430 Watt system build

Dr.PrepperDr.Prepper Registered Users Posts: 14
Hello all, I have been doing some reading on the forum here and trying to better my understanding of how to build a solar backup system(off grid). I want to build a small and reliable system for power outage backup and regular use. I am looking for some opinions and suggestions to help me put together the right components for my system. Let me start by saying that the only part that I have purchased so far is 2 215 watt panels, here is a link:
215 Watt Evergreen
I had purchased these from someone local, the price was great and I feel sure I can accomplish what I want. My main use will be to power a 12 volt water pump(simple pump) and use some power for lighting(12 volt LED) and small fans. I have come to the conclusion that because of the high voltage that these panels put out that I will need to use a MPPT controller, which I am happy to do as I feel it will maximize output to recharge batteries. Are there any suggestions for a good controller that anyone has experience with? I had been looking at a BZMPPT500 and a Morning Star TriStar MPPT-45. I would also be interested in hearing about what kind of monitors or accessories that everyone feels would be essential with this type of controller? Secondly, I was looking at some batteries that are sold by my local Sam's Club. They are 6 volt golf cart batteries that are made by East Penn in the USA. It is the same as a Deka GC10(just with the Energizer name). Does anyone have any experience with this battery, and how long of a life could I expect? With my average sun hours at 4.6 per day, how many amp hours could I put into this type of battery using these two panels and a good charge controller? I was thinking of getting two batteries, but if I could handle recharging 4 within a couple of days of sunlight I may go that route. I would like to have a couple of days worth of power in reserve. I probably have not included enough information, but this is where I am at right now, any help would be appreciated.

Comments

  • DillDill Solar Expert Posts: 170 ✭✭✭✭✭
    Re: 430 Watt system build

    stay away from the BZ controllers, junk, junk, junk!

    http://forum.solar-electric.com/showthread.php?16254-BZ-Products-500MPPT-CC
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Re: 430 Watt system build

    Welcome to the forum,
    You can get lots of good free engineering design at this site, but it requires that you provide info on the load. How much current does your pump and fans draw? How many hours per day will they run?

    BTW, your panels should be able to charge about 300 AH of 12 volt battery (if the loads are not too great).
    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • PhotowhitPhotowhit Solar Expert Posts: 4,276 ✭✭✭✭
    Re: 430 Watt system build

    I had very good fortune with Sam's club 'energizer' branded batteries. I had a set of 4 setup for a year in a 12V configuration and setup for 4 years in a 24 volt configuration. They lasted 4 years being drawn down near 50% every day runnning an air conditioner during the summer. I had only expected them to last 3-4 years. More than 3 years out of an off brand is good, IMHO.

    I understand that batteries marked 'Energizer' are not always made by the same company, but rather a brand, perhaps a house brand of Sam's Club, so your milage may vary, I thinkl mine were marked 215Amp.

    FWIW - I'll use them again in the same system, though perhaps 2 strings, since I'm not getting any younger and we;ve had such a Hot summer here in Missouri. I had bought a big forklift battery, but plan to move it to a new system and use this cabin setup on weekends only.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, ForkLift battery. Off grid for @13 of last 14 years. 1000 watts being added to current CC, @2700 watts to be added with an additional CC.
  • Dr.PrepperDr.Prepper Registered Users Posts: 14
    Re: 430 Watt system build

    Thank you so much for the replies so far.
    Dill, I had been reading that about the BZ controllers, and I believe I will shy away from them. I do want something reliable.
    vtmaps, on the question of loads, I do not have all the details on that yet, but I am working on it. I know the pump will draw about 16 amps, and will run for about 2-3 hours a day. I don't want to sound to ignorant but is that 16 amps per hour? If I can return about 300ah to the batteries, then I could probably be able to draw about 225ah a day off of them?
    Photowith, thank you for the information on the batteries. I am sure you are right about them being branded Energizer by different manufacturers. I had noticed the ones that I looked at this past week were from East Penn, but who knows where they may come from next time? They were marked at 215ah. Did you do anything special besides monitoring water levels?

    Thanks
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Re: 430 Watt system build
    Dr.Prepper wrote: »
    I don't want to sound to ignorant but is that 16 amps per hour?

    No, its 16 amps. Amps is a flow rate of charge.
    Dr.Prepper wrote: »
    vtmaps, on the question of loads, I do not have all the details on that yet, but I am working on it. I know the pump will draw about 16 amps, and will run for about 2-3 hours a day.

