Ragone plot

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

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).