our solar shower worked well on sunny days but when a person really wants a shower after evening chores it was no longer warm. i decided we needed a batch solar heater that will retain a bit of solar energy into the evening. our requirements are small so i used a five gallon air pressure tank that i had been planning on replacing the schrader valve. it was mostly taking up garage space anyway. the main problem was there is only one opening (port) to the tank. i needed to put cold water into the bottom and remove the solar heated water from the top--that requires two ports. i don't own a welder and my brazing kit is in a shambles so i couldn't simply add another port. i used the old heat exchanger concentric piping trick.
sorry for the lame drawing our mouse is acting up. the idea is that the water will stratify. hot water will raise to the top. as the shower is on cold will add to the bottom. this strategy works for a larger tank much better. this little tank works fine also.
the tank likes to be insulated from the cooler evening. so, i built a box around it with a glass window for the solar collection part. i also integrated solar oven technology. a parabolic reflector which happens to be r-6 insulation. everything was going fine. i built the box/collector sized for a window that i already had. during the final moments of construction--the last screw i cracked the glass. ...damn... i got out the caulk and caulked the crack and called it fine for this temporary solution.
the shower works great the entire family can easily take a shower on five gallons of water. re-heat time is minimal maybe an hour in full sun. we are very pleased.