    OK, now we're getting somewhere. 16 amps for 3 hours is 48 amphours. If you have a 12 volt battery bank with 215 ah capacity, 48 ah of draw is a bit less than 25% of battery capacity. That sounds like a reasonably balanced system, except that you also mentioned fans and lights... how much do they draw and for how many hours per day?
    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • Dr.PrepperDr.Prepper Registered Users Posts: 14
    Re: 430 Watt system build
    OK, now we're getting somewhere. 16 amps for 3 hours is 48 amphours. If you have a 12 volt battery bank with 215 ah capacity, 48 ah of draw is a bit less than 25% of battery capacity. That sounds like a reasonably balanced system, except that you also mentioned fans and lights... how much do they draw and for how many hours per day?
    I was looking at 6 12volt 5watt LED bulbs running for 2-3 hours per day, very minimal load there. Everything to this point would be DC(pump and lights), for the fans or other AC use I was going to use a small inverter(not grid tie) that would be used during power outages. I basically want some extra electricity on standby. This is the area I am quite lost in. Lets say I have a battery bank with a total of 430ah(4 6volt batteries at 215ah each). Would I be better to maintain two battery banks of 215ah, one for DC and one for AC, or draw everything from one battery bank of 430ah? I know it is best to know what you want to run, then build a system, but basically half of this system is a backup. I already was fairly sure I had plenty of PV to run the water pump and DC lights with just one panel, but I don't know how to figure how much extra I will be producing. At this point I could even run two completely separate systems, two charge controllers, one DC system and one AC system, if that would be better. I was thinking that I would have about 1000w of surplus that I could use daily, or produce daily, if there is no grid power. This is probably a confusing mess, sorry for that. I really do appreciate your help.
    Thanks
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Re: 430 Watt system build
    Dr.Prepper wrote: »
    I was looking at 6 12volt 5watt LED bulbs running for 2-3 hours per day, very minimal load there.
    30 watts at 12 volts is 2.5 amps. 3 hours of that is 7.5 amphours.
    Dr.Prepper wrote: »
    for the fans or other AC use I was going to use a small inverter(not grid tie) that would be used during power outages. I basically want some extra electricity on standby.

    Now we need to know your peak AC loads (in watts) as well as your average loads and the amount of time you are drawing those loads. You need to get a kill-a-watt meter. Your inverter will also consume a certain amount of power.
    Dr.Prepper wrote: »
    Would I be better to maintain two battery banks of 215ah, one for DC and one for AC, or draw everything from one battery bank of 430ah? I know it is best to know what you want to run, then build a system, but basically half of this system is a backup. I already was fairly sure I had plenty of PV to run the water pump and DC lights with just one panel, but I don't know how to figure how much extra I will be producing. At this point I could even run two completely separate systems, two charge controllers, one DC system and one AC system, if that would be better.

    I don't know how to advise you regarding two systems. Depends on what they are used for and when. With 430 ah of battery you could stand to have a bit more panel... unless your power needs are very low. Some folks with weekend cabins are a bit undersized on their panels because they have 5 days to get recharged before the next weekend.

    You are asking for design and engineering advice. Tell me exactly what you want to do and I will tell you exactly how to do it.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • Dr.PrepperDr.Prepper Registered Users Posts: 14
    Re: 430 Watt system build
    Now we need to know your peak AC loads (in watts) as well as your average loads and the amount of time you are drawing those loads. You need to get a kill-a-watt meter. Your inverter will also consume a certain amount of power.
    Would I be able to power a small AC chest freezer drawing 5 amps?
    Thanks
  • icarusicarus Solar Expert Posts: 5,090 ✭✭✭✭
    Re: 430 Watt system build

    5 amps at 120 vac is 50 amps at 12vdc. (remember double the voltage/halve the amps or in this case increase the voltage by 10, decrease the amps by a factor of 10.)

    So 50 amps running on a 12 vdc system is going to take a big battery,, and a big PV. Kill-a-watt the freezer for a week or so, to see what it draws per day in kwh, and watch the starting and running amps to get an idea of how much it actualy draws.


    Just as a rule of thumb, a battery based PV system will deliver numbers like this: take the name plate rating of the PV, divide in half to account for all CUMULATIVE SYSTEM LOSES,, then multiply that number by 4 to account for the number of hours of good sun one might expect on averge, per day' over the coure of the year. So your 213 watt panel might look like this: 213/2=106.5*4=424 watt/hours/day.

