Construction of gravity water tank for home solar heater

The homemade tank that we are going to build, or at least I, will be made of plastic.

What reasons led me to build my storage tank in plastic format

• Plastic is much easier to work with than metal
• Plastic is a better thermal insulator
• Plastic has no electrical interactions
• Plastic does not rust
• I don't need devices to prevent limescale build-up (like sacrificial anodes)
• Metal facilitates limescale formation
• Plastic will last us many years (due to no rust punctures)
• It can be very cheap

It goes without saying that a plastic tank cannot be used for pressurized water (but I don't want pressurized water)

Where to buy a cheap or disused plastic tank

Any drum that is commonly used to transport food or liquids is enough for us.
Plastic drums of various sizes are used in rural settings.
They use them to store water and irrigate.

Many drums are used to transport processed food, such as olives, corn, boiled carrots and etc ...
This type of container for food transport has a deadline for use.
When this date exceeds, companies need to get rid of them.
So, at that time, it is withdrawn from circulation.
They can sell it for private uses, as is the case in our interest.
I got my 260 liter drum from someone who collected it for private use in a vegetable garden, at the low price of € 10.

It will be very important to give it several cleanings and disinfect very well with degreaser, bleach and hot water, we must not forget that it will be the water that will come out of our taps and we do not want strange odors.

Isolation in our home warehouse

Like the box, the insulation can be anything.
We must provide several layers of the best insulating materials, or the most correct insulators that we can acquire.

For my home deposit I have used in this order: (ordered from the inside to the outside)

1. Several layers of aluminum foil glued with white glue, as a thermal barrier.
2. Cut-out pieces of expanded polystyrene, known as white cork.
   Glued with small globs of polyurethane foam.
   Both polystyrene and polyurethane are very good insulators,
   Expanded polystyrene is readily available in discard boxes at markets and fishmongers.
3. Cardboard glued and filled with polyurethane foam, to make the boat thicker.

Tips on the use of expanded polystyrene

• Do it outdoors, since each cut and shredding will release an endless number of white balls
• Never leave it as the last outer layer, as it is not compatible with direct sun. (Can be covered with any material or paint)

Tips on handling polyurethane foam

• Polyurethane foam is extremely sticky. Wear gloves, or prepare for a quick cleaning with some acetone or solvent.
• Improvise a makeshift floor out of cardboard or plastic bags.
  Polyurethane foam that falls to the ground is very difficult to remove.
  The foam on the floor that is accidentally stepped on is going to suppose an extra work in a rather complicated cleaning.
• The polyurethane that sticks to clothing is also very difficult to remove.
• Polyurethane foam cannot be left outside, since the sun deteriorates it in the short term.

Isolation step by step graphically

Like I said before, my first layer is several layers of aluminum foil.
And on this I am applying the layers of expanded polystyrene (widely known as white cork)

 

Insulating the home deposit

The homemade tank with pieces of polystyrene glued with polyurethane foam, will cover the largest possible extension of the drum.
I have fastened the corks with a ratchet tape.
The foam swells and dries fast, but I'm not interested in getting too far apart.
The intention of the foam is to act as an adhesive, and what sticks out will cover the gaps between the plates.

 

Once the gluing and sealing of the polystyrene pieces is finished, the result should be a very well protected and very solid boat.
The homemade tank with sealing of the gaps with polyurethane foam: (add 1/3 of what you think is needed, because the foam swells a lot over the hours)

 

My last layer is cardboard, to shelter the entire assembly of the home warehouse.
Here I give the last touch with the foam, filling between the cork plates, and gluing the cardboard.

 

You can make some holes in the cardboard, to make filling and not leave air between the cardboard and the interior.
More than anything, so that the cardboard is part of the body, and there are no malleable lumps.

 

Right now the home deposit is in the state as shown in the last photo, and the insulation seems to be quite good, it loses in the cold night between 5ºC-8ºC only, not bad for a home assembly and taking into account that there are 260 liters of water, which is not the same as isolating 100 liters.

Finally we will cover it all to protect you from the sun.
We can cover it with outdoor plastic, or something similar.
Or we can also cover it with some silicone paint.

Tank connections

The connections to the tank must be watertight.
For this we will make these connections with cable glands.
And the temperature sensors will be coupled by "Tes".
To learn more about attaching and installing the temperature sensors, visit the Installing Temperature Sensors page.

I describe the connections that you will need to make in the tank: (The diagram belongs to my design using a fishing tube)

 

• A) Breather so that the tank can inspire and exhaust the expansions and contractions of the air volume according to its temperature at all times.
• A) Temperature sensor for the upper water layer (optional T2)
• B) Entry of drinking water (Cold water from the house)
• C) Collector water inlet (Hot water from collector)
• D) Temperature sensor for the lower water layer (mandatory T1)
• E) Outlet of drinking water (Hot water to the house)
• F) Water outlet from the collector (Cold water to the water pump and collector)

Variable level hot water supply

For variable level use, we only have 2 ways to "suck in" the hot water.

1. Limiting the minimum level and the supply catch the water below this
2. Using a "fisherman" tube
   On point 1 nothing to comment, the disadvantage is that it will not be collecting the water from the hottest point of the tank, and I am not saying that the idea is bad.

Using a fishing tube has seemed more suitable, and it has been quite good for me.

A "fisher" tube consists of a tube that is submerged, but tied to some floating element that makes the tube always draw the water from the highest possible level.

This is the fishing tube:

More detailed information on this type of pressureless tank that works by gravity in Article about pressureless tank