Salt: The Hidden Power Source of the Future

The Energy Hidden in Plain Sight

Every day, millions of tonnes of freshwater flow from rivers into the sea. And every day, an enormous amount of energy is quietly released and lost — energy generated by the mixing of salt water and fresh water.

This energy source — known as Salinity Gradient Power (SGP) — has been understood by scientists for decades. The thermodynamic potential of mixing seawater and freshwater is equivalent, per unit volume, to water falling from a height of approximately 230 metres. Yet until recently, harnessing it efficiently and at scale remained elusive.

MediSun is changing that.

How SGP Works: The Science of Salt

When water of different salt concentrations is separated by a semi-permeable membrane, ions migrate from high concentration to low concentration — generating voltage. This is the principle behind Reverse Electrodialysis (RED), the core technology in MediSun's WEGen system.

In a RED stack, alternating cation-exchange and anion-exchange membranes are placed between high-salinity water (such as seawater or desalination brine) and low-salinity water (such as freshwater or treated wastewater). As ions flow through the membranes, electrical current is produced — clean, continuous, and without combustion.

Unlike solar or wind, SGP is not intermittent. Rivers flow day and night, all year. Estuaries are constant. And in the context of desalination, the brine reject stream represents a permanent, concentrated source of salinity gradient — one that is currently discharged as waste.

The Global Potential

Researchers estimate that the global potential of SGP at river estuaries alone is approximately 30 terawatts — roughly equivalent to twice the world's current electricity consumption. Even capturing a small fraction of this potential would represent a transformative contribution to the global energy mix.

For the desalination industry specifically, the opportunity is even more targeted. Desalination plants create an artificial salinity gradient — the concentrated brine they discharge is far saltier than seawater. By passing this brine through RED stacks alongside lower-salinity water, operators can recover energy directly from their waste stream, reducing the net energy cost of producing freshwater.

WEGen: Making SGP Practical

MediSun's WEGen system is designed as a retrofit — it integrates with existing SWRO desalination infrastructure rather than requiring greenfield construction. WEGen stacks are inserted at two points in the desalination process:

• At the intake: RED stacks use the salinity difference between incoming seawater and lower-salinity source water to pre-generate power and reduce feedwater salinity before it enters the RO membranes — reducing Specific Energy Consumption (SEC) by up to 30%.
• At the brine reject: Additional RED stages process the concentrated brine through multiple salinity gradient steps, extracting energy and simultaneously diluting the brine before discharge.

Each WEGen stack handles 500 m³ of water and can generate up to 2.9 kWh of renewable electricity — while reducing discharge salinity to levels that match natural seawater.

A Future Powered by What We Already Have

The elegance of SGP lies in its simplicity: it requires no fuel, no combustion, no rare materials, and no disruption to existing infrastructure. It runs on the same physical process that has been occurring at every river mouth since the oceans formed.

We envision a future where every estuary is a power plant, every desalination brine stream is an energy asset, and the water that has always given life begins also to power it.

Salt, it turns out, was never just a seasoning. It was always an energy source. We just needed to learn to listen.