Wireless carriers can chalk up the majority of their power bills to one item: running networks. Base stations transmitting at 800 watts and power-hungry subsystems, as well as air-conditioning to keep those overactive circuits cool, pile millions of dollars on to the capex bills of operators — and those charges are only increasing. The rising cost of energy and fuel drive up power costs and operators' overall opex.

Vendors have been attacking the energy problem from environmental and operational perspectives, developing base stations that function at temperature extremes and systems that use less electricity. Some companies are investigating alternatives to the power grid and diesel generators that power the majority of the world's base stations.

CommScope is bringing fuel cells to base stations, having developed a cabinet for wireless and wireline networks that replaces a typical DC battery or diesel generator backup with two 8 kW fuel cells. Fuel cells generate electric current by passing hydrogen through a membrane, where a process called proton exchange occurs. The only fuel required is hydrogen, the most abundant element in world, and the only byproduct is water, which evaporates into the atmosphere. Considering the rising cost of petroleum, CommScope expects operators to look at any technology that lets them abandon their diesel-powered generators.

Nokia Siemens Networks is looking at alternative power sources not just for backup but for day-to-day operations. It's committed to making renewable energy the prime power sources of its base stations by 2011 and has identified solar and wind energy as the best candidates to replace diesel.

NSN launched its first hybrid solar/wind-powered base station in India with Bharti in late 2005 and since then has launched 200 cell sites that draw 95% of their power from the air and sun. NSN's plans, however, are growing more ambitious this year as it looks at solar and wind as alternatives to the power grid, even when a grid is available.

“Solar and wind technologies are mature, they have a long lifetime, their operational cost is almost nonexistent, and the capital expenditure required is decreasing,” said Anne Larilahti, head of environmentally sustainable business for NSN, speaking at Green Forum in Beijing in March.

In a sunny or windy area, NSN estimates a photovoltaic cell or wind turbine power supply could pay back its capital expense in two to four years through energy savings as well as reduced operational and maintenance costs.

Ericsson has also been experimenting with solar-powered base stations in Sumatra, Indonesia, but its most ambitious green project to date has been in developing biofuel-powered networks. Its project with Nigerian operator MTN and the GSM Association required organizing co-ops of farmers to cultivate pumpkin seeds, ground nuts, jatropha and palm oil, which they deliver to local biofuel processors where workers convert it to bio-diesel, which then must be delivered to the base stations themselves.

There are drawbacks, however. Ericsson estimated 80 soccer fields of crops would need to produce enough biomass to support 20 base stations for a year, taking land away from food production. Biofuel projects therefore only work well in regions with no access to the power grid and where the cost of buying and transporting petroleum-based diesel exceeds the cost of local agriculture — they're not optimal for the developed world, for which Ericsson has devised a different power-saving technology.

Vodafone Germany in December installed Ericsson software that essentially shuts itself down during periods of low activity. By powering down components when not in use, Ericsson estimates operators can cut down on 10% to 20% of the base station's daily power consumption.