Few Newbie Questions RE: Inverters and Well Pumps

IPSparkyIPSparky Posts: 7Registered Users
Hi, everyone. I just registered, and I've been looking through the beginner section for a bit and haven't found this info, so I apologize in advance if this has been asked dozens of times already.

I'm looking at going solar for everything aside from Central Air Conditioning. This isn't a big deal, since we do our laundry by hand, don't have a vacuum cleaner and wash our dishes by hand. All of our lights are high efficiency, etc. We use very little power, so going solar seems like common sense.

Only one problem....I have a well pump that runs on 240v.

What will it take to convert 12v or 24v to 2 phase 240v? I've been researching this for some time, and can't find a consistend and understandable explanation.

A little background, I'm an Electrician and Instrumentation Tech so you don't have to dumb things down too much.

Thanks for the help, and sorry again if I should have found this on my own.

Comments

  • BB.BB. Posts: 27,689Super Moderators admin
    Re: Few Newbie Questions RE: Inverters and Well Pumps

    Pretty simple..

    DC Batter bank => AC Inverter => 120 VAC or 120/240 VAC split phase => step-up transformer => 240 VAC well pump

    Of course, you need a large enough step up transformer, or an AC inverter that outputs 120/240 VAC. The inverter has to be large enough to supply pump surge current (~5x running current). And you need a battery bank large enough to supply starting/running energy to the AC inverter (12/24/48 VDC are common battery bank sizes, and usually for larger power draws, a 24 or 48 volt battery bank is a better choice (to keep DC current/copper costs down).

    There are other options... There are 120 VAC pumps with soft-start build it (basically a VFD--Variable Frequency Drive). And there are even pumps that can take from ~40-300 VDC or 100-240 VAC (again, a version of VFD inside)--One pump that can run from solar panels, battery bank, and/or backup AC power/genset.

    You can also get 120 or 240 VAC well pumps with three wire (well head starting cap) or three phase well pumps to run behind a VFD, etc.

    VFD's offer other abilities--Variable pump speed (slow pump down for lower flow rates/more efficient pumping, variable speed based on pressure feed back from point of use. In some places in the world, people are running solar panels into a VFD then running multi-HP pumps for irrigation--And saving a whole bunch on fuel and battery/support electronics costs.

    You can convert to a "slow pump" to a cistern, then run a surface pump to pressurize the home. Daytime pumping to cistern (get rid of expensive and maintenance hungry battery bank--surface pressure pump).

    In general, it is almost always cheaper to conserve/reduce peak power loads vs building out a larger Off Grid system capable of driving a large multi-HP pump that on runs a faction of the day.

    That is the 50,000 foot view-New install with existing well? How much power do you need anyway?

    Running a whole home with lots of "modern" electric loads--Adding enough to support a 240 VAC well pump may not cost "that much more"--However, this is still not a "cheap off grid system" that will save you money over utility power... Very roughly, off grid power will cost you on a $$$/kWH rate (20 year OG system cost + maintenance / 20 years of generated electricity) will cost something like 10x the present utility costs.

    If you are looking at back up power--A genset and smaller Off Grid system for the rest of the loads may be more cost effective... If you are a distance from the Utility Drop (1,000's of feet to miles)--Sometimes off grid power (with lots of conservation) doe make economic sense by itself.

    Your thoughts/requirements?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • vtmapsvtmaps Posts: 3,738Solar Expert ✭✭✭✭
    Re: Few Newbie Questions RE: Inverters and Well Pumps
    IPSparky wrote: »
    Only one problem....I have a well pump that runs on 240v.

    What will it take to convert 12v or 24v to 2 phase 240v?

    Welcome to the forum,

    I assume from your question that you want to build a battery based system. For many folks the water pump is a defining factor in the design of a system. It may be worthwhile to spend more on a new pump (BB gave you some options) rather than supersizing your system to handle your existing pump.
    IPSparky wrote: »
    We use very little power, so going solar seems like common sense.

    I disagree. Battery based system produce very expensive power... is it common sense to spend 10 times as much per kwh? A grid-tie system can make sense with enough rebates and incentives. Much depends on the laws in your state... something like 80% of the solar power in the US is in the 12 states that have favorable net metering laws.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • solar_davesolar_dave Posts: 2,337Solar Expert ✭✭✭✭
    Re: Few Newbie Questions RE: Inverters and Well Pumps

    How about just going grid-tie, you then get the benefit of all the watts you generate where with a battery system once the battery is full the electrons fall on the floor unused. Also the battery system is more expensive from a capital outlay perspective.
  • IPSparkyIPSparky Posts: 7Registered Users
    Re: Few Newbie Questions RE: Inverters and Well Pumps

    I have no interest in a grid tie system. Also, I'm not planning to go completely off-grid.

