Solar quartz is the system where a photovoltaic cell, set behind or around the dial, converts daylight or artificial light into electricity, stores it in a rechargeable secondary cell (a capacitor or a lithium-based cell), and feeds a standard quartz movement. There is no disposable battery, and a well-charged watch keeps running for months in the dark, often well past six. The category has a clear origin: Citizen launched the world's first analogue solar watch in September 1976, the Crystron Solar Cell (model SCQ-8629) with eight cells visible on the dial, and Seiko followed a year later in 1977 with calibre 4826.
The real examples run from cheap and cheerful to seriously refined. Citizen's Eco-Drive line is the deepest: the Promaster Diver BN0150-28E pairs the E168 solar movement with ISO 6425 dive certification and 200m resistance for roughly £185 to £240, which is honestly hard to beat. At the top, The Citizen collection's A060 calibre holds annual accuracy of plus or minus five seconds with a perpetual calendar programmed to 2100, and the 2026 Eco-Drive 50th Anniversary AQ4091-56W wraps that in a Super Titanium case and a hand-dyed washi paper dial, limited to 650 pieces at around £2,500. On the Seiko side, the Prospex Solar Diver, using calibre V157 (date) or V158 (day-date) with a roughly ten-month reserve, sits around £470 for the blue or black steel variants and £530 for the full black.
Buying comes down to how you live with a watch. If you spend time at a desk or outdoors, an Eco-Drive or a Tough Solar asks for almost nothing: as long as the wrist sees light, it runs. Casio's Tough Solar, including the solar G-Shocks, charges off even weak indoor light, and its capacitor-type cell typically lasts ten years or more in normal use. The one genuine maintenance item is the secondary cell, which loses capacity over the years; you notice it as a shorter dark reserve, and a watchmaker can swap it in a procedure much like a battery change.
A few nuances are worth knowing. Citizen hides its amorphous silicon cells beneath the dial, and Seiko mostly does the same, so neither demands a visible panel, while some Casio models still show the panel on the dial. Solar quartz suits the buyer who wants quartz precision and low fuss without the chore of replacing batteries. The trade-off is emotional rather than functional: you are buying a dependable tool that runs for years without opening the case, not the romance of an in-house mechanical movement.