Membrane-less osmotic power
Osmotic power is a newly emerging renewable energy gaining more and more recognition amongst scientists. This energy occurs where fresh water meets salt water, a natural phenomenon that occurs all over the world where rivers flow into the sea and ocean. As an approximation, every litre per second of fresh water flowing into the ocean represents a raw potential of 1kW. With the Amazon river being the largest in the world at an average flow rate of 209 000 000 L/s, the potential impact of this technology is tremendous.
The technology works as follows. By placing a semi-permeable (allows the water but not the salt to pass through) membrane between a fresh-water and salt-water compartment, the water will naturally flow through the membrane to the salt-water compartment due to a difference in pressure between the two liquid bodies. This will result in an increase in pressure in the salt-water compartment, until an equilibrium is reached. This equilibrium pressure is known as the “osmotic pressure” and is equivalent to the hydrostatic pressure at the bottom of a 300m high water dam.
The increase in pressure in the salt-water compartment can then be utilised to push water through a turbine to create electricity.
This sounds all good and simple, however there is one major downside to this technology… The cost of producing and maintaining the membranes! These membranes are so expensive that it caused Statkraft (the leading renewable energy generator) to shut down the first osmotic power plant in 2013 as it was just simply not financially profitable.
But what if there was a way to get the exact same energy without these membranes? Impossible? Well this is where DeltaDriven24 comes in.
At DeltaDriven24, we have developed a patented technology to entirely remove the need of membranes, reducing the cost of the technology by 50%. Put simply, we use evaporation to do the same job as the membranes.
In the same way that there is a difference in pressure between the two liquid bodies seen earlier, when a closed system as shown here is created, where the gas is solely vapour, the two liquids have different vapour pressures. This will result in the system trying to reach an equilibrium by evaporating the fresh water (high pressure) and condensate it in the salt-water compartment (low pressure). This vapor flow will result in an increase in the salt-water column which can be used in the same way as a dam to create electricity.
However, as seen previously, the equilibrium will only be reached once a height of about 300m is attained. This will result in the need for very big dimensions, making this solution not ideal.
This is why at DeltaDriven24, we took the technology a step further by replacing the gravitational force by a centrifugal force. Doing so allows the water column to be much smaller whilst maintaining the same output power. With everything else working in the same manner, the hydrostatic pressure at the bottom of the salt-water column is no longer used to push the water through a turbine, but instead, to create a water jet that will keep the cylinder in rotation.
These small dimensions allow the technology to be highly adaptable, with even the possibility to be on boats. As a result, there is no need to have permanent infrastructure and allows the technology to have minimal environmental impact, making it one of the most eco-friendly source of energy to date.
For example, boats placed at the Rhine river mouth in the Netherlands, only recuperating 1% of the average river discharge could provide electricity for 40 000 households, all without the need for permanent infrastructure! In contrast, the Yangtze river in China with the same percentage of flow captured would power roughly 550 000 households. This is simply due to the volume of fresh water moving every second.
The potential of membrane-less osmotic power recuperation as described in this article is non debatable and presents huge opportunities worldwide. Intrigued ? Feel free to reach out to the DeltaDriven24 team to know more !