For a truly ‘blue’ aquaponics system, as currently under development by the TopFarmers – team, the question about sustainable energy supply is central. In the long run the system shall be mainly supplied from renewable energy sources, which provides independence from fossil fuels, reduces CO2 emissions and saves money.
In the following we want to introduce a Do-It-Yourself Savonius turbine, with which one can easily harvest wind to provide small amounts of electricity. It requires very simple materials, only a few hours of work and no special tools.
The decision to build a Savonius turbine was developed after only some time researching the topic, and it became clear to us that this type of turbine fits our needs best. The Savonius turbine is a vertical axis wind turbine (VAWT) that was originally designed by the Finnish engineer S.J. Savonius in 1922 and has become increasingly popular in recent years. The construction of the turbine is fairly easy and does not require any special materials. We decided on a VAWT because it can be assembled from scrap materials like barrels, pipes, metal bars and wood. Although it has a lower efficiency as compared to horizontal axis wind turbines (HAWT), it does not require any instruments to move the turbine into the wind. This is due to the special design features that allow the turbine to intercept the wind coming from all directions, as opposed to HAWTs that need a mechanism of direction control, which is very complicated to build on your own.
Due to their way of catching wind power (working by “drag” force, not “lift” force) the Savonius rotor can be used for producing electricity as well as pumping water. Therefore we had to find a way of increasing the rounds per minute (RPM) value of the turbine to match it with an electric generator (which usually works at 90 RPM). Moreover, we had to consider the torgue as an important parameter to pump water. Consequently we decided to build the blades from a PVC pipe instead of using a barrel, because the slender of the pipe (whose ration height/diameter is greater than that for the plastic barrel) can guarantee a higher RPM at the same swept area.
We chose a simple PVC water pipe with a diameter of 160 mm and 100 cm length and cut it into two symmetrical parts.
For the axis that transmits the blade’s rotation to the generator we used a 100 cm long threaded rod with a diameter of 10 mm. This was passed straight between the two partially overlapping PVC blades.
To reduce the friction between the axle and the frame construction, we installed two ball bearings with an outer diameter of 27 mm. Both were placed in a small piece of wood that was fixed to the outer frame; one at the top and one on the bottom.
For the frame we used wooden slats because they are easy to assemble and give great stability. The top and bottom sides on which the blades and bearings are fixed are made from very thin wooden plates and have a diameter of 40 cm. Finally, we used metal clamps to connect the plates with the slats.
In the picture below you can see the end-product of our work. As you can see, the rotor is well supported which gives it maximum stability and support even in high wind speeds.Furthermore, due to the low weight and the ball bearings the rotation starts at very low wind speed. In the next step we want to match the rotor with a mechanical or belt gear to generate electricity. Most recommended are permanent magnet generators (PMGs) because they do not need an external source of power to initiate the turning and start to produce energy at relatively low RPM values.