Solar energy controller, one controller will complete the back flow.  A small round piece of paper will be placed on the positive and negative poles of the battery to connect the positive and negative poles.

When solar energy charges the storage battery, it is completely feasible for the storage battery to supply power to the outside. In this case, the electricity used by the load will preferentially directly use the electricity of the solar battery, and the rest will be charged into the battery.  On the contrary, if the solar cell has insufficient electricity, it will draw electricity from the battery at the same time.

When connecting, it is better to use a solar charge controller, which can control the output voltage of the solar cell and protect the cell from overcharge.