Introduction: Solar Hot Water System: Beer (...yes Beer) PET Keg RECYCLED

Yes I know, after the first look, your best idea is to have a more nice beer to drink with your friends... but not in this case! That is another story... I will explay in another Instructable!

So, why two beer keg on the roof of my garage?

So simple: my house is in the midlle of Italy 43° parallel, so from May to September (and some April/October sunny days) I want to use our star (the Sun) to heat my shower water.

Ok... did I "discovered hot water"? (... or invented the wheel) Sure not! :-)))

However, I made my 1st solar hot water system when I was 16 years old.... after an intersting "heating and plumbing" lesson by my hight school mechanic great professor: 30 years ago, he hastonished me!

At that time, I transformed the worst electrical energy eater, an old electric boiler, in a nice black, rocket shape, solar hot water system ...

... understood you, stop with my bla bla bla, and let start with this very easy project!

Step 1: Bill of Materials

a) 1pz used PET beer dark keg (but you can chose 2 or more...) - RECYCLED from a beer fest in the square

b) 1pz water pressure reducing valve setted to 2bar: this is a must! WARNING, not forgot this, if you will use net water with more then 3bar pressure.
c) 1pz water pressure gauge: this is a must! - RECYCLED from an old gas boiler

d) 1pz water 2,5bar pressure relief valve: this is a must! - RECYCLED from an old gas boiler (tested)

e) some pipe connection - I my case, more are RECYCLED from an old gas boiler and net.

f) 2pz water valve - RECYCLED from my old bathroom.

g) shower head - RECYCLED from my old bathroom.

OPTIONAL parts, for automatic water mixing:

h) 1pz hot water automatic mixer

i) 1pz water "one direction" valve

j) 1pz water termometer - RECYCLED from an old gas boiler

Step 2: Modify the PET Beer Keg

Take an used keg (Dante, my Abruzzo sheperd dog in the photo, is asking why... finished the beer :-( ), unscrew the white beer out fitting on the keg (each keg have the related way) and remove the internal parts (no need for our use).

So fix a brass tank connection on the white out fitting and screw on the keg (yellow arrow).

There are many different kegs maker, so different shape, volume, colour, etc.: the important is to use dark PET type one.

You know, dark is much better to capture energy.


Step 3: Create Our Specific Inlet/outlet (cold/hot) Water Connection

The heart of this solar system!!

1) The keg have only 1 hole (ok... it's clear!!!), but we need 2 holes: a cold water inlet and an hot water outlet.

2) I want input the cold water on the bottom of the keg and I want to take the hot water on the top of the keg (hot water come up... as a Mongolfier, hot air balloon, teach ;-) ).

How to do? Simple, need to build this part!

a) take a copper pipe (2) 12mm diameter and legth 100mm less then the keg length you have (have to inlet cold water in the keg bottom side)

b) solder a copper pipe on a 1/2/'x1/4' brass niples (1), in brazing way.

c) fix the niples+pipe soldered on the Tee 1/2'x1/2'x3/4' (3)

d) fix a 3/4' "pipe union" (4) ("bocchettone" in italian language), on the Tee



Step 4: Fix the Inlet/outlet to the Keg

a) Insert the copper pipe in the keg (1): if too long, you can cut it little bit.

b) Fix the "pipe union" on the keg (2)

The single keg heater element is done!

You can chose to make 1, or 2, or 3... or 50 if you need to shower a rugby team!!! The used kegs are free!!!!

Step 5: Keg Connection on the Roof

You have to buil a stand to fix the keg, inclinated for the lower sun level (depends where you live). I used RECYCLED metal parts to do this stand.

Connect all the keg to the cold (BLU arrow) and to the hot (RED arrow) water: do not mismatch!!!

I connected my 2 kegs heater in parallel way... double hot water quantity!

I added for each keg, a valve to isolate it for maintenace, or any damages... or other: it is an optional... francly I did not used until now.

Ok, finished your job on the roof!

Next step, need to go in the bathroom!

Step 6: Assemble the Water Managing System

...ok, here need some hydraulic skill, but not so much!

I'm not professionist... you can see with your eyes my not refined way!!!

Concerning this step, the photo is quite clear, I hope.

a) It need to assemble that system: the letters in the brackets show the materials in the list on the Step:1 page of this instruction. (h)(i)(j) are optional parts!

b) It need to connect this water managing system as showed by the 4 arrows numbers:

1: connect to cold water from net, or other cold water source.

2: connect to kegs cold water on the roof.

3: connect to kegs hot water on the roof.

4: connect to the shower head

Step 7: Assemble the Dashboard

Fix on a sheet (I used RECICLED alluminium sheet) the RECICLED termometer (j) and the RECICLED pressure gauge (c).

Step 8: WARNING, This Is Very Important to Avoi Damage the Kegs: Tune the Inlet Water Pressure

a) tune the water pressure reducing valve (b) to minimum pressure (please see your valve instruction).

b) open the 2 valvs (f) to fill the kegs with water, so from shower head will come out kegs air

c) when from shower head will come out water, close the shower head valve

d) tune the water pressure reducing valve (b) to 2bar pressure max. In my system you can see 1,5bar... for me enought. My keg manufacturer, on the safety sheet, ask for a maximum use pressure 3,5bar and explosion pressure 10bar.

Of course, there is the 2,5bar water pressure relief (d): it will work for safe.

Moreover, from my net, the maximum pressure is 4-5bar... so, quite impossible a 10bar explosion.

Step 9: ....wait the Sun, for a Nice ZERO Emission Shower!

...yes, your job is finished: now the sun will work for you!

Enjoy your ZERO emission shower!

Step 10: Improvements

This was an experiment with kegs. I made all that in fast way... 2 half saturday during last spring.

It worked well during the summer, but I will do some improvement to increase efficiency and effectivness:

1) kegs: isolation on the rear, top and bottom with sponge isolator. During windy days, can help to keep hot.

2) kegs: paint BLACK on the sun side. Sure will capture more energy from the sun. Is possible to paint the PET.

3) during winter, in my place the temperature can go under 0°C, so I manually partially discharge the water in the kegs to avoid the ice can break something on the roof, but possible to use an automatic valve. Actually is low priority.


PET material on the sun ultraviolet ray, years by years... and PET material on the roof, cold and hot...

How many time will resist? In the worst case, very simple to exchange with new ones.... but I hope not each year!!!

We will see!!!

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