Thinking about a PV well pump replacement system

Steve777Steve777 Registered Users Posts: 5
Hello. I'm new to these forums, but not PV and wind systems. I installed a grid tied PV and wind system back in 2000 or so, which we are still using. However I am now thinking about replacing our AC well pump with a PV based system, I'm just not sure what would be a useable design for our purposes. So here's what we need:

Currently have a 125' well with low flow (<0.5g/min), submersible 240V ac pump on a well minder (load detection and delay box), 1800g cistern, with a 120v AC pump to pressurize house water system from the cistern. There is approximately 100' of lateral distance between the well head and cistern. Typically the well pump runs the well dry in 2 mins of pumping, the well minder box delays it for ~10 min and that cycles continues until the cistern is full. (From testing that maximizes the water delivered over time) In the winter, the well refills the cistern maybe 1 time a week. During the summer, when we are watering gardens and orchard the refill cycle is daily. We have a pattern developed where we use the water during the day in the summer, and the cistern refills overnight. It has been working for us, but obviously not ideal for PV. Also, I should mention our well water comes with a fair amount of sand/grit, which falls out in the cistern, but is coming up thru the well pump.

So, here is what I had been considering as a PV/DC well pump replacement system (note cistern-house pump is already on the house PV-inverter system):

1. Need a submersible pump which can handle the sand in our water, and one that will last as I don't want to be pulling it every few years for repairs.

2. I will need a pump that can deal with lower levels of water in the well, and perhaps a controller which can sense low water and stop the pump for a while as we have now for the AC pump.

3. I expect I will need some batteries to allow for storing power during the day for pumping at night.


I realize that #3 might be eliminated, and the system made simpler, if I could move the watering cycle to the night and let the cistern refill during the day. Right now that would be hard, as much of the watering is manual and not doable at night, but if it could be automated then perhaps this could be done.

One possibility would be to stick with AC in the well, and just tie this into the current (or an enlarged) PV system, which has battery backup. But I think that would be far less efficient in terms of power per gallon pumped.

I'd be curious to get people's ideas and feedback on this. Any suggested designs? Recommended parts/models?

TIA

Comments

  • BB.BB. Super Moderators, Administrators Posts: 29,482 admin
    Re: Thinking about a PV well pump replacement system

    There are some pretty nice PV compatible/very efficient Well Pumps these days.

    Probably one of the high end, in well submersible pump, would be the Grundfos SQ Flex series. About 1,000 watts maximum power, lot of different pump options (shallow to pretty deep).

    And the pump will run off of something like 120-190 VAC and 45-190 VDC... So the same pump can run from solar panels, AC generator/inverter, or battery bank. They have some pretty extensive manuals that will help with a DIY project. Also, our host (NAWS) says that a version of this pump works pretty well with sand:
    Grundfos SQ-Flex solar pumps will pump water up to 600 foot total head, and can pump up to 85 gallons per minute for shallow wells, depending on model. The helical rotor pumps are what we recommend if you have any dirt, sand, sediment, or high mineral water from your well. The 3 SQF, 6 SQF, and the 11SQF are helical rotor type pumps. All others are centrifugal. All SQF pumps are 17 to 23 pounds in actual weight.

    These are not inexpensive pumps (probably north of $2,000 just for the pump), but they will do what you ask (in well run dry protection, etc.).

    My suggestion would be to go with solar power only and pump to the cistern. And use a pump at the cistern to pressurize the water for your home (smaller pump, AC or DC -- Your choice).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Volvo FarmerVolvo Farmer Solar Expert Posts: 209 ✭✭✭✭✭
    Re: Thinking about a PV well pump replacement system

    Your setup is almost exactly like mine, low production well into a cistern. I put in a Lorentz PS200. It sounds like exactly what you need, the pump is a helical drive and is resistant to wear from sand and clay. The one really nifty feature of the Lorentz is that it has an adjustable rheostat in the control box that controls how fast the water is pumped. I think this is a far superior way to pump water with a low producing well than what you have now. I spoke with a hydrologist and they told me it is not good for a well to be pulling the water way down below the static level on a regular basis like your current pump is doing. They said it actually encourages more grit in the water because the when the column gets drawn down, there is no hydrostatic pressure holding the water table back. They also said that the underground vanes that feed the well tend to get clogged up more when you do this.

