Grundfos dc well pump- adding more panels?

[1 watt]

Helping out a friend here in AZ. His well gpm rate is pretty wimpy. He has 2 extra panels lying around.

The system is a twenty year old Grundfos ac/dc well pump, low output (3gpm), only pumps when the sun is out. It fills a 1500g storage tank (float switch back to the pump) up on a hill, and then this gravity feeds a two small tanks several hundred feet away.

Currently the system has 3 “Grundfos” 65w panels in series. Surprisingly high voltage, with vmp of 31.4v. So when this was new, the panels would have provided 195w, 94.2v (2.07a).

The mppt/pump is rated 300w max, 30 to 300v, 8.4a max.

The other two panels are also twenty years old.

I did an amprobe/short circuit test on all 5 panels, and surprisingly, they produce a little over what you might expect for old panels. But the sun is strong here!

The amperage will be 6 times higher and the voltage right at the bottom operating range. I believe the wiring to the pump is 10g UF, but might be 8g. The cable length might be 50’ to pump and 250’ down, so total of 300’. Voltage drop could mean mppt doesn’t work.

Anyways, here’s a picture that describes this better. Please tear this apart

Thanks,
Roy

 

[TM48]

Your new plan has more problems than solutions. First of all the well may just not put out more than 3 gpm. Or the pump is just worn. Your proposed plan exceeds the pumps specifications for both wattage and amperage and the voltage is way low. If the well can flow more I would replace the whole system.

 

[v_green57]

We need the model of the Grundfos before we can be of any real help. It may be that the pump is doing just what it is rated to do. There are several that fall within the electrical ratings you describe.

Based on your "30-300V input" statement, I am assuming you have one of the SQFlex series. As long as you don't exceed the 300V max rating (over that and the pump will shut down) you can add more panel capacity and nothing bad will occur. The GF will take what it needs up to its max input power rating and ignore any over that. You'll need to observe all the things that need to be taken into consideration regarding connecting panels in series/parallel to actually GET more power.

More power WILL work for you in one way - the pump will start pumping sooner in the morning and stay running longer in the afternoon.

Many other things also need to be known to get the full picture:

Current static water level
Depth to bottom of well
What depth the pump is set at
Drawdown rate
What was the original GPM as determined by the well driller at the time the well was drilled
Original static water level also determined at the time the well was drilled
Geology - where in AZ is this?

All this stuff will affect your yield.

Some of it should be contained within the documentation of the Water Right connected to the well.

Did your friend install the well or did he just inherit it?

 

[1 watt]

Thank you both for the good points. I don’t know details on the well, which you point out is necessary information.

This is in Patagonia AZ; he had the well dug and system installed. Perhaps 280’. I’ve learned that recently he had the pump replaced (with the same or similar model) as a precaution. Likely a 3-SQF-2?

3 SQF-2

Renewable energy submersible pumps with built in inverter for solar, wind and AC powersource. Runs on both AC and DC voltage.

product-selection.grundfos.com

My intent was to see if gpm was being limited by available power. The pump specs show 300w draw maximum. When the panels were new the maximum potential was only 195w. Perhaps one more panel twenty years ago would have yielded more gpm.

Yesterday, measured in full sun the panels maxed at about 50w each.

My main concern is the MPPT struggling with the borderline voltage with the different configuration. It should max at 8.2a draw at 30v. Same as if it was supplied by a 30v 280ah battery.

Thanks again!

 

[TM48]

Thank you both for the good points. I don’t know details on the well, which you point out is necessary information.

This is in Patagonia AZ; he had the well dug and system installed. Perhaps 280’. I’ve learned that recently he had the pump replaced (with the same or similar model) as a precaution. Likely a 3-SQF-2?

3 SQF-2

Renewable energy submersible pumps with built in inverter for solar, wind and AC powersource. Runs on both AC and DC voltage.

product-selection.grundfos.com

My intent was to see if gpm was being limited by available power. The pump specs show 300w draw maximum. When the panels were new the maximum potential was only 195w. Perhaps one more panel twenty years ago would have yielded more gpm.

