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A large portion of the energy generated by a typical PV system will be exported to the grid and there is increasing demand for solutions to enable better use of this energy through the use of energy storage.
- Adding battery storage enables this excess generation to be stored for use later when consumption is higher than generation.
- Some systems can also provide backup power in the event of grid failure.
Grid-interactive battery inverters, can export power to the utility grid, can charge a battery using surplus energy for use in times of low generation and some can also supply backup power to protected loads during a grid outage.
- These inverters use a battery bank for energy storage and will not operate without batteries. They are used in addition to grid connect solar inverters.
Depending upon inverter type and which loads need to be powered an automatic transfer switch that enables them to safely operate off-grid during a blackout may also be required.
For back-up applications the inverter is connected to the battery bank (usually 24 or 48 VDC), an AC distribution board for loads needing back-up, and the building supply, using an automatic transfer switch if required.
The battery bank is charged by the PV array connected through a charge controller or through the battery inverter via AC coupling and an energy meter is used to measure import/export.
If more power is being generated than being used then instead of it being exported to the grid it is instead sent to charge the battery. As loads increase above generation and power starts to be imported it is instead taken from that stored in the battery.
During a power cut, the switch box will automatically disconnect from the grid and supply AC power to the protected loads by drawing energy from the battery bank and solar array. When the grid is restored, the inverter will automatically switch back to grid-connect operation and recharge the batteries.
Some energy is used to maintain the battery bank. Because of this systems with battery backup produce less energy (kWh) per kW of PV array than equivalent grid-tie systems that don’t include batteries.
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