Newbie - just need to power refrigerator during power outage

yakapo7
yakapo7 Registered Users Posts: 27 ✭✭
edited August 2020 in Solar Beginners Corner #1
My setup would need to power the side by side fridge 24/7.  Let me know what I’m missing..

solar panels 320w x2
Trojan t105 x2 (or Duracell gc2 x2)
1750 watt inverter 
Renogy Wanderer 30amp controller

Let’s say the panels give me 200 watts in full sunlight each.  I’m guessing the inverter is inefficient, so that’s why I’m opting for two panels.  

What brand of inverter would you suggest?  
Do I have enough batteries?  Should I consider a different brand? 

Thanks for your time. 
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Comments

  • Photowhit
    Photowhit Solar Expert Posts: 6,002 ✭✭✭✭✭
    Unfortunately it's never simple. I suspect you have the right idea, but you should look at where you are and local available sun hours on average. Put in your type of array mount (fixed normally) and the angle of mount, usually your latitude is the most productive through out the year, but 10-15 degrees steeper than you latitude will give you a more balance sun hours throughout the year.
    You can find them here and do a rough calculation of your available sun. Mostly ignore the rest of the data now as you don't have enough info to understand the variables, at this site;

    https://pvwatts.nrel.gov

    Knowing the energy use of your side by side would be a great place to start on loads. You can look at the energy star rating for most friges made in the last 20 years;

    https://www.energystar.gov/productfinder/product/certified-residential-refrigerators/results

    yakapo7 said:
    solar panels 320w x2
    Likely a good guesstimate on your needs, at least until we see what your fridge uses. For standby/outages you could abuse your batteries a bit and run higher than normal loads, but just a couple cloudy days will make a dent in the batteries life.
    yakapo7 said:
    Trojan t105 x2
    Trojan makes a GREAT battery, might go to an AGM if you aren't good about checking their electrolyte levels from time to time. 2 batteries might be light depending on your fridge and weather. Most fridges will use 1.5 kWh a day 2 - T105's have 12 volts at 225 amp hours or (12x225=) 2700 watts or 2.7 kWhs. It would be marginal after a cloudy day and 2 nights.
    yakapo7 said:
    Renogy Wanderer 30amp controller
    Unfortunately most solar panels over 160 - 200 watts are not designed to charge a 12 volt system with that type of charge controller. You would need an MPPT type charge controller, such as Renogy's Rover 30 amp.yakapo7 said:
    Let’s say the panels give me 200 watts in full sunlight each.  I’m guessing the inverter is inefficient, so that’s why I’m opting for two panels.  
    There are many inefficiencies in a battery based system, Flooded lead acid charging has 15-20% losses, Inverters have 10-15% losses as well as the difference in rated and actual output of solar panels. Generally you can use 50% system losses.
    yakapo7 said:
    What brand of inverter would you suggest?  
    I think Xantrex/Schneider make some affordable 1800/2000 watt 12 volt models that should run most side-by-side fridges. If you happen to have one of the new inverter fridges, you can likely run on a much smaller inverter.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,433 admin
    Welcome to the forum Yakapo7,

    Can you tell us a bit more about your refrigerator? There is usually an "Energy Star" Rating... Looking for how many kWH (kilo-Watt*Hours) per year the fridge uses. Is it a "standard" frost free refrigerator, or is it a new "inverter" or "linear compressor" model?

    The short answer is refrigerators are what take "small solar systems" to "medium sized" solar power systems.

    Is this for a few days/week of outages? Do you have lots of sun, or do you have "dark winters" and long/dark storms? A general solar power system we start with would have enough battery storage for 2 days of operation (no-sun), and 50% maximum discharge (for longer life).

    If your outages are longer (at the end of a long rural road with your power last to be restored--I.e., weeks or month of outsages), then solar power can be interesting--But you may need a genset for backup (depends on how far north you are, do you have marine layer clouds for days/weeks at a time, etc.).

