If your home solar heater design is going to work by thermosyphon, you will not need to know anything about forced circulation with a water pump.
Forced circulation with a water pump is obviously done with a water pump, did you doubt it? :-D
I briefly explain what would be understood very easily with the graphic illustration of the following photo:
As marked in the previous photo, with the letter "E", here we can install a solenoid valve or return valve.
The intention of both devices is the same.
This is to prevent the water from circulating when the pumping process is stopped.
When the device that manages the pumping, normally a differential thermostat, is not operating the pump, it is because the temperatures of the collector and reservoir do not meet the necessary or ideal requirements for them to exchange the water.
But it can happen and does happen, that in cold conditions (as is usually the night) there will be a situation in which the tank will be hot and the collector cold. (The opposite of what the day usually is)
Then a natural thermosyphon circulation suddenly arises, due to temperature differences, in which the movement of water will go from the hottest place (reservoir) to the coldest place (collector).
Which is the opposite of what we want.
This circumstance is easily avoided by stopping the passage of this circulation.
And to be able to carry out this solution, we need an appropriate device for it.
This is a check valve:
The non-return valve offers us this "stop" in a simple way without the need for any electronic device.
This allows the water to pass in one direction, and stops it in the opposite direction.
Advantages of the check valve
Disadvantages of the check valve
This is a solenoid valve:
The solenoid valve is a more modern device. It consists of a membrane that allows or stops the passage of water depending on whether we activate it or not by applying an electrical voltage.
There are solenoid valves of various types, alternating current or direct current.
This solenoid valve must be connected to a device that activates it when it is convenient for the water to circulate or stop.
The function and intention is exact to the non-return valve, but its mechanism is totally different.
Advantages of the solenoid valve
Circulation will be when the sump of the tube that brings the water from the collector, is not submerged.
Then the water is poured into the tank, gushing out, like a tap.
The "S" represent the probes (although it does not come to the subject, it is something that will be present)
The water between the tank and the collector will be moved by the pump, which will suck the lower part of the tank, and will push it to the lower part of the collector.
This flow and pressure of water will push the water in the collector upwards, forcing it to leave the same.
Finally, the water that comes out of the collector inevitably ends up in the tank.
And so on repeatedly until the water pump stops.
At this point, it is assumed that it is understood that the pump will work only when the water in the collector is hot enough to bring its temperature to the tank.
Recirculation will be when the sump of the tube that brings the water from the collector is completely submerged in the water in the tank.
The installation that I did on the roof floor had the tank and collector at the same level.
But as this roof did not have access and you had to climb 6 meters high with a ladder, I lowered the water pump to a window with the idea of being able to act if it gave me problems.
The water pump would be about 2.5 meters down, and although the water flow was level, it did need pressure to move the water.
The pump used by this project was this:
It is a centrifugal pump with a brushless motor, specially designed for very hot water (up to 100ºC).
It is an extremely silent pump whose electrical consumption does not exceed 10W.
At the time I started this project, it was very difficult to find this type of pump, and I did not want to use large complex pumps with high electrical consumption.