    Tony
  • Dr.PrepperDr.Prepper Registered Users Posts: 14
    Re: 430 Watt system build

    Reviving this thread because I am finally putting this system together. Hope that is ok, wanted to build on the previous information. I want to get some opinions on what I have planned. I have the panels previously discussed and now have a charge controller(Outback 60) and I am buying batteries this week. I plan on getting 6v batteries(wired for 12v) for a combined capacity of 645ah. I want several days of reserve power if needed, I can help recharge with a small generator if I have to on prolonged cloudy days. My loads are going to be in two categories, 12v and I will have an AC inverter with one load. On the 12v side I have a motor(driving a pump) that will draw around 13 amps for an average of 2 hours a day, I will also have lighting that will need around 200 watts combined per day. On the AC side I plan on having a 1000 watt inverter that will power a small chest freezer that will draw around 900 watts a day(according to my kilawatt meter). Amperage on that is pretty low, around 5 amp surge then under 1 amp during cooling cycles. I am wanting to find out if my 645ah sounds like enough to power this for a few days without destroying my batteries and if I should be able to run these loads on a daily basis with the pv wattage I have?
    Thanks
  • BB.BB. Super Moderators Posts: 26,867 admin
    Re: 430 Watt system build
    Dr.Prepper wrote: »
    Reviving this thread because I am finally putting this system together. Hope that is ok, wanted to build on the previous information.
    Not a problem... And usually a good idea. Makes it easier to follow your system evolution.

    I want to get some opinions on what I have planned. I have the panels previously discussed and now have a charge controller(Outback 60) and I am buying batteries this week. I plan on getting 6v batteries(wired for 12v) for a combined capacity of 645ah. I want several days of reserve power if needed, I can help recharge with a small generator if I have to on prolonged cloudy days.

    That is probably around the maximum AH capacity you would like to see for a 12 volt battery bank--Larger solar charge controllers are around 60-90 amps or so maximum output. If you had a larger bank/more solar panels, you would need a second charge controller.

    If you went to 24 or 48 volts, the current is 1/2 or 1/4 -- And the charge controllers can support a 2 or 4 times larger solar array (with the same single charge controller).
    My loads are going to be in two categories, 12v and I will have an AC inverter with one load. On the 12v side I have a motor(driving a pump) that will draw around 13 amps for an average of 2 hours a day, I will also have lighting that will need around 200 watts combined per day.

    For your 12 volt loads--You might look and see if there are 24 volt versions available (cost effective for your needs). 24 volts is 1/2 the current and you can send the same power several times further than 12 volts (which needs very short/heavy cables--relatively speaking).

    Regarding the lighting--I am guessing that the 200 Watts per day is really 200 Watt*Hours per day.
    On the AC side I plan on having a 1000 watt inverter that will power a small chest freezer that will draw around 900 watts a day(according to my kilawatt meter).

    That is probably 900 Watt*Hours per day (people drop the Hours units all the time, and talk about Watts or power as Watts/Hour--Which is wrong too). Watts is the rate (like miles per hour), and Watt*Hours is the amount (like miles driven).
    Amperage on that is pretty low, around 5 amp surge then under 1 amp during cooling cycles.

    Remember the 1 amp running / 5 amp surge is at 120 VAC -- At 12 VDC, the current is ten times larger (ignoring inverter losses):
    • 1 amp * 120 volts = 120 Watts
    • 120 Watts * 1/12 volts = 10 amps @ 12 VDC
    • 5 amps * 120 VAC/12 VDC = 50 amps @ 12 VDC

    So--your little 120 VAC loads are much more robust at 12 VDC (current wise--Watts and Watt*Hours wise--12v vs 120v does not matter--A Watt is a Watt).
    I am wanting to find out if my 645ah sounds like enough to power this for a few days without destroying my batteries and if I should be able to run these loads on a daily basis with the pv wattage I have?
    Thanks

    Since you are already running an AC inverter 24x7 -- You might want to re-think your DC loads. You might be able to run the 120 VAC versions of the pumps/lighting to your advantage (120 VAC devices/lighting is frequently less expensive, and motors will last longer if they are not "brushed" motors which are used in many 12 volt pumps).
    • 13 amps * 2 hours * 12 volts = 312 Watt*Hours per day of 12 volt plumping
    • 200 Watt*Hours per day of 12 volt lighting.
    • 900 Watt*Hours per day of 120 VAC refrigerator power

    Translating that to the battery bank--The 12 volt power is fine as is. However, the 120 VAC to 12 VDC involves some losses:
    • 900 Watt*Hours * 1/0.85 inverter losses = 1,059 WH per day @ 12 VDC
    • 20 Watt Inverter Tare (unloaded) * 24 hours per day = 480 WH per day just to run a "typical" AC sine wave inverter 24 hours per day

    So, your mixed AC+DC power requirements are:
    • 312 WH + 200 WH + 1,059 WH + 480 WH = 2,051 WH per day @ 12 VDC

    A battery bank is usually around 1-3 days of storage and 50% maximum discharge (for long life)--Pick 2 days of storage as a nice round number:
    • 2,051 WH * 1/12 volt battery bank * 2 days of storage * 1/0.50 maximum discharge = 684 AH @ 12 volt battery bank

    Remember the 20 watts inverter tare is a guess--You need to find the actual number for your AC inverter.

