Seite - 106 - in Clean Water Using Solar and Wind - Outside the Power Grid

106 Clean Water Using Solar and Wind: Outside the Power Grid Yamakura Dam, the world’s largest floating PV project (see Chapter 13). The water cools the panels, which will make them perform more efficiently. Since elevated temperatures can reduce the lifespan of the panels, they have a longer lifespan than ground-mounted panels. Another important secondary effect is that the panels prevent evaporation from the water surface. Since evaporation is a major problem in many water reservoirs (Olsson, 2015, Chapter 10) in water- scarce areas, it has been suggested that covering the dam with solar panels partially solves this problem. 8.3.5 Technology development As indicated, in coming years there will almost surely be an emphasis on developing solar cells with higher efficiency, improved thermal stability and a longer PV module lifetime. There is also an interesting move towards raising the energy efficiency by capturing the light from the rear side of the solar cell, and to capture diffused light. As indicated, the conversion efficiency will exceed 20% within a few years and the degradation will be as low as <0.3%/year (WEC, 2016, Chapter 8). 8.4 SYSTEMS OF SOLAR CELLS A single PV cell is usually quite small and may typically produce 1–2 W of power. By connecting solar cells in series and parallel large modules are formed that can produce a higher power output. Typically, 36 cells are connected in series to form a module. There are many different types of PV modules and their structure depends on the type of application. Then the modules can be further connected to larger units called arrays. Therefore, typical solar PV systems are built up from a number of modules and arrays. A single solar cell provides a voltage of around 0.6 V. By connecting several cells in series, a higher voltage will be produced. It is common that modules are designed to be able to charge a 12 V battery. Thirty- six cells in series provides an open circuit voltage of 21 V. Depending on temperature reductions and best operating conditions the module may produce 17–18 V. Since it will only require around 15 V to charge a 12 V battery, this will be sufficient. The voltage may well drop due to Downloaded from https://iwaponline.com/ebooks/book-pdf/520710/wio9781780409443.pdf by IWA Publishing user