Citizen Eco-Drive history explained: 50 years of light-powered watch innovation
Zach Blass“A watch that keeps running as long as there is light will surely be loved by people all over the world.” This is the mantra and reason behind Citizen’s Eco-Drive technology. The solar segment has certainly seen expansion in recent years, but one brand was long ahead of the curve, debuting the technology 50 years ago: Citizen. In celebration of this milestone, today I want to walk through the origin story of what we all know now as Eco-Drive, how it has evolved over the years, and key models past and present.
What is the origin story behind Eco-Drive? What prompted Citizen to look into creating the technology?
To get the answers I was looking for, I spoke with Shoichiro Morita, a master movement engineer at Citizen, and he explained to me that in the 1970s, the world was searching for new sources of energy and that following the first oil shock, the development of alternative energy sources became a major global social priority. Awareness began to grow around the subject of energy conservation, and this prompted Citizen to bring this conversation into the world of watchmaking. How can the life of a battery be extended to minimise waste? By 1974, Citizen had its first prototype, and two years later, after further R&D, the world’s first analogue light-driven watch was formally introduced to the world in 1976: The Citizen Crystron Solar Cell. The name is somewhat misleading, as it feeds into a common misconception about Eco-Drive that continues to this day.
How Citizen Eco-Drive evolved over time
From inception in 1976, Citizen had realised a watch that was not only capable of being powered by sunlight, but also by artificial light as well. Mr Morita explained to me that although it was possible to generate electricity using solar energy, the realisation of a light-powered watch was challenging because there was no compact rechargeable battery suitable for storing the generated power, and therefore developing a light-powered watch using a primary silver battery was a significant challenge. Charging a silver battery generates hydrogen gas, which can cause the battery to swell or leak. To address this, a circuit was developed to control the generation of hydrogen gas while charging. But this was just the first outing.
In the decades since, Citizen has continued to innovate and improve its light-driven, Eco-Drive watchmaking. As the first, the Crystron set the bar. Its dial had eight monocrystalline silicon solar cells that charged a silver oxide battery, enabling up to five years of continuous operation on a full charge when exposed to light before the watch would need maintenance – significantly extending the longevity of a battery and reducing the need to constantly throw a depleted one in the trash and replace it. The watch also offered improved accuracy within 15 seconds per month. The Crystron made wearing a highly accurate light-driven watch possible, but its ability to store power and continue operating if left in a dark environment, then only for a day or two, had room for improvement.
In 1986, Citizen introduced amorphous silicon solar cells, which Mr Morita explained are more suitable for generating power from indoor light, along with large-capacity electric double-layer capacitors. These advancements improved power generation efficiency and introduced a proper power reserve element that extended the operating time to approximately 200 hours on a full power reserve – 8 days of continuous operation on a full charge without light at a time when two days was considered the norm, and with a charging time to reach a full power reserve that was reduced to one-third of its competitors.
By 1995, Citizen was able to make a massive endurance leap, achieving a power reserve or autonomy of six months – nearly 23 times more than the 8 days boasted 9 years prior. Five years later, in the year 2000, Citizen launched an Eco-Drive Radio-Controlled watch that extended the service interval to 10 years, twice that of the original Crystron. It is worth noting that Citizen debuted the first radio-controlled light-powered watch in 1996 – a watch capable of keeping effectively perfect time while connected to its radio signal and while without it accurate within 20 seconds per month – far superior to any mechanical chronometer then and now.
Precision continued to improve within Eco-Drive technology, and by 2011, when Citizen introduced its calibre A010, the brand had an Eco-Drive movement in its arsenal that astoundingly pledged an accuracy of plus or minus five seconds annually. For context, a COSC chronometer runs within +6/-4 seconds per day. Citizen’s A010, however, is accurate within 5 seconds per year. Very, very accurate. This movement is typically found in its higher-end collections like the THE CITIZEN range.
Eight years later, Citizen bested its A010 with its 0100, five times more accurate, running within just one second per year. This movement is typically found in its higher-end collections like the THE CITIZEN range. Eight years later, Citizen bested its A010 with its 0100, five times more accurate, running within just one second per year.
