The necessity for storage implies both significant investment and lifetime costs for outdoor stand-alone PV systems . Significant investment costs for charge storage may equally be the case for IPV autonomous power systems (see Figure 7.18). It is therefore worth considering the various technologies available for fulfilling this role, both mechanical (subsection 6.3.3) and electrochemical (subsection 6.3.4).
Given that electrochemical technologies are used for the majority of applications, these are reviewed in turn (see subsections 6.3.5 to 6.3.7).
All such storage technologies may be compared with respect to common units and properties which are presented first in subsection 6.3.2.