I'm tinkering with some sketches on using collected rainwater to run across black galvanized panels boxed into foam insulating panels with salvaged sliding glass patio doors sealing off the top.
The real trick is controlling the temp as experienced with another water heating test -- used black 5 gallon buckets buried in the ground with 2" foam insullation packed around to hold temps and covered with a clear acrylic cover - dag gone near burnt my hoof off when I tested it mid afternoon one day.
-------------------- May you experience a mule day --- stubbornly good!!!