Yep, that's all it is, solar power heat. It breaks down pretty fast in the summer, plus I don't want to bring it in in winter because my apartment building has mice (*though I have never had any in MY apartment, because I have cats. So maybe I'd be okay, but that feels a little like tempting fate to me, so I don't. The buckets live on my balcony outside). So I've never added wormies.
I shred paper and cardboard for browns. It also gets dead leaf pruning from my houseplants, dead cat grass, coffee grounds, eggshells, table scraps, wooden matches, occasionally dryer lint (only when I'm doing a load of linens, so I know it's like 99% cotton and not really any poly fibers), it's had a few paper tissues, nail clippings, cat claw sheaths, hairbrush and catbrush cleanings, and incense stick ends and ashes. ALL THE THINGS from the apartment homestead in the sky. LOL. If I had quit adding to it, it would have "finished" a few times, but I just keep adding to it as the bucket isn't full when it breaks down. The last batch of shredded paper, I filled it to the brim, and even though it's on pause so there is still identifiable paper shreds (when in the summer, paper breaks down the fastest, so that's how I know it's on pause), it's probably sitting at 2/3 full. I might just add to it over the winter and then let it bake (with stirring, of course) come spring until it's done.