How Do Eco Drive Watches Work

Developed and manufactured by the Citizen Watch Company, ECO DRIVE CHRONOGRAPH receive their power from any light source. Since the watches run on both solar or artificial light, their power supply is continuously being replenished. Eco Drive watches look like other watches and are made in a variety of styles and designs. This quality watches also contain the same type of quartz movement found in watches powered by other methods.

How They Work

The two main components of the power system of an Eco Drive watch is an energy cell and a solar conversion panel. Located under the watch dial, the microns thin solar panel is a disc made of amorphous Silicon. After capturing the energy from the light source that enters through the watch crystal and dial, the solar panel converts the energy into electrical power through a process called photovoltaic. The electrical energy is then stored in the energy cell providing the needed power supply for the watch to run. From then on, an Eco Drive watch operates in the same way as a regular quartz watch.

The energy cell of an Eco Drive watch is not like a regular watch battery. The following are the main differences:

• It is not affected by the normal cycle of charge and discharge.
• The energy cell is environmentally friendly as it does not contain the chemicals found in most other types of watch batteries.
• The energy cell never needs to be replaced when used properly.

The technical platform that made the Eco-Drive concept possible was the Eco-Drive caliber 7878 movement. This movement was the first light powered movement where the solar cells could be mounted under the dial. Previous light powered watches from Citizen and other manufacturers had the solar cell(s) mounted directly on the dial. This innovation was enabled by marked improvements in thin film amorphous silicon solar cells, which, by the early 1990s had become significantly more efficient. By locating a sufficiently translucent dial material over the now more efficient solar cells, enough light could pass through the dial face to power the movement. Though the Eco-Drive caliber 7878 movement solar cells remained slightly visible through the dial, the physical styling of the light-powered watch was no longer constrained by visible solar cells.

To store electrical energy the first Eco-Drive movements employed titanium lithium-ion rechargeable or secondary batteries. This battery type became available in the early 1990s, enabling an Eco-Drive 7878 movement to run 180 days on secondary power before requiring recharging via light exposure — a marked improvement in energy storage over previous light-powered watches. The movement also featured an "insufficient recharging" indicator.