Using Solar Photovoltaic Energy for Irrigation: A Review of the Application

Modern agriculture, orcharding, gardening, as well as the use of grassy sports fields cannot be realized without irrigation. Such a procedure requires water and energy resources. Water resources define even consideration for the possibility of irrigation, while energy source is the second task which must be satisfied. Nowadays, using renewable energy sources for irrigation is a very promising solution, despite the still extensive use of fossil fuels. Application of the solar photovoltaic (PV) energy is a very promising solution, due to the availability of insolation and its overlapping with water needs for the plant growing. PV energy could be implied in isolated and remote locations and islands, as well as in desert areas. This paper will give insight into the actual “state of the art” of using solar photovoltaic energy for the purpose of the irrigation. Check for updates Citation: Đurin B, Lajqi S, Plantak L, et al. (2020) Using Solar Photovoltaic Energy for Irrigation: A Review of the Application. Adv Environ Stud 4(2):358-367 Đurin et al. Adv Environ Stud 2020, 4(2):358-367 Open Access | Page 359 | mum power available from the PV panels. However, inverters are designed to being incorporated with an MPPT device, so that additional MPPT devices are not required. Role of the switch controller is controlling the solar battery (accumulator) overcharging [2]. Due to the purpose of this review paper, procedure for usually diesel generators, or connection with an electro distribution grid, are required as an additional source of energy for the case of lack of the insolation. This refers to cloudiness, or even for days without insolation. Generally, motors powered by PV are connected to any variable-speed (centrifugal) pump. Maximum power point tracking (MPPT) system scan be used to track the position of the Sun, i.e. to obtain maxiFigure 1: Energy flow (circle) between the Sun, the atmosphere and the ground. Figure 2: The most common parts of PV water pumping systems [2]. Citation: Đurin B, Lajqi S, Plantak L, et al. (2020) Using Solar Photovoltaic Energy for Irrigation: A Review of the Application. Adv Environ Stud 4(2):358-367 Đurin et al. Adv Environ Stud 2020, 4(2):358-367 Open Access | Page 360 | Figure 4. Generally, a salient pole rotor is used on which rotor winding is mounted. Rotor winding is fed with a DC supply with the help of slip rings. Rotors with permanent magnets can also be used [7,8]. An asynchronous motor is also popularly called as Induction motor. At the Asynchronous or Induction motor, stator winding is similar to that of a synchronous motor. It is wound for a specific number of poles, Figure 5. A squirrel cage rotor, or a wound rotor can be used. In a squirrel cage rotor, the rotor bars are permanently short-circuited with end rings. In wound rotor, windings are also permanently short-circuited, hence no slip rings are required [7]. Stator poles of the synchronous motor rotate at the synsizing, as well as all required equations will not be written here, but they can be found in [3-6] where authors have in details explain all nomenclature, order and procedures for sizing of the solar photovoltaic irrigation systems. Such was done regarding different configurations of analyzed PV irrigation systems. Motors Generally, motors for pump driving can be divided as an AC and DC motors. AC motors can be divided into two main categories; these are Synchronous and Asynchronous motor. Stator of the Synchronous motor has axial slots, which consist of a stator winding wound for a specific number of poles, Figure 3: Main composing parts of the solar photovoltaic generator. Figure 4: Synchronous motor [8]. Citation: Đurin B, Lajqi S, Plantak L, et al. (2020) Using Solar Photovoltaic Energy for Irrigation: A Review of the Application. Adv Environ Stud 4(2):358-367 Đurin et al. Adv Environ Stud 2020, 4(2):358-367 Open Access | Page 361 | justed to lagging, unity or leading by varying the excitation, whereas an induction motor always runs at a lagging power factor. Synchronous motors are generally more efficient than induction motors. Synchronous motors are costlier [7]. The main characteristics of a squirrel-cage induction motor are: Motor speed, slip, torque, and efficiency. In the following, each of these characteristics are written in more details [9]. The speed of a squirrel cage motor depends on the electric line frequency and the number of poles in the motor. The synchronous speed of motor is the design speed of the motor based on frequency and the number of poles. The stator windings can have any even number of pairs of poles. Most motor designs have between 2 and 12 pairs of motor poles. An induction motor’s rotor must turn slightly slower than the stator’s rotating magnetic field for a current to be induced into the rotor. The difference between the synchronous speed and the actual speed is known as slip. Motor torque is the work that a motor does and is defined