Homemade solar water heater

I present to you my homemade solar water heater, also known as solar thermos or solar boiler.
Some call it a solar water heater.

I explain how to build a completely homemade water heater, capable of supplying hot water to 4 people every day, at a very low cost, without the need for subsidies.

If you are able to understand the project of my homemade solar water heater, you will be able to build and maintain your solar heater without help and without maintenance costs and without paying a high cost for a breakdown.

The purpose of this project

But it's not all about saving money.
The purpose of this homemade solar water heater project is to understand how the resources of a homemade solar water heater work.
Solar water heaters are so efficient that they have been commercially exploited for some time now.

Of course it was also inevitable, it is an open secret that heating water in a black bag or painted bottle is a child's thing.

I will briefly explain why it works. How to do it at home. How to take advantage of such a good and free resource as the sun, and how to make it ourselves little by little at home and comfortably.
Above all, by learning a little DIY and plumbing.

Without having to pay such a high price, which is surely what you like the most.
And with a performance comparable or superior to many commercial models.

What is a solar water heater?

First we have to understand what a solar water heater is and how it works, consisting of a collector and a tank.
And how does a solar collector heat large quantities of water to such a high temperature in a very short time.

Because in the end it consists of that, in heating a lot of water very quickly.

How a solar heater works?

Any home solar water heater, or commercial one that you can buy, seeks the same function.
Accumulate a lot of heat inside a box (collector). Transfer that heat to the water that is inside, and take all those heated water loads to a tank (accumulator).

What a solar thermal equipment does is heat the water in cycles and transport it to the accumulator, and while the water is heating, or if it is the case that it is not heating, simply do nothing.

There are many determining circumstances that make a solar water heater better or worse.
The quality of the collector and the tank, the way in which the water flow is circulated and controlled.
Everything will be explained clearly and the different configurations in which each system can be built.

Parts of the solar water heater and their functions

All solar heaters, both commercial and home-made, consist of 3 parts to achieve the above described:

• Collector: The most important element, which heats the heat-carrying fluid or the water itself.
• Accumulator: That is, the tank.
  An equally important element, it must be properly assembled and prepared, and correctly insulated. A poorly insulated tank will ruin our entire assembly and will cause our water to heat very little and cool quickly.
• Water pump: It may or may not have one.
  If it has a water pump, the solar heater will be of the “Forced circulation” type.
  If it does not have one, it will be of the “Thermosifon” type.
  The mission of a water pump in a solar water heater is to circulate small parts of water strategically so that the water passes through the collector, is heated, and finally spills it into the accumulator.
• Temperature probes: Small wired components that are inserted at certain points in our system.
  If the system is a thermosiphon, the probes will be used to know the temperature of the accumulator and to optionally control an auxiliary resistance to heat the water.
  If the system is a forced circulation system, it will be used for the above, and to control the water recirculation pump.
• Water circulation controller: In the case that it is not a thermosiphon system.

The efficiency of our homemade solar heater will depend on the materials used in the collector and its insulation.
It also depends significantly on the insulation of the water tank.

There are few industrial secrets to this, insulation with polyurethane foam for the most part.
We can use whatever comes to hand, polyurethane, cardboard, polystyrene, rock wool.
It is simpler than it seems, we can practically do it 100% at home and with perfectly comparable and superior performances.

Homemade solar water heater in thermosiphon mode

Without a pump, without a differential thermostat, and if we want, even without probes.

I'm not saying it's bad. It can be as respectable as buying a Seat Panda now.

A thermosiphon solar heater, which is still found on many roofs, has its advantages and disadvantages.

The advantages are that it does not depend on electricity, because the water or fluid circulates by itself as if by magic, and it is cheap to build and maintain.

The disadvantage is that the performance is much lower, and that the configuration is very specific.

It requires a certain height and distance in the tank with respect to the collector... those that we see with the tank raised horizontally.
The thermosiphon system circulates the water automatically by pressure difference.