Yesterday, measured in full sun the panels maxed at about 50w each.

My main concern is the MPPT struggling with the borderline voltage with the different configuration. It should max at 8.2a draw at 30v. Same as if it was supplied by a 30v 280ah battery.

Thanks again!

He could try powering it temporarily with generator just to see if production goes up before changing the panels. I wouldn't use a mismatch of panels like that. New matched panels may be the best option.

 

[v_green57]

Thank you both for the good points. I don’t know details on the well, which you point out is necessary information.

This is in Patagonia AZ; he had the well dug and system installed. Perhaps 280’. I’ve learned that recently he had the pump replaced (with the same or similar model) as a precaution. Likely a 3-SQF-2?

3 SQF-2

Renewable energy submersible pumps with built in inverter for solar, wind and AC powersource. Runs on both AC and DC voltage.

product-selection.grundfos.com

My intent was to see if gpm was being limited by available power. The pump specs show 300w draw maximum. When the panels were new the maximum potential was only 195w. Perhaps one more panel twenty years ago would have yielded more gpm.

Yesterday, measured in full sun the panels maxed at about 50w each.

My main concern is the MPPT struggling with the borderline voltage with the different configuration. It should max at 8.2a draw at 30v. Same as if it was supplied by a 30v 280ah battery.

Thanks again!

I have 3-SQF-3. Excellent piece of machinery. Went with that one as it'll pump from a depth of 650' and it's set in my well at 320'.

My static level is 120'. I am running the pump off of two Suntech 170W panels connected in series, giving me 80V/4.8A +/- @ 350W.

At solar noon, I get 2.61 gal/min when starting to pump at 120'. That yield goes down a small amount as I draw the well down and need to pump from a greater depth.

I would say if you are getting 3 gal/min and you indeed have a 3-SQF-2, you are getting all you can get.

If you can find out what depth the pump is set at and what the static water level is when you start pumping, the interactive pump curve chart on the Grundfos site will tell you exactly what to expect from a given power input:

3 SQF-2

Renewable energy submersible pumps with built in inverter for solar, wind and AC powersource. Runs on both AC and DC voltage.

product-selection.grundfos.com

3 SQF-3

Renewable energy submersible pumps with built in inverter for solar, wind and AC powersource. Runs on both AC and DC voltage.

product-selection.grundfos.com

Those curves for the SQF-3 are spot-on when I check them against what I'm getting in "real-world" use.

My well is drilled into Navajo sandstone so I knew it would be a low producer. But I can pump close to 1K gal./day when I have six hours of daylight. The 350W of panel helps here, getting pumping started early in the morning and allowing it to go late into the afternoon.

Since my culinary use is about 10 gal/day, I have more water than I will ever need. But the drip-irrigated garden is still a work in progress... Everything wants to eat anything I try to grow, regardless of the "industrial strength" barriers I put up. I will win this battle eventually, when I get serious about it.

In your case more panel would help by providing a longer daily "pump window", as already mentioned. Since you're in AZ, you can perhaps make a trip up to SanTan Solar in Gilbert and get some cheap used panels. A couple of 250W / 40V panels will run you about $100. Wired in series, the higher voltage will keep the current low on the submersible cable. More power than is necessary, but the SQF will take only what it needs.

Additionally, the SQF series is more efficient with higher voltages (this from the installation manual):

Voltage effect on pump efficiency

The pump efficiency can vary depending on the input
voltage. This chart shows the dropoff in efficiency as the
voltage gets lower. For example, if you have two systems
with the exact same wattage rating, but System A is running
at 120 V and System B is running at 35 V, System A will
produce 20 % more water than System B.

SQ Flex optimal efficiency

Panel output voltage (% loss in gallons/day)
120-300 V -0 %
90 V -5 %
60 V -10 %
35 V -20 %

 

[1 watt]

I have 3-SQF-3. Excellent piece of machinery. Went with that one as it'll pump from a depth of 650' and it's set in my well at 320'.

