Areas where river water and seawater converge are not typically the first place one thinks of as a renewable energy opportunity, but researchers from MIT are assessing hydroelectricity’s place in the burgeoning renewable energy grid.
The team studied a new method of power generation called pressure retarded osmosis (PRO), where water streams with different salinity levels pass across a barrier and create a flow that can be sent through a turbine to produce power.
The study found that an increase in the membrane’s area generally resulted in more power. However, this is not true all the time – up to 95% of a system’s maximum output could be generated with only half or less of the maximum membrane area. The study’s authors suggest that reducing the necessary membrane areas to maximize return on investment could help reduce the initial costs associated with the implementation of such a system.
The authors also mention that research to reduce membrane size and area in relation to their power output potential is still in its infancy.
The study went on to note that the salinity of the water streams being used can vastly impact the energy production of PRO facilities. As opposed to simply using river water and seawater, the team found that a mix of brine and treated wastewater can produce twice as much power. Extrapolating from this idea, the researchers posit that in the future, coastal wastewater treatment plants could generate all of their electricity by combining the brine byproduct of desalination with normal river water.