Seite - 125 - in Clean Water Using Solar and Wind - Outside the Power Grid

Handling variable production 125 pressure container or an underground cavern. When electricity is needed the pressurised air is heated and drives a turbine that is connected to a generator for power production. The discharge time can be several hours, but the efficiency is quite low. • Pumped storage: Using excess power to store water in a tank at an elevated level. Pumped storage can be used at any scale, from household level to large-scale utility level. The discharge time is typically from several hours to a day. • Hydrogen: Electric energy can be converted to hydrogen by electrolysis. The stored hydrogen can be converted back to electricity, but the overall efficiency is quite low, around 30–50%. Hydrogen storage may have an increasingly important role to play, since the energy density of hydrogen is higher than in most other storage technologies. However, hydrogen technology is probably not relevant for low-cost installations. • Diesel-powered generators: To manage longer-term storage there is still a possibility in some areas of using traditional diesel- powered generators. The storage technologies are at different development stages. Some of them are mature and proven over a long time, like pumped hydropower. Flywheels are getting more common in certain applications. Battery technology has been developed over many decades and lead-acid batteries are used everywhere. More advanced battery technology is being developed at a high rate, driven by the growth in development of electric vehicles. For lighting and clean water operations we are considering the following alternative storage technologies: • Batteries, • Hydrogen, • Pumped storage, and • Traditional diesel generators. 10.3 BATTERY STORAGE Globally, battery storage for large-scale as well as small-scale applications has grown rapidly over the last few years. Grid-connected stationary battery storage capacity has grown from 345 MW in 2010 to Downloaded from https://iwaponline.com/ebooks/book-pdf/520710/wio9781780409443.pdf by IWA Publishing user