During certain periods such as inclement weather or at night, there is little or no sun to keep any solar array in a state of generating useful electrical energy. On the contrary, most applications need continuous supply of electricity (Häberlin, 2012:223). In other words, sunlight is clearly unavailable during night hours while there is still demand for electricity. In addition, peak sun hour (psh) available at a particular time may not exactly match with the time of peak demand for electricity. Therefore, energy storage is required in most off-grid systems, as energy generation and consumption do not generally coincide (James, 2008:298). That is, a device (or solar battery) is needed for effective energy storage and efficient recovery of same for continuous electricity supply from solar PV systems.
As already stated, the non-simultaneity of energy supply and energy consumption leads to the use of batteries. Thus, batteries are a vital component not only of PV systems but of renewable energy systems in general (Jager, et al., 2016:288). Energy storage is very important at both small and large scales in order to tackle the intermittency of renewable energy sources.
In the case of PV systems, the intermittency of the electricity generation is of two kinds. The first intermittency is diurnal fluctuations, i.e. the difference of irradiance during the 24 hour period. While the second one is the reality of seasonal fluctuations which usually create a difference of irradiance between the summer and the winter months (Jager, et al., 2016:288). The latter is of critical importance in the design of PV systems, particularly off-grid type. Our suggestion is that consumers should ensure that batteries with the right specifications and quality are only used in their battery bank to guaranty power supply from the PV system. You may check out our article on Solar Battery Selection, Management and Maintenance.