Battery storage and energy management for rooftop solar system

The intermittent nature and wide fluctuations in the availability of solar irradiation mean that provision has to be made to secure a continuous electricity supply in remote and off-grid areas. Especially for distributed generators and consumers, energy storage can be more cost-effective than grid extension and is indispensable for a power supply system that is not grid-connected (see Figure 33). The need for storage and grid extension increases with the expansion of renewable energy use. The driving force here is not only to provide power when the sun is covered or after it has set (off-grid), but also to allow excess generation to be stored for use later when consumption is higher than generation (grid-connected).
Especially for off-grid applications, electrical storage can be applied for the following tasks:

» power shifting from fluctuating renewable energy sources to match the daily load profile

» smoothing out short-term fluctuations of demand

» reduction of operation of peak-load power plants

» backup system and supply of spinning reserve capacity

» frequency and voltage regulation

»  provision of an electrical consumer to prevent reverse current flow into other generation systems

» evening out short-term fluctuations of solar PV supply due to, for example, passing clouds

» providing short-circuit current

» black start capability

» reactive power compensation.