A battery backup system can operate in a few different ways.
One option is a grid tied battery backup system. This type of solar system first charges the batteries then runs the house / connected loads from batteries and the solar panels through the inverter. In the event that the connected loads are not using the energy produced and the batteries are fully charged. The inverters turn the meter backwards selling the power to the utility company. If you are using more power than the solar system with batteries has available, you draw power from the utility grid.
Another option is a stand-alone battery backup solar system where the system is not tied into the utility grid. This type of system uses the sun light to charge the batteries, then runs the house / connected loads from the batteries and the solar panels through the inverter.
Frequently Asked Questions & Answers
The following information helps answer the most frequently asked questions concerning off-grid, and Grid tie systems with backup (battery and/or generator) hybrid solar electric power systems. Keep in mind that much of this information is “rule of thumb”; your individual situation, if analyzed in detail, it may differ somewhat from the general application.