This spring I'm putting in a small PV system to pumpwater from the creek to some IBC totes we've strategically placed around the orchard. I've installed a few small scale off-grid PV systems for tiny homes and cabins before, but never a pump, so I would love to hear some feedback from you all on my design! I'll lay it all out in detail here, and please fire away with any questions or thoughts you have on it.
- there are two 100-watt panels, 18.6 volts Vmp, 5.38 amps Imp each
- these are connected in parallel, for a total of 200 watts, 18.6 volts Vmp, 10.76 Imp
- these are mounted to the top of an IBC tote in the closest sunny location
Cable from panels to charge controller:
- from my point of view this is the stickiest part of the design.
- the controller, battery bank, and pump are all in a small pump house alongside the creek (in separate rooms so the pump doesn't accidentally spray the electronics).
- the distance between the PV panels and the charge controller is 110 feet.
- 18.6 volts, 10.76 Imp, traveling 110 feet, with 4% Vmp loss, I would need to use 4-gauge cable.
- I'm splicing together two 6-gauge cables I already have to create the same effect as a single 4-gauge cable.
- 12 volt, 20 amp MPPT charge controller
- I'll be connecting the pump to the load terminals on the controller, and setting the controller to shut off the pump when the panels aren't receiving sunlight. The controller also has an over-discharge shutoff to protect the batteries
- Rated load current is 20 amps, so the pump can't exceed 20 amps
- rather than buy an actual pump controller, I'm using a couple of old sealed AGM batteries I have laying around, now that we've upgraded our off-grid tiny home to lithium. These batteries are old and don't hold much charge, but if the pump is only running during the day then I figure these batteries will just be providing a little padding while most of the power comes from the PV panels
- two 12-volt, 55 Ah sealed AGM batteries, connected in parallel, for a total of 110 Ah (but they're so old it's probably more like 25 Ah total)
- Shurflo 2088-514-145 diaphragm pump
- it has an adjustable pressure switch, so it'll mostly be on standby and will automatically turn on when a float valve opens (I'm installing float valves in our tanks)
- 12 volts, up to 9.5 amps, so I'm hoping that even if the start-up current is twice as much it'll still be 19 amps and won't scare the charge controller
- it's also self-priming up to 9 feet (I'll position this 2 feet above a suction strainer in the creek bed, on the bank 5 feet away)
Hose to Tanks:
- this is probably the weakest part of the design. I don't even really know how to calculate the loss in flow on paper. On top of that, my old 2" discharge hose is leaking badly so I'm switching to all the old 3/4" garden hoses I've collected over the years. If they restrict the flow too much I think I'll upgrade to 2" schedule 40 pvc. But I really just pulled 2" out of the air. If anyone knows how to calculate the proper pipe diameter I should be using, please let me know! - the first tank inlet is 110 feet from the pump, with an 8 foot rise
- the second tank inlet is 300 feet from the pump, with a 10 foot rise
- the third tank inlet is 500 feet from the pump, with a 10 foot rise
Thanks to everyone who actually reads all of this, and thanks in advance for any advice or feedback you might have!
I'm no expert at this but I'll give you my thoughts.
To start, this I am sure of... forget using 3/4" for anything. Water creates friction , you might get to your first tote but not to the others.
I think you are asking a whole lot from your panels. They will not be making the full 10 amps all the time and your tired old agm's will not support much before dropping into low voltage.
So I think you need a few improvements before this would work at all. I do think it can work with refinement.
We have some very sharp folks on permies who are up on all the newest inovations.
Hopefully one will chime in and give you some technical help.