My static level is 120'. I am running the pump off of two Suntech 170W panels connected in series, giving me 80V/4.8A +/- @ 350W.

At solar noon, I get 2.61 gal/min when starting to pump at 120'. That yield goes down a small amount as I draw the well down and need to pump from a greater depth.

I would say if you are getting 3 gal/min and you indeed have a 3-SQF-2, you are getting all you can get.

If you can find out what depth the pump is set at and what the static water level is when you start pumping, the interactive pump curve chart on the Grundfos site will tell you exactly what to expect from a given power input:

3 SQF-2

Renewable energy submersible pumps with built in inverter for solar, wind and AC powersource. Runs on both AC and DC voltage.

product-selection.grundfos.com

3 SQF-3

Renewable energy submersible pumps with built in inverter for solar, wind and AC powersource. Runs on both AC and DC voltage.

product-selection.grundfos.com

Those curves for the SQF-3 are spot-on when I check them against what I'm getting in "real-world" use.

My well is drilled into Navajo sandstone so I knew it would be a low producer. But I can pump close to 1K gal./day when I have six hours of daylight. The 350W of panel helps here, getting pumping started early in the morning and allowing it to go late into the afternoon.

Since my culinary use is about 10 gal/day, I have more water than I will ever need. But the drip-irrigated garden is still a work in progress... Everything wants to eat anything I try to grow, regardless of the "industrial strength" barriers I put up. I will win this battle eventually, when I get serious about it.

In your case more panel would help by providing a longer daily "pump window", as already mentioned. Since you're in AZ, you can perhaps make a trip up to SanTan Solar in Gilbert and get some cheap used panels. A couple of 250W / 40V panels will run you about $100. Wired in series, the higher voltage will keep the current low on the submersible cable. More power than is necessary, but the SQF will take only what it needs.

Additionally, the SQF series is more efficient with higher voltages (this from the installation manual):

Voltage effect on pump efficiency

The pump efficiency can vary depending on the input
voltage. This chart shows the dropoff in efficiency as the
voltage gets lower. For example, if you have two systems
with the exact same wattage rating, but System A is running
at 120 V and System B is running at 35 V, System A will
produce 20 % more water than System B.

SQ Flex optimal efficiency

Panel output voltage (% loss in gallons/day)
120-300 V -0 %
90 V -5 %
60 V -10 %
35 V -20 %

Very helpful information, I really appreciate your help explaining all this. Your suggestion of a visit to Santan to pick up 2 panels is spot on; I’ll forward that recommendation to the owner.
Hope your battle with the garden enemies gets more successful. Javalina have decimated “young tender” cactus my wife planted in the unfenced front yard. But 4” non graduated goat panel fencing (Tractor Supply) in the back yard works well against them and skunks. It’s so dry, can’t blame them for going after what they can.

He could try powering it temporarily with generator just to see if production goes up before changing the panels. I wouldn't use a mismatch of panels like that. New matched panels may be the best option.

Great suggestion! I did that yesterday (1600 watt 120v inverter) and it did increase a bit. Not as much as expected. Running off the three 65w panels a few weeks ago on a sunny day, the owner reported it did one gallon in 45 seconds. The 120v test may have added another 3/4 gallon. So head pressure and cable loss probably are likely responsible for reducing production to under 3 gpm.

Yesterday I experimented with different panel combinations. Here’s what I found, as measured at panel end with 2 Kaweets (one clamped on and one measuring voltage. It was partly cloudy and all 5 panels mounted, laying flat on sawhorses.

3 65w in series (original config). Measured 95v/1.1a. 104w. Pump ran.

3 65w inverter in parallel, 2 120w in series, combination in parallel. Measured 35v/4.2a initially. 147w. Voltage steadily dropped with amperage rising. Pump turned off within 30 seconds (below 30v at the mppt). Fail.

All 5 panels in series. Measured 143v open circuit. Volts dropped immediately and pump didn’t start. Fail.

2 65w in series, 1 65w and 2 120w in series, combination in parallel. Measured 64v/4.2a. 256w. Pump ran.

