There are Off-Grid Solar systems that basically just run from batteries that are charged from Solar Panels, then there are Grid Connected systems that may be similar to Off-Grid systems but have the backup of the Grid to support the electrical Load demand and also help keep the Batteries charged, low voltage batteries are used in these systems and can be 12, 24, (36) and 48 volt DC.
The voltage of the system is often chosen based on its environment it is attached to, it may have additional generation or integrated batteries already in use such as Car, Boat, truck, Ship or Off Grid House, basically the higher the Voltage the less the system has to work to increase the Voltage to the 220 volts mains required.
There is also a High Voltage system that can be used with or without High Voltage Batteries, it uses the Grid all the time and feeds in electricity as it is generated from the Solar panels reducing or eliminating the Grid power being consumed, it is the easiest system for people who are not used to Solar electric because the consumer does not have to constantly consider the power being used to prevent it failing due to heavy demand, or just that they don’t want the cost / restraints of the battery system
It is constantly connected to the Grid for it’s supply to the consumer, what it does is to feed in what it can from the Solar Panels to add Solar generated power to the electricity being used thus reducing the consumption bill and carbon footprint.
Normally with this system what the consumer does not use is just lost and can only be thought of as the more the constant consumption during daylight hours the more potential saving is possible.
It is possible to get a credit for surplus that is fed back to the Grid, however the Electricity Companies have restrictions on what can be fed back into the Grid and how much they will credit for this surplus power that is generated from this private Solar supply.
Because of this loss or low credit from the Electric companies it is worth considering storing this surplus generated power into a High Voltage battery (400 Volts) to consume overnight when the Solar Panels can not produce power, this High Voltage Battery is more efficient because it is already higher than 220 voltage it needs to produce, so efficiency increases dramatically.