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Ragone Plots and Specific Energy

If Specific Energy in either Wh kg-1 or Wh m-3 is plotted against Specific Power in either W kg-1 or Wh m-3, using logarithmic scales, comparisons can be made over a much wider range.

Ragone plot illustrating the energy-power characteristics of various electrochemical power sources.

The time lines can be especially useful in selecting batteries for a particular duty. For example, Lithium, Silver-Zinc and Alkaline Manganese batteries have specific energies of approximately 400, 150 and 120 Wh/kg respectively, when discharged steadily over 10 hours; but the specific energies drop to 200, 100 and 7 Wh/kg when the full discharge takes only 20 minutes. These characteristics can be used to highlight batteries, which are best suited for slow or fast discharge.

Note: the time lines now become parallel to one another because log(energy) = log(power) + log(time).