what will it take?

justsumguyjustsumguy Registered Users Posts: 9
what will it take as far as solar panels, charge controller, batteries and inverter to keep three small chest freezers 110v 1.6 amp each and 24 9 watt 110v LED light bulbs in worst case situation of four days of heavy cloud cover/rain. currently have 6 15watt 12v panels (harbor freight) but am looking to put in 4 70 watt 12v panels (polycrystalline). any and all help is greatly appreciated. by and by the freezers will be on timers 30 minutes on 90 minutes off with no more than 2 on at any given time.

Comments

  • icarusicarus Solar Expert Posts: 5,090 ✭✭✭✭
    Re: what will it take?

    Welcome,

    Yet once again, the answer is pretty simple. Do a load calc and then figure backward. up a p3 kill-watt meter, measure the strting and running loads of the hardware, and then figure out how much they draw on a daily average daily basis. Once you have the peak and daily loads, then you can figure out how much battery you will need, then you can figure out the inverter you need to power it, nd how m ich PV you need to keep them charged.

    Avoid the biggest single pitfall of off grid solar, tht is "Ready, fire, aim!"

    Tony
  • BB.BB. Super Moderators Posts: 26,870 admin
    Re: what will it take?

    First, I would suggest getting a Kill-a-Watt meter (or similar) and measure you current power usage.

    Next, conservation... It would not be unusual to find that one full size Energy Star Freezer uses about the same amount of power as any one of the smaller freezers.

    Assuming that you need 2 kWH per day for 4 days of power... I would next suggest a Honda eu2000i genset would should keep at least 2 of the freezers running for 12 hours (possibly all three) on about 1.5 gallons of fuel--Or call it 2-3 gallons of fuel per day (if running 24 hours per day--use an extended run fuel setup or even convert genset to propane). And upwards of 12 gallons for 4 days of backup power. Put stabilizer in the fuel and recycle into a car once per year. That is my own plan/setup (I store 20 gallons of fuel).

    If that was the ultimate power requirement (only a few outages per year), for less than $1,500 you are done (you would need to manual start and service the genset during this time).

    However, if you wanted a battery bank + Inverter instead for 4 days of backup power. Here is a "home made/large UPS system" design.

    First, assume 2kWH per day, 4 days of battery only backup power and discharge to 80% of capacity maximum to avoid battery damage (don't worry about solar, at least from your requirements):
    • 2,000 WH per day * 1/0.85 inverter eff * 4 days of backup * 1/0.80 max battery discharge * 1/48 volt battery bank = 245 AH @ 48 volt battery bank

    A suggested good quality battery with reasonably low distilled water needs (newer battery from Trojan--note this is just a cut and paste from our host's website--None of us moderators are connected with NAWS other than as volunteers here):
    So 8x of those batteries for a 48 volts @ 325 AH for ~$2,500 plus shipping and handling (you may buy batteries locally as they can be costly to ship).

    Next, an inverter... Here is a very nice 48 volt inverter that may be way overkill for your needs--But it does include a very nice integrated/power factor corrected battery charger:
    For ~$2,200 120/240 VAC inverter.

    At this point, we have met your 4 days of power requirement... And you can probably get a decent genset for backup power (solar is never good as the only backup power source--as you say, you can have days of heavy weather which provides virtually no solar power for your loads/recharging). But we can talk about solar panels too for longer term outages (months+).

    Anyway, some quick information. Questions/comments/suggestions?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • justsumguyjustsumguy Registered Users Posts: 9
    Re: what will it take?

    I have the kill a watt meter on order as I saw from other postings here it is a must. I'm on the coastal bend of Texas so sun is not a big issue, but the grid is shaky at best the last big rain storm the power was out for three days. I was stationed in the Philippines when Mount Pinatubo erupted lost power to the house there for two months. As it is right now I can keep some lights on and run a fan but mostly use what I've got now to power the blower for my blacksmith forge as all I can get locally is anthracite coal which requires more air than I can pump using my hand cranked blower. and no I don't shoe horses, I'm a blacksmith not a farrier.
  • justsumguyjustsumguy Registered Users Posts: 9
    Re: what will it take?

    so far as a test I've been able to keep one freezer going for 12 hours using 3 15 watt solar panels run into two very old car batteries in parallel (amp hours is any ones guess) powering a 1200/2400 modified sine wave 12v inverter, of those 12 hours 5 1/2 were dark hours.

    I don't think the batteries made a recovery as the next day after 7 hours of sun light with no load the batteries were at 12.1v and could only power the washing machine for about ten minutes of the wash cycle before the low volt alarm on the inverter sounded.

    no loss on the batteries as they were ones I'd collected as cores. the charge controller is the one that came with the solar panel kit and seems to be rated at 4 amps a 30 amp replacement is on the way.