The last setup produced the most (next to 120vac), so I let it run for the last few hours of daylight.

Last month I saw a Craigslist seller who was reselling inventory of a failed solar business. My friend with the well bought 8 Trina 270w 60 cell panels ($48/unit new old stock) to put on a workshop roof. 2 strings of 4 panels paralleled for most power in cloudy skies.
In a few months these will connect to an Easun 4.3kw 24vdc/230vac aio, 2 100ah 12v lifo, and a Vevor 5kw 220v to 110v box (very heavy btw). All fused and dc breakered.
At that point, if he chooses, the well pump can be fed by either the 140vdc panel output (shared with the Easun), or the (shared with the Vevor) Easun 230vac output, or most likely and least efficiently- a 110vac output on the Vevor voltage converter. The last option simply because the well pump line has a male 110v Edison plug on it already (connected to the 64vdc panel output).

I’m returning to MN tomorrow- thank you for your help!
Roy

 

[v_green57]

Very helpful information, I really appreciate your help explaining all this. Your suggestion of a visit to Santan to pick up 2 panels is spot on; I’ll forward that recommendation to the owner.
Hope your battle with the garden enemies gets more successful. Javalina have decimated “young tender” cactus my wife planted in the unfenced front yard. But 4” non graduated goat panel fencing (Tractor Supply) in the back yard works well against them and skunks. It’s so dry, can’t blame them for going after what they can.


Great suggestion! I did that yesterday (1600 watt 120v inverter) and it did increase a bit. Not as much as expected. Running off the three 65w panels a few weeks ago on a sunny day, the owner reported it did one gallon in 45 seconds. The 120v test may have added another 3/4 gallon. So head pressure and cable loss probably are likely responsible for reducing production to under 3 gpm.

Yesterday I experimented with different panel combinations. Here’s what I found, as measured at panel end with 2 Kaweets (one clamped on and one measuring voltage. It was partly cloudy and all 5 panels mounted, laying flat on sawhorses.

3 65w in series (original config). Measured 95v/1.1a. 104w. Pump ran.

3 65w inverter in parallel, 2 120w in series, combination in parallel. Measured 35v/4.2a initially. 147w. Voltage steadily dropped with amperage rising. Pump turned off within 30 seconds (below 30v at the mppt). Fail.

All 5 panels in series. Measured 143v open circuit. Volts dropped immediately and pump didn’t start. Fail.

2 65w in series, 1 65w and 2 120w in series, combination in parallel. Measured 64v/4.2a. 256w. Pump ran.

The last setup produced the most (next to 120vac), so I let it run for the last few hours of daylight.

Last month I saw a Craigslist seller who was reselling inventory of a failed solar business. My friend with the well bought 8 Trina 270w 60 cell panels ($48/unit new old stock) to put on a workshop roof. 2 strings of 4 panels paralleled for most power in cloudy skies.
In a few months these will connect to an Easun 4.3kw 24vdc/230vac aio, 2 100ah 12v lifo, and a Vevor 5kw 220v to 110v box (very heavy btw). All fused and dc breakered.
At that point, if he chooses, the well pump can be fed by either the 140vdc panel output (shared with the Easun), or the (shared with the Vevor) Easun 230vac output, or most likely and least efficiently- a 110vac output on the Vevor voltage converter. The last option simply because the well pump line has a male 110v Edison plug on it already (connected to the 64vdc panel output).

I’m returning to MN tomorrow- thank you for your help!
Roy

You shouldn't connect the pump in parallel to the panels and the AIO. That will confuse the charge controller.

Far better to have a couple panels dedicated to running the well.

 

[TM48]

The advantage of running off of the inverter/battery would be 24 hr operation if needed. A float switch (probably already there) would be required.

 

[1 watt]

You shouldn't connect the pump in parallel to the panels and the AIO. That will confuse the charge controller.

Far better to have a couple panels dedicated to running the well.

I suspected that might be the case, with 2 mppt fighting each other.