    I've got mine turned way down so it only pumps about 250 gallons/day, because that is more water than we need for domestic use. The Lorentz does have a low water shutoff and will pause itself if the float switch in the well detects a low water level. I use a single 170W panel. My well is 200'deep with a static level of 80'.

    I don't understand why you need batteries if you have a cistern. Are you using more water than you can pump at .5 gal/min during daylight hours? You might even find that your grit problem goes away if you can keep the hydrostatic pressure in the well up by not pumping faster than it can recharge.
  • Ralph DayRalph Day Solar Expert Posts: 886 ✭✭✭✭
    Re: Thinking about a PV well pump replacement system

    Do you guys also catch rainwater off your roofs? I can probably last all year on that production, but I shut down the cistern system for a month or so in the dead of winter (no input of water). Rainwater is also nice and soft, my well is not, it requires running a water softener (which is pretty much pooched after 30 years). Some window screening over the tank inlets catches any critters and crud, except for dust.

    \ralph
  • Steve777Steve777 Registered Users Posts: 5
    Re: Thinking about a PV well pump replacement system

    Thanks Bill & Volvo Farmer. Good to know there are alternative which would work.

    VF, the Lorentz pump would seem to match my system needs quite well, I will investigate it further. And to answer your question, the only reason for a battery to enable nighttime filling is the water use pattern I am currently using. No doubt it would make more sense to change the pattern to a nighttime water use and daytime fill, rather than add a battery bank.

    Ralph, I do collect rain water, but only for ag uses. My state has rather arcane water use laws.

    A few more q's on some practical matters:

    1. Is there a general conversion for horizontal run length to additional head, for figuring load on the pump?

    2. I am curious, is the install of these DC pumps generally a manual operation, or is heavy equipment needed? (I am familiar with plumbing, well installation and PV wiring).

    3. While I realize that the price of PV modules has gone down, it still seems wasteful to me to let the power from dedicated well PV panel go unused when the pump is not working. Are there systems which can shunt this power to a DC system or the like?

    4. Any recommendations on type of drop pipe (rigid vs flex, etc) on these pump installs?

    TIA
  • tmarchtmarch Solar Expert Posts: 143 ✭✭
    Re: Thinking about a PV well pump replacement system
    Steve777 wrote: »
    Thanks Bill & Volvo Farmer. Good to know there are alternative which would work.

    VF, the Lorentz pump would seem to match my system needs quite well, I will investigate it further. And to answer your question, the only reason for a battery to enable nighttime filling is the water use pattern I am currently using. No doubt it would make more sense to change the pattern to a nighttime water use and daytime fill, rather than add a battery bank.

    Ralph, I do collect rain water, but only for ag uses. My state has rather arcane water use laws.

    A few more q's on some practical matters:

    1. Is there a general conversion for horizontal run length to additional head, for figuring load on the pump?

    2. I am curious, is the install of these DC pumps generally a manual operation, or is heavy equipment needed? (I am familiar with plumbing, well installation and PV wiring).

    3. While I realize that the price of PV modules has gone down, it still seems wasteful to me to let the power from dedicated well PV panel go unused when the pump is not working. Are there systems which can shunt this power to a DC system or the like?

    4. Any recommendations on type of drop pipe (rigid vs flex, etc) on these pump installs?

    TIA

    Depending on the amount and size of the pipe the installation can be manual or with machinery. Drop pipe can be simple poly, flex pipe or steel. If your pump is close to the bottom of the well a hand install may be difficult due to the weight of the pump and pipe.
    One suggestion would be to add another cistern and alternate usage so you could irrigate during the day instead of using batteries. From experience battery systems are more costly than another cistern over time.
    Any time you are drawing the well much below static water level it's hard on the well and consistently stopping and restarting the pump is hard on it.
    What you need to establish is what depth the current pump sets at and if possible lower it to eliminate part of the problem. Then work on pumping for a longer period with less output.
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Thinking about a PV well pump replacement system
    Steve777 wrote: »
    A few more q's on some practical matters:

