Hi Members

I need some help.

Some back ground.

We need to install a borehole pump with a solar supply. Head = 145m with 20,000l/hour. The AC requirement on the pump is 11-15kW. From the main DB to the pump = 110m

With a 70mm2 cable over that distance (3+N) there is approx 30-40V drop. My first choice will be a grid-tied inverter option, as we need to irrigate after sunset. Are there any grid-tied inverter options that can function without a battery when the grid is down?

2nd option would be an island installation with a controller, VSD and DC pump

Does anyone here have some experience in this regard?

Thanks

 

1 hour ago, Cobus Watt said:

Hi Members

I need some help.

Some back ground.

We need to install a borehole pump with a solar supply. Head = 145m with 20,000l/hour. The AC requirement on the pump is 11-15kW. From the main DB to the pump = 110m

With a 70mm2 cable over that distance (3+N) there is approx 30-40V drop. My first choice will be a grid-tied inverter option, as we need to irrigate after sunset. Are there any grid-tied inverter options that can function without a battery when the grid is down?

2nd option would be an island installation with a controller, VSD and DC pump

Does anyone here have some experience in this regard?

Thanks

 

This is a massive system. The cost will be very high due to the need to run from batteries when no grid. 

Could it not just be used from the grid or perhaps short periods from solar/battery when there is load shedding. Even so cost will be very high. 

What is produced that needs water also during the night? 

Hi @Cobus Watt 

CFP Technologies have Solar Inverters for pumps up to 30Kw so am pretty sure they will have something suitable for your pump./

There are single and 3-phase inverters and have the ability to use a single or 3-phase grid supply as a backup if there is no solar. 

https://cfptechnologies.co.za/product/veichi-si23-d3-series/

Hope that helps.

https://www.veichi.org/solar.html

i have a 1ha field where i want to use drip irrigation. should i get a DC or AC submersible pump. the land is off grid. borehole was drilled 80m deep. field is 20-50m from the borehole site.

On 2023/01/17 at 4:14 PM, Cobus Watt said:

Hi Members

I need some help.

Some back ground.

We need to install a borehole pump with a solar supply. Head = 145m with 20,000l/hour. The AC requirement on the pump is 11-15kW. From the main DB to the pump = 110m

With a 70mm2 cable over that distance (3+N) there is approx 30-40V drop. My first choice will be a grid-tied inverter option, as we need to irrigate after sunset. Are there any grid-tied inverter options that can function without a battery when the grid is down?

2nd option would be an island installation with a controller, VSD and DC pump

Does anyone here have some experience in this regard?

Thanks

 

Personally I'd invest in a thicker grid cable. 

 

For example (if you currently have up to 40V drop with 110m of 7mm2 cable - this is 75A of current):

- with 16mm2 copper (around $1100 here in Europe) you'll have 17V drop, perhaps it is acceptable? You would still be loosing almost 10% of power on cable losses.

- with 25mm2 copper (about $1700 here) the drop would be much better at 11V - loosing about 850W of power in the cable

 

Do you have access to cheap aluminum ground cables? If I was in your position and I wanted to use the grid I'd probably buy aluminium ground wire 4x50mm2 (this is 50 fifty square mm, not five) like this 

For the cost of $700 and the voltage drop will be 9V peak.

 

Then you have to bury it of course and you still have the cost of electricity and possibly uncertainty over supply. But it is by far the cheapest outright and easiest option IMO.

16 hours ago, fiddy.static said:

i have a 1ha field where i want to use drip irrigation. should i get a DC or AC submersible pump. the land is off grid. borehole was drilled 80m deep. field is 20-50m from the borehole site.

For me the key metric would be what L/min in volume and at what pressure do you need in order to irrigate the 1Ha. From this a size of pump can be calculated. 

Also included would be if you need to run the system 24/7 or hours per day.