Blue Electricity Offers Enormous Clean Energy Potential
Generating energy on a large scale by mixing salt and fresh water is both technically possible and practical, and worldwide potential for this clean form of energy – known as ‘blue energy’ or ‘blue electricity’ — is enormous. However, in order to reap the benefits, it will be necessary to work actively on several essential technological developments and to invest heavily in large-scale trials.
The principle of generating electricity by mixing salt and fresh water, taking advantage of the difference in charge that results, has been known for more than 100 years. It was first tested in practice in a laboratory in the 1950s. There are two methods for generating blue energy: pressure-retarded osmosis and reverse electrodialysis.
J.W. (Jan Willem) Post, of Wageningen University, has focused his research mainly on the latter because it is the more attractive method of generating energy from sea and river water. With his research into the practical applicability, techniques and preconditions for large-scale energy generation from salinity gradients, he was the first to demonstrate that very high yields are possible. In the laboratory, it is possible to recover more than 80 percent of the energy from salinity gradients. The technical feasibility would be 60 to 70 percent and the economic feasibility a little lower than that.
There are differences among continents. For example, the technical potential in Australia (65 percent) or Africa (61 percent ) is greater than in South America (47 percent). There also are considerable differences between the 5472 large rivers worldwide. These differences depend on the salt concentration in the rivers and seas, temperature, and environmental factors. The Rhine is one of the most ‘energetic’ rivers in Europe.
Post has investigated the possibility of recovering energy from the Rhine and the Maas rivers. He estimated the technical potential of both rivers to be 2.4 gigawatts per year and believes it would be economically feasible to recover 1.5 gigawatts; enough to supply 4 million households in the Netherlands. A power station of around 200 megawatts — comparable with a park containing 200 wind turbines — could be placed at the Afsluitdijk (the famous Closure Dike in the Northern part of the Netherlands) which, according to Post, is a rather suitable place for the large-scale trials that need to be carried out.
This test location on the Afsluitdijk could be combined with the redesign of the dike that is already being planned. Heavy investment is necessary, but this type of clean energy is extremely promising and, since it is essential to look for alternatives to fossil energy, this investment could be worthwhile in every respect. However, it will be at least 10 years before the first commercial power stations are operational, Post says.
Post believes that, in the next few years, it will be necessary to work even more intensively on two technological developments that will bring down the present, rather high, price of generating blue electricity. An appropriate membrane technology should be developed and, furthermore, such membranes should become much cheaper by introducing mass production. The technique also should be robust enough to work both when the water is polluted and when living organisms accumulate on the membranes (biofouling). His research showed that both hindrances could be removed in the future.
