Especially for systems with the Energy Maximizer it can be financially interesting to be able to discharge the battery to the grid, when electricity prices are high enough (provided you do not need the stored electricity yourself at that moment). Follow these steps to configure it:
Step 2: Configure Energy Maximizer
Go to Configuration and then to Energy Management. Click on 'Configure' at the 'Energy Maximizer' box.

Step 3: Battery Behavior
Go to the heading 'Battery behaviour with respect to the utility grid' and click on 'Configuring the battery behaviour'.

Step 4: Configure and Save
Here you can check whether or not the battery can charge from the grid, and whether or not the battery can discharge back into the grid. Then click on 'Save'.

Step 5: Done
Done. You can change the setting at any time, via the same steps.