I'm not aware of a word in Welsh for one, but even the English doesn't actually convey what it IS really. It may catch the sun, but it lets it go again. I wonder if Heliwr Haul would work in Welsh? Hela (HELL-ah)means to collect, but also to hunt; Haul (Hile) is sun. I can think of other possibilities which might be more poetic, but more difficult in terms of pronunciation...

sian