Comparison of Energy Densities

If a C02-free energy conversion is required, only hydrogen and electrical energy can fulfill this demand. In spite of progress in battery technology, at present electrical energy densities are still quite low. Of course, both hydrogen and electricity would have to be produced in a C02-free way. 

Until now most solid storage systems have been on a laboratory scale only. Apart from the weight and volume of the storage systems, topics of research are the conditions of charging and discharging the system (pressure, temperature, heat transfer, time), the potential number of charging cycles (lifetime) and of course costs. 

Hydrogen in a pure form can be stored as a highly compressed gas at up to 700 bar, cryogenically liquefied at —253 °C or in hybrid form. 

Higher storage densities are possible with liquid hydrogen the density at 2 bar is 67.67 kg m . The physical limit of the volumetric energy density at 2 bar is thus 2.3 kWhdm for pure hydrogen. However its very low boiling point at -253 °C 

Eichlseder, H., Klell, M., Schaffer, K, Leitner, D., and Sartory, M. (2009) Potential of Synergies in a Vehicle for Variable Mixtures of CNG and Hydrogen, SAP paper 2009-01-1420. 

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TABLE 17.5 Comparison of Energy Densities of Doubie-Layer Capacitors Using Various Electrolytes... 

Comparison of energy density (kWh/m ) for various storage systems of electric power such as pumped hydropower, redox-flow battery, lead battery, NAS battery and methylcyclohexane (MCH) and decalin (TEPCO = Tokyo Electric Power Company). 

Comparison of Energy Densities under Various Operating Conditions... 

Fig. 5. Comparison of energy densities per volume and cycle lives for cylindrical sealed Ni-MH and Ni-Cd batteries (nominal capacity 1-3 Ah charged at 0.25 C for 5 h and discharged at 0.3 C to 1 V) Ni (sintered) and Ni (pasted) stand for sintered-type and foamed-type nickel electrodes, respectively (Sakai et al. 1992b).

Figure 9.1 Comparison of energy density of iithiumceiis and other types of cell (Courtesy of Honeywel)...

FIgureS.S Comparison of energy density of organic versus magnesium batteries at various temperatures at nominal 30h rate (Courtesyof Honeyvtell)... 

A comparison of energy density (volumetric energy density) and specific energy (gravimetric energy density) for different electrochemical power sources. (Reprinted from http //www. nexergy.com/battery-density.html. Accessed online 11 February 2010.)... 

Figure 41. Comparison of calculated density of states (solid line) with UPS (crosses) (Fujimori et al. 1986) and inverse UPS spectra (diamonds) (Ciccacci et al. 1991) [Used by permission of lOP Publishing Limited, from Sandratskii et al. (1996), J Phys CondMat, Vol. 8, Fig. 3, p. 987]. The calculations were performed using LDA. The calculated data for the oeeupied and unoccupied DOS have been shifted independently on the energy seale to align with the experimental features. The ability of the calculated DOS to prediet the features in the spectra is clearly remarkable.

A schematic representation of a typical zinc/air button battery is given in Fig. 13.2. A zinc/metal oxide battery is shown for comparison. The reason for increased energy density in the zinc/air battery is illustrated graphically by comparing the anode compartment volumes. The very thin cathode of the zinc/air battery (about 0.5 mm) permits the use of twice as much zinc in the anode compartment as can be used in the metal oxide equivalent. Since the air cathode theoretically has infinite life, the electrical capacity of the battery is determined only by the anode capacity, resulting in at least a doubling of energy density. 

Table 5 Comparison of Spin Densities, Orbital Energies (eV), and g-Tensor Contributions (Relativistic Mass Correction [RMC], Diamagnetic Spin-Orbit [DSO], and Paramagnetic Spin-Orbit [PSO] Contributions) of the DPNO Radical in Water, Obtained from COSMO, D-COSMO-RS, and from COSMO Emplo3dng Additionally the Supermolecule Approach (B3LYP/IGLO-11)...

Fig. 30. Comparison of CPA density of states with experiment for Cu-Ni alloys (after Stocks et EDC refers to the observed photoemission energy distribution, ODS...

For comparisons of population densities in foraging (hunting and gathering) societies with those of shifting sedentary farmers see Smil, V. 1994. Energy in World History. Boulder Westview, pp. 27, 57-78. 

Numerous m.o.-theoretical calculations have been made on quinoline and quinolinium. Comparisons of the experimental results with the theoretical predictions reveals that, as expected (see 7.2), localisation energies give the best correlation. jr-Electron densities are a poor criterion of reactivity in electrophilic substitution the most reactive sites for both the quinolinium ion and the neutral molecule are predicted to be the 3-, 6- and 8-positions. ... 

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