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Thread: Prepping: solar power calculation for well pump

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    Prepping: solar power calculation for well pump

    For prepping, I found this useful.
    PVWatts Calculator

    I have various means for getting water in a SHTF scenario but I always like to have alternatives. So I'm planning on having the capability to operate a well pump if the grid goes down and generator fuel is unavailable.

    I needed to figure out a solar power design that would be sufficient to charge batteries daily to run a well pump for 15 minutes a day.....with some reserve.

    I considered the short days and low sun angle in the depths of winter. That link was invaluable for that.

    I will charge two 12 volt batteries in series with solar panels but will use them in parallel to feed a 110 volt inverter that then is transformed to 220 volts with a transformer. That's what the pump needs... 220 volts at 8 amps running power.

    I am using AGM batteries for this purpose. I have some LiFePO4 batteries for other lighter duty. I am sensitive to the lifetime of cycling AGM batteries every day and realize I likely won't have more than a year or so before the batteries are kaput. The LiFePO4 that I have are superior in the number of cycle they can be recharged but they can't handle the current draw of the pump.

    So ... What I concluded was that I need 600 watts of panels and appropriate mppt charge controllers. I'll use 3 parallel sets of 2 panels in series. Considering the winter sun, my new york latitude, and some shading, that only gives me about 1 KWhr per day. But that is enough. More than enough by a factor of about 2, considering the pump will take 1760 Watts for a quarter hour or 440 watthours. The inefficiencies of the solar system are already considered in that web site I linked to. But then battery to inverter and inverter to transformer will be another 10 to 15 percent loss. So say 500 watt hours will be drawn from the battery. I'll get 1000 from the solar system on a good day deep in the winter.

    Regarding the controllers, I'm going to use a Renogy 40 amp controller. I have a couple of 15 amp victron charge controllers and some cheapies too for charging some LiFePo4 batteries using 250 watts of panels for other uses. I'd like another victron controller but ... ugh... twice the price of the Renogy. Renogy should be fine for Lead Acid AGM batteries.

    I have already purchased most of the equipment but still need a few more panels and that Renogy charge controller.


    I post this because I know that in prepping for SHTF scenario, some here have wells and may want to consider how to run the pump if power goes out and generator fuel becomes unavailable.

    The cost is this: (I will fill in prices shortly)
    I bought stuff over the years so a thoughtful redesign could probably achieve the same capability cheaper.

    2 Odyssey Extreme PC1500T batteries ....$700 (350 apiece)

    1 Aims 3000 W pure sine wave inverter (6000 peak to handle pump starting current) ....$530

    6 Renogy monocrystaline 100 watt panels....$600 (100 apiece)

    1 renogy 40 amp charge controller....$140

    1 victron 32 amp auto transformer ....$600
    Various cables/connectors... estimated $200

    Total .... $2770

    Usually I buy important stuff for prepping in duplicate but this is not my only solution for water. So the transformer and inverter have no backup if they fail. I do have mitigations if any of the other stuff fails.
    Last edited by Call_me_Ishmael; 08-17-2022 at 10:16 PM.

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    That sounds like a bigass pump. You're irrigating a field?

    The transformer won't fail unless it corrodes, or unless you try to draw so much current the insulation melts. (Is the system fused?)

    The inverter however, is a different story, and there's no way to really back it up short of getting a spare.

    The only thing I can suggest for redesign is eliminate the two-step conversion, go direct from 12v to 220, this for instance is just a few watts below your spec and I'm sure there's a bigger model:

    https://www.bittychoice.com/products...r?currency=USD

    It'll take 12, 24, or 48v input.

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    Quote Originally Posted by renaissance man View Post
    That sounds like a bigass pump.
    Just a home well pump. Maybe deep well. Not sure.


    A 220 volt inverter would be great. That's a good price but ...modified sine wave? I'd feel better with pure sine. Maybe MSW would work. I know there are some issues sometimes with certain kinds of motors and pumps.
    Last edited by Call_me_Ishmael; 08-17-2022 at 11:07 PM.

