Page - 165 - in Clean Water Using Solar and Wind - Outside the Power Grid

Water operations using renewables – some cases 165 The cost of these panels was less than 1 USD/W. The panels are mounted on a wheel cart that can easily be pushed around. This innovative thinking made it possible to turn the panels into the best possible position, towards the sun and avoiding shadows from trees: in other words, they became a manual tracking system. The panels were placed at the irrigation site at some distance from where people live and could easily be stolen at night. With the cart the panels can instead be moved to a safe stored location overnight. The aim was to find an affordable pump and keep the cost down by avoiding using batteries. By using a DC pump the cost of DC/ AC conversion was avoided. The drawback is that DC motors have a shorter life than AC motors. Marine pumps were found to be a good choice, but many of them are designed only for low heads (see Chapter 4). The actual pump can deliver around 15 m3/hour or 4 litres/second at zero head. It can work at 5–6 m head, but then the flow rate is lower (compare Figure 4.2) albeit sufficient for the purpose. In this case the motor is assumed to have a life of around one year. However, the profit from the irrigation could pay for the replacement of the motor. Altogether the pumping system cost was less than 1,000 USD. No electronic controllers were used, only a simple circuit breaker. The pump can irrigate around half a hectare (=5000 m2). A flow rate of 4 m3/hour for six hours will provide almost 50 m3/hectare/day. 14.3 DESALINATION The integration of renewable energy resources in desalination and water purification is becoming more viable as costs of conventional systems increase, commitments to reducing greenhouse gas emissions are implemented and targets for exploiting renewable energy are set. Many PV-based desalination systems have been demonstrated throughout the world, especially in remote areas and on islands. The examples and cases illustrate both utility-scale installations and small-scale implementations. They are shown to exemplify both efficiency and economy. 14.3.1 Solar PV desalination installations Example 14.2: Village of Ksar Ghilène, Tunisia A solar PV-based system for water supply was already in existence in 2005 in the village of Ksar Ghilène, located in southern Tunisia (www. Downloaded from https://iwaponline.com/ebooks/book-pdf/520710/wio9781780409443.pdf by IWA Publishing user