Hi guys,

Please help me to size a system for the following? Size of the inverter and the batteries, recommended brands for both 

A potable water supply system on a farm, to several residential dwellings. Needs to be convertible for adding solar in the future  purpose for now is to be loadshedding bulletproof.

One of 1kW jockey pump runs continually to keep the system pressurized. When someone opens a tap, the jockey pump may supply sufficient pressure. When another tap opens the pressure drops and a 3kW pump starts up to feed the system. When more taps open, a next 3kW pump starts up. Two pumps will not start up simultaneously, but all can end up running simultaneously. As and when water user taps close and the pressure rises, the 3kW pumps drop out one by one, and the 1kW pump is left running permanently.

Two scenarios then; all as above explained and the other one leaves out the one 3kW pump from the system entirely.

 

The best way to go about this is to start measuring amps on the pumps. Startup as well as running amps. Don’t consider kw when looking at inverters in this case - look at the maximum amps.

Borehole pumps pull ridiculous amps when starting - my 2.2kw uses up to 35 amps to start up. It has tripped my 8kw inverter a few times. My system was installed before I went solar and now it is not cost effective for me to scale down. My 2.2kw pump has an output of way too much 15kl per hour pumping from 65m. But it is what it is.

You must look at all the options like solar and variable speed controllers (to minimize startup amperages). With solar pumps you don’t need inverters.

You must know how much water you need per day. It might be more cost effective to increase your container sizes - that can reduce pumping rates but also serves as emergency when pumping goes wrong. 
Why do you need a 3kw pump? Is it a 3-phase system?

It is more cost effective to reduce your electrical consumption than trying to supply an oversize solar system.

Dwellings for example could each have their own JoJo tank and small pressure pump.

Instead of running a pressure pump 24/7 you can also look at a header system - with many mines (for example) closing shafts they should be on the 2ndhand market.

You have the advantage of expenses being tax deductible. 

Edited March 31, 20232 yr by Johandup

7 hours ago, Johandup said:

The best way to go about this is to start measuring amps on the pumps. Startup as well as running amps. Don’t consider kw when looking at inverters in this case - look at the maximum amps.

Borehole pumps pull ridiculous amps when starting - my 2.2kw uses up to 35 amps to start up. It has tripped my 8kw inverter a few times. My system was installed before I went solar and now it is not cost effective for me to scale down. My 2.2kw pump has an output of way too much 15kl per hour pumping from 65m. But it is what it is.

You must look at all the options like solar and variable speed controllers (to minimize startup amperages). With solar pumps you don’t need inverters.

You must know how much water you need per day. It might be more cost effective to increase your container sizes - that can reduce pumping rates but also serves as emergency when pumping goes wrong. 
Why do you need a 3kw pump? Is it a 3-phase system?

It is more cost effective to reduce your electrical consumption than trying to supply an oversize solar system.

Dwellings for example could each have their own JoJo tank and small pressure pump.

Instead of running a pressure pump 24/7 you can also look at a header system - with many mines (for example) closing shafts they should be on the 2ndhand market.

You have the advantage of expenses being tax deductible. 

Thanks very much, very informative. This installation is already quite a few years old. Owner now wants solar and be loadshedding bulletproof. So these pump motors don’t have soft starts and will draw plenty inrush. Given the new tax rebate, it’s probably worth replacing the pump motors with variable speed drives. Then the inverter won’t break the bank. 

15 minutes ago, Cory said:

Thanks very much, very informative. This installation is already quite a few years old. Owner now wants solar and be loadshedding bulletproof. So these pump motors don’t have soft starts and will draw plenty inrush. Given the new tax rebate, it’s probably worth replacing the pump motors with variable speed drives. Then the inverter won’t break the bank. 

On a farm you pay for the transformer (and size) supplying you

It is in your own interest to keep your consumption as low as possible. 
Keep in mind Eskom might fail 100% in future.