On boats with extra solar, running a dump load when batteries are full often happens by producing fresh water (desalination) or heating up water. If useful dump loads are available (pumped water?) then it's a good idea but bitcoin mining is better than nothing I guess.

However having bitcoin mining as defacto dump load would probably demotivate work needed toward creating useful dump loads. I'm also wondering what incentives bitcoin as dump load would have in less wealthy regions where purchase power is no match to compete with BTC mining.

Think of a world where most electricity is unaffordable to people, being wasted to hash some coins instead, because it's more "efficient" from a monetary standpoint.