Here is how we made a sun heater to get warm water in a sink in our annex. Making our own warm water will protect the planet a tiny bit more, as the heat will not come from burning fossil fuels.

Materials that we had already and which we re-used:

1 aluminum window frame
1 window glass in frame that fitted with the aluminum frame
2 hinges with screws and bolts
2 water pipe connectors
A piece of roof plate
Foam pieces

Materials that we bought:

40 cobber tubes 2’ long fitting to with of window frame less 3’ in each side
40 tripods of cobber – same size as cobber tubes
Foil (aluminum) same size as window frame
Collecting joints fitting inside the cobber tubes

Assembling the sun heater:

Cut the roof plate so it fits the window frame. Fasten it to backside of window frame with screws. Make two holes diagonal from each other in a corner and fit the two water pipe connectors in the holes

Cover inside of roof plate with foil, fasten with duck-tape

Assemble the cobber tubes with the tripods and collecting joints to the latter like structure you see in the picture. Solder the connections.

Place foam pieces between backside and the cobber latter structure as you lay down the cobber structure in the window frame.

Fit the cobber structure to the two water pipe connectors

Put water in through the top water pipe connector and watch it come out of the second water pipe connector

Fit the window to the bottom window frame.

Fasten top and bottom window frame to each other with hinges and screws.

Any size of window frame can do, and then you just have to fit everything else accordingly.