With the rising popularity of solar home storage systems, studies on reliability and performance are also becoming increasingly important. The energy conversion pathways, system ageing, standby consumption and control efficiency determine the performance of these systems.
Methods have been developed, and the relevant test environments for determining the performance of solar storage systems have been implemented and realised at ZSW’s testing facility as part of a joint project funded by the Federal Ministry for Economic Affairs and Energy entitled “Sicherheit und Netzdienlichkeit von elektrischen Heimspeichersystemen mit Lithium-Ionen-Batterien” (Safety and Grid-compatibility of Electric Home Storage Systems with Lithiumion Batteries). The efficiency of the energy conversion pathways describes losses occurring in the power conversion systems (e.g. inverters, DC-DC converters and so on) and is an important indicator of performance. Depending on the system topology, there are different energy conversion pathways, e.g. AC2BAT (energy from the power grid to the battery), BAT2AC (battery energy to the power grid), and others (see fig.).
The efficiency of the energy conversion pathway as a function of power is shown in the figure below. Another important performance indicator of a home storage system is its usable capacity. It corresponds to the actually available battery energy and is lower than the nominal storage energy due to conversion losses and safety limits.