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    If you were doing something from scratch, digging a new well and putting in pump that is designed for a solar system... this looks like a turnkey system.

    https://shop.rpssolarpumps.com/produ...ew-summer-2018

    Just need to add storage tanks, a well and some plumbing. You can fill up during the day and don't need batteries. Might need an extra solar panel for winter in certain latitudes. But still.... looks interesting.


    For me....already have the well and pump and plumbing. So I have to accommodate what I have.
    Last edited by Call_me_Ishmael; 08-17-2022 at 11:07 PM.

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    Quote Originally Posted by Call_me_Ishmael View Post
    For prepping, I found this useful.
    PVWatts Calculator

    I have various means for getting water in a SHTF scenario but I always like to have alternatives. So I'm planning on having the capability to operate a well pump if the grid goes down and generator fuel is unavailable.

    I needed to figure out a solar power design that would be sufficient to charge batteries daily to run a well pump for 15 minutes a day.....with some reserve.

    I considered the short days and low sun angle in the depths of winter. That link was invaluable for that.

    I will charge two 12 volt batteries in series with solar panels but will use them in parallel to feed a 110 volt inverter that then is transformed to 220 volts with a transformer. That's what the pump needs... 220 volts at 8 amps running power.

    I am using AGM batteries for this purpose. I have some LiFePO4 batteries for other lighter duty. I am sensitive to the lifetime of cycling AGM batteries every day and realize I likely won't have more than a year or so before the batteries are kaput. The LiFePO4 that I have are superior in the number of cycle they can be recharged but they can't handle the current draw of the pump.

    So ... What I concluded was that I need 600 watts of panels and appropriate mppt charge controllers. I'll use 3 parallel sets of 2 panels in series. Considering the winter sun, my new york latitude, and some shading, that only gives me about 1 KWhr per day. But that is enough. More than enough by a factor of about 2, considering the pump will take 1760 Watts for a quarter hour or 440 watthours. The inefficiencies of the solar system are already considered in that web site I linked to. But then battery to inverter and inverter to transformer will be another 10 to 15 percent loss. So say 500 watt hours will be drawn from the battery. I'll get 1000 from the solar system on a good day deep in the winter.

    Regarding the controllers, I'm going to use a Renogy 40 amp controller. I have a couple of 15 amp victron charge controllers and some cheapies too for charging some LiFePo4 batteries using 250 watts of panels for other uses. I'd like another victron controller but ... ugh... twice the price of the Renogy. Renogy should be fine for Lead Acid AGM batteries.

    I have already purchased most of the equipment but still need a few more panels and that Renogy charge controller.


    I post this because I know that in prepping for SHTF scenario, some here have wells and may want to consider how to run the pump if power goes out and generator fuel becomes unavailable.

    The cost is this: (I will fill in prices shortly)
    I bought stuff over the years so a thoughtful redesign could probably achieve the same capability cheaper.

    2 Odyssey Extreme PC1500T batteries ....$700 (350 apiece)

    1 Aims 3000 W pure sine wave inverter (6000 peak to handle pump starting current) ....$530

    6 Renogy monocrystaline 100 watt panels....$600 (100 apiece)

    1 renogy 40 amp charge controller....$140

    1 victron 32 amp auto transformer ....$600
    Various cables/connectors... estimated $200

    Total .... $2770

    Usually I buy important stuff for prepping in duplicate but this is not my only solution for water. So the transformer and inverter have no backup if they fail. I do have mitigations if any of the other stuff fails.
    Your 40A charge controller is a little underpowered for a 600W solar array on day 1, but with the Latitude of NY state this should be a minor detail. Make sure that June 21 there and a hot day won't overwhelm it.
    I did not run all of the math, but I like the 4x overkill on the power. This also allows that as the system (batteries, solar cells...) degrade, you could supplement this system with 1 out of 5 days supplying water from other sources to top off batteries as the system degrades over time.

    A couple of thoughts, that I have been mulling on SHTF type stuff...
    How do you hide it?
    Can you lock it up at night?
    Maybe augment it to include some cattle/bear/220V defense fence and a light and alarm?
    I did not see the words Deep Cell, or Marine on the batteries?

    Lastly, so before the SHTF, what do you use this for? Lead/Acid batteries like to be used, lightly, and recharged a little, infrequently.
    You could grid tie this for the near term, to decrease your power costs, and periodically switch it over to charge the batteries.

