In the influential H. G. Wells story, The War of the Worlds, the Martian fighting machine has a heat ray capable of projecting intense heat against anything it is turned on. I think the most impressive feat we see it perform is melting a hole in the ironclad Thunderchild. You'd think the water would provide an effective heat-sink, making the ship harder to melt.
About how much power output did it take to perform this feat in the (presumably) few seconds it took?
The book doesn't say explicitly, but can we work it out from the information available? (I'm not counting the films because they have completely different plots to the book and don't share any authorship.)