When I was a kid at science camp we demonstrated this effect. They had a very long sausage-shaped black plastic bag that we all rand around filling up and laid

When I was a kid at science camp we demonstrated this effect. They had a very long sausage-shaped black plastic bag that we all rand around filling up and laid out in the sun until it rose. I always assumed this strange bag was designed for such demos. In our case something happened (a person let go, a tether broke; I don't recall), and the "solar sausage" flew away completely until we could no longer see it.