Energy density is a parameter used chiefly to compare one type of battery system to another. The energy density of a battery is the capacity of the battery divided by either the weight of the battery, which gives the gravimetric energy density in Wh/kg, or by the volume, which gives a volumetric energy density in Wh/dm3 (or Wr/litre3). A battery with a higher energy density will be lighter than a similar capacity battery with a lower energy density. In portable systems, the energy density is a critical parameter but in conventional PV systems which provide power for a stationary object, the energy density may be less important. Nevertheless, the costs of transporting batteries to remote locations are considerably high, so a high energy density battery is typically an advantage.
The power density of a battery is related to its energy density, as well as the ability of the battery to discharge quickly. While the power density is important in some applications, particularly transport, it is typically not critical in photovoltaic systems.