Page - 104 - in Clean Water Using Solar and Wind - Outside the Power Grid

104 Clean Water Using Solar and Wind: Outside the Power Grid Energy is needed to produce solar cells. One way to express the energy requirement is to calculate how much time is needed for the solar PV system to produce as much energy as was required to manufacture the panels. The payback time naturally depends on the geographical location. The payback time is displayed as function of the irradiation (in kWh/ m2/year) in Fraunhofer (2016). The energy payback time (EPBT) for 1,000 kWh/m2/year (typically for northern Europe) is found to be 2.1 years, and for 1,700 kWh/m2/year (typically for southern Europe) is 1.2 years. In comparison to the highest irradiation in Africa, which is more than 2,700 kWh/m2/year (Table 8.1), the EPBT can be as short as 0.7 years. Assuming the solar panels have a 25-year lifetime, this means that a solar PV system in Africa can produce as much as 35 times the energy that was needed to produce it. Example 8.1: Power Density of a Large-Scale Solar PV A large solar PV array located in the Mojave Desert, California is documented in Rever (2017). The huge plant of 550 MW covers an area of 16 km2. Assuming that all the area is covered with solar panels it means that the power production from the solar modules is 34 W/m2. 8.3.3 Temperature dependence As well as the irradiation the solar module output is dependent on the temperature. Under standard testing conditions the module temperature is assumed to be the same as the ambient temperature. However, under normal conditions the solar cells are heated and will give out a lower voltage output when they are subjected to heating. A typical PV module will convert only 14–20% of the sunlight into electric power; the rest of the sunlight is converted into heat. The resulting operating temperature will be at a point between the heat loss to the surroundings and the heat generated in the module. Heating of the solar panel can result in a power loss of around 8% in a year. This of course means that less energy will be produced by the PV system. It can also reduce the PV system’s lifespan. The temperature dependence is expressed as the relationship between the short circuit current and the open circuit voltage versus the temperature, respectively. The temperature coefficients indicate how much the voltage and current change for each degree increase from the standard 25°C reference. Downloaded from https://iwaponline.com/ebooks/book-pdf/520710/wio9781780409443.pdf by IWA Publishing user