Stanford scientists harness energy from mixing of fresh and saltwater

Scientists at Stanford University have announced the development of affordable, durable technology that could harness so-called blue energy. A research paper recently published describes the battery and claims that the battery could be a source of renewable energy in places where freshwater and saltwater mingle. The team says that blue energy is an "immense and untapped source of renewable energy."

The battery the team at Stanford has created is a significant step forward in capturing that energy without membranes, moving parts, or putting energy into the effort. The battery taps into salt gradients. The battery prototype was tested, and the scientists monitored its energy production while flushing it was alternating hourly exchanges of wastewater effluent from the Palo Alto Regional Water Quality Control Plant and seawater collected from Half Moon Bay.

Over 180 cycles, the battery materials maintained 97% effectiveness in capturing the salinity gradient energy. The team says that the tech could work anywhere freshwater and saltwater intermix, but wastewater treatment plants are a particularly viable case study. The treatment of wastewater is energy-intensive and accounts for about 3% of the total US electrical load. The battery tech could help make wastewater plants energy independent.

The team says that every cubic meter of freshwater that mixes with seawater produces about .65 kilowatt-hours of energy, which is enough to power an average home for about 30 minutes. Globally the team says that theoretical recoverable energy from wastewater treatment plants located on coasts is about 18 gigawatts, enough to power 1,700 homes for a year.

Energy is produced when sodium and chloride ions from the battery electrodes are released into the solution, making current flow from one electrode to the other. The rapid exchange of wastewater effluent with seawater leads the electrode to reincorporate the sodium and chloride ions and reverse current flow. The result is a battery that constantly charges and discharged with no need for upfront energy investment.