    Standard compressor based refrigerators--Need a fairly large AC inverter to start the compressor (high surge current approaching 1,000 VA) and while the compressor takes ~120 Watts (running 50% of the time), the defrost heater(s) can take upwards of 600 Watts (once or twice per day, for a few 10's of minutes per day).

    I can give you some idea of what you are looking at... A minimum sized system and battery bank. Here are what the numbers look like:
    • Say 500 kWH per year refrigerator
    • 500,000 WH per day / 365 days per year = 1,370 Watt*Hours per day average
    • Battery bank sizing based on loads: 1,370 WH per day * 1/0.85 AC inverter eff * 1/24 volts battery bank * 2 days storage * 1/0.50 max discharge = 269 AH @ 24 volt battery bank
    • Using 200 AH @ 6 volt "Golf Cart" flooded cell batteries: 4x 6 volt batteries in series (24 volts) * 2 parallel strings (400 AH) = 8 GC batteries in 4s x 2p = 24 volt @ 400 AH battery bank
    Then there is sizing the solar array... First sizing based on the size of the battery bank. Need 5% minimum rate of charge (for "emergency use" and/or summer/weekend usage) to 10%-13% for full time off grid:
    • 400 AH * 29.0 volts charging * 1/0.77 solar panel+controller derarings * 0.05 rate of charge = 753 Watt array minimum
    • 400 AH * 29.0 volts charging * 1/0.77 solar panel+controller derarings * 0.10 rate of charge = 1,506 Watt array nominal
    • 400 AH * 29.0 volts charging * 1/0.77 solar panel+controller derarings * 0.13 rate of charge = 1,958 Watt array "typical" cost effective maximum
    And there is sizing the system for loads... Say you are in Los Angeles California. Fixed array facing south:
    http://www.solarelectricityhandbook.com/solar-irradiance.html

    Los Angeles
    Average Solar Insolation figures

    Measured in kWh/m2/day onto a solar panel set at a 56° angle from vertical:
    (For best year-round performance)

    JanFebMarAprMayJun
    4.50
     
    4.82
     
    6.05
     
    6.78
     
    6.83
     
    6.80
     
    JulAugSepOctNovDec
    6.69
     
    6.67
     
    6.40
     
    5.85
     
    5.07
     
    4.41
     

    So, for December at 4.41 hours of sun (long term average) (if you want to cover winter storms and earth quake "weather" outages):
    • 1,370 WH per day * 1/0.52 off grid AC system end to end eff * 1/4.41 hours of sun = 597 Watt array minimum (December "break even" harvest)
    And, the reality is, you should only plan on using 50% to 65% of your predicted harvest for your "base loads' (those loads that have to run 365 Days per year--Like refrigerator. Other loads like computer, water pumping, vacuuming, etc. can be put off until another sunny day):
    • 597 Watt array (December "break even") / 0.65 "base load fudge factor" = 918 Watt array "comfortable" for 12 months a year running a "typical" refrigerator in Los Angeles
    So, the minimum array suggested ~918 Watts. A nice "full time" off grid system array ~1,506 to 1,958 Watt array

    Of course, if your location is less sunny (especially in winter), more array and/or backup genset.

    If you are in California and looking for week or two of outages due to hot weather/fire shutdowns, typically in the summer/early fall--Then upwards of 6.4 hours of sun (Los Angeles) is possible, and a smaller array.

    For an AC inverter... At a minimum 1,200 Watts @ 24 volts, and this one also can charge from the AC input (mains or genset, I think):

    https://www.solar-electric.com/cotek-sc-1200-124-1200-watt-24-volt-inverter-charger.html  ($650)

    There are a lot of different inverters from our host (NAWS aka Solar-Electric.com). And there are probably hundreds (or more) of different ~1,200 to 1,800 Watt 24 VDC input AC inverters out there--With lots of different options (remote, fail over from mains to battery, generator support, remote panels, Internet support, etc.). Depends on how far you want to go...