    My home is already built and on the grid. It's 6 years old. My well pump is submerged, not sure if it's 1/3 or 1/2 hp.

    I've been going to a more primitive lifestyle for the last 2 years. I have 5 acres and a pond. I grow vegetables and raise rabbits for supplemental food. I cut my grass/pasture with a scythe and a reel mower. I have no carpet, so floors are swept, no vacuum cleaner to run. Laundry and dishes done by hand, even though I have a working dish washer.

    We don't watch television. I don't have cable, satellite or home internet of any kind, so no tv, no modems, no routers, etc.

    For entertainment, we read books and listen to the radio. Radio is solar/hand crank style.

    Basically, my only loads are 2 cell phones to keep charged, one laptop, a coffee pot, efficient lights...and that sums it up. I want all these small loads on solar.

    The big loads are central heat, central AC and the well pump. I will keep the heat and AC on the grid, I want everything else off, if possible. The only reason I want the well off the grid is so I have water in the event of a power outage.

    Would it be better to just buy a 120 well pump than deal with converting to two phase 240 for my existing pump? I have been looking at inverters online for days, but those that claim to be 240 all have negative comments claiming they are not split phase and will not work.

    If anyone could give me a link to a 12v or 24v to 240v split phase inverter, I would really appreciate it so I can compare prices and decide if I would rather just replace the pump.

    The cost of the system isn't a big issue. I don't want grid tie because I would feel really dumb in the event of a power outage, looking at those solar panels and having no electricity....

    I'm thinking, for my small loads and the pump, a 2,500 watt system would be more than enough. Am I correct?

    Thanks for the help.
  • IPSparkyIPSparky Posts: 7Registered Users
    Re: Few Newbie Questions RE: Inverters and Well Pumps

    A little more info...wiring cost is not an issue. I'm an industrial electrician, so wiring, breakers, lugs, connectors, junction boxes and etc will not cost me anything.

    I can also keep my batteries topped off with grid power if I need to, and only rely completely on solar in the event of a power outage.

    I'm also planning to switch to deep cycle batteries in both of my trucks, so I will always have 2 backup batteries kept charged by alternators.
  • jcheiljcheil Posts: 719Solar Expert ✭✭✭
    Re: Few Newbie Questions RE: Inverters and Well Pumps

    If you only want to power certain loads with the solar, it will get rather complicated in that you would have to install a seperate breaker box and wire all those circuits into the inverter powered by the solar. If your house is already built, that could be difficult and expensive.

    I suppose you could also add a transfer switch using the grid as one of the sources and if/when your solar could not keep up with the demand, it would switch those circuits back to the grid.

    There are grid-tie systems that can have batteries also so you can have the best of both worlds (to a point) but that would all depend on how much $ you are willing to invest. Like many have said, it is about 10x the cost of grid power to make it happen with solar. If you are only worried about the occasional power outage, a small generator is going to be way cheaper in the long run.
    Off-Grid in Central Florida since 2005, Full-Time since June 2014 | 12 X Sovello 205w panels, 9 X ToPoint 220w panels, 36x ToPoint 225w panels (12,525 watts total) | Custom built single-axis ground mounts | Complete FP2 Outback System: 3 x FM80, 2 x VFX3648, X240 Transformer, FLEXnet-DC, Mate-3, Hub-10, FW500 AC/DC | 24 x Trojan L16RE-B Batteries 1110ah @ 48v | Honda EU7000is Generator and a pile of "other" Generators | Home-Made PVC solar hot water collector | Custom data logging software http://www.somewhatcrookedcamp.com/monitormate.html
  • IPSparkyIPSparky Posts: 7Registered Users
    Re: Few Newbie Questions RE: Inverters and Well Pumps

    As I mentioned, I'm an electrician so installing a separate breaker panel for the loads I want on solar will not cost me parts or labour.

    You could say I'm sort of a doomsday prepper, but not really. I just want to know that I will always have lights and water in case of emergencies.

