Page - 153 - in Water, Energy, and Environment - A Primer

• Flywheels:mechanicaldevices thatuserotationalenergyto store anddeliver electricity • Superconducting Magnetic Energy Storage: energy is stored in persistentmagnetic fields • Compressed Air Energy Storage: uses compressed air to create an energy reserve • Pumped Storage Hydropower: uses water stored at an elevatedheight to create an energy reserve • Thermal Storage: capturing heat and cold to create energy ondemand 9.2.1 Traditionalandadvancedbatteries Traditional batteries are those that have been in use for many years – for example, lead–acid batteries, which are still the dominant battery storage technology today. 9.2.1.1 Lead–acid Theyarewidelyused incars, trucksandmanyother applications because of their low cost, high power (power per unit volume), andhigh reliability. Disadvantages are lowenergy density (stored energy per unit volume), large size and weight, and the need for an acid electrolyte. Lead (Pb) is also a toxic material when inhaled or ingested. Research to improve lead–acid batteries has been underway for more than a century, and considerable progress has been made – for example, lead–acid batteries that require no maintenance, and widespread recycling of used batteries to recover thePbelectrodes. Further progress is anticipated. 9.2.1.2 Sodiumsulfur Sodiumsulfurbatteries,whichoperateathightemperatures(300– 350°C) use molten sulfur as the positive electrode and molten sodiumas the negative electrode. Energystorage 153