    And there is the other option... Get a Honda inverter-generator like the eu2200i--quite enough to run in a residential neighborhood, and would use around 2 gallons of gasoline per day:

    https://www.homedepot.com/p/Honda-2-200-Watt-Super-Quiet-Gasoline-Powered-Portable-Inverter-Generator-with-Eco-Throttle-and-Oil-Alert-EU2200i/312975868 ($1,050)

    Currently out of stock (at my local Home Depots)--But you can usually find them around / on the Internet.

    Store 10 gallons of gasoline (with preservative, replace the gasoline once per year, and/or siphon from your car)--And you can go for ~5 days.

    Get an "extended runtime" kit (fuel cap and hose--drop hose in 5 gallon gas can; or get/build a full system with an "outboard type fuel tank"), and you can run for 2+ days without stopping to refuel:

    https://www.amazon.com/s?k=honda+eu2200i+extended+run+kit

    I have run a couple of Honda eu2000i (previous generation) inverter-generators for a few days running 2x refrigerators and 1x freezer, with some extra loads (lights, koi pond aerator, etc.). Worked really nice. I had stored the gensets by running them out of fuel, drained the carburetor float bowel, put a teaspoon of oil down the spark plug hole) and have stored them for 10+ years (without running). When needed, just fueled them up, pulled the starter cord a 1/2 dozen times (to get fuel to the carburetor), and they ran without skipping a beat for hours (for one) and a few days for the other.

    If you are looking for "emergency power" and don't expect failures to be common or long--A genset can be more cost effective (standard Golf Cart Batteries typically last 3-5 years, whether or not you run the system).

    In my case, in the 65 years I have lived in the SF Bay Area, last year (fire shutdowns with PG&E) and this year (dry lightning storms that took out power for 1/2 a day, and we still have lots of fires & smoke today)--These are the first time I really needed gensets for emergency power (power outages that lasted more than a few hours). Off Grid Solar Power systems are not really that great for rare needs (expensive, cannot/hard to move them from place to place if needed, need constant maintenance--Monitoring batteries, replace bank every ~3-5 years, etc.). A genset and 10-20 gallons of gasoline was much cheaper and very portable.

    The modern "suitcase" and "insulated" inverter-generators are pretty quite and light weight. Not like the old 3.5 kWatt noise Briggs and Stratton "noise makers" that would keep everyone in the block awake at night.

    Anyway--Some food for thought. Your comments/questions/corrections to my guesses?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    With the smoke in the air, my solar harvest was way down this morning, I'm really glad it cleared this afternoon and I didn't have to run the generator.

    The smallest "system" I would consider, to reliably run a fridge 90% of the time, would be Four GC-2 batteries wired in series for 24V @200ah (2400watt hours usable)
    And then use 800-1kw of PV to feed it . It just might withstand 1 lightly cloudy day,

    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • yakapo7
    yakapo7 Registered Users Posts: 27 ✭✭
    Thank you kindly for all the informative responses.  I readily admit, this is a bigger task than I had imagined.  Also, I have a small confession.  Even if a gas generator is more practical, this project seems more fun. 🙂

    I checked the fridge energy use, it’s 1.5kwh per day.  I guess that’s more than I expected.  I’m willing to just shut it off for 24 hours on a cloudy day.  Or I could use the deep freeze instead. From what I understand, a deep freeze is more efficient. 

    Assuming I buy a 3,000 watt inverter or larger and I added several extra panels with more than enough power, could I use that extra power in the daytime, even without the proper number of batteries to store it?  Let’s say I have five 300 watt panels giving me 1,000 watts in bright sunlight, but I only have two batteries.  Can I use that extra power for other things in the daytime?   If so, I’d be willing to buy extra panels.  I found a great deal on used panels.

    this may be a silly question but, will one mppt charge controller suffice for all the batteries?  


  • BB.
    BB. Super Moderators, Administrators Posts: 33,433 admin
    edited October 2020 #6
    I know that the solar projects can be fun... But they are a lot of work too (got a good place to mount your solar array? Must be free of any shade/shadows for at least 9am to 3pm--Even a little shadow on a single cell can cut the harvest by 50% or more very easily).

