Oh.
Ya needs MORE energy (to make the CO2 into CO) than what ya get from da sunlight falling on da (incredibly expensive) solar panels (which only generate usable power from 9:00 AM to 3:00 PM local every day anyway) .... So ya need to burn (some kind of mythical fuel) to convert (useful) CO2 into (poisonous) CO....
Read the article I linked to. It states that they used a silicon based semiconductor that doesn’t provide enough power. Next they are going to try a gallium-phosphide semiconductor which should produce better results. No mention of whether or not they will have to still add non sunlight energy to the mix then. Hey, if Orville and Wilber had as many nay sayers on their first 10 second flight at Kittyhawke we’d still be blimping it around the world. :)