A solar watch is a quartz timepiece that uses a photovoltaic cell beneath the dial to turn both sunlight and artificial light into electricity, storing it in a rechargeable cell so you never swap a battery. The idea traces to 1976 and Citizen's Crystron Solar Cell (model SCQ-8629), the world's first analogue solar watch, which wore its eight cells openly on the dial and needed roughly ten minutes of direct sun for a full day of running. The real turning point came in 1995, when Citizen tucked the cells under a translucent dial (calibre 7878) and paired them with a lithium secondary cell, freeing designers to build conventional, handsome dials. That architecture is what we now call Eco-Drive, and as of 2026 it has passed the half-century mark.
The real examples come overwhelmingly from three Japanese makers. The headline Citizen is the Promaster Eco-Drive Professional Diver 300m, launched April 2025 with calibre E365: a full year of running on one charge, ISO dive certification, a helium escape valve and a 46mm steel case, at around £500. The far cheaper Promaster Diver BN0150 sits near £200 and is the genre's everyman entry point. On the Seiko side, solar movements like the V157 hold roughly a ten-month reserve. From Casio, the G-Shock GW-M5610 fuses Tough Solar with Multi-Band 6 radio sync and the 1983 DW-5000C shape for about £120, while the Pro Trek and Edifice lines lean on the same charging system.
The single most important thing to check is the rechargeable cell, since it is the only component with a finite life. On a Seiko, that capacitor (the MT920, for instance) typically lasts well past a decade, with service running roughly £40 to £100, and you should always have it pressure-tested for water resistance afterwards. A solar watch suits the person who wants one grab-and-go watch and zero battery anxiety, someone who values quiet practicality. The trade-off is honest: most remain quartz, so you are buying flawless reliability and accuracy rather than the heartbeat and prestige of a mechanical automatic.
Within the category, a few distinctions matter. Analogue solar models still drive a quartz movement, and the higher-end Seiko and Citizen pieces layer GPS or radio sync on top of the solar charging. On the digital side, Casio's Tough Solar sips so little power it survives months in a drawer. Open dials with visible cells gather light faster, while hidden-cell classics protect the aesthetics, so the choice comes down to whether you prioritise looks or charging speed.