roof rack water heater

Franken

i havent done this my self but the idea sounds good. Some thick black poly would be the go.100mm sounds good, that will give you 8 litres per meter lenght so if you want about 20-30 litres maybe put two lenghts of 100mm 1.5-2.0 meters long or so.

Cheers

Seems like a lot of trouble,cost & weight for a bit of warm water to me, tedious to fill,requires a heap of plumbing. Wont work when covered, black pipe absorbs heat quickly but dissipates just as quickly.
I doubt temp will increase much unless in sun for many hours. Apart from that, probably a great idea..:))). Boil the billy, add to cold water in bucket..connect to
shower & all is well, but I was always a simple bloke..cheers.....oldbaz.

The plastic bag type that you lay on the ground in the sun work quite well(actually very well)....we normally try to park our car in the shade when camped so having pipes on the roof rack would not be much good to us...I doubt very much if being on the car the water would get very hot at all.....on the roof of a house you have the reflection of the heat from the roof helping it and if it was an iron roof then that would be considerable....on the ground the heat reflects as well...cheers

Not quite what you're thinking of, but close - We carry a black 10 litre (ex-oil) bottle full of water lying horizontally on the roof rack. The plan was that it would absorb heat during the day for a couple of minimal showers. Works fairly well in that the water warms up sufficiently for comfortable showers, IF the vehicle is stationary for a few hours. The heat losses to the air if the vehicle is moving though lead to a cold shower. I'm thinking of some simple insulation - maybe wrap in bubble wrap to avoid losses while still collecting heat from the sun? Still to be tried.

Your black polypipe would probably be similar. Lossy if in motion, ok otherwise.

HTH

John