Speaking of a year, in 2023 Citizen introduced Eco-Drive 365 – Eco-Drive movements, which, on a full charge, have an autonomy of 1 year of continuous operation. For example, if you were to expose one of these Promaster dive watches equipped with the calibre E365 to 11 to 40 hours of direct sunlight or 130 hours under artificial fluorescent light, the movement, with its full charge, can continue to keep time in darkness for a full year.
Citizen Eco-Drive aesthetic innovations
Incredible. Now, Citizen, of course, has not just been improving Eco-Drive technology in regard to performance alone, but decreasing the aesthetic limitations using such technology entails. With the Crystron, the solar cells were proudly showcased on the dial, but what if Citizen did not want to have them front and centre?
Today, Citizen has a variety of solutions that afford the brand more freedom and exploration when it comes to dial design and layout, with structural ink dials, washi paper dials, among other solutions. But in 2001, the Eco-Drive Eclisse and the calibre F810 introduced within it debuted Citizen’s Ring Solar: a flexible solar cell strip formed into a seamless ring and positioned so its light-receiving surface stands at right angles to the dial. This technology overcame a key limitation – metal dials do not transmit light. With the ring absorbing light at the periphery of the dial, the dial itself no longer needed to be translucent. Though not technically a complication, most watchmakers acknowledge ultra-thin watchmaking as a complication in its own right. It is, of course, very complex to have a high-performing ultra-thin movement.
In 2016, Citizen did the unthinkable, creating a movement just 1mm thick, and placed it inside a watch dubbed the Citizen Eco-Drive One, which, depending on the model, hovers around a total case thickness of 3mm. But, despite being so thin, the Eco-Drive One’s movement boasts a 1-year autonomy like the E365 and is accurate within 15 seconds per month. Okay, so we’ve covered some key moments in regard to performance and aesthetic innovations in the five-decade history of Eco-Drive. But what are some Eco-Drive watches on offer today that people should know about?
Mr Morita’s 3 Citizen Eco-Drive picks
I asked Mr Morita to nominate three pieces I should quickly highlight. The first is the limited edition ATTESA Light in Black Eco-Drive 50th Anniversary Edition F950 Timepiece. Launched to commemorate 50 years of Eco-Drive, the dial really showcases Citizen’s dial manufacturing mastery with a black dial that overcomes the difficulty of black absorbing light before it can pass through – and in style. It has this sort of meteorite-like look that feels both natural and out of this world. This is possible because today, Eco-Drive includes models that operate with less than 15% light transmission, enabling greater design flexibility without compromising performance.
It’s housed in a handsome and faceted black DLC Super Titanium™ case, 44.6mm in diameter, and is affixed to a matching bracelet. Through its Eco-Drive Satellite Wave GPS movement, it is highly accurate and offers world time in 27 cities (40 time zones), a 1/20-second chronograph, dual time zones, a (UTC) universal coordinated time display, a perpetual calendar, accounts for daylight saving time, and power reserve and light level indicators. Limited to 1,900 pcs. And priced at US$2,195.
Next we have the Promaster Dive E365, a saturation diver’s watch equipped with a helium escape valve and 300 metres of water resistance. Its E365 ensures the watch will always tell you the time whether on land in the sunny sand or down in the dark depths of the ocean. Eye-catching glossy dials are housed within a 46mm steel case that is lugless – letting the strap integrate and start its camber early. So it suits smaller wrists better than the diameter suggests. And these handsome, robust divers are priced at just US$725.
Lastly, the Eco-Drive models within the THE CITIZEN collection are an excellent way to harness the hassle-free high performance of Eco-Drive with an elevated aesthetic for your wrist. For example, these two THE CITIZEN Eco-Drive limited editions have 38.3mm zaratsu-finished Super Titanium™ cases, one with a DURATECT platinum coating and the other a DURATECT gold-toned coating, and both are paired with mesmerising washi paper dials and an A060 movement with a running time of 7 months, with an operating time of approximately 1.5 years on a full power reserve when the power-save function is activated, and, despite being a clean three-hander with a date, is also a perpetual calendar. Watches like this pair are priced at just above US$3,000.
With the interest in light-driven watches surging, it will be fun to check in 50 years from now and see what even greater heights Eco-Drive has reached for its 100th anniversary.
Editor’s Note: This content was made in partnership with CITIZEN. CITIZEN is a registered trademark. Eco-Drive powering varies by light intensity,