    Mounting solar panels (roof, need to make sure the roof is in good shape and does not leak after install--Ground mounts can be nice, if you have the room) is a lot of work. Wind and snow loading means the frames have to strong enough to withstand something like 30-50 lbs per sq foot). If you have lightning in the area, you have to address that to prevent nearby lightning strikes from taking your system down, and that the wiring does not bring lightning directly into your home.

    Yes, a deep freeze can be more efficient. A full size refrigerator can get down to near 1,000 WH per day (365 kWH per year) if you shop around. There are upright Deep Freezers that have 2-3x thicker insulation than standard fridge (replace/upgrade thermostat to refrigerator temperature range). And some folks have converted chest freezers to chest refrigerators--And get down towards 250 WH per day... Chest freezers can be a cost effective/low energy solution--But to be honest, most spouses do not like them for long term use--Have to keep moving the upper baskets around to find the food needed to make dinner.

    However, that still leaves the high surge current for standard refrigeration compressors--Something like a 1,200 to 1,500 Watt inverter needed--Plus a large enough battery bank to supply the surge.

    A larger inverter does not solve any problems--They create more issues too--A small(er) inverter may take 6-10 Watts just to turn on... A larger/less efficient inverter can take upwards of 20-40 Watts to run, not including loads. A 100 Watt refrigerator and a 40 Watt inverter means >140 Watts from battery bus because of high inverter "tare" losses.

    Also larger inverters mean you really need higher voltage battery banks. Because of lots of reasons, realistically, the maximum inverter for a 12 volt system is around 1,200 to 1,800 Watts max. Larger, and it gets very difficult to carry the 100's of amperes in very thick (expensive) copper cables. A 24 volt system, around 2,400 to 3,600 Watt max suggested--Anything larger, and you should be looking at a 48 VDC battery system.

    Then there are the loads... Smaller loads, smaller battery bank. Larger loads (aka assuming 3,000 Watt inverter), you need a larger battery bank for loads and support starting surge current. Larger battery bank needs more solar panels to properly charge.

    Yes, you could use a larger array with a small(er) battery bank--And during sunny weather, the "extra" power from the solar array would help a small battery bank to run your fridge. Down side is you have to now actively manage your loads--For a few days, probably OK. Long term, the "fun" generally goes away.

    Remember that batteries are really a group of 2 volt cells -- For lead acid batteries (6 volt battery has 3 cells in series, a 12 volt battery has 6 cells in series).

    You can buy, for example, a 12 volt @ 100 AH battery, or a 6 volt @ 200 AH battery. They are about the same size and weight and actually store the same amount of energy:
    • Energy = Voltage * AH capacity
    • 12 volt battery: 12 volts * 100 AH = 1,200 WH of stored energy
    • 6 volt battery: 6 volts * 200 AH = 1,200 WH of stored energy
    Generally, for many reasons, I like to suggest using 6 volt @ 200 AH golf cart batteries for a lower cost/first time battery bank. They are cheap, relatively rugged and easier to maintain (larger battery bank has lots of batteries in series and parallel to make a full battery bank--12 volt batteries generally have more cells and battery caps to check electrolyte levels in, more wiring+batteries for parallel operation, etc.).

    For larger bank, you can even get down to 4 or 2 volt batteries (2 volt is a single cell) with high AH capacity ("GC" size battery = 2 volts @ 600 AH).

    Other issues, large batteries (especially lead acid) are heavy... A "fork lift" size battery can weigh 1,000 to 2,000+ lbs. You need the equipment to move it, and even lift on/off the truck or trailer, smooth ground to use a pallet jack or hand truck to move. Stairs to basement are a pain, etc.

    You asked for a "smaller" system dedicated to run a fridge. Now you asked about a 3,000 Watt AC inverter--Which is a relatively large system--If you plan on running 2-3 kWatt of loads at one time.

