Paddling Pool Solar Water Heater




About: Retired educator/writer

Simple & CHEAP backyard solar water heater, based around a kids clam shell paddling pool! The approach uses a wide & shallow (100-150mm) water tight container,& in high summer (or with high angle tropical sun) this readily provides 60 litres of shower temperature water.  It can be left at ground level, OR perhaps elevated enough for a good head to supply a simple garden hose connected backyard shower.

Sturdy plastic bag camping showers abound of course, but these hold only 20 litres, and can be heavy to lift up into position. Further more they may become dangerously hot, and sunny positions are not always the most private for later ablutions either! Having a hose fitting allows a length of garden hose to be run into a discrete location (perhaps even to an indoor bathroom ?)

More ambitious plumbed in solar water heating installations can easily cost $$$$,& require pumps or well placed header tanks. Such systems annoyingly work best at just the sunny time of year when you may be on holiday elsewhere-or when you are short of gardening water that could be doing double duty solar showering! This simple one can just be rolled out as needed.

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Step 1:

Mark a position low down on the plastic shell wall, suitable for fitting an access pipe. (An old stainless 900mm x 900mm shower base could instead be used, but these bases are now quite costly even as scrap,with inconvenient bottom outlets, & can be difficult to drill anyway).

If threaded stock is not available,an old tap can provide both a useful threaded 15mm pipe and the hex screw rings. Hacksaw free this off cut, then drill and file the plastic shell base to suit. Remove any metallic burrs & sharp edges.

Step 2:

Fit the pipe off cut and tighten the securing rings, using plumbers hemp or PTFE tape to make a water tight seal. If done neatly the paddling pool can still be safely used normally by kids & toddlers.

Step 3:

A hex cap screwed onto this pipe end retains normal use of the shell as a paddling pool,and also aids it's draining. Your lawn will no doubt appreciate the watering!

Step 4:

A 15mm-20mm threaded adapter, fitted to the outlet,then allows normal cheap garden hose fittings to be simply used, with long hose runs if need be.

Step 5:

Of course a bit of elevation will allow more convenience! Ensure the support is up to the weight however ...

Step 6:

Clear agricultural grade plastic approximately 1m x 1m (~US$3) was found suitable as a cover, but this naturally will need securing or weighting against wind. Corrugated baby PVC also performed well, as did glass from an old window. Use whatever is convenient.

Ensure any plastic top cover is well secured against wind and animal damage! Although screwing down may tempt, this makes cleaning harder,so consider a lift off wooden framed support.

A bottom layer of gravel-or even black paint-may assist with solar pickup (and stability in winds),but water itself is a strong infra red absorber.


Step 7:

Case study 1:  Sat. Dec 6th 2008-Wellington,NZ (early summer "down under" of course). Latitude 41 South. Note research assistant "Molly" testing progress!

Under clear skies,with max air temp. ~25 Celsius,no wind & VERY bright sun,60 litres of tap water (initially at 20 Celsius) warmed from 11 am at ~4 degrees C an hour, reaching a very cozy 42 C by 4pm. By mid night,under a ~15 degree evening, this had cooled back to 22 Celsius.

Using Q = m x c x deltaT, then 60 x 4185 x 22 = 5.52 Mega Joules of energy gained. At ~US 20c a 3.6MJ "unit" this is worth just ~US 30 cents,(& over 100 days of summer capable of saving US$30 = ~paying for itself), but the "solar shower" convenience may be much more valuable, especially off grid.

The benefit of dirty feet and salty body washing remaining outdoors of course are near priceless for harassed summer housekeepers!

Step 8:

If the sun remains too strong at "splashing time", then a ground level setup can perhaps even be dragged by an adult  across grass into nearby shade.

Step 9:

An old stainless steel shower base will be sturdier and hold more water, plus (being uniform) it'll be easier to cover too. However plumbing into the usual bottom drain may be a hassles without assorted fittings or brazing gear. 