    I'd like to stay with a twelve volt system as I have 9watt 12v LED lights and can also use the system to power my security cameras so by looking at your computations for battery amp hours unless I'm reading something wrong I should be able to go with four 12v 95AH deep cycle lead acid batteries in parallel.

    and again thanks to all for your help on this.
  • BB.BB. Super Moderators Posts: 26,870 admin
    Re: what will it take?

    The "average" fridge/freezer probably averages between 25 and 100 watts over an hour (25 to 100 WH per hour, or 0.6 to 2.4 kWH per day).

    A fully charged average 80 AH 12 volt battery with inverter will supply:
    • 80 AH * 12 volts * 0.85 inverter efficiency = 816 Watt*Hours till dead

    A 75 watt average load will run:
    • 816 WH / 75 watts = 10.9 hours (very roughly)

    Running a car battery (good or not) often below ~85% state of charge (15% of stored capacity) will usually have a short life (few months) to one cycle (if taken to 0% state of charge).

    There are lots of issues using car batteries, and more issues using parallels strings of batteries (more than 2-3 strings of batteries do not share current very well--It is much better to get one large AH cell and have one string of cells to 12/24/48 volts than to use a "bunch of smaller 12 volt batteries" in parallel.

    While it is possible to make very large 12 volt power systems--It gets expensive and dicey to make them supply much more than 1,200 watts (and requires more maintenance).

    Anyway, 4x 12 volt @ 95 AH batteries to supply a load to from 100% to 20% state of charge (if you don't want a "one time" battery bank) for 4 days:
    • 4x 12 volts * 95 AH * 0.85 inverter eff * 0.80 maximum discharge / (4 days * 24 hours per day) = 32.3 Watt average AC output

    So, you may, be able to run a very efficient small fridge/freezer at 32 watts for 4 days:
    • 32 watts * 24 hours = 768 Watt*Hours load per day = 0.768 kWH per day

    Note that a 1,200-1,500 watt inverter may run 10-20 watts "tare" losses (just being turned on, inverters waste energy). So, you may have to add 10-20 watts to your "32.3 watt" load...

    Note, losses in solar / off grid systems are nasty... Typically, from a Solar Panel Name plate to actual AC power out of an inverter is around 52% overall efficiency. Solar panels have "Marketing" spec. for numbers... Converting energy through a charge controller, storing in a battery bank, taking from a battery bank, and converting DC back to 120 VAC -- All adds up to you with 1/2 your power "missing in action".

    -Bill

    Note that a 1,200 to 1,500 watt inverter is usually the minimum recommended to run a typical Energy Star frostless refrigerator. Starting loads and defrost heaters need quite a bit of power (for short periods of time). Around 1,000+ watt starting surge, and 600 watts for defrost heaters.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • justsumguyjustsumguy Registered Users Posts: 9
    Re: what will it take?

    I have no intentions of using automotive starting batteries as installed equipment, they were used for testing purposes only the deep cycle batteries I am going to install arrive on the 1st.

    another question; what if any is the PV panels to batteries charge time before applying loads for new batteries of the flooded lead acid type, or should the batteries be pre-charged using a dedicated battery charger prior to integration into a PV system?

    also; for a system supplied by four 70 watt panels (poly) with vMpp 17.5 and iMpp 4 VOC 21.3 is an MPPT charge controller necessary or even beneficial or will a PWM charge controller suffice? set up area will allow for wire runs of < 15 feet between cells and charge controller, charge controller to batteries using 8AWG multi-strand copper wire, common connections of panels made using screw lug bus terminals. I have full open south side mounting for the panels. we are at 21 degrees plus some minutes and intend to mount to roof that sits at and angle of 40 degrees.
  • BB.BB. Super Moderators Posts: 26,870 admin
    Re: what will it take?

    You should:
    1. Log any shipping damage (electrolyte on sides of batteries/pallet/leaks/etc.)
    2. Measure the resting voltage of each cell/battery and log it (any battery/cell with less than 75% state of charge, call factory).
    3. Inspect the electrolyte level in each cell (exposed plates/over filled, call factory).
    4. Measure Specific Gravity in each cell... If any cells very high or less than 75% state of charge, call factory.
    5. If there is a large spread in SG levels (over approximately 0.015 to 0.030 ore more, call factory)

    Now move them into your installation, get wired up and verify charging parameters/functions.

    Ideally, fully charge battery bank, and measure high/low specific gravity.

    If specific gravity difference is more than 0.015 or so, equalize bank until all cells stop rising in SG (check cells every 30-60 minutes, typically at a maximum of 5% of battery AH capacity). Log temperature and specific gravity for each cell. That is your "100% Charged" state.

    Obviously, if you have AGM/Sealed batteries, you cannot measure specific gravity. And many cells you cannot measure their individual voltages (buried bus bars).

    There have been a couple of reports with batteries having 1.000 sg (pure water:confused:)--So the checks are important.

