A solar-powered watch or light-powered watch is a watch that is powered entirely or partly by a solar cell.

Some of the early solar watches of the 1970s had innovative and unique designs to accommodate the array of photovoltaic solar cells needed to power them (Synchronar, Nepro, Sicura and some models by Cristalonic, Alba, Rhythm, Seiko and Citizen). In the 1990s, Citizen started to sell light-powered watches under the Eco-Drive series name. Since their introduction, photovoltaic devices have greatly improved their efficiency and thereby their capacity. Watchmakers have developed their technology such that solar-powered watches are now a major part of their range of watches. Several other watch manufacturers offer similar watches or are developing such technology. These other watch manufacturers include (amongst others) Junghans, Casio, Seiko, and Orient.

Typically, sunlight and artificial light are absorbed by a solar panel behind the crystal. The dial is either on a layer above or actually on the solar panel. This solar panel converts the light into electrical energy to power the watch. The watch will usually store energy in a rechargeable cell to power itself during the night or when covered such as a wearer’s clothing (e.g., sleeve). Citizen’s watches use lithium-ion batteries to store sufficient energy to power the watch for several months/years without light exposure, by allowing the watch to enter a power-saving or hibernation mode during which the seconds hand stops until the watch is re-exposed to light. Not all have a power-save mode, yet will still hold a charge for typically six months, as with uncomplicated (date only) analog versions made by Citizen.

Inexpensive solar-powered watches were first sold in the 1980s and were popular amongst children, often featuring famous fictional characters such as Transformers or G.I. Joe.

Overview
The driving mechanism of the watch itself is a quartz type operating with low electric power, which is common in electric power watches, but using solar cells, electric power is generated to obtain the electric power necessary for driving a watch There. In order to drive it even in darkness and at night, the secondary battery or capacitor is temporarily charged with the generated electric power, and electric power is taken out therefrom. Although no external power supply such as a commercial power supply is performed, some home wall clocks are backed up with primary batteries such as dry batteries.

Outdoor clock
In the type that is installed on the street such as a park, in most cases the solar panel is installed near the main body in the direction of the sun (in the northern hemisphere, in the direction of the south) apart from the watch main body. Currently the time correction function by the standard radio wave is often installed. By using a solar battery power supply, there is a merit that basically eliminates maintenance such as external power supply wiring installation and periodic battery replacement (or maintenance cycle becomes long), and as an outdoor installation clock High practical functionality is high.

Watches
Watches have solar power stuff as well. It is unnecessary to replace a battery like a common quartz wrist watch (it can be used within the range of capacitor life), and it does not have mechanical moving parts for power generation (such as a generator driven by a weight). Due to the advantages that it can be made concise and lightweight, it is getting demand as a practical watch-oriented system.

Since the 1970s commercialization of micro solar cells and the spread of quartz wrist watches have been commercialized in application of these technologies. In the 1990s, Citizen Watch began manufacturing and selling solar watches under the name “Eco Drive”, and other clock manufacturers such as Casio and Seiko developed and adopted similar technology.

Products sold at the beginning of the 21st century are equipped with solar cells under the dial (or around the dial). In the early 1970’s, the priority was given to solar cells to give priority to securing the power supply as a priority order to increase power generation efficiency, the face of the dial is transparent, solar cells (dividing line) can be seen through, purple black series of letters There were many board colors (so there were also cases where it became a strange design). Due to technical development and aging in the later years, various dials and design dials are adopted in a way that increases power generation efficiency year by year and does not sacrifice light transmittance.

Most solar-powered watches have a power saving function such as stopping the second hand when no electricity is generated in the nighttime or in the dark in order to avoid consumption of the secondary battery. Further, when the battery remaining amount becomes small, the needle is completely stopped and only the clock part in the middle becomes functional so that the time information does not go out of control over a long period of time.

Name by manufacturer
Casio: Tough Solar, Solar Charging System
Citizen: Eco Drive
Second line etc: Solar Tech
Q & Q Brand: Solar Mate
Seiko: Eco Tec Solar (currently not used as a name at the moment, simply called “Solar”)

Source from Wikipedia