Page - 107 - in Clean Water Using Solar and Wind - Outside the Power Grid

Solar PV 107 less light or further voltage reduction in parts of the system. More on batteries can be found in Chapter 10.3. The current from a module is a function of the size of the solar cells and their efficiency. A single solar cell has an area of typically 100 cm2. As a rule of thumb, the current from a module will be of the order 3.5–4 A. Having 36 cells in the module means that the area is 3,600 cm2, or a square of 60 ⋅ 60 cm2. The most common PV system consists of flat-plate cells. Another more advanced category is systems where the sunlight is concentrated. Concentrating optics are used to focus the light on small solar cells. This increases the power output and decreases the number of required cells. A complete solar PV system needs more than the solar cells to provide the output electric power. It includes a charge controller, an inverter (see 4.5) and batteries that provide adequate electric power. Pumps are usually powered by alternating current (AC) motors, which are typically more robust and cheaper than direct current (DC) motors. Since the solar panels produce DC currents a DC/AC converter is required for the AC pumps. Energy storage is a concern (further examined in Chapter 10) and batteries are used to store the PV output in order to smooth or sustain the system operation when the solar irradiation is insufficient. Control system aspects are illustrated in Chapter 11. 8.5 ENERGY REQUIREMENTS FOR WATER OPERATIONS Example 8.3: Solar PV Output for Pumping, Eastern India The actual power production of a solar array over a day for different months in eastern India has been measured by Rahman and Bhatt (2014). Since the solar irradiance varies with the length of the day, the DC power output from a 3 kWp solar array in the Patna region was measured every 15 minutes on bright sunshine days in different months of the year. The array tracked the sun with a manual mechanism. From 9:00 to 14:30 in almost all months, except November to January, the power rating of the array was within the interval range 1.9–2.4 kW. As a result, a 2.2 kW (3 hp) pump could be operated at close to rated power for six hours daily. So, a rule of Downloaded from https://iwaponline.com/ebooks/book-pdf/520710/wio9781780409443.pdf by IWA Publishing user