This is quite a complex system that combines the ability to sell electricity back to the grid via the export meter (8) with backup power should the grid fail. The electricity generated by standard grid tie photovoltaic systems designed to export power can't be used when there's a power cut. This is because they are designed to protect the grid from making it live when there's a problem or scheduled maintenance. This system overcomes this problem by transferring the power produced by the solar panels to the secured backup side (4) The protected/secured side is fed power by a second, non-grid tie inverter (6) that draws its power from the batteries. When the solar panel power is transferred to the secured side the grid tie inverter (2) thinks that the output from the backup inverter (6) is the grid and injects its power into the secured side. There's nothing more embarrassing than having 20K worth of solar panels on your roof and no power when there's a power cut and it's sunny!
This system is design to pump water from a well during daylight hours into a storage tank. The water filter removes sediment and bacteria to give a clean drinking water supply. This configuration requires no batteries so is very low maintenance.