    I need to check my static water level, but I live in Louisiana so I know it's not too deep. I may just get a pitcher pump for the water issue.
  • Blackcherry04Blackcherry04 Posts: 2,486Solar Expert ✭✭✭
    Re: Few Newbie Questions RE: Inverters and Well Pumps

    This will run your pump. Add this transformer your good to go.

    http://www.solar-electric.com/psx-240.html


    Since these Inverters have came out it's hard to beat the price, all the features and 240V split phase. $1,300. This how I would go.

    http://www.solar-electric.com/schneider-electric-sw-conext-inverter-2524-120.html
    .
  • IPSparkyIPSparky Posts: 7Registered Users
    Re: Few Newbie Questions RE: Inverters and Well Pumps

    Thanks for the link.

    The item description is rather lacking, so I assume this is s 120v to 240v transformer, not a 24v DC to 240v AC inverter?

    Since it specifically says transformer, I'm sure it's the former, just checking.
  • Blackcherry04Blackcherry04 Posts: 2,486Solar Expert ✭✭✭
    Re: Few Newbie Questions RE: Inverters and Well Pumps

    120 V to 240 V, I put you a new link on something might be better for you. Here is the manual for the transformer http://lib.store.yahoo.net/lib/wind-sun/PSX-240-manual.pdf



    http://www.solar-electric.com/schneider-electric-sw-conext-inverter-2524-120.html
  • IPSparkyIPSparky Posts: 7Registered Users
    Re: Few Newbie Questions RE: Inverters and Well Pumps

    Wow, you just made my day. That is a beautiful and perfectly suited piece of awesome. That inverter is exactly what I need, especially since I will be using grid power every now and then to top off my batteries if needed.

    Something like that was exactly what I was looking for. Many thanks.

    Based on the loads I mentioned, would you think that would be enough juice? I think so.
  • Blackcherry04Blackcherry04 Posts: 2,486Solar Expert ✭✭✭
    Re: Few Newbie Questions RE: Inverters and Well Pumps

    It sounded like just what you were asking for. I am switching all my old customers to the new one when they buy and need 240V. The next size up is 4000 watt, maybe more than you need, but loads can grow over time, your choice, price is not that much. Later if you want some solar, you can.
  • BB.BB. Posts: 27,689Super Moderators admin
    Re: Few Newbie Questions RE: Inverters and Well Pumps

    To use the "full" capability of a 2.5 kW inverter, you would want around a 500 AH @ 24 AH battery bank (based on flooded cell batteries).

    A 500 AH @ 24 volt battery bank, with 2 days of energy storage and 50% maximum discharge will run:
    • 500 AH * 24 volt battery * 0.85 inverter eff * 1/2 days of storage * 0.50 max discharge = 2,550 WH per day = 2.5 kWH per day

    To run from solar panels, a 500 AH battery bank should have 5% to 13% rate of charge. Or:
    • 500 AH * 29 volts charging * 1/0.77 panel+controller derating * 0.05 rate of charge = 942 Watt array minimum
    • 500 AH * 29 volts charging * 1/0.77 panel+controller derating * 0.10 rate of charge = 1,883 Watt array nominal
    • 500 AH * 29 volts charging * 1/0.77 panel+controller derating * 0.13 rate of charge = 2,448 Watt array "cost effective maximum"

    Assuming you deeply cycle and use the system every day, you should try for 10% or larger solar array... Such an array in the Dallas area of Texas, fixed, tilted to latitude ~33 degrees from horizontal, using PV Watts:
    Month    Solar Radiation (kWh/m 2/day)
    1      4.32     
    2      4.77     
    3      5.50     
    4      5.98     
    5      6.02     
    6      6.25     
    7      6.39     
    8      6.31     
    9      5.83     
    10      5.56     
    11      4.43     
    12      4.10     
    Year
    

    Use 4 hours of sun as minimum:
    • 1,883 watt array * 0.52 end to end system eff * 4 hours of sun per day = 3,917 WH = 3.9 kWH per day

    That is enough power to run a very efficient home/life style (full size Energy Star rated refrigerator, lights, laptop, well pump, washing machine, cell phone charger, etc.) purely from solar with a little bit of generator use when you have more than ~2 days of bad weather in row (assuming you do a little conservation when the sun is not shining).

    The above is based on the rules of thumbs that we use to size a system... Usually conservative enough to not have any surprises (for an off grid home/emergency use, you don't want surprises). You can adjust based on your needs (both functional and wallet).