    This is an interesting topic, Ish, thanks for posting it.
    Scientist, Evangelical Christian - reformed, father, entrepreneur, hunter, outdoorsman, motorcyclist, Constitutional Conservative.

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    Quote Originally Posted by Call_me_Ishmael View Post
    Just a home well pump. Maybe deep well. Not sure.


    A 220 volt inverter would be great. That's a good price but ...modified sine wave? I'd feel better with pure sine. Maybe MSW would work. I know there are some issues sometimes with certain kinds of motors and pumps.

    Mechanical stuff is fairly impervious to the choppy modified sine wave inverters.
    I have always wondered if there was some sort of sine wave smoother... Does not sound that difficult to design.
    Scientist, Evangelical Christian - reformed, father, entrepreneur, hunter, outdoorsman, motorcyclist, Constitutional Conservative.

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    Quote Originally Posted by Physics Hunter View Post
    Mechanical stuff is fairly impervious to the choppy modified sine wave inverters.
    I have always wondered if there was some sort of sine wave smoother... Does not sound that difficult to design.
    Try an isolation transformer. In fact you could use 110 in 220 out saving you from buying a 220 volt inverter. Remember inverters produce a balanced output rather than the split phase common to household appliances. In addition the starting draw will be quite large. A large capacitor bank can act as a surge supplier. How will you pressurize the water for distribution in the home as well as heating it?

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    I have a well and I have a 1hp Gould pump, however im moving in sept and going to city water.

    2 yrs ago before I planned to sell, I had two solar guys knock on the door and I said Ok give me an estimate. One wanted 10,000 just to power my hot water heater, and the other 9500. I told them both I wont live long enough to even begin saving any money..

    I have a duel fuel generator propane, gasoline, I fill 4 propane tanks during the peak of hurrincane season and 4 gas cans 5 gallon. The generator will run approx 9hrs on a tank of gas and 6 on propane.

    When I lose power I run it in the morning to make coffee etc and take "COLD" shower, its doesnt run hot water heater AC or dryer...but it runs window units in bedroom and all the fans and well, microwave and refriderator and freezers. I run it no more than 45 mins a day and it makes it livable...but ive only lost power for more than 1 day twice in 18 yrs. After the season the gas goes in my gas tank and the propane is used in the grill
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    Quote Originally Posted by JMWinPR View Post
    Try an isolation transformer. In fact you could use 110 in 220 out saving you from buying a 220 volt inverter. Remember inverters produce a balanced output rather than the split phase common to household appliances. In addition the starting draw will be quite large. A large capacitor bank can act as a surge supplier. How will you pressurize the water for distribution in the home as well as heating it?
    I think this is more for Ish, but I can definitively to the large startup draw.
    During relatively short local power outages I run the 2 fridges and 2 freezers, round robin one at a time, on a 800W inverter that I run off my running pickup truck. When a 340W fridge kicks off, the wattage draw goes to 1000W for a few seconds, about 25% of the time this will pop the breaker on the inverter.
    Scientist, Evangelical Christian - reformed, father, entrepreneur, hunter, outdoorsman, motorcyclist, Constitutional Conservative.

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    Quote Originally Posted by Call_me_Ishmael View Post
    For prepping, I found this useful.
    PVWatts Calculator

    I have various means for getting water in a SHTF scenario but I always like to have alternatives. So I'm planning on having the capability to operate a well pump if the grid goes down and generator fuel is unavailable.

    I needed to figure out a solar power design that would be sufficient to charge batteries daily to run a well pump for 15 minutes a day.....with some reserve.

    I considered the short days and low sun angle in the depths of winter. That link was invaluable for that.

    I will charge two 12 volt batteries in series with solar panels but will use them in parallel to feed a 110 volt inverter that then is transformed to 220 volts with a transformer. That's what the pump needs... 220 volts at 8 amps running power.

    I am using AGM batteries for this purpose. I have some LiFePO4 batteries for other lighter duty. I am sensitive to the lifetime of cycling AGM batteries every day and realize I likely won't have more than a year or so before the batteries are kaput. The LiFePO4 that I have are superior in the number of cycle they can be recharged but they can't handle the current draw of the pump.

