Page - 133 - in Clean Water Using Solar and Wind - Outside the Power Grid

Handling variable production 133 rate  >1C is called a “high current” use. Usually a manufacturer specifies the maximum rating. An E-rate defines the discharge power, so a 1E rate is the discharge power to discharge the whole battery in one hour. Generally, the useful lifespan of a battery is 5–15 years, which is much shorter than the typical guarantee time of 25 years for solar cells. However, there is a lot of effort currently being devoted to battery development. Two particular demands are causing this: the rapid expansion of renewable energy and the increasing interest in electric vehicles. 10.4.4 Battery charge controller A solar charge controller must match the voltage of the solar PV array and the batteries. It is usually defined by the current (ampere) and voltage (V) capacities. The charge controller need to have sufficient capacity to handle the current from the PV array. A standard practice is to design the solar PV charge controller 30% larger than the short circuit current (ISC) of the PV array (see Chapter 8.2). The charging voltage must be higher than the battery voltage for current to flow into the battery. There are two basic ways to charge a lead-acid battery: • A constant voltage is applied across the battery terminals. As the voltage of the battery increases the charging current tapers off. This method requires only simple equipment, but is usually not recommended. • Constant current charge: an adjustable voltage source maintains a constant current flow into the battery. This requires a more sophisticated charge controller but is the more commonly recommended technique. 10.5 HYDROGEN ENERGY STORAGE Hydrogen as an energy storage system is receiving increasing attention and some systems are already in use. The systems are probably still too expensive for low-income countries but there is a huge research effort into hydrogen energy storage technology, so it should be mentioned here as a realistic possibility for energy storage in renewable energy systems. Downloaded from https://iwaponline.com/ebooks/book-pdf/520710/wio9781780409443.pdf by IWA Publishing user