    To recharge a 12 volt 645 AH battery bank (using your numbers--close enough to 684 AH from my calculations), we use ~5% to 13% rate of charge:
    • 645 AH * 14.5 volts charging * 1/0.77 panel+controller deratings * 0.05 rate of charge = 607 Watt minimum array
    • 645 AH * 14.5 volts charging * 1/0.77 panel+controller deratings * 0.10 rate of charge = 1,215 Watt array nominal
    • 645 AH * 14.5 volts charging * 1/0.77 panel+controller deratings * 0.13 rate of charge = 1,579 Watt array "cost effective maximum"

    Using PV Watts for Tallahassee FL, fixed array, tilted to latitude:
    Month    Solar Radiation (kWh/m 2/day)
    1      4.10     
    2      4.86     
    3      5.07     
    4      6.05     
    5      6.15     
    6      5.73     
    7      5.28     
    8      5.52     
    9      5.38     
    10      5.32     
    11      4.51     
    12      3.92     
    Year      5.16      
    

    Tossing the "bottom 3 months" (assuming generator used during poor weather), February at 4.82 hours will be "break even" month:
    • 2,051 WH per day * 1/0.61 DC system efficiency * 1/4.82 hours per day = 691 Watt Array Minimum (February)

    So, the recommended array would be from 691 watts to 1,579 Watt array, with 1,215 Watt array being a healthy nominal array.

    And a 1,215 Watt array would generate during February:
    • 1,215 Watts * 0.61 DC system eff * 4.82 hours per day = 3,572 WH per day @ 12 vdc loads
    • 1,215 Watts * 0.52 DC system eff * 4.82 hours per day = 3,045 WH per day @ 120 vac loads

    So--that is a pretty good sized system for a small/efficient home and/or for use when there is a long term power outage.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Dr.PrepperDr.Prepper Registered Users Posts: 14
    Re: 430 Watt system build

    BB, thanks for the reply. Yes, I meant watt hours. I would like to run 24 volt but I already have the 12 volt pump. I can get a 24 volt version but it would cost $400. I have another factor with the pump. I have to run the wire for it 40 feet from the batteries. I can add another panel to help, bring the pv wattage closer to 700. What about breaker sizing? I have the panels in series so it is about 7.5 amp to the charge controller so I was thinking a 12 amp breaker there. I would need about a 20 amp breaker for the 12v motor I think. What about between the batteries and the inverter?
  • BB.BB. Super Moderators Posts: 26,867 admin
    Re: 430 Watt system build

    Running a 12 volt pump 40 feet @ 13 amps... Assuming there is no starting surge (i.e., if this is a piston pump or diaphragm pump pushing against water in a pressure tank--You might have higher starting surge current), at the very least, you want no more than ~0.5 volt drop. Using a generic voltage drop calculator:
    • 0.5 volt drop @ 13 amps and 40' of one way trip wiring=> 40' of 6 awg cable gives 0.5 volt drop

    This is the problem with 12 volt loads, very low voltage, very high current, very low voltage drop allowed (11.5 volts minimum battery voltage and 10.5 volt minimum pump voltage--Allow some drop for fuse/breaker and a bit of surge current). And if you have high surge current, you may be looking at 2 awg or even heavier wire.

    The minimum size breaker for the motor would be:
    • 13 amps * 1.25 NEC derating for wire/breaker/fuses = 16.25 amps minimum

    20 amps would be a good minimum number--But even 25 or 30 amps would be OK if the motor draws more current than you have planned (reducing the chances of a false trip).

    Hard to tell from 3,000 miles away--But 700 Watts would be too small, in my humble opinion, if you plan on using the pump+fridge every day... Drawing almost 100% of the estimated system power is cutting it too close, unless your loads are variable (i.e., less than full sun, your irrigation/water pumping needs are less) unless you plan on making more use of a generator. Even the solar data is variable--You can get a +/- 10% variation from year to year--And if you have highly variable marine layer (clouds) or summer thunderstorms, day to day variations in solar irradiation can be much higher.

