Archive for 18 de noviembre de 2012


Posted By  On Nov 16, 2012 In Water In AmericaWater Technology & Innovation

Logan in lab, 2012

Penn State researchers see a great deal of unused, available energy in saltwater. Bruce E. Logan, a professor at the university who is leadingresearch on the topic, says the salinity differences between fresh and saltwater can produce electricity.

Salinity gradient energy technology uses the naturally occurring energy found when fresh and salt water mix. The concept was originally developed in the 1970s, but research and development has progressed slowly despite its potential.

“A remarkable amount of energy is available from the salinity difference between sea water and fresh water,” explained Logan. “In theory, up to 0.8 kilowatts per cubic metre could be extracted — equivalent to the energy generated from water falling over a dam more than 280 metres high. The limiting factor in obtaining this energy is the supply of fresh water: about 2 terawatts (1 TW is equal to 1,000 gigawatts) is available globally from rivers flowing into the sea, of which perhaps 980 GW could be harnessed.”

Those places where effluents are discharged, such as coastal sewage treatment plants, could prove ideal locations for these types of systems. Wastewater released into the ocean could create another 18 GW of salinity-gradient power.

“You always have wastewater where you have people. And you’ve got a lot of wastewater being generated at the coastline,” said Logan.

Among the possible technologies that might be applied for creating salinity gradient power are pressure-retarded osmosis and reverse electrodialysis. Pressure-retarded osmosis uses flowing water that passes through membranes to produce pressurized water. Electricity is generated in this system using mechanical turbines. Reverse electrodialysis creates energy based on ion flow.

These systems have been used for capturing natural salinity-gradient energy using sea water and river water; however, both technologies are relatively costly. Another challenge is that these systems are hampered by membrane fouling.

Salinity gradients are one of five different ways in which ocean energy can be harvested. In a 2007, it was estimated that salinity gradients could generate 2,000 TWh of energy per year, or 11.5% of theglobal energy production.

Most of the research being conducted on this type of osmotic power generation is reportedly occuring in Norway and the Netherlands.

Additionally, the Penn State scientists are working on adapting the concept to work with low-temperature waste heat from which additional energy can be extracted. Logan says power plants typically generate two times the waste heat versus the electricity produced. Pressure-retarded osmosis and reverse electrodialysis technologies can be adapted to capture the waste heat.

Because these technologies are still relatively undeveloped, questions remain about their potential environmental impact — which may be negligible — and costs when operating at a large scale.

However, these innovations should not be ignored. As Logan explains:

Water can continue to make energy for us in many new ways, not just channeling it through a hydroelectric dam. […] We’re just not taking advantage of it. And we’re wasting a lot of energy every day at wastewater treatment plants and existing power plants around the world. It’s time to change that.

Logan and his colleagues published (PDF) their findings earlier this year in the journal Science.

18 de noviembre de 2012 at 21:53 Deja un comentario

noviembre 2012