Seite - 98 - in Clean Water Using Solar and Wind - Outside the Power Grid

98 Clean Water Using Solar and Wind: Outside the Power Grid The most widely used solar PV systems are flat panels. The useful power amount of a solar beam striking a plane surface is its normal component with respect to the plane. The solar power absorbed by the surface depends on the beam’s angle of incidence θ with the normal direction from the plane. The maximum power transfer (h0) is reached when the incident beam is perpendicular to the surface: that is θ = 0. For angles different from zero, the share of useful power collected on the plane (h) is h(θ) = h0 ⋅ cosθ. 8.2 SOLAR PV CHARACTERISTIC PARAMETERS Solar PV cells generate DC power in rough proportion to the total incident solar irradiation. The PV power output also depends on the PV cells’ operating temperature. As the temperature increases the output power will decrease, as shown in 8.3. Solar electricity systems are given a rating in kilowatts peak (kWp). This is essentially the rate at which it generates energy at peak performance, for example at noon on a sunny day. Obviously, the true electricity generation rate will depend on the system’s orientation, shading and how sunny the location is. Solar irradiation of 1 kW/m2 is used to define standard testing conditions (STC). To give an order of magnitude: for each m2 of commercial solar cells there is about 140– 200 W of electric power produced. In other words: the solar cell will have an efficiency of the order 14–20% (see also 8.3.2). When sunlight hits a solar cell, it will show a typical characteristic relation between output current and voltage. Four parameters characterise the solar cell: • The short circuit current ISC, • The open circuit voltage VOC, • The peak power Pmax, and • The fill factor FF. These parameters will determine the efficiency of the cell. If the module were to be short-circuited then the current ISC would flow through the circuit, at least in theory. The short circuit current represents the upper limit of the current that is generated by the solar cell. It is proportional to the irradiation and the cell area. Commercial silicon solar cells can deliver a high current. For a cell of 150 ⋅ 150 Downloaded from https://iwaponline.com/ebooks/book-pdf/520710/wio9781780409443.pdf by IWA Publishing user