    Nominally, I would plan on ~66% to 75% of maximum power for minimum daily usage:
    • 691 Watt array * 1/0.75 = 921 Watt Array
    • 691 Watt array * 1/0.66 = 1,047 Watt Array

    The minimum array size for such a daily base load would be around 921 to 1,047 watt array minimum for better system performance and, probably, longer battery life.

    Regarding your 1,000 Watt inverter, we would do the same thing just did with the 12 volt pump--Must a bit more math to get the DC current usage by the inverter. Using typical numbers:
    • 1,000 Watt inverter * 1/0.85 inverter efficiency * 1/10.5 volt battery cutoff = 112 amps DC typical max input current

    Note, 0.5 volt drop for wiring and a 1,000 watt inverter may have a 2x surge rating for starting loads (Note, you will have to confirm your 1,000 watt inverter will work with the refrigerator compressor starting loads--Many times, a 1,200 to 1,500 watt inverter is around the minimum inverter that will reliably start a refrigerator and run a few lights). Using 5' cable run (short and heavy) and 0.5 volt max drop at 112 Amps:
    • 5' @ 112 amps and 0.5 volt drop => 4 awg wiring -> 0.4 volt drop

    Note that the same issues apply for the Charge Controller too... Keep wiring very short and heavy between the charge controller and the battery bank. Using a 1,047 watt array:
    • 1,047 watt array * 0.77 panel+controller deratings * 1/14.5 volts charging = 55.6 amp charge controller minimum
    • 60 amps @ 5 feet and 0.1 to 0.05 maximum drop -> 1 AWG @ 5 feet will give you 0.09 volt drop

    Again, lots of copper for a largish 12 volt system. You don't want too large of voltage drop from controller to battery bank--Charge controller "sees" a high voltage and cuts back on current output--Taking longer to recharge the bank and reducing overall harvest during the day.

    Sorry for all the math--But better than me giving you "magic numbers". You can adjust them based on your actually needs/choices/assumption corrections.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Dr.PrepperDr.Prepper Registered Users Posts: 14
    Re: 430 Watt system build

    Bill,
    This is why this forum is great. I get really good answers to my questions. It really sounds like I will not be able to effectively run that freezer without a considerable increase in cost. My controller can only handle 750 watts at 12v. I would have to get more panels and another controller. I believe I will just plan on the pump and lights at 12v with a 1000 watt inverter left disconnected but available for use when needed. A 60 amp fuse between the controller and batteries? I was planning on 4awg wire to the pump, and possibly 2awg if I can find some cheap. I know a couple of electricians and my be able to get it very reasonable. This being the case I should be fine using just 4 batteries? As far as the freezer draw goes I know it will run on a 1000 watt inverter, I have tried it.
  • BB.BB. Super Moderators Posts: 26,867 admin
    Re: 430 Watt system build

    Yep--Adding a 24x7 load for something like an 120 VAC freezer (plus inverter losses) really pushes up the system requirements.

    You can certainly try running the AC loads and see what happens. I have made lots of guesses here and one or more of them certainly can be wrong (I try to error towards the more conservative answers).

    Even then--Try it and monitor the batteries. At least you will have the knowledge for when you really need the system during a power failure.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Dr.PrepperDr.Prepper Registered Users Posts: 14
    Re: 430 Watt system build

    On the wire gauge for the 12 volt run to the pump. If I use 2 awg on a 50 foot run do you think that would work ok? I also can get some 1 awg aluminum for free. I would have to buy the 2 awg copper.
  • BB.BB. Super Moderators Posts: 26,867 admin
    Re: 430 Watt system build

    Using a generic voltage drop calculator:

    13 amps @ 50 feet one way run => 2 AWG copper is 0.24 volt drop
    13 amps @ 50 feet one way run => 1 AWG aluminum is 0.28 volt drop

    So--your choice. Either looks fine.

    If I could get the cable for "free"--I probably would try the pump and cable first, before I cut a trench and buried the cables. Also--I believe in putting some conduit/ABS pipe/etc. in the trench so you only have to open the ground up once. You can then pull more cable through a second pipe later.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Dr.PrepperDr.Prepper Registered Users Posts: 14
    Re: 430 Watt system build

    I did put in some conduit, also acquired for free. I ended up using 1/0 awg aluminum(free). Best I could tell from the charts it would work just fine. Pulled the wire today and the run ended up being just under 40 feet that will end at a disconnect. From the disconnect I will run about 8 feet of 8 awg to my pump through conduit. I think it is going to work out fine. I should have very little voltage drop at that distance with that big of a feed line. Thanks!
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