Application of small independent solar cell system in pumping irrigation and cathodic protection

Application of small independent solar cell system in pumping irrigation and cathodic protection

Photovoltaic pumping irrigation system

Most areas of China’s Tibet, southern Xinjiang, Qinghai and western Inner Mongolia are arid and rainless, rivers are scarce, surface water is lacking, and the groundwater depth is more than 10m, but the reserves are abundant, and the solar energy resources in these areas are abundant, and the irrigation season is the peak period of the sun. Therefore, it is very beneficial to use solar energy for water lifting and irrigation. The photovoltaic water pumping system mainly includes three parts: solar cells, water pumps, water storage and water distribution systems.

Photovoltaic pumping irrigation systems can generally be used in occasions with large water demand. They can be set up scattered or close to the water supply location. The parameter selection of irrigation equipment depends on the solar radiation, temperature, pump output of the specific location, and external conditions in mechanical technology.

Application of solar cells in cathodic protection

Generally, natural gas or other pipelines buried underground will cause corrosion if they are soaked in an environment with soil characteristics similar to electrolyte for a long time, which will seriously affect their safety and service life, especially for long-distance transmission, due to the long pipeline, maintenance and inspection are more difficult. In order to prevent or slow down the corrosion of the pipeline, when laying the pipeline, a small solar panel can be installed as a DC power source at a certain distance. It is used with the auxiliary anode to protect the metal pipeline of the cathode by sacrificing the anode. Therefore, it is the most effective and economical way to protect a metal pipeline of tens of kilometers or longer in sections, and to provide a DC voltage with a solar array.

Metals used under various conditions are generally subject to two types of corrosion, namely chemical corrosion and electrochemical corrosion. Chemical corrosion is caused when the metal is in contact with the medium chemically. Its characteristic is that there is no current generated during the action: electrochemical corrosion is another type of extremely extensive corrosion. It is because when the metal surface is in contact with the electrolyte solution (such as water and soil), the potential on the metal surface is not the same, some places have high potentials, and other places have low potentials, resulting in the formation of corrosive galvanic cells. Therefore, the electrochemical corrosion process can be seen as consisting of the following three links:

① The metal dissolves at the cathode and turns into metal ions into the solution, that is, Me→Me++e (anode process).

②The electrons flow from the anode to the cathode through the metal.

③At the cathode, the flowing electrons are accepted by the substance (D) that can absorb electrons in the solution, that is, e+D →[D, e] (cathode process).

The above three links are interrelated and indispensable. If one of the links stops, the entire corrosion process also stops. Electrochemical corrosion has electric current, so the applied electric current method as shown in Figure 1 can be used to protect metal pipes from corrosion. It connects the negative pole of the DC power supply to the protected metal pipe so that the entire surface of the protected metal is the cathode, and connects the positive electrode to an auxiliary anode made of insoluble materials such as graphite, high-silicon iron, carbon ferrite, lead-silver alloy, and platinum-plated titanium. When the applied driving voltage is higher than the minimum protection potential required by the metal, the pipeline is in the current protection range. For remote areas, solar cells are economical and convenient as a direct current source.

Application of small independent solar cell system in pumping irrigation and cathodic protection
Figure 1 – Schematic diagram of impressed current cathodic protection

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