A video can be seen at:
Here is what you'll need:
-Plywood and some assorted pices of wood
-Copper tubes, elbows, couplings, connections, etc.
-copper or brass sheets
-Plumbers solder and paste
-A plumbers torch
-Used engine oil (just a little to coat the wood)
-Acrylic or polycarbonate transparent sheet
Sizes depend on what you have at hand. The longer the pipes run, the more energy they will absorb. The wider the pipe, the less pressure losses. JUst consider it, because copper is the most expensive item on the list.
You can lay out your exchnager in a series or parallel design. For me, I chossed the series one. So I used 1 meter long sections of 1/2" pipes (8 pcs). plus the smaller ones, which gives a total of 9 meters of pipe. Then I welded the copper sheets to increase absortion area.
Then run water thrugh it and test for leaks. Rework if needed.
After the leak test, clean it with paint thinner. And coat it with black mate paint.