This guide covers battery energy storage systems for domestic or small commercial grid-connected solar photovoltaics (PV). It is intended for two audiences:
-Customers. Information is provided to enable the benefits of energy storage systems to be assessed. The pros and cons of different system types are discussed, as well as the implications of different system sizes and operating regimes.
-System designers and installers. Information is provided to enable the safe and effective design, specification and installation of energy storage systems.

This guide focuses on grid-connected solar PV systems, although some principles also apply to other forms of energy generation. Systems that make use of any 'spare' storage capability available from an electric vehicle are not covered.
The guide looks at the design, sizing and specification of energy storage systems that use established battery technologies to store solar surplus for use later in the day. Typical operating patterns and characteristics of these systems are also examined. Examples are given of how such systems can be configured and connected within a building, and the process for sizing batteries and other system components is examined.