PV field irrigation system using a 3 phase pump...

The PV pumping system is replacing a diesel pumping station that has been nothing but trouble to the owner with continuous brake downs and maintenance costs since it's original conception over 20 years ago, in which time he has replaced the diesel pump sets 3 times. The cost of fuel and the ongoing regular maintenance required for these type of pumps is also another aspect he is looking forward to enjoying being without!! The owner knows full well that the installation is going to be an initially costly proposition, and is more than happy having a payback period of 10 years or so., not that it'll be anywhere near that time...

A quick calculation puts irrigating with brought in water, at around 8000+ Euros per year and seems to get more expensive every year....

I guess you can pump all the water required during daylight hours with the system you have designed? One thing about irrigating at night in hot countries is less evaporation than during the day.Diesel sets at least run when you want them to.

Non standalone Solar PV works with grid tied inverters, so that means there must be connected to the grid to wk.
If you don't have a grid near buy,you will need batteries to the make the PV work. I assume you will need around 30kw of PV, but I am no expert regarding off grid PV

@Engineer54,, PV doesn't provide constant power, it is dependant upon, time of day, date (in the year) weather - sun / cloud. What you have therefore is a highly variable supply with no gaurantee that it can pump the water when needed.

You are filling a water tank so that the water can be drawn as and when needed, which will be variable flows for variable periods of time, effectively your water tank is a "battery" of water.

In this case your power supply - the sun is exactly the opposite, a variable flow (power) for varaible periods of time, however your pumps needs to be able to draw what it needs, when it needs, so you need a 'tank' of electricity aka battery.

You won't get 11kW out of an 11kW PV Array, on occasions you'll be lucky to get even 500W...

If you've been running pumps direct of generators, I'm not suprised both have given trouble over time, they almost certainly have been abused by each other.

Here's you're problem graphically (this is a snapshot of one of our systems three lines, generation, consumption, import/export,) if we didn't want to import / weren't connected to the grid, we would have to put a battery in place to store what we are currently exporting:

Go to the China Hi-Tech Fair in Shenzhen from 16-21 Nov. You might find a local company able to help you out with this.http://www.chtf.com/english/

your issue here is that what you're trying to do is to use inverters to run directly off the solar PV to power a specific load directly on 3 phase, which is a pretty unusual situation, and I'm not aware that such inverters exist, primarily because if you were going to do this from scratch you'd use a direct PV powered variable drive pump, not a 3 phase pump.

Stick a battery in the mix and you have a fairly standard set up with a wide range of inverters to choose from, plus you can be sure that the pump will actually have the power to pull the water to the surface when needed, as opposed to potentially only having he power to pull the water half way up for an entire day, which is no use to anyone.

The system is going to be installed in Cyprus, not China. Now in Cyprus it is sunny from middle of March all the way through to October. You can almost guarantee no rain in that period. so you stand more chance of losses through high PV panel temperatures than the system suffering from lack of sun to power the system. The irrigation system isn't required much at all between November and March, plenty of rainfall in the winter months....

The system is a daylight only operation that supplies a large raised storage tank. The well water level has remained pretty much constant over the last 6 years, in fact the well passes through 2 water courses the first is at 230 feet the other at 560 feet.....

I'm just waiting for a couple of system component quotes, one from a UK company and one from a Cyprus based company!! So we'll see if these batteries are needed or not. The two companies have the full details of the pump motor and it's controller which i believe has a soft start or some other form of efficiency control, As i say, i'm waiting myself for the full details of the pump motor...

Engineer54 said:

Unless i'm missing something here, why would you need battery backup if the PV system is sized correctly to the pump and it's requirements??

At the moment i'm waiting for confirmation of the pumps rating (eg if its 11 KW or 11HP.)
there is a little confusion going on there.

Click to expand...

My response is pretty clear as to why you would need batteries.

We need the spec of the pump, as it won't have a constant supply available to it, Voltage "constant" available current "variable". to pump from 550 ft below ground, your pump loads are going to be quite high. - pipe pressure will be in the order of 20 bar at the bottom of the well (where the pump is)

Despite what everyone is saying on this thread, you are obviously convinced what you are doing is spot one, so it seems we have something to learn - could you post up a link to your design spec - a simple sketch with component specs on it would do (and links to the component datasheets)

kW or hp it's only 34% difference the question remains over the design not PV array sizing...

Have you considered the Lorentz systems? Complete kits for well pumping direct off solar. Let me know if you need more direction or design options.

Lots of information here....https://www.lorentz.de/en/products/submersible-solar-pumps.html

Over the years I've installed many solar bore hole pump systems in remote locations for the UN and a couple of other charities so I have some experience.

Because of the particular environment we operate in we try to keep the systems very simple and as low-tech as possible because there's never local access to skills and spares etc sometimes for over a thousand Km. It's possible to run smaller pumps reliably directly from solar without battery storage but after a certain size the technology required to ensure reliable starting and the complexity it introduces outweighs the benefits of being without batteries for us. This might not be the case however in Cyprus which might be considerably more first world.

I'd ask you to take a step backward and go back to the actual water volume requirement of your system. By standards an 11kW pump is very large. What is the daily water volume required for irrigation? What type of irrigation system is it ie is it impact sprinklers or porous pipe below ground etc? Finally how much tank storage do you have available?

I agree that generators and pumps are a mix that's very difficult to get reliable from both sides and also a generator / PV hybrid system will become a control nightmare plus you end up using the generator regularly at a small fraction of its full capacity which introduces a whole new set of problems as well as the fuel to power output efficiency will plummet. Neither of these options would be my first choice.

nice one Marvo, I wrote a post pointing out that we need to know the volume per day of water required, and tank storage volume as well, but apparently didn't post it up.