They are either completely or partially powered by solar cells.
They’re not only a good choice in terms of convenience, because you don’t have the hassle and expense of changing the battery, but also an environmentally friendly choice too.
Solar powered watches use Silicon cells containing semi-conductors. When light strikes these Silicon cells some of it is absorbed by the semi-conductors causing electrons inside to flow. This flow of electrons is a current which can be harnessed by attaching metal contacts. The electricity is then stored in a rechargeable battery.
Modern solar watches use Lithium-ion rechargeable batteries which don’t suffer from the usual charge/discharge deterioration of typical rechargeable batteries and are intended to last the lifetime of the watch.
Solar Watch Evolution
The first version of a solar watch was produced by inventor Roger Riehl in March 1968, a prototype followed in 1970 and a full production version called the ‘Synchronar‘ was released in 1972.
The Synchronar was a very unique and futuristic looking watch for its time , what would be termed as ‘Space Age design’ back then.
On the top of the watch where the time would usually be displayed there were instead two banks of solar cells and, rather uniquely the time is displayed on the side of the watch.
Most LED watches were unable to compete with the much more power efficient LCD watches that started to appear later in the seventies.
However the Synchronar due to its solar power was able to survive and has had one of the longest production runs in watchmaking history, available in one version or another up until 2007.
It also had some rather advanced features for the time, including being certified for diving up to 700ft, magnetically controlled switches on top and the ability to automatically adjust for Daylight savings as well as Leap years.
The next landmark would be the introduction of the Citizen Crystron in 1976 the first solar watch with an analog display. As you can see it was traditional in appearance except for a large array of four solar panels
at the centre of the dial.
This would be the watch that started Citizens commitment to solar powered watches which would culminate with the development of their renowned Eco-Drive series.
The commercial for the original Synchronar.
Contemporary Solar watches
Whereas the earlier solar watches had visible external solar cells modern ones have them hidden beneath a light absorbent dial.
The light is converted to electricity using the solar cells which power the watch and charge the battery.
The battery is unnecessary to replace and used to store electricity and also power the watch in the dark.
So long as the watch is exposed to enough light the battery will remain fully charged.
A lot of the major Japanese watch manufacturers make solar watches, there are Citizen’s Eco-Drive watches, Casio’s Tough Solar and Seiko’s Solar watches amongst others.
Citizen in particular is the only watch manufacturer to base a whole range around Solar powered watches with its Eco Drive watches.
Further Reading: Solar Atomic Watches