellular base station requires a 5-10kW power generation source. In more remote areas, the power requirements for "last mile" mobile services provision may be substantially reduced together with the number of subscribers and service offerings. Sustainable solutions In 1912, Rudolf Diesel is quoted as saying that "…the use of vegetable oils for engine fuels may seem insignificant today, but such oils may become, in the course of time, as important as petroleum and the products of the present time." Prophetic words which now, a century later and with the development of advanced diesel engines, have found new resonance in the form of modern biodiesel fuels. In terms of operational reliability, many modern diesel engines will run 16-18,000 hours before requiring servicing, other than routine maintenance, and are increasingly installed in tandem with wind and/or solar powered generators. Operating for four hours a day as an integral part of a hybrid solution, 18,000 running hours translates to, potentially, twelve years between major servicing! Advanced remote monitoring techniques also ensure that fuel efficiency and power output continuity is maintained. Biodiesel is a sustainable fuel that offers clean burning characteristics. Produced from nut oils (e.g. coconut, palm, castor, jatropha , etc.) and other vegetable oils (e.g. rapeseed, soya), research into methods of prolonging storage life is ongoing, since it is prone to microbiological degradation if stored for long periods. Biodiesel and biodiesel/fossil fuel mixes (from B10 to B100) can be utilised in many existing diesel gensets although some modification may be required to maximise the efficiency and reliability of older gensets (bio-fuels are not compatible with certain plastics and rubbers). Emission benefits are also gained even on low blends and, if the biodiesel can be sourced locally, transportation costs may be reduced and a degree of insulation against the price fluctuations of fossil fuels attained. However, in many countries, the use of biodiesel as a primary fuel attracts excise duty, albeit to a lesser degree, in the same way as fossil fuels. Fortunately, increasing global awareness of "green" issues has resulted in some governments, especially in emerging markets, providing bio-fuel subsidies in a bid to encourage industry to reduce both its carbon footprint and reliance on fossil fuels, as well as encouraging its production to provide sustainable economic development in some remote regions. MNOs will, undoubtedly, be looking closely at any "sunset" clauses incorporated in fuel subsidy agreements since the cost of refining biodiesel to a level whereby it can be reliably used in a genset can prove to be more costly than commercial diesel fuel -- even at current prices. Green power hybrids For MNOs, the task of specifying the right technology that can provide a reliable, long-term, cost effective solution to powering off-grid cell towers and BTS plants based on "green" solutions calls for a multi-disciplined approach. The introduction of power systems that use wind and/or solar energy as the prime fuel source, in addition to diesel gensets, will add significantly to the number of variables that need to be considered. Green power solutions such as solar panels, wind turbines or hybrids using both technologies are totally dependent on both the availability and variability of the renewable resource: energy derived from wind or the sun. Obviously, the terrain, local metrological conditions and seasonal changes need to be considered together with battery capacity requirements to support site autonomy when no power is produced (i.e., at night or on still days). Additional switch and control gear will also be required to monitor power flow and charge capacity. Traditionally, solar technology has provided an alternative to the stand-alone diesel genset for powering BTSs in off-grid areas. OpEx for solar modules is low due to minimal maintenance requirements and low fuel costs, but CaPex is high, especially for sites with high load demand where large areas are needed for solar panel arrays. Using a solar/diesel hybrid solution can extend the viability of solar power into even higher loads whilst reducing battery and solar CapEx. At standard base station loads, the installed cost of energy from wind is lower than that of a solar system with equivalent power output due to a lower basic equipment cost. In off-grid situations, wind power can also be used to reduce the operating cost of diesel generators, saving up to 50% of the diesel fuel consumption required for existing remote rural sites. Such hybrid solutions are set to play a major role in empowering local communities. Recent "green" initiatives announced by the GSMA suggest that MNOs should consider increasing power generation capacity by at least 5kW in off grid scenarios and then sell the excess electricity back to the local community, creating a win-win situation. Under this scheme a network operator will not only be able to offset electricity generation costs by selling on the energy produced, it would also resolve the problem of charging mobile phones in remote regions (so increasing call revenues) as well as providing electricity supplies for key local services, such as medical facilities. As with any consumer service, supply continuity and reliability is key to commercial success, and it is here that integrated wind/diesel and solar diesel hybrid solutions will attract much attention. The specter of climate change, the need to reduce CO2 emissions and the depletion of our fossil fuel resources coupled with ever-increasing price hikes, has heightened the challenge of improving existing, and pioneering new, power generation technologies with the goal of maximizing natural energy resources. For many years, leading manufacturers of diesel gensets and associated electrical switchgear have been active in development of reliable, off-grid power solutions based on both eco-friendly design and sustainable energy concepts. Organizations such as the GSM Association in collaboration with network operators, infrastructure suppliers and governments are working to pioneer new approaches to off-grid power generation. In the future, data based on commercial criteria obtained in real-life scenarios will be available to make informed decisions, rather than hypotheses based on the extrapolation of performance data from short term trials. Shantanu Roy is Manager of Telecom Power at Cummins Power Generation , an industry leader in introducing advanced low–emissions power generation solutions around the world.