Low-tech thermosiphon

[mikenash]

Hi Guys

If you have off-grid and time & space on your hands - then you don't have to be very efficient, especially if you live on your own

Where I live there's lots of sunshine & I have a water supply from an elevated spring that gives me a 2-bar head - or maybe a bit more

So I have a "solar shower" with the solar part outside in the sun and the shower part inside in a conventional shower cubicle with hot & cold taps etc etc

The "solar panel" is a rectangle of 8mm black plastic sheeting measuring 1400mm X 1600mm, more or less - on a timber support frame, aligned to the sunshine, on which is wound 100 metres of 20mm black "alkathene" poly pipe - ordinary farm stuff - in a big, flat, sun-facing spiral.  It's held flat on the black plastic sheet by about a million cable ties

Cold water at 2 bar goes in and - when there's direct sunshine - really hot water come out and goes to the shower cubicle.  The water's hot-enough that you have to feed in quite a bit of cold.  There's enough hot water for a good shower and then enough left over to think "well I might as well stand here until the hot runs out as both the water and the energy are free

Of course there are two downsides:  There's no storage of hot water - it's just direct on line.  And it only works when the sun shines.  But, since I have a wetback on the stove for winter or overcast, and since I'm on holiday whenever I'm there - who cares.  When the sun shines you can have a shower

It has worked well for years.  And. since there are no moving parts, it will still be working well when I'm dead

Next, then, is a similar panel, probably mounted flat, and a nearby small insulated tank into which I would like to think water will thermosiphon, getting hotter and hotter with each cycle, whenever the sun shines.  I guess it's probably only 10% efficient in turning solar energy into hot water - but if it's simple and it works, then who cares?

My question is - does anyone have experience with a low-tech, thermosiphoning, pump-free, water heater?  If they do - I'd like to hear about it.  No sense re-inventing the wheel

Cheers, Mike

[Mad_Labs]

Never had much luck getting a solar thermal panel to thermosiphon. I have had it work great with a wood fired heater. I think the shorter, wider path of the wood heater is more conducive. The panels I used had fairly narrow tubing.

[mike90045]

( trying again, post doesn't seem to complete with a 400kb pic attached )

I have a commercially made system from Rheem.

It has a flat, glass,  glycerol panel mounted on the sloped roof. At the high end is a insulated 30gallon water tank with the glycol heat exchanger .  The two of us, in the summer, have an excess of 150F stored hot water on our roof all summer.  fall, winter, spring, the solar angle is not so good, and it only heats up to about 90F, which is still fine to feed to our tankless water heater as it only has to boost the temp a little bit.

Winter, we have a 1" SS thermal loop in our Masonry Heater, which heats a 80 gal tank on the 2nd floor above the heater, heats that 80 gallon up to about 90F

[Tom Reed]

Hi Mike, I don't have that exact experience, but thermosiphon does work and is very reliable. The trick is the flat coil of pipe and not getting any air pockets in it. I'd feed the coil from the bottom center.