    So ... What I concluded was that I need 600 watts of panels and appropriate mppt charge controllers. I'll use 3 parallel sets of 2 panels in series. Considering the winter sun, my new york latitude, and some shading, that only gives me about 1 KWhr per day. But that is enough. More than enough by a factor of about 2, considering the pump will take 1760 Watts for a quarter hour or 440 watthours. The inefficiencies of the solar system are already considered in that web site I linked to. But then battery to inverter and inverter to transformer will be another 10 to 15 percent loss. So say 500 watt hours will be drawn from the battery. I'll get 1000 from the solar system on a good day deep in the winter.

    Regarding the controllers, I'm going to use a Renogy 40 amp controller. I have a couple of 15 amp victron charge controllers and some cheapies too for charging some LiFePo4 batteries using 250 watts of panels for other uses. I'd like another victron controller but ... ugh... twice the price of the Renogy. Renogy should be fine for Lead Acid AGM batteries.

    I have already purchased most of the equipment but still need a few more panels and that Renogy charge controller.


    I post this because I know that in prepping for SHTF scenario, some here have wells and may want to consider how to run the pump if power goes out and generator fuel becomes unavailable.

    The cost is this: (I will fill in prices shortly)
    I bought stuff over the years so a thoughtful redesign could probably achieve the same capability cheaper.

    2 Odyssey Extreme PC1500T batteries ....$700 (350 apiece)

    1 Aims 3000 W pure sine wave inverter (6000 peak to handle pump starting current) ....$530

    6 Renogy monocrystaline 100 watt panels....$600 $630 (100 105 apiece)

    1 renogy 40 amp charge controller....$140
    1 Victron 100/50 Smartsolar charge controller $325

    1 victron 32 amp auto transformer ....$600

    Various cables/connectors... estimated $200 $250

    Total .... $2770 $3035

    Usually I buy important stuff for prepping in duplicate but this is not my only solution for water. So the transformer and inverter have no backup if they fail. I do have mitigations if any of the other stuff fails.
    I made some changes.
    I only need to run the pump half of the time I originally planned. The pump is at least 1 HP and likely 1-1/2. Water is not very deep and at the very worst I can get 10 gallons/minute. Seventy five gallons a day will have to do. Again... with no knowledge of what I'm preparing for - outage of city water or just outage of electric power - I don't know how many people must share this water. While I will provide the power, the well and pump belong to the landlady. So .. my design assumes 75 gallons a day will suffice for consumption and cleaning at several notches about the survival level.

    As I mentioned in my OP, I was going to charge two batteries in series so in charging a 24 volt battery bank, the 40 amp renogy charge controller would have been fine. While I have a total of four of those Odyssey Extreme batteries, and have hardly used them, they were bought over a several year period and I don't want to charge batteries with different conditions in series. But for other reasons as well, I opted to use a Victron 100/50 smartsolar charge controller. The other reasons are that I like its interface and versatility better than the Renogy. Yeah... it costs more than double but I bit the bullet and did it anyhow. (Ugh.. my retirement income hates me for it.) I have several PWM charge controllers that I could have used to really save money - at a cost of significant solar power loss - but I felt an odd sense of urgency to get that good Victron item now.... like while we can still buy such things

    I was going to use two batteries in parallel to run the pump and then charge them in series. Since I decided not to charge them in series, I have a choice: charge them in parallel or use just one battery for each daily run. For deep winter, I opted to plan on using a single battery and alternate between 2 or 3 batteries. This requires that each battery be discharged deeper than if I used them in parallel but according to the specs of these batteries, I need all the current I can get on a deep winter day to properly charge each battery. I'm at a point on the "depth of discharge vs number of charge cycles" curve for these AGM batteries where using 2 batteries in parallel vs alternating between 2 batteries gives me approximately the same number of cycles... at least a thousand days of water. At least. So I'm going with alternating the batteries. And that ensures I can fully recharge a battery with sufficiently high current (which Odyssey says is at least 20 Amps). For operation in July, I may change the configuration.

    I'm adding some cost to the miscellaneous wiring and stuff. Heavy battery cables and cables to connect the panels is more than I had accounted for before.
    Last edited by Call_me_Ishmael; 08-31-2022 at 02:21 PM.

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