Osmosis power: Mini generator creates energy from salt water

Nanoscientist Aleksandra Radenovic, explores the wonder of osmosis (also known as blue energy) power generation.

Wind and solar power are some of the ways in which the world is progressing towards clean and sustainable renewable energy than its traditional coal and oil energy sources. Unbeknown to many, osmosis, also known as blue energy is another sustainable energy source. To Aleksandra Radenovic, a nanoscientist at the Swiss Federal Institute of Technology, a world of untapped renewable energy is at our fingertips.

Radenovic recently published the schematics of a brand-new flatly shaped, membrane-like mini power generator. It operates by drawing on osmosis-produced energy – this occurs when the salts in the salty water are expelled into the fresh water through the membrane. At its thinnest point, the generator compromises of three atoms and has been suitably identified to be used in areas where waters of different salinities constantly mix.

Unpacking the generator

Radenovic’s generator has at its epi-centre a thin sheet (the membrane) that is made from an inexpensive compound called molybdenum disulphide. This sheet is dotted with a series of tiny holes that are only just large enough that salts of a specific size can funnel through it. As a result of the type of material used to produce the sheet the holes are electrically charged naturally and this repels other salts.

Together with her research team Radenovic started an experiment using a small piece of the membrane punching only one hole into it – it was dubbed by the team as a nano-pore. A box with two compartments was then erected, each filled with water with varying salinity levels. Radenovic then used the small-scale membrane to connect the two compartments. With each movement of the salts towards equilibrium the grains pushed through the nano-pore and generated a small surge of electricity. This occurred as a result of the salts already having a small amount of electrical charge and it therefore enabled it to create current through their movement.

This mini generator holds a great deal of power potential – with Radenovic explaining that if you were to simply expand on the nano-pore experiment to a larger scale (say 3 x 3 sq. ft. made up of her device) and only stud 30 per cent of the membrane material with these nano-pores, it could produce a megawatt of power through the osmosis of fresh and salty water. To put it into perspective: That is sufficient energy to run about 50 000 energy-saving light bulbs.

Although Radenovic and her team have made this prototype with the nano-pore, the team is still unsure how to evenly puncture millions of nano-pores for larger membranes. “So we are still far away from this [megawatt] number,” she notes. The research is still underway but with a little innovation and perseverance the power of osmosis will soon be realised.