Pressurized
solar shower. I have a 3 gallon sprayer which is meant for orchard use. It's dark green and warms up just about as well as a black
shower bag. I lay this tank on its side facing the sun resting on a piece of memory foam to insulate the shaded side for greater efficiency. Since most of my camping is done in the
city at demolition sites I often cheat and fill my container up with
hot water at a gas station
Once the container is heated I pump it up and place it in a high position with the spray wand propped in the right direction. The trigger has a lock which allows hands-free operation and the nozzle is adjustable from a solid stream like a squirt gun to a very fine mist. Set midway between these extremes the sprayer provides a comfortable shower while using very little
water.
If this system were scaled up to a 40 gallon tank in a cottage situation you could have an open non-pressurized batch system consisting of a tank in a breadbox style
solar collector which has an open valve at the top. Once this tap is closed the tank is ready to pressurize with either a bicycle pump or from your compressor.
If a pressure relief valve were included and the tank were only filled one quarter of the way, pressure could be allowed to build up naturally as the air expands. But with the pre-pressurized system you wouldn't have the option of adding cold water to the mix. A separate hot air expansion tank could provide this pressure and would allow for temperature adjustment before use.
Of
course decent shower pressure can be obtained by placing the tank 20 feet in the air, but in any situation where water is pumped by hand or delivered to the heater in pails a tank mounted at waist height would be convenient to load, have minimal piping and and could be safely supported. A foot pump could be permanently affixed just outside of the shower for emergency pressure top up.