When Louis Cartier designed the Tank watch, in 1917, its rectangular dial was a bold departure from the round cases of the era. Inspired by an aerial view of the combat vehicle for which it was named, the model’s clean shape hasn’t aged a bit over the years, as the Tank’s quiet, strategic evolution has allowed it to maintain its relevance while preserving the purity of its design. In the 1970s, when the rising popularity of quartz watches sent the mechanical-focused Swiss watch market into a downward spiral, the French company released the more affordable Must de Cartier Tank with a vermeil case, quartz movement, and lacquer dials in colors including red, blue, and black. A symbol of modern luxury, the Tank has long been favored by the style-, design-, and art-minded (Jackie Kennedy and Andy Warhol were among its fans). Even over the past few decades, when bigger, bolder, and more complicated timepieces have been all the rage, the model has held its own as an elegant and timeless standout.

Its newest iteration demonstrates not only its staying power, but Cartier’s ability to pair classic style with forward-thinking ideas. Following two years of in-house development, the recently unveiled SolarBeat Tank Must (available for purchase this fall) is Cartier’s first solar-powered timepiece, and has an average lifespan of 16 years. The technology is so seamlessly integrated into the dial that you’d never suspect the watch is running on the sun’s energy: Light reaches the movement’s photovoltaic charging system through invisible perforations in the Roman numerals on the dial, which is flanked by straps made using scraps of apples grown for the food industry.

The design is less about creating a set-it-and-forget-it watch and more of an example of Cartier’s ongoing work to reduce its environmental impact. Earlier this month, the company’s president and CEO, Cyrille Vigneron, told Forbes that the brand has been working to reduce its carbon footprint for years, and aims to lower its emissions by a minimum of 75 percent across its entire supply chain in the next year alone; it’s also reassessing how it sources diamonds. In this context, the SolarBeat Tank Must seems to symbolize what’s to come in luxury watches: planet-conscious accessories with functionalities that reach far deeper than their dials suggest.