    1. Is there a general conversion for horizontal run length to additional head, for figuring load on the pump?


    The conversion (linear feet to pressure loss) depends both on the size of the pipe and the flow rate (GPM). If you know these two factors you can find either formulas or tables online.
    The pressure loss caused by flow will have an equal effect on both the horizontal and vertical runs of pipe and is just added to the static head pressure to get the numbers to use looking at the output curve of your pump.
    SMA SB 3000, old BP panels.
  • Volvo FarmerVolvo Farmer Solar Expert Posts: 209 ✭✭✭✭✭
    Re: Thinking about a PV well pump replacement system

    We used flex pipe on our install, and I was able to both install and pull the pump by myself. If you can get an old wire spool or something to give the pipe a radius at the top of the well head, you can use a tractor or car to help get the pump back out should you ever need to. I was able to install mine totally by hand since there was no water in the drop pipe yet.

    As for wasted power, the way mine is wired, the cistern has a float switch which turns the pump on and off. I would think it would complicate matters somewhat to try and divert power at the odd times when the pump isn't running. Besides, my panel lives out near the well head, where there is no nearby need for DC power.
  • BB.BB. Super Moderators, Administrators Posts: 29,482 admin
    Re: Thinking about a PV well pump replacement system

    The cost of just a solar array vs solar array+charge controller+batteries+new batteries every 3-7 years to get 24x7 power, pretty pricey choice.

    We have had people ask if they can share the pump solar array with their main off grid system... You could put a DPDT relay in the array--Swap the pairs of leads between the pump and the main bank charge controller(s)--But I think it is more trouble that it may be worth.

    Setting up your pump system and having it work 10-20 years without maintenance (don't know if you will have to pull the pump every ~7 years for repairs/replacement or not)--Vs monthly checks on battery water, corrosion, etc...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Steve777Steve777 Registered Users Posts: 5
    Re: Thinking about a PV well pump replacement system

    Thanks again for the info.

    One question which I have is what is a reasonable expectation for these DC submersible pumps maintenance interval. I've seen everything from just a couple of years to 20 years. I'd be curious to hear from people here what their experience is.

    I am aware that the quality of the water will play a big role in what number one gets, but taking that into account what is the expected range of numbers?
  • BB.BB. Super Moderators, Administrators Posts: 29,482 admin
    Re: Thinking about a PV well pump replacement system

    Our host is in Flagstaff--Don't know if they are "close enough" to be worth your contacting them (cost of shipping, traveling to pick up components, etc.). I believe Arizona does not tax some (all?) Renewable Energy products (in California, we are at ~10% sales tax on everything but groceries and possibly labor).

    Otherwise, look for a vendor in your region that gives you good support (you will probably pay a bit extra for that support too) and perhaps will let you help with the initial installation (in many things, the first time having your hand held, makes the subsequent jobs where you are doing it yourself much easier--And you learn your capabilities--Perhaps lifting a 125' of water filled pipe and pump is not your cup of tea). Many times, the professional makes a job look easy--When it is very difficult work and requires a lot of skill/experience (I still cannot get a decent looking drywall installation).

    The less expensive stuff (like in-well Shurflo with diaphragms) will last 2-3 years between rebuilds (I think I remember some posters here with that sort of experience).

    Will the the Grundfos pumps which cost 3x as much last three times longer? Probably. And it will be 2x pulling the pump from the well for 12+ years of service vs 4-6 times for the less expensive pump.

    Sorry, I find pumps a fascinating subject--But it is one that I never has much direct experience with.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • stephendvstephendv Solar Expert Posts: 1,571 ✭✭
    Re: Thinking about a PV well pump replacement system
    Steve777 wrote: »
    One possibility would be to stick with AC in the well, and just tie this into the current (or an enlarged) PV system, which has battery backup. But I think that would be far less efficient in terms of power per gallon pumped.

    Just to double check: you currently have a 100% working AC well pump and you want to throw it away/flog it, and then buy PV + a DC pump to replace it?

    IMO, you'd be MUCH better off getting a quote for the PV + DC system, then ignore it and spend that amount on more PV :) You'd easily make up for the efficiency losses of using an AC pump with the difference in price, and then some.
  • tmarchtmarch Solar Expert Posts: 143 ✭✭
    Re: Thinking about a PV well pump replacement system
    Steve777 wrote: »
    Thanks again for the info.

    One question which I have is what is a reasonable expectation for these DC submersible pumps maintenance interval. I've seen everything from just a couple of years to 20 years. I'd be curious to hear from people here what their experience is.

