A solar watch is an electric or electronic watch which derives its power by converting solar energy into electrical energy by means of solar cells. This technology was invented in the 1960s and patented in 1969 by the United States Time Corporation. The first solar digital quartz watch was produced by . The first analog quartz solar watch came from Citizen in 1976, with Seiko close behind. Today, this technology is widespread, with hidden solar panels in conventional-looking watches from Junghans, Citizen. Casio, and Seiko.
The photoelectric effect was first used in experimental clocks as early as the 1950s. Patek Philippe showed a novel “perpetual” solar-powered clock at the Basel Fair in 1952 which used an electric motor powered directly by a solar cell to wind the spring of a mechanical clock. Such clocks were available commercially in the late 1950s, though they were not widely produced. Indeed, photoelectric cells were considered more important in the field of sports timing than as a power source.
The first photoelectric electric clock was introduced by Seikosha in 1965. It used a sealed nickel-cadmium rechargeable battery which could store 100 mAh, recharging in four hours using a photoelectric solar cell. This technology was not able to power a quartz clock or watch due to high current drain of the electronic counters used to divide the frequency at the time.
In 1969, the United States Time Corporation received a patent on the concept of a solar powered wristwatch, though the company had no plans to produce such a watch. The first solar-powered quartz watch would appear in July 1972. The Synchronar, later produced by the American firm Ness, was a casket case digital LED quartz watch with two large solar panels on the top. It was invented by Roger Riehl in the 1960s but he was forced to wait for the development of CMOS integrated circuits and low-power LEDs before he could produce his first prototype in 1971. The Synchronar was the first watch to be called “solar” in popular press, and was later sold in Europe by Eurotime as the Solar II.
The American company Uranus Electronics was the first to mix solar cells and the LED display on the dial of a conventional watch in 1975. The next year, the German company Cristalonic went into mass production of a standard solar watch movement with a digital LCD display. This movement had six solar cells positioned above the display, and was also used by the Swiss company Allorgan. Later that year, Swiss movement giant ETA released their own solar movement, with three solar cells above and below the LCD display. Other solar watches appearing that year were produced by Nepro, the LCD Neprosolar, and Sicura, the Solar Star.
Uranus also introduced a solar-powered calculator watch in 1976, with 12 buttons around the dial and an LED display. A more conventional solar calculator watch came from Marcel in the United States the following year, with a pad of 20 tiny buttons on the face.
The first solar watch with an analog display appeared for sale in late 1976. Citizen of Japan introduced their Crystron Solar Cell watch, with four large solar cells arranged on the dial. Seiko's first solar analog watch, using Cal. 4826, was introduced in 1977. It used 12 smaller solar cells arranged around the dial as a chapter ring. The first Swiss solar analog watch came from Sicura in 1978, with the power cells on the right side of the case and the crown at 9 00. Junghans introduced their Solar I in 1988, which boasted a 100 hour power reserve.
Work continued on solar digital watches as well. The Japanese firm, Orient, introduced a solar LED watch in 1976, and Mikado created an LCD watch with two batteries, one for a backlight. The Swiss Mondaine produced their own full calendar LCD watch, the Digi-Solar, the following year. Another Sicura model in 1977 moved the solar panels to the side of the case. Seiko introduced the first digital quartz chronograph with solar power in 1979.