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Processes and Applications of Energy Conversion and Storage

Knowledge related to electric charges is considered as old as human history. For example, in approximately 600 BC, Thales of Milet described the phenomena when rubbing amber as electrostatic charging. The generation of electric charges (more precisely, charge separation) and the phenomena caused by charges of the same or opposite signs have been the subject of curiosity and scientific investigation for several centuries. However, such studies have been limited by an inherent problem: the storage of electricity, i.e. electric charge. Some condenser-like devices, e.g. the Leyden flask (1745), had very limited capacity, and similar condenser-based contraptions did not help very much. Only recently (starting with a patent in 1957), the principle of the condenser has been developed resulting in novel devices: the supercap(acitor) and the ultracap (see Chapter 11).

In 1800 Alessandro Volta discovered that placing zinc and silver plates close to each other with a piece of brine-soaked pasteboard in between produces an electric voltage. This became the first source of continuous supply of electricity and the device is still called a voltaic cell. Placing many of those sandwich-like devices on top of each other resulted in a multiplied electric voltage because of the serial connection - the Volta-pile. For quite some time this device together with the Daniell element (1836) was the only source of electricity providing a continuous flow of current compared to the short-lived discharge current from any condenser, which was popularly used in telegraphic systems in the 1850s. The French physicist Gaston Planté constructed the first lead-acid accumulator in 1859. Waldmar Jungner (1899) discovered the nickel-cadmium accumulator, which was substantially improved up to the point of commercialization by the invention of porous electrodes by Schlecht and Ackermann in 1932. Complete sealing of the cell enabled by changes in cell and electrode setup provided by Neumann in 1947 yielded the secondary batteries very popular in numerous applications until recently, when the toxicity of cadmium was identified as a major problem and when suitable substitutes for the cadmium electrode were reported. The discovery of huge hydrogen storage capabilities by intermetallic compounds such as SmCo5 and LaNi5 provided a nontoxic substitute for the cadmium electrode, with the resulting NiMH accumulator replacing NiCd accumulators in many applications. Finally lithium-ion batteries were successfully commercialized in 1991 after initial failures of secondary lithium batteries utilizing metallic lithium electrodes.

The development of the dynamoelectric principle and the invention of a first electric generator by Werner (von) Siemens (1866) enabled engineers in the 1850s to solve problems dealing with electric cars and more generally with the utilization of electric energy. Now electricity could be generated by converting mechanical energy derived from a multitude of sources by coupling this source in a suitable way to the generator. Although not quite clear from the beginning, alternating current (AC) rapidly gained commercial importance and has been preferred than direct current (DC). Because both power and energy of batteries had always been limited by size and number, the huge demand for electricity from the many different consumers could only be met by supplying AC. Batteries then were moved out of the focus of attention for some time - but only relatively shortly. The early development of mobile devices such as a car or an electric bike gave rise to the need for mobile sources of electric energy, which quite obviously only batteries could provide and with some success. The first cars driven with electric motors enjoyed wider commercialization, unlike the first vehicle driven by a steam engine in Paris in 1769. The first electric car has been reported to be built by a Scottish inventor Robert Anderson approximately between 1832 and 1839, later known as a carriage. Not much is known beyond reports of the first experiments in 1837, and because rechargeable batteries had not yet been invented, his creation moved into oblivion. Professor Stratingh and his assistant Christopher Becker (Groningen, Holland) and the blacksmith Thomas Davenport (Brandon, Vermont) built small electric cars in 1835. Using the slowly improving (but still not rechargeable) batteries, Davenport and Robert Davidson built around 1842 slightly more practical and successful electric vehicles. An electrically powered tricycle built by Gustave Trouvé premiered once again in Paris in 1881 with a reported speed of 12 km h-1. Serial production of electric cars started in 1890; William Morrison produced carriages with an electric motor of about 2.5 hp. In 1899 a car constructed by Camille Jenatzy aptly named Ne Jamais Contente (The never satisfied one) already passed the 100 km·h-1 benchmark with a maximum speed of 105.8 km h-1; the postal service in Germany operated the first electric transport vehicles. At an exhibition in Berlin, Germany, in 1899, the vehicle named "Electra" (Figure 1.1) operating with a zinc/PbO2 battery was presented.

Around 1903 in large cities such as Paris, London, and New York, vehicular fleets comprised about at least one-third electrically driven vehicles, one-third steam driven, and less than one-third vehicles with internal combustion engines. F. Porsche, later famous for his sports cars and other developments, mounted two electric motors of 2.5 hp each into a carriage for the manufacturer L. Lohner - this Lohner-Porsche is sometimes considered as the first electric car. To charge the battery, Porsche added a small internal combustion engine.1 In 1919 R. Slaby began building electric vehicles in Saxony, and later his company was acquired by J.S. Rasmussen, the proponent of AUDI. However, its lack of success resulted in the termination of its production in 1927. The car shown in Figure 1.2 weighs only 180 kg, and the 12 V battery provides 2 hp at the wheels, resulting in a top speed of 24 km h-1.

Figure 1.1 Battery-operated vehicle (Krüger, Berlin, Germany) of 1899.

Figure 1.2 Battery-operated car built by R. Slaby around 1919.

In 1938 more than 2600 electric trucks were operated by German mail services, some of them lasted more than 40 years of service.

Somewhat in the shadow of the development of cars, battery-powered main line railcars were put into service by, e.g. railway companies in Germany in 1894.

The inventions of Otto and Diesel brought new developments (and German postal service put its last electric truck out of service in 1973). The rapid development of internal combustion engines, which were not inherently more powerful than electric motors (actually it was the other way round), but which did not need bulky, heavy batteries filled with etching liquids prone to crack and spill, quickly overwhelmed electric propulsion.

For a short period of time in history, everything seemed to be settled: Steam engines were suitable for heavy devices like locomotives, electrically driven cars were suitable for urban traffic, and cars with internal combustion engines were most suitable for the countryside because of their long range of operation. Further developments particularly in electrical engineering changed all these. The production of the magnetic ignition (Bosch, 1902) and of a reliable electric starter (Kettering, 1911) as well as the availability of cheap gasoline caused a steady decline of the electric car; thus the long journey of electric vehicles into some niches and oblivion elsewhere started.

Elsewhere the rapid development of the electric grid operated nation- or even continent-wide ensured a reliable supply of electricity up to the most remote villages - almost. As described in Chapter 2 in detail, devices for the storage of electric energy have always been used in remote places, and because electric energy can economically be stored only by converting it into chemical energy (and vice versa), energy conversion devices have always been associated with storage.

This is currently changing again, but slowly in some places and in dramatic steps. Several factors can be identified easily:

• Many energy conversion processes are based on the use of fossil fuels, which are limited in supply; in some cases, the end of its use is imminent (peak oil).
• The excessive use of fossil energies results in a substantial generation of carbon dioxide. Whether this is really a cause of climate change remains an open question for many. The prevailing advice is that we better not wait for the outcome of an experimental verification of this thesis as there might be only one try.
• Mobility causes not only congestions and traffic jams but also noise and air pollution. This again can be traced back to vehicles using internal combustion engines. Their replacement by other types of engines can possibly provide substantial relief.
• The use of other forms of energy like wind, photovoltaics, hydropower, or solar heat requires large storage devices for matching fluctuating supply and demand,2 peak shaving, and power quality management. Most of the renewable sources are coupled to the grid by DC intermediates, thus...