This passive hot water heater was made in the eighties and from what I can tell there were 2 major manufactures, one making the container, and the other supplying the prism glass, which is the primary item used to complete the process. The third aspect of the panel is the design of the element its self, and in theory there are as many of those as their are people to think of one. Here are the two I've come across.
This design is a pump design,
You can see here a pump is needed to force the water in and out of the heated metal tubes, that heated material is then sent off to its destination and returned to be reheated.
And the other design is a 7 foot long container with copper tubes that once heated force an upward flow of heat with water as its medium of exchange.
It requires a container above to collect the heated water and then circulate the colder water back to be reheated. As time goes on the temp heats to boiling but the amount per day of 200 degree water produced is
about 20 gallons and then you still have to find a way to work with it.
I will show you the best way to design the passive rising panel and another way that works but would work better with the opposing panel and efficiency increases.
One is the domestic hot water panel system, and the other the room heated panel system, each one a dollar and in similar format, occasionally I will add a url if need be, but you have to go online to see that one.