After our first attempt at a proof of concept home built solar thermal panel, we were a little 'disappointed with the results. It took about 4 hours before it began its work, and was a bit 'expensive (over $ 50) to do.
I knew it could be done better and cheaper. My first mistake with the first one was buying everything new. With large reusable resources in the local town dump I knew it could be done cheaply.
Another flaw in the first solar 0water heater was using cloth as our means of collection. Pond liner is plastic, does not absorb the heat and other materials (such as metal) and is more difficult to work with as it is necessary to use glue or adhesive tape to create an air pocket to hold the water. It 'leaked the first couple of times we used and took extensive repairs to make it work.
We solved this problem by using a manifold ready. Something that has already been designed to distribute the heat, and in the absence metal.The last great in our first panel was using plexiglass for the cover. It 'difficult to work with because it will crack, and the use of two pieces left a crack in the middle difficult to close. We solved this problem by using the good old fashion of a window pane.