    Does this give you some ideas/more questions?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • IPSparkyIPSparky Posts: 7Registered Users
    Re: Few Newbie Questions RE: Inverters and Well Pumps

    I generally work 12 hours a day, 5 to 7 days a week. My wife stays at home, but her time is spent listening to our solar powered radio while she cleans house, or reading. We don't use lights during the day since we have lots of windows. We always turn off all lights we aren't using.

    We also unplug any appliance not in use, like the coffee pot. The only constant loads on my system would be 1 or 2 high efficiency light bulbs (at night), an electronics charger (cell phone, laptop) and possibly a ceiling fan during the summer.

    The only big load on my system would be the well pump. I also have a small (rv size) fridge that I may put on the solar system.

    Assuming the well pump is 1/2 hp.

    I was thinking of starting off with 400w of solar panels, 2 115 AH batteries and the inverter linked earlier in this thread.

    Considering I can use the grid to charge batteries if needed and our power outages never last more than 2 days, would this work?

    I intend to keep expanding the system as I go, but that's my plan to get started.
  • BB.BB. Posts: 27,689Super Moderators admin
    Re: Few Newbie Questions RE: Inverters and Well Pumps
    IPSparky wrote: »
    We also unplug any appliance not in use, like the coffee pot. The only constant loads on my system would be 1 or 2 high efficiency light bulbs (at night), an electronics charger (cell phone, laptop) and possibly a ceiling fan during the summer.

    There are two types of loads that drive Off Grid Solar design. Large peak loads (well pump, microwave, coffee maker, starting loads from refrigerator, etc.). And loads that run for many hours per day (refrigerators, computers, networking gear, etc.).

    A Kill-a-Watt placed for 1 day to 1 week on each load will give you a lot of this information (peak starting current is beyond a K-a-W's capabilities).

    The only big load on my system would be the well pump. I also have a small (rv size) fridge that I may put on the solar system.

    What type of RV fridge? Compressor or Propane type Ammonia/Absorption Cycle? Propane refrigerators are very energy inefficient when running from 12 VDC/120 VAC power.
    Assuming the well pump is 1/2 hp.

    A good 2 kW inverter should be OK... You might ~250 AH @ 24 volt battery bank (depends on surge and hours per day of pumping--Home use vs irrigation, etc.).
    I was thinking of starting off with 400w of solar panels, 2 115 AH batteries and the inverter linked earlier in this thread.

    That is a bit on the small side--I would suggest 4x 6 volt @ 220 AH "Golf Cart" type batteries. Easy to add a second string if needed. Pretty cheap and rugged batteries (need to check water levels/keep top of batteries clean/vented area due to hydrogen gas+a little acid mist/sulfur smell.
    Considering I can use the grid to charge batteries if needed and our power outages never last more than 2 days, would this work?

    You can go in this order (if money outlay or want to add to system over time):

    1) Install ~220 AH @ 24 volt battery bank + 2.5 kW AC inverter (with integrated AC charger and/or external AC charger).
    1.5) Check pump function and ensure can meet your load needs. If not, add a second string of batteries.
    2) Install a smallish genset (support minimum loads and battery charging). A new/high-tech Inverter can do "generator support"--A neat function that allows a small genset to "run" larger loads (inverter will support starting surge current/loads larger than the genset itself can support by itself).
    3) Add 5% solar array, add more panels a needs/wallet permit

    Growing a system is not easy or (many times cost effective). Mixing old+new batteries creates a bit of a maintenance nightmare (diagnose problems/replacing only 1/2 a bank every 3 years vs a whole bank every 6 years). Old batteries can "take down" good batteries, etc.

    If you grow your power needs too much, then you need to go from 12 to 24 to 48 volt battery bus... New batteries, new inverter, possibly an upgraded Charge Controller, more solar panels (mixing old and new brands/models of panels is not always easy), etc.

    I try to dissuade people from "growing" their system, but (at the very least) do a paper design and see what the "ideal system" would be. And if you have grid power, grow the system by adding functions (as above) vs growing by adding batteries/inverters/etc.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Blackcherry04Blackcherry04 Posts: 2,486Solar Expert ✭✭✭
    Re: Few Newbie Questions RE: Inverters and Well Pumps

    I didn't see anything about batteries. I'd buy 4, 6 volt GC-2 Golf Cart batteries and run them in series for 220 amp hr. They are relatively cheap at Sams club ( $89 ea ) and they will give a 5 year window to make more decisions where you want to go. That is about the minimum that would start your pump. You'll have to run 4/0 cable to keep the voltage sag to a minimum, Inverters like a constant input.
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