    You can use the batteries right away--But the 100% charging is handy so you can have something to compare with months/years down the road.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • justsumguyjustsumguy Registered Users Posts: 9
    Re: what will it take?

    back in my automotive mechanic days we would test battery cell to cell charge by putting DVM probes into the electrolyte and note any voltage differences between the cells, any cell that read 10% below any other cell was cause for rejecting the battery. of course this test was done in conjunction testing specific gravity. back in the 70s the batteries we received came from the factory dry so we had on hand containers of electrolyte to fill the cells and than charge the battery.

    on a preventative maintenance schedule how often should SG and cell to cell volt testing be done and are there any seasonal times when this testing should be done more often. also should the batteries be disconnected from the charge and load points for a period of time prior to conducting the above tests?

    let me be counted as one more of the forum users who thinks you guys are the best. your help is much appreciated.
  • BB.BB. Super Moderators Posts: 26,870 admin
    Re: what will it take?

    "Resting Voltage" tests should be after 3 or more hours of no charging/discharging.

    SG tests can, in theory, be done at any time and represent the present state of charge of the cell/battery. Typically your daily/weekly SG measurements would be one cell (pilot cell, change energy few months to a new cell). Check all cells every few months (more or less).

    Note that SG tests can be "fooled" if the battery electrolyte is "stratified" (tall cased batteries with low charging currents/not equalized once in a while). Also, if you add water then measure, you may just pick up the water floating on top.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • justsumguyjustsumguy Registered Users Posts: 9
    Re: what will it take?

    when testing SG I always squeeze cycle the electrolyte five or six times before taking the reading, it goes without saying that the SG meters with larger reading reservoir and bulb provide for better electrolyte mixing.

    so if I have this straight each cell of a twelve volt battery would be checked over a six day period.

    as far as distilled water goes is what they have on the store shelf okay or are there preferred brands/sources?

    I stay up pretty late so I'd be okay with making my own from snow boiled at midnight on a waning moon LOL:D
  • BB.BB. Super Moderators Posts: 26,870 admin
    Re: what will it take?

    No, check the same cell once a day to once a week until you are sure of the health of the bank.

    Change pilot cell every few months.

    Check all cells every month or so for equalization. As needed.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • justsumguyjustsumguy Registered Users Posts: 9
    Re: what will it take?
    BB. wrote: »
    No, check the same cell once a day to once a week until you are sure of the health of the bank.

    Change pilot cell every few months.

    Check all cells every month or so for equalization. As needed.

    -Bill

    thank you for clarifying that. should the cells need water is there a preferred distilled water or will any COTS distilled water work?
  • BB.BB. Super Moderators Posts: 26,870 admin
    Re: what will it take?

    Trojan has a pretty decent battery manual:

    Trojan Battery 12 page Maintenance FAQ (PDF).
    Trojan Battery Maintenance FAQ in español (PDF).

    On page 11 is a whole list of maximum contamination levels for various minerals.

    I don't know what "COTS" distilled water is.

    Distilled, de-ionoized, and even filtered rain water can be used (recommend that rain wash the roof/catch system of dust first, then capture/store).

    Note that checking cells for specific gravity is a bit of a pain (do as often as needed to understand your bank and your loads)... A battery monitor (Victron makes a nice one too) can be used by spouse/kids/guests as a simple guide to current battery state of charge. For example:
    • Battery state of charge >75% -- Everything OK
    • Battery below 75% SOC, start genset next morning if cloudy weather. Turn off genset at 80-90% SOC.
    • Battery below 50% SOC, start genest right away, turn off excess loads. Turn off at 80-90% SOC. If battery remains below 50% SOC, call you for help.
    • Battery approaching 20% SOC--Turn off all loads, call you for help.

    Battery Monitors are not perfect--But they can make day to day battery management much easier and more transparent. And possibly save you a toasted battery bank.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • inetdoginetdog Solar Expert Posts: 3,121 ✭✭✭✭
    Re: what will it take?
    BB. wrote: »
    I don't know what "COTS" distilled water is.

    Commercial Off The Shelf distilled water (e.g. nothing special or ultrapure.)
    SMA SB 3000, old BP panels.
  • nielniel Solar Expert Posts: 10,311 ✭✭✭✭
    Re: what will it take?

    as far as cots goes (i never heard of that either) i had measured the ppm on a local distilled water and it showed 2ppm. btw, true distilled water is 0ppm. now 2ppm is quite low and probably wouldn't hurt anything, but after the adding of this water over time it will cause the ppm to build up in the battery as the contaminants are cumulative. to what extent this small contamination goes towards the batteries demise i am not sure, but one could filter that water with a quality water filter to further reduce the ppm before adding it to the battery.
  • VicVic Solar Expert Posts: 2,815 ✭✭✭✭
    Re: what will it take?

    I look for Distilled Water that states that it is prepared by "Steam-Distillation". And prefer to use a Name Brand. I DO wonder about the purity of the container, and just what might be leaching into the water as it sits, waiting to be used.

    We do collect rain water for all domestic water needs, but would not think of using that as battery water -- batteries are expensive, but buying water is cheap, like me. Opinions on this differ, as well, Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
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