I have been experimenting with solar water heating for those times when there is no hookup available...........and because I'm bored at home...........man coming in a week or so to update my gas regulator system.

Anyhow.....it all started with me having a black car and the satnav being too hot to work one sunny day. I thought being only 94 odd million miles from the biggest nuclear furnace for several light years there must be a way for me to make use of this free heat..............no battery in the van so solar panels not a lot of use.........that just leaves solar heating, there are lots of novel ways to heat things and even cook using solar energy on youtube but none that I saw that would be small enough to take away in an Eriba.

So working from the start point of the car being black and metal I got a metal petrol can and painted it black. On a sunny day after about 3-4 hours it heated water from 16 deg C (tap water temp) to 30 deg C just about doubling the temp and warm enough to wash up or have a wash in the van.
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Then came the next step ..........did it have to be metal? did it have to be black?

This set up then followed

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The plastic bottle did raise the temp of the water but was 3 degrees behind the black metal one on top temps.

The next logical step was to paint the plastic one black.

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This had the effect of making both the same temp within less than one degree (the white wires you can see are temp probes)

Conclusions.............on sunny days it can be done to a useful temp, plastic is as good as metal, black is well known to be the best colour (and may have got a better result if I had some matt black paint)

Any old plastic container will do provided its painted black and left in full sun (out of the wind if you can) the more water you put in the longer it takes to heat to a reasonable temp. Beyond early evening it will start to cool down again.

So if you are off grid and want to save a bit of gas or are an eco person who likes solar power and saving the planet have a go at the Hobgoblin © solar water heating black plastic bottle thingie

The bigger the surface area the bigger the solar gain so maybe a large black heavy duty plastic bag would be even better!

Quote: Frantone wrote in post #2

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The bigger the surface area the bigger the solar gain so maybe a large black heavy duty plastic bag would be even better!

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Camping 'solar showers' use a black plastic 'bladder' - very effective !

why not put the metal container in the black car, the sun will heat the car interior perhaps putting the container on front seat on a cover may heat water faster
autumn camping could leave container next to heater while visiting various place.. or put in night before to heat when sun rises

I usually boil the kettle and add water to cold water in sink container, some rally people said they boil kettle and fill a flask to save having to keep boiling kettle,
they also said the tap was behind the white caravan, hehehe the field was full of white caravans

Try the black plastic waste pipe, works very well in a twin wall pvc box.
The coil type is easy to make and try.
https://www.youtube.com/watch?v=1tTtPLGjOJo