system for farm irrigation well pump

[wpbuntin]

I am looking into setting up a system to run a 5hp deep well pump. It takes around 4.5kw to startup and then requires about 2.5kw running power. I would like a self contained system such as the Growatt 5kw that I could tie onto the grid if needed. Still not sure if I want to add batteries to this system. The pump can sometimes run 24 hrs/day. Should I buy the Growatt 5kw system, should I use (15) 345 watt panels(please make suggestion if there is a better wattage to use), and what lithium battery setup should I use. Would this require a 48v system or can I get away with a 24v system?
Also, would I be able to tie a system such as this directly into the electric grid panel currently running the pump? Would anything be required to prevent power from going back onto the grid from my system and causing issues with my power company?

 

[Hedges]

It probably takes 10 kW to 20 kW instantaneous startup, if only for 1/4 second. Need an inverter that can surge to that, or else tied to grid.
Hardly practical to use batteries to keep that running at night. Better to either run only when sun shines on PV panels, or run from grid at night.
Best solution if net metering is available would be to run pump off the grid, install grid-tie PV as well.
If backfeed not allowed, you can hook up a system like grid-tie, but with a monitor on the wire by the meter that tells GT inverters to reduce production so no backfeed.

PV is cheaper than grid power. Batteries are more expensive than grid power. So the only reason to use batteries is if you want to keep operating when the grid is down. There might be a couple hours late afternoon/early evening when PV production would be low and utility rates would be higher than the cost of batteries, but for most uses, batteries are a money-wasting proposition.

 

[wpbuntin]

Thank you Hedges. Great info. Can I still go with a 5kw system if I tie to the grid? Ill have to look and see if the MPP system or Growatt system allows grid tie. What kind of monitor exactly are you talking about to prevent backfeed?
If I am looking to avoid batteries, but want an all inclusive system, where should I look? The Growatts and MPPs seem to be based on utilizing batteries.

 

[Hedges]

You could put in 100W, or 10 kW for grid tie with net metering, feeding surplus into the grid part of the day.

To avoid backfeed, It would either need to be an all-in-one that had a no-backfeed feature, or something with communication to the inverters.

The SMA inverters I have use shift in frequency > 60 Hz to signal for reduced power output. That works off-grid but not to reduce power for zero-export on-grid because frequency would always be 60 Hz.

Enphase has a micro-inverter per panel and a separate box which can measure current at meter and command inverters with a signal to reduce output. Only certain models support that. I'm not sure what other brands.

If running power is always 2.5 kW, and you wired a standard grid-tie inverter like SMA to the motor side of the switch, it would only deliver power when the pump was switched on. So that would probably work, never export (so long as a thermal disconnect in the motor doesn't shut it off.)

A fixed array of panels will produce about 5 or 5.5 equivalent hours per day. So a 2500W inverter fully loaded with panels would produce 12500 Wh. Having half the panels one series string) aimed at 10:00 AM sun and half aimed at 4:00 PM sun would spread power over the day, maybe 18000 Wh but peak 2500W at any given time. Avoiding backfeed and without batteries, that's how much pumping you could get from PV.

Is your pump 3-phase or split phase? What voltage?

If you need more than 5 to 8 hours pumping, setting up net metering with the utility would be better. And avoid pumping during peak rate hours, which are probably 4:00 PM to 9:00 PM.