Seiko yesterday announced it has developed the world’s most solar-efficient clock [JP]. The HS533W will go on sale in Japan at the beginning of next month (price: $310). Seiko hasn’t said yet if the device will ever find its way outside Nippon.

The clock, which is just 8.5mm thick, comes equipped with a CR2032 battery as a backup power supply. Seiko says in dark places, the clock will work for 2 years powered by the CR2032 alone. The company promises that solar energy alone is enough provided the clock gets around 8 hours of sunlight each day.