as a force of one Newton a lever of one meter. The unit of measure is [Nm]. In current practice, motors tend to be between 80-95% efficient. Motors usually achieve peak efficiency at around 75% of full load. The motor’s efficiency will be significantly less at light loads. Care must be taken when replacing a motor to be sure that the replacement motor is not oversized, which causes reduced efficiency [9]. chronous speed when fed with a three-phase electric energy supply. The rotor is fed with a DC supply. The rotor needs to be rotated at a speed near to the synchronous speed during starting. If done so, the rotor poles get magnetically coupled with the rotating stator poles, and thus the rotor starts rotating at the synchronous speed. Regarding asynchronous motors, when the stator is fed with two or three phase AC supply, a Rotating Magnetic Field (RMF) is produced. The relative speed between the stator’s rotating magnetic field and the rotor will cause an induced current in the rotor conductors. The rotor current gives rise to the rotor flux. According to Lenz’s law, the direction of this induced current is such that it will tend to oppose the cause of its production, i.e. relative speed between stator’s RMF and the rotor. Thus, the rotor will try to catch up with the RMF and reduce the relative speed. Induction motor always runs at speed which is less than the synchronous speed [7,8]. Synchronous motors require an additional DC power source for energizing rotor winding. Induction motors do not require any additional power source. Slip rings and brushes are required in synchronous motors, but not in Induction motors (except wound type induction motors in which slip ring motors are used to add external resistance to the rotor winding). Synchronous motors require additional starting mechanism to initially rotate the rotor near to the synchronous speed. No starting mechanism is required in induction motors. The power factor of a synchronous motor can be adFigure 5: Asynchronous or Induction motor [8]. Citation: Đurin B, Lajqi S, Plantak L, et al. (2020) Using Solar Photovoltaic Energy for Irrigation: A Review of the Application. Adv Environ Stud 4(2):358-367 Đurin et al. Adv Environ Stud 2020, 4(2):358-367 Open Access | Page 362 | In a series DC motor, the field is connected in series with the armature. The field is wound with a few turns of large wire because it must carry the full armature current. A characteristic of series motors is the motor develops a large amount of starting torque. However, speed varies widely between no load and full load. Series motors cannot be used where a constant speed is required under varying loads. Additionally, the speed of a series motor with no load increases to the point where the motor can become damaged. Some A DC motor consists of two basic parts stator and rotor, Figure 6. The outer frame of a DC machine is called a yoke. It is made up of cast iron or steel. It not only provides mechanical strength to the whole assembly but also carries the magnetic flux produced by the field winding. Poles are joined to the yoke with the help of bolts or welding. They carry field winding and pole shoes are fastened to them [10]. Figure 6: DC motor [10]. Figure 7: Centrifugal pump [14]. Citation: Đurin B, Lajqi S, Plantak L, et al. (2020) Using Solar Photovoltaic Energy for Irrigation: A Review of the Application. Adv Environ Stud 4(2):358-367 Đurin et al. Adv Environ Stud 2020, 4(2):358-367 Open Access | Page 363 | motion is imparted to the fluid through the rotation of the vanes and the water is then discharged through the outlet of the casing. By varying the particular designs and arrangements of centrifugal pumps, they can be constructed to suit specific needs or requirements [13]. Fluid enters the pump through the intake and reaches the impeller along, or near to, the rotating axis. It is accelerated by the impeller before flowing outwards through a diffuser or volute chamber. The pressure increases or the head of fluid that can be lifted by a single impeller is limited. Some centrifugal pumps will use several impellers and diffusers in series, with each impeller/diffuser stage increasing fluid pressure by a set amount. When combined the head of fluid that can be lifted becomes significant [14]. More suitable for well are centrifugal multi step Submersible Pump, Figure 8 [15]. Volumetric Pumps use volume variation within a chamber to create suction and thrust of a fluid, Figure 9 [16]. The fluid is first sucked into the chamber, creating a vacuum therein and then expelled from the chamber, thus increasing the pressure inside it. For example, the heart of a mammal is a volumetric pump. Volumetric pumps move constant volumes of liquid for each operating cycle since the chamber has a maximum defined and invariable volume. One operating cycle corresponds to a complete rotation (360°) of the drive shaft. The volume pumped per unit of time (l/min or gpm) is independent of the fluid pressure, while it is directly proport