How to Connect Pumps to Two Different Power Supply Sources

Er, um, why can't the organisation that will be supplying the panel do this?

The simplest method would be to just plug the pump line cord into the desired power source outlet. When you desire the other source, you just move the pump line cord.

A careful reading of this simple approach identifies some but not all of the unidentified information needed (why switch between supplies at all?) to design such a switching panel.

The question of why the switch takes place is of interest. Maybe it could be better addressed by making the <...PV cells...> the preferred source of power and the <...diesel engine...> the alternative, with auto changeover on the basis of crossing the boundary between sufficient and insufficient power being available from the <...PV cells...>?

Just sayin'.

Yes this is my intention.

This is a fairly common application and there are systems you can purchase without having to design something from scratch out of individual parts.

Have a look online for source transfer switches or automatic transfer switches, there are many manufacturers and solutions available.

You can't connect a pump to a PV panel.

Why not? If the pump has a DC motor of appropriate size and design for the PV panel available, it should work. The speed of the pump would vary according to the brightness and angle of the light, but if the task is filling a tank or other kind of reservoir, that's not a problem.

OR, if the PV panel includes an appropriate inverter , then the pump(s) could work just fine with an AC motor.

It should be obvious that the PV panel and associated devices must be sized according to the amount of liquid to be pumped.

Before I say anything more, just try it and you will find it will not work.

You better say no more.

There is plenty of solar driven pumps.

While this is Wiki https://en.wikipedia.org/wiki/Solar-powered_pump,

there is plenty of more information available in the net to check out.

This says otherwise (usual disclaimer).

If he is talking about a contactor, he is talking about a pump requiring a high current.
The pumps you are describing take about 500mA.
Totally different issues.

Size is important. Especially for hanging wallpaper.

Likewise, he's talking about a diesel alternative, so yes, he is certainly talking about something considerably larger than a birdbath.

But, solar panel arrays (and diesel engines/generators) must always be sized according to the energy requirements of the system. A PV Panel is just a source of energy (DCV*Amps*hours=Watt-hours); how that energy is used depends on what is connected to the panel. These days, it's pretty common to have the solar panel array charge a large battery, which in turn provides power to an inverter to generate AC for a home or other installation. Many installations will include a pump for a well.

Your drawing executed 4 times, one for each pump motor will be fine. Each of the 3 vertical lines to the left connect together, showing the common power source for each motor.

I don't think I agree. If I follow you correctly, there would be four changeover circuits, with a separate one for each pump. That would certainly be possible, but much more complex than necessary, and there would be times when one or more pumps were connected to the PV panel, and the rest would be connected to the diesel generator. Such a system would in fact make the most efficient use of the solar energy available, but would have roughly four times as many potential failure points.

I'm assuming that he wants to run all four pumps from the solar panel array whenever possible, and only run the diesel generator when the solar panel does not have sufficient power available. If that is correct, then he only needs a single changeover circuit, and all four pump starters can be connected in parallel to the same three wires at bottom left of the diagram.

Unfortunately, I can only decipher a little of the text in the drawing, even after considerable enlargement, so I'm not at all confident in the circuit. Specifically, I'm not sure about the circuitry that prevents both power sources from being connected simultaneously. Unless there is a method to guarantee that the PV panel inverter and the diesel generator are in sync for all three phases (not likely), then connecting both at once would likely result in fireworks.

You need starters for each pump, and, as you note, you may want to split the load between pump & diesel, so you need four switches. Not sure how you could do this with fewer switches, or somehow less complex?

We might assume that the primary purpose of this install is to pump, under all foreseeable conditions. Energy source selection and efficient use of the solar energy is likely a secondary consideration.

Your objection to having four times the failure points fails to take into account that any one failure of the quadrupled equipment will not take out of service the entire installation, maintaining the ability to pump. Four identical systems, the servicing tech learns one, they know all four. Maybe not so complex...