Solar PV Theory.pdf

E 35c 63f above the nominal operating temperature of

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Fahrenheit) operates at a cell temperature of 60°C (140°F), i.e. (35°C (63°F) above the nominal operating temperature of 25°C (77°F), the maximum output power is 14% lower than the maximum output power obtained when the same PV module operates at a PV cell temperature of 25°C (77°F).
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Solar Power 2 1 The Discussion covers the following points: Energy storage Lead-acid batteries Battery charge using a PV module Battery connected to a PV module in the dark Equivalent diagram of a PV cell Blocking diode Energy storage When electric power is produced using PV panels, electrical energy is available only during sunny periods. Therefore, to ensure continuous and reliable energy supply, some means is required to store electrical energy when it is available. This is where batteries enter into action as they serve as a means of storing the excess in electrical energy produced during sunny periods. The energy stored in the batteries during sunny periods can be pumped out afterward to achieve a continuous electric energy supply. In brief, the batteries are charged during sunny periods and discharged during cloudy periods as well as at night. Lead- acid batteries are commonly used to store electrical energy produced by PV panels. Lead-acid batteries Lead-acid batteries that are commonly available have a nominal voltage of 12 V. Although several lead-acid batteries can be connected in series to obtain higher operating voltages (e.g., 24 V, 48 V, 60 V, etc.), the rest of this discussion deals with storing energy produced by PV panels into 12 V lead-acid batteries. The same principles apply when energy is stored in lead-acid battery systems operating at higher voltages. As Figure 42 shows, when a battery supplies power to an electrical load (discharges), current exits from the positive terminal and enters at the negative terminal of the battery, and the battery voltage decreases gradually during discharge. Conversely, a battery is charged by forcing a current to flow in the opposite direction, i.e., by making current enter at the positive terminal and exit from the negative terminal of the battery (see Figure 30 ). The voltage of the battery increases gradually during charge. 5 . Storing Energy from Solar Panels into Batteries D ISCUSSION O UTLINE D ISCUSSION
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Storing Energy from Solar Panels into Batteries Discussion 2 2 Solar Power Figure 30 Charge and discharge cycles of a battery. Figure 3 1 shows the relationship between the open-circuit voltage E OC and the state-of-charge of a 12 V lead-acid battery. The open-circuit voltage E OC of any lead-acid battery increases with the state-of-charge of the battery. 11.8 11.9 12.0 12.1 12.2 12.3 12.4 12.5 12.6 12.7 0 10 20 30 40 50 60 70 80 90 100 State-of-charge (%) Figure 3 1 . O pen-circuit voltage versus state-of-charge of a 12 V lead-acid battery. Battery charge using a PV module Figure 32 , shows a PV module connected to a 12 V lead-acid battery. When the PV module is illuminated, it produces current that flows through the battery.
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