Eco-Drive (Solar) is Citizen's light-powered quartz technology. A photovoltaic cell sits beneath a translucent dial, converting whatever light reaches it, bright sun or dim indoor lighting, into electricity that charges a rechargeable secondary cell. The story starts with the 1973 oil shock: Citizen launched the world's first analogue solar wristwatch, the Crystron Solar Cell, in 1976, then spent fifty years refining it for daily life. A fully charged Eco-Drive runs at least six months in total darkness, and some power-save models stretch to seven years. When charge runs low, the second hand jumps in two-second steps as a warning to give it some light.
The Promaster family carries the line. The new Promaster Navihawk CA4664-60E pairs the B620 Eco-Drive calibre with a sapphire crystal at roughly £475, while the Promaster Diver 200M sits around £300 in Europe and the popular Promaster Dive lands near £315. Fresh movements keep things current, including the E168 calibre with a 180-day power reserve, found in the new dive models that reached stores in July 2025. At the top of the range is the Eco-Drive One, the thinnest light-powered watch in the world at 2.98mm, built around the 85-part calibre 8826 that is just 1.00mm tall and holds +/-15 seconds a month. Most Promaster references hover near £320, with the broader catalogue running from about £70 to £800.
When you buy, weigh three things: the movement's power reserve, the case water resistance, and dial legibility under real light. Eco-Drive's headline appeal is convenience. The secondary cell typically lasts 10 to 15 years and never needs a conventional battery change, so a watch on a wrist that sees a few hours of light a day simply never stops. A collector chasing the living rotor or hand-finishing of a mechanical piece may find Eco-Drive emotionally cool, but for anyone who wants quartz accuracy, a slim profile and near-zero running costs, it is hard to beat.
Citizen does not own solar alone. Seiko Solar (roughly a ten-month dark reserve on the V157 calibre) and Casio Tough Solar (which holds a full charge for about two years) are credible rivals. Citizen tends toward the more elegant designs, Casio toward rugged and affordable cases, and Seiko toward an opaque-dial look. Within Eco-Drive itself you will also find radio-controlled and GPS-synced models, so the choice comes down to how much technical depth you want versus pure grab-and-go simplicity.