    Anything can be done (there are other battery types/chemistry that can do more surge current vs a typical flooded cell lead acid battery bank--Such as AGM and Li Ion type--LiFePO4 is typical for home power systems. But the batteries do cost much more than FLA batteries (flooded cell lead acid deep cycle storage batteries). LiFePO4 batteries are about the closest you can get to a "perfect" battery these days--But there are other issues. Pretty expensive, and generally a Battery Manage System (BMS) is needed to run the batteries safely and get long life out of them... Definitely more reading suggested.

    A single MPPT charge controller with 80 amp output, can manage up to a:
    • 80 Amps * 58 volt charging * 1/0.77 solar panel+charge controller deratings = 6,026 Watt array maximum cost effective
    But that is assuming a 48 volt battery bank. If you were doing a 12 volt bank, then the max array would be:
    • 80 amps * 14.5 volts charging * 1/0.77 panel+charge controller derating = 1,506 Watt array "typical" cost effective maximum
    A 80 amp MPPT controller (high end USA company) costs around $500 to $800 each.

    I really like to do "balanced" system designs... First is conservation (most efficient loads you can find, like a 1 kWH per day or less Refrigerator)--It is almost always cheaper to conserve power than it is to generate the power. Your loads define your battery bank. Your battery bank and loads define your your array size. And you only get an AC inverter that is just large enough to efficiently run your loads.

    Yes, you can design and build "unbalanced" systems. The rules of thumbs above are starting points. To go "outside" the standard guidelines should be reviewed to make sure that is what you really want/need.

    I highly suggest you define/measure you loads--A kill-a-Watt type meter is a very good starting point:

    https://www.amazon.com/s?k=kill+a+watt+meter

    See how much energy you need--Then design the system to support those loads.

    And do paper designs before you purchase any hardware. See which design will best meet your $$$ and energy needs. You have to pick the right parts to play together and buying hardware before you have a full paper design--It can be difficult to get the different parts to play well together. Plus you will learn a lot more about solar power and its hardware during the paper design.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • RCinFLA
    RCinFLA Solar Expert Posts: 1,484 ✭✭✭✭
    You are likely in 2kWH per day range on refrig but get a Kill-A-Watt meter and track refrig use for a while to get a real number. I had a 18 cu ft refrig that averaged 1200 wH/day.  My 'high efficiency' inverter compressor 28 cu ft Samsung is averaging about 2900 wH/day.

    One thing that can sometimes trip you up is defrost cycle.  The duty cycle is low but refrigs can have a few hundred to 1000 watt heater elements for defrosting.  Greater wattage heating element shortens defrost cycle time but has higher peak loading.  The cycle usually occurs on a timer from every 16 to 28 hours so you are never sure when it is going to happen.

    Other thing is startup surge when compressor kicks on.  1500 watt inverter should do the job.

    Beware most folks end up wanting more things powered then original planned when they get system running. First its a few lights, then its TV, then comes microwave oven.
  • yakapo7
    yakapo7 Registered Users Posts: 27 ✭✭
    edited August 2020 #8
    Ok, I’m ready to make the first few purchases.  I’ll upgrade stuff as needed.  Also, if i can’t disable the defrost cycle, I’ll use the deep freeze instead of the side by side. We have a deep freeze with no defrost. 

    industrial 1250 watt inverter.  Tripp lite. 
    2x 12v deep cycle gel batteries (Better than agm?)
    2x 330watt solar panels (possible 3)
    mppt Controller


    Here’s my last question.  Later on, if I add more panels, can I use those extra amps in the daytime (without upgrading battery bank)?
    Edit.  I see that Bill answered this already.  Thanks.  

    The reason I asked is, it might be useful to use other low wattage things in the daytime and I can get more panels really cheap used. 

    Thanks to everybody who helped me put this together.  I’ll post again when it’s all done. 
  • BB.
    BB. Super Moderators, Administrators Posts: 33,433 admin
    Some observations:

    You cannot disable standard frost free defrosters... If you do, within 24 hours, the evaporator coils will start to ice up and block air flow in the fridge/freezer. Frost free NEED the defrost cycle.

    Review the specifications for the Tripplite inverter. Many are MSW (modified sine/square wave) type inverters. Pure/True sine wave (PSW/TSW) inverters are really recommended for refrigeration compressors/induction motors.

