Switching solar panels between 1 phase inverter and a 3 phase VFD

[Homad]

Hi everybody,
I'm facing a challenge and I'd like to consult you guys whether my thoughts are feasible and safe.
The situation: a residence is equipped with a single phase grid connection and the owner wants to install a 3 phase well pump powered by solar panels through a VFD. As the pump is not running all days, there is this idea to use the solar panels to power the home as well.
The challenge: As far as I'm aware off, there is no way to run an inverter with only one phase connected to the grid while the rest is kind of off-grid.
The solution (well it is rather theoretical): Install solar panels to feed the VFD which will run the pump on its turn. Next to it, install a single on-grid inverter to power the house when the sun is shining. A DC switch/selector will be installed between the panels on the one side and the VFD and the inverter on the other side. When the pump needs to be used, the panels will be tied with the VFD en when the pump is not needed (which is the majority of time) the VFD will be switched off and the panels will be connected to the inverter to feed the residence.

What do you think guys? Does this make sense and will it work without issues and for a long time as one would expect from a solar installation? Are you aware of any DC switch/selector with one input and two outputs?
Thanks

 

[Ampster]

@Homad
It is complicated and requires user intervention to run things. I would cost out the alternatives to see which one is more economical and/or practical from a wiring perspective. Some of the alternatives in addtion to the one you proposed are; 1) a grid tie solar system and a soft start 240 volt well pump; 2) a GT solar system and a 240 Volt 3 phase converter to drive a 3 phase pump. I am sure there are more. Many soft start pumps contain a variable frequency inverter and the advantage is there is a warranty on that as a system.

 

[Homad]

@Homad
It is complicated and requires user intervention to run things. I would cost out the alternatives to see which one is more economical and/or practical from a wiring perspective. Some of the alternatives in addtion to the one you proposed are; 1) a grid tie solar system and a soft start 240 volt well pump; 2) a GT solar system and a 240 Volt 3 phase converter to drive a 3 phase pump. I am sure there are more. Many soft start pumps contain a variable frequency inverter and the advantage is there is a warranty on that as a system.

Yes, you are right, it needs a human intervention and it is not something that should be done automatically. The big challenge is how to manage the transition states, when selecting inverter or VFD!
Anyway I think your idea may be the way to go: installing a single phase system and using a 3 phase VFD. The next challenge is to make sure that the pump only runs when there is enough solar energy. I know of at least one inverter brand that has several outputs that can be programmed to enable/disable a relay depending on the surplus power. I can then use one of this outputs to start the pump when there is enough sunshine. Thanks for your thoughts.

 

[Ampster]

The next challenge is to make sure that the pump only runs when there is enough solar energy. I know of at least one inverter brand that has several outputs that can be programmed to enable/disable a relay depending on the surplus power.

I am not sure I understand why that is important if he will have a GT inverter? What king of consumption are we talking about here? Does the well pump provide water pressure to the home or fill a cistern?

You will increase your choices of GT inverters if you pick a low cost generic GT Inverter and use a simple programmable relay that controls another high voltage relay to energize the pump. Some can be set for a critical number of Watts in order to turn on. Of course a simple timer set for Noon would probably cover ninety percent of the days with solar.
Inverters with programmable outputs are likely going to cost more or have features like hybrid inverters.

 

[Homad]

I am not sure I understand why that is important if he will have a GT inverter? What king of consumption are we talking about here? Does the well pump provide water pressure to the home or fill a cistern?

You will increase your choices of GT inverters if you pick a low cost generic GT Inverter and use a simple programmable relay that controls another high voltage relay to energize the pump. Some can be set for a critical number of Watts in order to turn on. Of course a simple timer set for Noon would probably cover ninety percent of the days with solar.
Inverters with programmable outputs are likely going to cost more or have features like hybrid inverters.

Sorry Apmster, I failed to give the background in order to have the context. The residence is in Morocco. Owners of solar installations are not allowed to inject into the grid. Each solar installation must be equipped with a smart meter in order to apply the zero-feed injection in order to avoid any trouble with the energy company. So in order to use self produced energy as much as possible, the owner wants to use the pump only when there is enough solar energy. That is why it is a challenge to have this in place.
The pump is used solely for agricultural purposes and there is no pool to accumulate water. Not yet, it is something that is planed for later.
The inverter I was referring to is a Fronius, it is a GT inverter. They are a bit expensive but very reliable.
Having a separate device that monitors the surplus and enables the pump will become complicated I think and it may be an expensive solution. I think getting this information from the inverter itself may be a better option.

 

[timselectric]

Some inverters can shed excess power to alternative loads. Like water heating or air conditioning. That could be setup for any load.
Deye, is one that does this.

 

[Ampster]

I presume the Fronius has or can be equipped with Current Tranformers so it can be configured for zero export.

 

[再生可能 エネルギー]

So in order to use self produced energy as much as possible, the owner wants to use the pump only when there is enough solar energy.

I noticed that sigineer provides 380V 3 Phases Solar Pumping Systems that might be of some interest in your situation