I had not heard of these. The mechanism seems to be to circulate a cooling fluid, such that more heat is generated than used by the circulating pump.
A relatively new addition to the solar panels market, solar dynamic panels produce hot water in all weather conditions. Attached to the roof of the home, the panels do not require a backup system of gas or oil and a single solar dynamic panel can provide 55˚C hot water sufficient for a family of five every day throughout the year.
Has anyone used them, and are they still a thing? They seem to cost about as much as a big boiler.
http://thegreenhome.co.uk/heating-renewables/solar-panels/solar-dynamic-panels-overview/
https://www.thegreenage.co.uk/buy-thermodynamic-panels/
Can @Onoff make one out of beer cans and an old fridge?