Toyota, maker of the eco-friendly Prius hybrid car, has also achieved an energy-saving breakthrough in vehicle painting technology.
The new "3-Wet" method has dropped one "drying oven" step and achieved a 15% energy saving compared with old-style methods.
A spokesman said other energy-reducing innovations in manufacturing, such as shaping parts more speedily and introducing smaller robots, are also being tested at Toyota.
Meanwhile, the solar panels at its Tsutsumi plant add up in size to the equivalent of 60 tennis courts, producing enough electricity to power 500 homes.
That reduces 740 tons a year of carbon dioxide emissions, or equal to 1,500 barrels of crude, according to Toyota.
The company also uses simple toy-like measures to slash energy needs: scooting along parts with pulleys and springs, tapping into excess energy from nearby machinery, reusing grease, and other shop-floor ideas to scrimp and save.
Yasuaki Iwamoto, analyst at Okasan Securities, said efficient production was a plus both as cost cuts and an image boost. "It makes sense to grow fuel-efficient, and getting exposure is good for company image," he said.
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