Winafrique

Green power for mobile networks

It has been estimated that about a third of the world’s population have unreliable power supplies —or no access to electricity at all. In order for them to be able to take advantage of mobile communications, base stations have to be powered by such means as diesel-driven generators. However, as diesel prices rise and network infrastructure spreads to more remote areas, other alternatives are required, not only in order to save money, but also to help combat climate change.

The GSM Association (GSMA) launched in September 2008 a programme called Green Power for Mobile to promote the use of renewable energy sources by the mobile phone industry. Its goal is to see 118 000 new and existing off-grid base stations powered in this way by 2012. It says that this would save up to 2.5 billion litres of diesel a year and cut annual greenhouse-gas emissions by up to 6.8 million tonnes. It would also give a boost to the provision of mobile phone services in places that cannot yet use them.

Assessing the situation

GSMA carried out a survey of operators, vendors, green power suppliers and financiers to evaluate the market and technical landscape. Its report*, published in March 2009, says that of the estimated 300 000 base transceiver stations that will be built in developing countries up to the end of 2012, some 75 000 will not be connected to electricity supply grids (see Figure 1). It points out that extending the grid to such sites would be enormously expensive. Reliability is another problem, in both rural and urban areas. For example, in rural India, electricity supplies might be cut off for up to 14 hours a day, according to the survey.

To power base stations that are not on the grid, diesel fuel has often been chosen for electricity generators. However, the price of diesel has risen substantially in many places, as well as the cost of delivering the fuel to remote locations.

Sustainable sources of power

As alternatives to diesel, GSMA analysed the viability of other sources of power for mobile base stations: solar, wind, biodiesel, pico-hydro (very small hydroelectric systems) and fuel cells (see Figure 2).

Solar power

There is often an abundance of sunlight in rural areas of developing countries, and this, together with the increasing availability of solar equipment and its relatively low running cost, makes solar power a popular choice for sites that need up to 2 kW of power. Solar solutions are less economically attractive for larger sites, the report says, but it foresees that the price of installing solar power is likely to fall in the coming years.

Wind

The equipment to trap wind energy is cheaper than for solar-powered stations that have standard load requirements. It costs about 10 or 11 US cents per kWh to produce electricity at small wind-powered stations, according to a study by the American Wind Energy Association, and this is projected to drop to 7 US cents within five years. However, wind power is only viable in such areas as coastal and mountainous regions, where wind blows sufficiently strongly and frequently. In other places, hybrid solutions may be used that combine wind and solar power.

Pico-hydro

Pico-hydro refers to very small hydroelectric power generators that typically produce up to 10kW from the energy of streams and rivers. It is a mature technology for other applications such as rural electrification and has one of the lowest capital investment requirements of all. But again, it is applicable only in a limited number of places.

Biodiesel

Biodiesel fuel (derived from vegetable oils or animal fats) can be used as a direct replacement for conventional diesel in base station generators, but it is not necessarily a universal solution. Among the factors that must be considered are local access to supplies of biodiesel, and how its production could affect agriculture.

Fuel cells

Fuel cells, or batteries, are mainly used as back-up electricity supplies for base stations that have limited power requirements. So far, the commercial viability of using fuel cells as the prime power source has not been greatly tested. However, research and development is being undertaken on the technology, and suppliers have forecast a cost reduction of 30 per cent by 2010, according to GSMA.

Saving money too

Figure 2 shows that it is comparatively inexpensive to install a diesel-powered generator for a mobile base station; however, the operating costs in fuel and maintenance are “high and extremely vulnerable to market conditions,” the GSMA report says. At present, solar and wind power solutions require about 50 per cent more capital investment, but they have much lower running costs. They more quickly pay for themselves in cases where the site load is below 2 kW. In other situations hybrid systems can be valuable, combining diesel with green power solutions to reduce operational costs along with the environmental impact.
 

If operators look for a three-year payback on investment, GSMA suggests that 9 per cent of mobile base stations could be powered by green energy sources by 2012, saving 3 million tonnes of CO₂ emissions each year and USD 1.3 billion in fuel costs (see Table 1). With a five-year payback period, the figures rise to 30 per cent of base stations using green power and thereby saving 10 million tonnes of greenhouse-gas emissions — as well as USD 4.4 billion in fuel costs. After 2012, GSMA predicts that “up to 50 per cent of new off-grid base stations in the developing world will be powered by renewable energy.”

Energy-efficient design

Another aspect of green technology is improved design that reduces energy consumption. The GSMA survey shows that manufacturers of telecommunication equipment are making considerable investments in developing devices that need less power. ITU’s work is important in this effort, such as in the energy-efficiency checklist created in 2008 to be used when developing technical standards.

In addition, major energy savings can be achieved by designing equipment that can work in temperatures of up to 45°C without the need for powered air-conditioning systems to cool it. Instead, temperatures can be moderated by much more cost-effective solutions such as simple fans, shading, or the heat sinks provided by thick stone walls.

The need for cooling is a significant element of the costs of a base station — it can be at least equivalent to the cost of powering the transmitter itself, according to the GSMA analysis. Achieving energy efficiency is thus an important part of creating viable green power solutions, especially for stations with higher load requirements.

Better and innovative design will help to reduce the costs of expanding mobile networks into remote areas that do not have a mains electricity supply. In many cases, building mobile base stations that use green energy will not only create economic and environmental benefits; it also seems likely to become a major means of connecting people to the information society.