    I am aware that the quality of the water will play a big role in what number one gets, but taking that into account what is the expected range of numbers?

    Not only will the quality of water affect the life of a pump, but also how it is used. I've had some pumps last 10+ years and some barely make it half that. The biggest problem is starting and stopping too frequently or leaving the pump set in the well when it isn't running for extended periods. The helical rotor pumps are better with sediment and minerals.
  • Steve777Steve777 Registered Users Posts: 5
    Re: Thinking about a PV well pump replacement system

    Hmm. Interesting.

    Stephendv, it may seem crazy, but my current AC well pump is 40+ years old. It was installed in 1969. I've been expecting it to go for over ten years; but it just keeps on pumping. It may the exception, but it is going to be hard to match that longevity in any other pump, DC or AC I suspect. However given its age, I think it's prudent to try and figure out what I should be replacing it with.

    As to whether or not it would be better to go with a replacement AC pump and just increase the size of my current PV array, I am not so sure...

    The difference between summer and winter grid AC usage (current PV/wind system does not supply anywhere near all our electrical needs) is roughly 200KWH per month additional summer use. 75-80% of that is the water pumping I'd estimate. So let's say 150KWH per month for pumping water, or roughly another 1KW of panels to capture that for the summer. (I would also need a new inverter too as my current one is only 120v and the well pump needs 240v, but let's ignore that expense). So with mount and wiring, I'd be looking at very roughly the same cash outlay for either solution, about $3500 for parts (not including labor and not including the replacement of the AC well pump, when that becomes a necessity).

    The advantages of the AC well pump and more PV panels are several: It allows the use of grid pumping during extended cloudy days. AC pumps seem to be more trouble free and longer lived than the DC units. And it solves the "issue" I had with dedicated PVs for the well pump, any PV output not used in pumping will be in the system for use elsewhere.

    The advantages of the DC solution would seem to be: A potential longer lived pump design (the helical rotor), although that may not be the case in real life. The advantage of a well pump which could be lifted and replaced by hand in the future. Potentially a slower pumping well system which might extend the useful life of the well.

    The difference in efficiency are pretty obvious. The AC pump requires ~1KW of PVs to support it. The DC pump 100-220W. Quite a difference. Although in fairness, the AC has the potential of pumping the water quite a bit faster. But given that this is a low output well, that potential cannot be utilized.

    Stephen, you may be right, that all in all, another AC pump and inverter/wiring change may be the simpler solution. I'll have to do some more checking and thinking about this.

    Bill. I have contacted our host, and gotten a bid from them. They have a very good price. The question for me now is, is a DC pump the way to go, or would a AC pump with tie in to my PV system be a better solution.

    And just a general note regarding the switching of DC pump power elsewhere when the pump is not in use... It seems that this would be rather hard to do with current controller designs. However it should/could be a simple thing to accomplish, if the pump controllers were designed for it. All of these controllers "know" when they are trying to run the pump and when it is off. All they would need to do is put a relay and set of output terminals on the controller (or if they wanted to limit cost, just the output to control an external DPST relay). The relay would switch the power from the controller to the output terminals, shunting any power from the well PVs elsewhere when the controller no longer needed it. When the pump was required, the relay turns off, keeping all the power for the pump. It seems this could be done in the controllers with minimal additional costs. Perhaps the manufactures can be convinced to make this addition.
  • stephendvstephendv Solar Expert Posts: 1,571 ✭✭
    Re: Thinking about a PV well pump replacement system
    Steve777 wrote: »
    The advantages of the DC solution would seem to be: A potential longer lived pump design (the helical rotor), although that may not be the case in real life. The advantage of a well pump which could be lifted and replaced by hand in the future. Potentially a slower pumping well system which might extend the useful life of the well.

    I'd bet you could find an AC well pump that met all three of those properties. There are far more AC pumps to choose from, so if you specifically look for one that's designed for sandy/dirty water, you're likely to find it.
    Regarding lifting the pump out there are a few options; ours uses the flexible high strength with NO safety cable and when the well guy first installed it, he removed a small screw from just above the pump which slowly releases water in the pipe. So it was possible to pull it out by hand between 2 people. This is a 1.5kW pump on a 120m pipe. Since then I replaced the screw and just last month had to pull it out again, this time it had the column of water on top of it, but it was still possible to lift it out with a metal pole for a leaver, then hitched it to the back of the tractor. It was slow going and took a few hours, but no real heavy machinery required.

