I found it cool to add a LED lighting behind the battery box. The LEDs are lit only at night and create then a peaceful atmosphere in the house.

The "base" color of the LEDs depends of the current supply status of the house:
Blue: the electricity is provided by the PV system
Red: the power is provided by the grid

I added also some proportion of green to indicate the battery state of charge. So I get 4 basic colors:

Cyan (blue + green) : PV supply and fully charged battery
Blue: PV supply and nearly discharged battery
Red: supplied by the grid and the battery is fully discharged
Yellow: the house is grid supplied and the battery is nearly fully charged

Of course, all intermediate colors exist, depending on the battery state of charge

Cyan: PV mode and fully charged battery	Yellow: grid mode and fully charged battery

The light is provided by a short piece of low cost chinese RGB LED strip.

The LED strip is connected to a small Cortex M0+ controller board designed by my friend Gilles

The controller board gets its 12 VDC supply from the PVBM board (PV Battery Manager). The PVBM provides also the intensity of each color through a serial line.