reflector
add mirrors on the top flap to increase reflection + bury it in the ground + add stones at the bottom (slate type which absorb heat)
Materials: recovery water heater, pex plumbing tube,
connection
sharkbite connection black paint, wood, stone, glass
(be careful with the purge (winter) and the water filling, you must provide an outlet for the air evacuation - call a plumber)
My personal conclusion: the best investment for a DIYer in solar energy (time/cost/installation/profitability ratio)
because water heater tanks are generally all good when they are thrown away
they can last 30 years! and more - it's just the elements inside that deteriorate over time! (change the
anode of the recovered tank)