    If you want a slower pumping system, again, you could check the wide range of AC pumps available- I'm sure there's something that would fit the speed you want to pump at. If not, you can always use a VFD (variable frequency drive) and a 3 phase AC pump. With the VFD, you can basically select the pump you speed you want, and you can also program it to ramp up slowly to full pumping speed to reduce wear on the pump. (There are quite a few posts on this topic in the forum)
    Steve777 wrote: »
    The difference in efficiency are pretty obvious. The AC pump requires ~1KW of PVs to support it. The DC pump 100-220W. Quite a difference. Although in fairness, the AC has the potential of pumping the water quite a bit faster. But given that this is a low output well, that potential cannot be utilized.

    200W is 200W AC or DC, maybe DC can be slightly more efficient, but it sounds like the big difference is that you're comparing an oversized AC pump vs. a correctly sized DC pump ;)

    DC + dedicated PV is a good choice for remote installs that can make 100% use of all the PV power all the time and that need the water in exactly the amount the PV produces. Think cattle drinking trough in the middle of nowhere.

    But if you already have the grid in place and you have PV, then I think an integrated system works better because you can take advantage of 100% of the PV power, even when you're not pumping. AND you can supplement the PV power with grid power when the PV isn't producing enough.

    And just a note regarding the Lorentz, be aware that you cannot power it with AC, only DC. They sell an additional connector box if you want to power it with AC and that baby costs upwards of 500 Euros when I checked 3 years ago.
  • westbranchwestbranch Solar Expert Posts: 5,142 ✭✭✭✭
    Re: Thinking about a PV well pump replacement system

    have you asked your local dealer about the costs to rebuild that pump.
    I have had 2 pumps, that we pulled as the well was deepened to 305' , serviced/rebuilt and used elsewhere. It was quite reasonable compared to a new one. The electric motor seldom fails it is the pump vanes that wear.
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • BB.BB. Super Moderators, Administrators Posts: 29,482 admin
    Re: Thinking about a PV well pump replacement system

    If you have a three wire pump (remote capacitor at well head), you can also look at using a VFD. They give you soft start and can let you throttle down the pump RPM/GPH--If that is appropriate (pump slower speed to tank, and use a small surface pump to pressurize for home/low pressure irrigation--low pressure to reduce pumping energy).

    I don't know enough about VFD's--Some people love them, some people are not too excited... I believe that if you can find the right unit (mated to the proper AC pump) will be a pretty good solution.

    I guess that if you went with a real permanent magnet motor (with internal VFD), you might use 20% less power overall (induction motor losses).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Volvo FarmerVolvo Farmer Solar Expert Posts: 209 ✭✭✭✭✭
    Re: Thinking about a PV well pump replacement system

    Something is not quite adding up here. According to the OP, his well will only supply .5GPM. That's 720 gallons a day if pumped to the maximum capacity of the well. His other calculation is that he uses about 5KWhr/day to pump water, out of a well that's only 125' deep.

    I get 250-300 gallons during daylight hours with a single 170W panel, maybe six hours of sun, 1KWhr. Why is he using 5 times as much electricity to pump twice as much water? Is the well bottom 125' or is that the static water level?
  • Steve777Steve777 Registered Users Posts: 5
    Re: Thinking about a PV well pump replacement system

    VF, I think the numbers do add up, at least at the back of a napkin level.

    You are pumping using a DC helical rotor pump. I am using a 40+ year old AC induction centrifugal pump (which is probably oversized for this application). From what I have read, your pump should be 2-5x as efficient. So the fact that I seem to be using 2.5x the power you do (5x the power / 2x the water) for the equivalent water sounds right in the ballpark of the efficiency differences of the two types of pumps.

    Bill and Stephen have pointed out, if I could get an AC pump which was better suited to my well characteristics (low flow, moderate lift), the efficiency might improve. I believe that my current well pump is a 1hp 240v model, although this was from the memory of the PO as the paperwork has been lost); so I won't know until we pull this pump. If this is right, then it is way overkill in terms of power and flow capability as compared to what the well can produce and its depth. A more modest 1/2hp or smaller AC well pump would likely better match the well's water delivery, and should be more efficient. (Another thing to investigate.)

