RENEWABLE ENERGY
W ENERGY BLUE
hen you want to disgorge a cucumber, you sprinkle it with salt. Tis creates a very salty solution on its surface that
causes water to move from the inside of the cucumber to the outside. Tis is an example of osmosis. Te key point is that the water moves under the action of a driving force, called the osmotic pressure, caused by the concentration difference of salt. Tis force is also important in our harnessing of blue energy, a sustainable type of power from sea and river water. Osmotic forces are found in the biological world in a considerable variety of phenomena: to store energy, induce mechanical motion, or control ejection and absorption of compounds, for instance. Humanity faces a major challenge for the near future: if we want to minimise climate change caused by human activity, it is of the utmost importance to change our energy consumption habits and turn to viable,
renewable and non-polluting energy sources. In this context, nanomaterials play a
role that we believe will become essential in the future, providing solutions to technical problems and often opening up new perspectives. In our search for new energy solutions, it might be useful to draw inspiration from living organisms. For example, research mimicking photosynthesis is being conducted to find new solutions for energy storage. We are also seeking to use osmotic
pressure as a new source of energy in the same way as wind, hydraulic force or the sun. More precisely, we can ask ourselves whether it would be possible to use osmotic force to efficiently extract energy from sea water, the so-called blue energy. Blue energy is the energy that could
be harvested from differences in salinity, by mixing sea water and fresh river water. An estimate could be done by counting estuaries over the Earth, amounting to
Stéphane Pleutin reveals how nanomaterials can trigger off a new source of energy
8,500TWh. When we compare this to energy production from other resources, we see the scale of the potential. In 2015, hydraulic energy production was about 4,000TWh, nuclear energy around 2,600TWh and wind and solar a combined 1,100TWh. According to this estimate, blue energy is so plentiful that it could feed all our needs, if we can just find an effective way to tap it. How can we manage this fantastic driving force to harvest electricity? Among several approaches that are being developed, the most promising are pressure-retarded osmosis (PRO) and reverse electro-dialysis (RED). PRO uses the flow of water through the membranes, producing pressurised water that generates electricity using mechanical turbines. RED, on the other hand, uses membranes for ion transport, not water, and the electrical current generated is captured directly from the flow of ions. Tis technique is currently being explored
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www.engineerlive.com Blue energy has remarkable
potential but also many challenges
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