What device uses solar power to communicate?

The heliograph is a device that specifically uses sunlight to communicate messages over distances. It does this by reflecting sunlight with a movable mirror, which can be directed toward a specific location. The light can be turned on and off by manipulating the mirror, allowing it to send coded messages, often in Morse code, through flashes of light.

This communication method relies solely on solar power; it harnesses the energy from the sun rather than depending on batteries or other forms of electricity. Thus, it's an embodiment of using solar energy effectively for long-distance signaling.

In contrast, while transmitters and signal mirrors may use various energy sources for communication or signaling, transmitters can rely on electrical power and are typically more complex electronic devices. Signal mirrors, while capable of reflecting sunlight, do not function as a communication device in the same manner as a heliograph since they lack the mechanism for coded messages. Flashlights also do not primarily use solar power; they require either batteries or a power supply to generate light. Therefore, the heliograph stands out as the sole device mentioned that utilizes solar power directly for communication purposes.