    Unfortunately the current pump does not have an above ground cap, so a VFD modification may not be possible (yet another things to investigate). I also need to see what effect on efficiency slowing the RPMs of a centrifugal pump would have. Seems to me that the vanes/turbine were designed to be efficient at a certain RPM range, and getting out of that range may increase the life of the pump and electronics, but may be doing so at the cost of decreased efficiency in pumping.
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Re: Thinking about a PV well pump replacement system
    Steve777 wrote: »
    I also need to see what effect on efficiency slowing the RPMs of a centrifugal pump would have. Seems to me that the vanes/turbine were designed to be efficient at a certain RPM range, and getting out of that range may increase the life of the pump and electronics, but may be doing so at the cost of decreased efficiency in pumping.

    That is correct. see: http://www.pumpfundamentals.com/centrifugal-pump-tips.htm

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • stephendvstephendv Solar Expert Posts: 1,571 ✭✭
    Re: Thinking about a PV well pump replacement system

    Here's an example of one that might fit: http://it.calpeda.com/file/43170328a1ca93347d888fa8af826207.pdf page 303 model 4SDF 36/5 EC, if I'm reading the graph right it'll do 4 gallons/minute at 130ft depth with 450W.
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Thinking about a PV well pump replacement system
    Steve777 wrote: »
    2. I will need a pump that can deal with lower levels of water in the well, and perhaps a controller which can sense low water and stop the pump for a while as we have now for the AC pump.
    Since the Grundfos inverter-based pumps puts the inverter and electronics inside the pump itself, that integrated controller can also easily sense zero load on the pump and shut it down for a time period when it detects low water. That function comes along for free (on an expensive pump!)
    SMA SB 3000, old BP panels.
  • LynnLynn Registered Users Posts: 1
    Re: Thinking about a PV well pump replacement system

    Agree with Volvo Farmer that the critical issue is the low productivity of this well. Running an AC pump is inefficient, and hard on the pump because of the frequent cycling. I've used both Lorenz and Sun Rotor DC helical pumps at my and my friends' places. Although my well has good productivity, these pump controllers can match the pump speed to the well capacity, with a small solar panel driving it. The problem with the dc pumps is that the local well contractors don't deal in them, so I keep a spare on hand, to have ample time to send the failed pump to the out-of-state dealer to repair or replace.
  • stephendvstephendv Solar Expert Posts: 1,571 ✭✭
    Re: Thinking about a PV well pump replacement system
    Lynn wrote: »
    Running an AC pump is inefficient, and hard on the pump because of the frequent cycling.

    This has nothing to do with the pump being AC or DC. An oversized DC pump will also suffer from frequency cycling. The advantage of using an AC pump with an already existing off-grid system, is that you have flexibility in directing your solar power where you need: e.g. pump when it's sunny and charge batteries when it's cloudy.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Thinking about a PV well pump replacement system

    Technically a standard AC induction motor as used on most well pumps is less efficient than a DC brushless motor. This has nothing to do with the frequency of cycling.

    Frequent cycling of the AC motor is worse than of the DC type because the former requires a higher amount of power to get it started, so every time it starts a bit more power is used than for just running. Frequent starting is hard on either type of motor, and can best be alleviated by matching the pump size to the pressure tank size and usage demands.

    It is never as simple as "this is better than that". Would that it were.
  • denlowdenlow Registered Users Posts: 8
    Re: Thinking about a PV well pump replacement system
    .... (I would also need a new inverter too as my current one is only 120v and the well pump needs 240v, but let's ignore that expense)....

    You might consider a 115v 2 wire submersible pump. I just replaced our pump with a Grundfos 5 SQ05-180 (under $1000). It pumps 6 gpm (measured at well head) with 115' static water level and pump set at 150' pulling 8.2 amps. This pump has a built in "soft start" feature and "dry running protection".

    We use this with our 2.02kw off-grid system, pumping into a 2500 gal. gravity flow storage tank fitted with a float switch which signals a start when tank is drawn down to 2250 gallons. I use a manual switch to shut off power to the pump during periods of no solar production as we still have a large reserve of water in the tank.
Sign In or Register to comment.