Ragone chart

Ragone chart showing specific energy versus specific power for various energy-storing devices

A Ragone chart (pronounced "ru-GO-nee") is a chart used for performance comparison of various energy-storing devices. On such a chart the values of specific energy (in W·h/kg) are plotted versus specific power (in W/kg). Both axes are logarithmic, which allows comparing performance of very different devices (for example, extremely high and extremely low power).

The Ragone^[1]) chart was first used to compare performance of batteries. However, it is suitable to compare any energy-storing devices,^[2] as is shown in the graph on the right. The chart is named after David V. Ragone.^[3]

Conceptually, the vertical axis describes how much energy is available, while the horizontal axis shows how quickly that energy can be delivered, otherwise known as power, per unit mass. A point in a Ragone chart thus represents the amount of time during which the energy (per mass) on the Y-axis can be delivered at the power (per mass) on the X-axis, and that time (in hours) is given as the ratio between the energy and the power densities. Consequently, the iso curves in a Ragone chart are straight lines with unity slope. For example, powering a small light bulb may require low amounts of power, but the power should be delivered steadily enough to operate a flashlight for minutes or hours of use. Conversely, a high-speed electronic switch inside a computer may require very little energy to activate; yet it must be delivered rapidly enough to complete the transaction in mere microseconds. These two types of loads would be represented at opposite corners of the Ragone chart.

$\text{Specific Energy} = \frac{V \times I \times t}m,$

$\text{Specific Power} = \frac{V \times I}m,$

where V is voltage (V), I electric current (A), t time (s) and m mass (kg).

References

1. "President David V. Ragone". Case Western Reserve University. Retrieved 21 April 2015.
2. Christen, Thomas; Carlen, Martin W. (2000). "Theory of Ragone plots". Journal of Power Sources 91 (2). pp. 210–216. doi:10.1016/S0378-7753(00)00474-2.
3. Ragone, D. V. (1968). "Review of Battery Systems for Electrically Powered Vehicles". SAE Technical Paper. doi:10.4271/680453. 680453.