Plastics take a dip
Plastics excel in turbines!
Photovoltaics and wind power appear to have ousted hydropower, which is often associated with the disturbances caused by large dams. However, this type of energy still has a lot to offer: it is continuous, cheap and still under-exploited despite the 21,000 small power stations in Europe. This is the reason for renewed interest in small generators producing less than 20 kW. New Zealand-based company PowerSpout started the ball rolling with a mobile microturbine whose shell is made from polyethylene and whose mechanism is mostly made up of polyamide parts. The turbine is suited for low water flows from one litre per second, and outputs one kilowatt of power.
Aquakin, a German start-up company based near Nuremberg designed several hydroelectric microplants intended for various applications. The lightest, christened Blue Freedom, is in fact a portable "charger" intended for hiking. When immersed in a stream or river, this 400 gram plastic generator, the size of a frisbee, produces 5 W of power that can charge a mobile phone in an hour. For the home, Aquakin developed a prototype of a flat composite turbine to be anchored in shallow waters near dykes or diversion bays. With its 20 kW of power, it can produce around 160,000 kWh per year, the equivalent of the annual consumption of around thirty homes. Its Bavarian rival, Smart Hydro Power, is already selling a slightly less ambitious, although lighter floating, turbine. Its mixed high-density polyethylene (HDPE) and aluminium structure with composite blades has a more modest power of 5 kW.
Elastomers take to the seas
Driven by the ambitions of the Monegasque company SBM Offshore, piezoelectric technology took to the seas in 2007 with a wave energy system christened S3. It is comprised of a battery of 300-metre long flexible tubes immersed under the surface of the sea, whose electro-active polymer membrane is able to convert the movements of the waves into electricity. In the long term, a dozen of these snakes could produce around 400 kW of low intermittency power.
Across the pond, the Stanford Research Institute, working in the field of marine energy, is developing the first applications for the EPAM process (Electroactive Polymer Artificial Muscle) from Japanese start-up company Hyper Drive. For the time being, they are simply replacing the autonomous yet intermittent photovoltaic energy produced by signalling buoys with electricity generated by electroactive elastomer pistons. In the medium-term, however, the consortium expects to increase the process' capacity by increasing the number and size of its wave energy devices.
Synthetic fibres leverage osmosis to create energy
The principle of osmosis is a simple one: when two tanks are put together, one with salt water and the other with fresh water, the two volumes combine to balance their salinity. However, when they are separated through a membrane which lets through the water and captures the salt, the salt water tank sucks in the fresh water and fills up through the process of osmotic pressure. To take advantage of this phenomenon, the salt water can be emptied at the top of the reservoir in order to power an electric turbine at the bottom. This type of energy has many advantages. It is renewable, thanks to the water from rivers and the sea, it is constant and it is environmentally neutral.
The membrane is obviously the key element of the process. In order for it to be effective, the membrane has to be highly permeable to water, fine enough to filter the salt, and strong enough to withstand the pressure, and it has to be big. For a yield of 2 to 3 W per sqm, 200,000 to 250,000 sqm of cellulose acetate synthetic membrane are required to produce one megawatt in an experimental power station such as the one built by Statkraft at the mouth of the Oslo Fjord.
Nanotubes to boost osmotic power
Reverse Electro Dialysis aims to be an alternative to traditional osmosis. This technique is also based on the exploitation of the potential of fresh water and sea water and uses ion exchange membranes to separate sodium or chlorine from the salt water. It therefore serves to create an ionic current which can immediately be converted into an electrical current, bypassing the need for the mechanical energy of a waterfall or a turbine.
Since 2012, REDStack has been working with Fujifilm on experiments, on various types of copolymer-based membranes in this type of power station, in the Netherlands. The next step, the integration of nanomaterials, seems promising. Even more so because researchers at the Institut Lumière Matière in Lyon showed in 2013 that filtration through Boron-Nitrogen nanotubes could help boost the energy efficiency of the membranes..