This one has been in the kids tree hut since 2000, and is covered with perspex for safety. rather than glass.  It still works a treat - on Jan 27th 2013, with afternoon air temps ~ 25 Celsius, the ~100 litresof water within had warmed to an almost too hot 48 Celsius by 5pm as the sun left it.  ( The location was Wellington, New Zealand lattitude 41 South - Dec-Feb is NZ high summer of course)

Step 10:

Case Study 2: Wellington (NZ)-assorted occasions NZ summer 2007/2008  This steaming  setup was installed on a sturdy shed roof, giving a 2.8m head above ground level,and back filled from a garden hose when empty. Measured clear sky  high summer heating rates of ~4-5 degrees C per hour were typically observed, with cooling rates only ~1-2 degrees/hour. By mid afternoon,under clear sky conditions ,water temperatures could reach ~50 Celsius & a   "solar shower" sometimes was almost too hot !

Step 11:

Case Study 3: Wellington NZ -December 1st 2008 ( a very warm but overcast  day):   Outside peak conditions, early summer water heated from 20 Celsius  to  36 degrees Celsius water by 6:30pm,and remained still pleasantly warm until  well after dark.

Conclusion: The approach offers a versatile, educational & cost effective approach to DIY seasonal solar water heating, with temperatures to blood heat (37 Celsius/98 Fahrenheit) readily  achieved- even under non optimum solar conditions. The "backyard benefits"  of solar heating significant  volumes of water to modest temperatures outwaeigh heating a small volume to a higher temperature. Water rarely will get to an unsafe temperature, making the setup safer  for children too.

EXTENSION: Such enhancements as side insulation, double glazing top cover,heat exchanges, water depth & perhaps even "solar salt ponds" (or solar PV powered pumping) could readily be explored for greater performance.

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    10 Discussions


    6 years ago on Introduction

    Sure, BUT even 100' of hose will not hold that much water !  If you do the maths  (Volume - pi x rad.^2 x length) you'll find  ( in metric terms) 30 metres of ~10mm internal diameter hose  is only  3.14x.01x.01x30 = ~10 litres of water. The paddling pool setup holds more like 100 litres. It's high summer here & yesterday & this was enough to shower 2 adults, 2 kids & a dog & still have lots left.

    I take your point abot Arizona, but iIn regions with only "modest" heatwaves (New Zealand), a hose based setup can still get TOO HOT. The idea for backyard solar is of course is to boost a lot of water for balmy bathing/showering rather than a little water to elevated temperatures.



    6 years ago on Introduction

    Looks good. But couldn't you accomplish the same thing with 100 feet of black water hose on the roof with one end connected to the pressurized water supply and the other connected to a shower fixture? It's been done that way here in the Arizona desert and works even in the wintertime here.


    7 years ago on Introduction

    I don't want to seem like the grammar police because I am horrible at grammar myself but in step 6 I think you meant to put 11AM to 4 pm. unless you warmed it up during the night x) Regardless, nice instructable, any plans on making a large-scale version?

    1 reply

    Reply 7 years ago on Introduction

    Yikes! Indeed it should be 11am - I've edited OK. Thanks for spotting. I've no real plans for anything larger, but something wide, shallow & cheap (!) may come up. However yard clutter, loaded weight & out of season storage may then become an issue ...


    7 years ago on Introduction

    Float a black plastic trash bag on top of the water for extra gain and/or bubble wrap to let light and heat in while insulating.

    For extra hot add a higher below water fitting and attack a coil of black poly pipe.

    For mega hot super-lux, run a 12v bilge pump off a battery to circulate the water through the piping.


    10 years ago on Introduction

    ah, the old magnifying glass and sun trick! those were the days... ...i sure wonder where the time went.


    10 years ago on Introduction

    What a fantastic idea! A cost effective, great way to heat pools. Finally I will be able to enjoy the pool with the kids! They don't mind the cooler water temperature however I require another 5 or so degrees before I can manage to brave the pool....