@neauoire yeah, doing that kind of experiments on a boat is not ideal... I'm thinking about land-based solar collectors that are used just to heat water, but if you don't use enough water you lose a lot of energy. That alone makes me always prefer installing (more) PV panels that are not limited to heating. But in this case you could use the system to cook too and in some scenarios it could be advantageous, especially in areas with no electric grid.