The most important parameter of an Off-grid solar system is certainly the battery charge level. This analog Bar-graph indicator delivers an "eye friendly" indication of this figure.
A particular effort is made on overall power consumption. The design uses an ultra low power controller and a Low Energy Bluetooth module in order to make a solar supply possible. The indication is refreshed once every 5 minutes, reducing the power budget. A transistor controls the servo power supply line in order to power it only when it is necessary.
The project can be hacked for any other indication purpose, provided the value to indicate changes slowly.