Seite - 118 - in Clean Water Using Solar and Wind - Outside the Power Grid

118 Clean Water Using Solar and Wind: Outside the Power Grid adapt production to consumption some kind of energy storage is needed in order to compensate for short-term or long-term differences between production and consumption. Often, however, peak production times for solar and wind energy align with peak demand periods for water pumping and treatment. If there is an excess power production the extra energy can always be put to good use, for example to store as a fresh water buffer, as discussed in 10.1. However, electric energy also must be available when the solar PV or wind cannot deliver. Then electric energy storage capacity is needed. Various storage technologies are summarised in 10.2. The most commonly used is battery storage. Some battery technologies are described in 10.3 and characterising parameters are presented in 10.4. Hydrogen storage (10.5) is another possibility with a huge potential for long-term storage. A third possibility is to use excess energy to pump water to a high elevation, like pumped storage hydroelectricity, shown in 10.6. It is always possible to use traditional diesel generators as a last resort if both solar and wind fail to satisfy the load, as shown in 10.7. The cost of energy storage is of primary importance, discussed in 10.8. One thing should be remembered: production being variable and intermittent does not mean that it is unpredictable. Depending on the economic resources available, the production of both solar PV and wind can often be predicted quite accurately at least for the next 24 hours. Furthermore, it should be kept in mind that most electric energy generation does have some downtime. 10.1 INTERMITTENT PRODUCTION CHARACTERISTICS There are two key parameters that can characterise variable production from renewable energy sources: capacity factor and load profile. Both have consequences for water supply operations. 10.1.1 Capacity factor The capacity factor is a measure to quantify the total energy generated from a specific source. The variability of wind and sunshine is the reason that the wind power or solar PV cannot be used at full capacity at Downloaded from https://iwaponline.com/ebooks/book-pdf/520710/wio9781780409443.pdf by IWA Publishing user