Power on the sea bed

Fuel cells powered by energy from the sea floor could indefinitely supply electricity to instruments used to monitor ocean currents and water temperatures.

Fuel cells powered by energy from the sea floor could indefinitely supply electricity to instruments used to monitor ocean currents and water temperatures, according to a report in the December 2000 issue of Environmental Science & Technology.

The small, lightweight devices have been likened to cleaner, safer batteries that never run down. Fuel cell technology has been used by NASA for onboard power during space flight and is currently being investigated for use in motor vehicles and home power.

The researchers found that the electrical potential of sediment on the sea floor differs from the electrical potential of the surrounding salt water. According to Leonard Tender, a co-author of the study from the US Naval Research Laboratory in Washington DC, collecting power from that differential could supply energy for fuel cells for self-sustaining oceanographic equipment.

Organic matter in sediment on the ocean floor ordinarily releases energy as it decays. In shallow waters -less than 1,000 meters – that energy is concentrated just below the ocean floor.

Energy for the fuel cell – like the voltage between opposite poles of a battery – comes from a reaction involving chemicals released from the buried sediment and the oxygen, according to co-author Clare Reimers of the Oregon State University.

The battery-powered equipment now used for ocean monitoring must be periodically raised or replaced to replenish power, said Tender. This is a costly, time-consuming process, he added. In contrast, decaying marine organisms could continually recharge the fuel cell described in the research.

‘These devices could significantly reduce the cost of ocean monitoring, which is important for naval and commercial marine operations and early warning of changes in marine ecosystems and resources,’ said Reimers.

In laboratory testing, the researchers were able to harvest approximately one microWatt of power per centimetre of fuel cell – the amount needed to power a small light-emitting diode, said Tender. The researchers are field-testing the fuel cells in the ocean and trying to get more power from them, he said.

‘We calculate that optimised power supplies could run oceanographic instruments based on this phenomenon for routine long-term operations in the coastal ocean,’ concluded Tender.