The hot water rises and the cold water falls. But this happens slowly, and when the difference in pressure and temperature is significant.

This circulation is automatic, without any possibility of control.
It starts to work from a certain temperature difference and in a very slow way, it is a free but slow engine.

Why should we expect less performance than the forced circulation system?
Because this natural form of circulation starts late, and ends early. While in a forced system we can make the pump start at 1º of difference.

Homemade solar water heater by forced circulation

This is the system that interests us the most if we can assume a little effort.

The water pump can be activated and deactivated in the following ways:

• By a timer
  This is not usually the best idea, because a timer never knows when there is sun or rain.
  It is not the same 2pm in August as in January.
  Unnecessary circulation cycles would occur and that is counterproductive, and we would be losing heat, punishing and overheating the water pump.
  Although if It can be useful as a start and experiment. OK?
• Powered by a photovoltaic panel
  The pump would be activated when there is some solar activity.
  The problem is that the photovoltaic panel would start the pump at the same time that it receives sunlight. And the collector will not be hot at the beginning, it needs time to warm up.
  It will also happen that when the sun is covered or goes away, the photovoltaic panel will stop the pump immediately, and the collector will possibly have A lot of heat to give away.
  As a game it is much better than the previous proposal.
• Governed by a differential thermostat
  Ideal proposal.
  The thermostat is an electronic device that is plugged into the electrical network.
  It consumes very little, eh?
  It will give us 2 temperature sensors (at least) and the relay/switch to connect the water pump.

Differential thermostat in our homemade solar water heater

The function of this differential thermostat is to activate and deactivate the water pump.
The first occurs when the collector is hotter than the accumulator (tank).
And the opposite when the collector does not help to heat the accumulator more.

I must clarify that we are talking about a small and simple water pump.
There is no need for one of those pumps that look like a submarine.
The electrical consumption of the entire system (differential thermostat and water pump assembly) is usually very very low.
When the pump is not circulating, the consumption is negligible.
A suitable water pump can be between 10w and 15w of consumption. Obviously, the consumption is only when it pumps.

My example project on my homemade solar water heater

I have chosen to do it with a water pump (forced circulation) and I am going to base the entire project on that modality (but you can follow the same instructions omitting the part that you discard)
For 2 simple reasons:

• It gives you a lot of freedom to place the collector and the tank where best suits us, although it is always convenient that they are as close to each other as possible to avoid heat loss in the water paths, and in our case we are going to put them close to be able to use a cheap and low-power water pump.
  But you could perfectly put the collector on a roof, and have the tank in a patio and well sheltered.
• Because the performance is much higher.
• Because I can decide the The most suitable configuration according to my purposes and the climate.
• The implementation of the differential thermostat and pump can be a fairly affordable cost (between €100 and €200). : at 150€), taking into account that we do not need a large pressure pump.

The disadvantages of forced circulation are the cost (which is not much), and that we depend on electricity.
Although this dependence can be overcome with a backup electric battery.

A forced circulation system on the market can be very expensive.
But in our case we will assemble it ourselves and at cost price of material.
Once we have assumed how everything works, repairs and maintenance will also be at cost price.

This was my first prototype of a completely homemade solar water heater:

And first homemade solar water heater for daily use it was this:

Solar thermal equipment with heat exchangers

There are many more variants on solar heaters, with temperature exchangers, with heat-carrying glycols, with various devices.
These configurations bring advantages and disadvantages.
But in the best of cases any type of exchanger will lose performance.
I am going to do it with water and collector and accumulator directly with the same water, without exchangers.

Maybe in the future I will consider it, but right now the simple and basic configuration works very well.

Project content and construction

From here you need to follow the following articles for each link, these being segmented by each part of the heater.

Box

Building a box for a homemade solar heater

Solar collector

Construction of homemade solar heater
Building a homemade solar collector model 1

Tank

Homemade pressureless tank for solar thermal use 
Building a gravity water tank for a homemade solar heater

Circulation or recirculation pump

Water pump for home solar heater