University of South Wales Master of Sciences Thesis
Standalone hybrid generation system for the remote area of Thar, Pakistan
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- 2.2.3. PV Design and Array sizing approaches
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Standalone hybrid generation system for the remote area of Thar, Pakistan 2.2.2. PV Array System configurations In the stand-alone hybrid power systems, PV-array system is used in such a way that loads can be supplied any time in an efficient way. The intensity of solar irradiation varies with time and season. So, the most advisable and efficient way of harvesting the solar energy is by connecting energy storage devices (batteries) in such a way that loads can be supplied any time and the battery can store whenever there is excess supply from the PV-array system. Then, the stored energy in the battery can be used during times where there is less supply or there more demand. Commonly, most appliances and loads are designed to operate on AC. However, the PV-array system only gives a DC power. Thus, an inverter (DC/AC converter) is a must to be used so that AC loads can be supplied from the PV-system. Fig. 2.4: PV-system supplying AC loads connected at the main DC-bus Figure 2-4 shows PV-array system, which is a part of the whole system, with battery bank charging or supplying the AC load. When planning for a long-term operation of a stand-alone PV-system, the battery bank is playing important role and it is necessary to avoid the overcharge and deep discharge of the battery to enhance its usable life. Thus, a controller is an important element of the energy storage in the PV-array system. Over and above, it is important to note that a bi-directional converter of DC/DC type is used here allowing the battery to charge at times when there is more generation from the PV-arrays and to discharge (or supply to the load) during times of more demand on load or less supply. 2.2.3. PV Design and Array sizing approaches When designing the PV-array system, many factors have to be considered seriously. These include the technical specification, sizing of individual system components, safety considerations as well as system economics. As it can be referred from Figure 2-4 above, the system comprises basic components: the PV-arrays, inverters and battery. While dealing with the efficiency of the system, the efficiency of the basic components together with the wiring efficiency must be taken into an account. The gross daily energy demand of a load can be given [11] as: 2.3 Where End and Egd are the net and gross energy demands per day, is efficiency with subscripts i and w representing the inverter and wiring respectively. As it is explained in [9], inverters, batteries and the wiring of a well-designed PV-system have typical efficiencies of 85%, 85% and 98% respectively. Once the gross energy demand is calculated, the system voltage can be fixed. As it is suggested in [9], |