Load leveling batteries

Figure 10.15 NaS battery load levelling plant built by NGK Insulators (Japan). 

In the 1990s, the use of batteries in electric vehicles and for load leveling is being revived partly for environmental reasons and partly because of scarce energy resources. Improvements in battery performance and life, fewer maintenance requirements, and automatic control systems are making these appHcations feasible. Research and development is ongoing all over the world to develop improved lead—acid batteries as weU as other systems to meet these needs. 

Redox flow batteries, under development since the early 1970s, are stUl of interest primarily for utility load leveling applications (77). Such a battery is shown schematically in Figure 5. Unlike other batteries, the active materials are not contained within the battery itself but are stored in separate tanks. The reactants each flow into a half-ceU separated one from the other by a selective membrane. An oxidation and reduction electrochemical reaction occurs in each half-ceU to generate current. Examples of this technology include the iron—chromium, Fe—Cr, battery (79) and the vanadium redox cell (80). 

Other flow batteries investigated for both electric vehicle appHcation and utiUty load leveling include 2inc [7440-66-6]—[7782-50-5] Zn—Q.25 and zinc—bromine [7726-95-6]., Zn—Br2, batteries (78,81,82). 

Zinc—bromine storage batteries (qv) are under development as load-leveling devices in electric utilities (64). Photovoltaic batteries have been made of selenium or boron doped with bromine. Graphite fibers and certain polymers can be made electrically conductive by being doped with bromine. Bromine is used in quartz—haUde light bulbs. Bromine is used to etch aluminum, copper, and semi-conductors. Bromine and its salts are known to recover gold and other precious metals from their ores. Bromine can be used to desulfurize fine coal (see Coal conversion processes). Table 5 shows estimates of the primary uses of bromine. 

While the zinc/chlorine battery is preferred for utility load-leveling applications [49], the zinc/bromine system is the more promising one for electric vehicle requirements [50, 51]. 

Recently the development of Na/S batteries for car applications has been abandoned only Na/S batteries for stationary applications (load leveling) are still under development in Japan. Among the high-temperature batteries, the ZEBRA battery is the only system at present which is being commercialized for car applications. 

Nonwoven materials such as cellulosic fibers have never been successfully used in lithium batteries. This lack of interest is related to the hygroscopic nature of cellulosic papers and films, their tendency to degrade in contact with lithium metal, and their susceptibility to pinhole formation at thickness of less than 100 fjim. For future applications, such as electric vehicles and load leveling systems at electric power plants, cellulosic separators may find a place because of their stability at higher temperatures when compared to polyolefins. They may be laminated with polyolefin separators to provide high-temperature melt integrity. 

Load levelling batteries 5-100 MWh Spinning reserve, peak shaving, load levelling... 

Fig. 1.7 Artist s impression of a 100 MWh load levelling battery. (By courtesy of I.D.C. Cargill, University of St Andrews.)...

With the growing interest in large high rate batteries for traction and load levelling applications, the development of models for heat transfer... 

By far the largest sector of the battery industry worldwide is based on the lead-acid aqueous cell whose dominance is due to a combination of low cost, versatility and the excellent reversibility of the electrochemical system, Lead-acid cells have extensive use both as portable power sources for vehicle service and traction, and in stationary applications ranging from small emergency supplies to load levelling systems. In terms of sales, the lead-acid battery occupies over 50% of the entire primary and secondary market, with an estimated value of 100 billion per annum before retail mark-up. 

Over the past few years a number of studies have been made of the use of lead-acid batteries for load levelling. The service required is very similar to that of traction batteries except that energy density is less important than cycle efficiency. 

In applications such as load levelling, motive power or in consumer electronics, the battery is required to undergo a sequence of deep discharges followed by a recharge to maximum capacity. A number of methods may be used. 

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