    Also check the efficiency of the UPS type inverter... Their "tare losses" (power used turned on/no load) and efficiency at lower wattage (120 Watts for typical fridge).

    Some UPS systems will not start if you do not have a ground bonded AC Neutral on the input (may have to manual start the UPS inverter).

    Instead of 2x 12 volt @ 100 AH batteries in paralllel--I like to suggest 2x 6 volt @ 200 AH in series. You will have the same battery bank capacity (12 volts @ 200 AH)--But the 6 volt batteries are "easier" to maintain (6 cells to check water levels for 6 volt batteries, vs 12 cells for 12 volt batteries). Also, it is easier to check the voltage of each 6 volt battery (see weak/failing 6 volt battery, if you need to Equalize charge the bank, etc.). For 12 volt batteries in parallel, if you have a weak/failing battery, both 12 volt batteries are in parallel, so you can only measure the "combined" 12 volts (usually the voltage of the "good battery").

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • RCinFLA
    RCinFLA Solar Expert Posts: 1,484 ✭✭✭✭
    Disabling the defroster is not worth the effort.  The amount of time you can run without it depends on ambient humidity and how often you open the refrig to let humid air in.  Your refrig will run longer consuming more energy when evaporator coil gets air flow blockage from frost buildup.  Likely not more then a day and half or two before you notice compressor running longer.

    It would be nice if you could manually trigger a defrost cycle so you can plan when the extra power demand happens but that is not so easy especially with more refrig's having microcontrollers that control everything.
  • yakapo7
    yakapo7 Registered Users Posts: 27 ✭✭
    BB. said:


    Review the specifications for the Tripplite inverter. Many are MSW (modified sine/square wave) type inverters. Pure/True sine wave (PSW/TSW) inverters are really recommended for refrigeration compressors/induction motors.

    Also check the efficiency of the UPS type inverter... Their "tare losses" (power used turned on/no load) and efficiency at lower wattage (120 Watts for typical fridge).

    Some UPS systems will not start if you do not have a ground bonded AC Neutral on the input (may have to manual start the UPS inverter).

    Instead of 2x 12 volt @ 100 AH batteries in paralllel--I like to suggest 2x 6 volt @ 200 AH in series. You will have the same battery bank capacity (12 volts @ 200 AH)--But the 6 volt batteries are "easier" to maintain (6 cells to check water levels for 6 volt batteries, vs 12 cells for 12 volt batteries). Also, it is easier to check the voltage of each 6 volt battery (see weak/failing 6 volt battery, if you need to Equalize charge the bank, etc.). For 12 volt batteries in parallel, if you have a weak/failing battery, both 12 volt batteries are in parallel, so you can only measure the "combined" 12 volts (usually the voltage of the "good battery").

    -Bill

    These batteries are zero maintenance gel batteries.  Supposedly they are ideal for solar power.  They are designed for wheelchairs. They can be drained 100% and recharged.  Plus, I’m getting a good deal on them from someone who bought them and never used them. 

    Regarding the inverter.  🙁  just when I thought I had it all figured out, I’ve got to go do more homework.  Well, I’m certainly glad I didn’t just jump into this without asking.  Thanks.




  • BB.
    BB. Super Moderators, Administrators Posts: 33,433 admin
    edited August 2020 #12
    Check the charging current and voltage.

    Many gel batteries have a 5% maximum rate of charge. To high of charging current can damage gel batteries (check specifications, there are a bunch of different brands and specifications).

    For example, if you too a few battery dead with a 5% rate it charge, it would take 30 hours or more to recharge. We only get 6-12 hours of sun per day. Would take days to recharge that battery with solar only.

    Gel batteries are generally not great for solar because of the slow rate of charge. Otherwise, a good battery for UPS use.

    Even regular lead acid batteries with 13% rate of charge, taking the battery much below 75% state of charge, it can still take most of the day to recharge with just solar (2 hours on bulk, 2-6 hours on absorb charge cycle... Deeper discharge, longer absorb cycle).

    Regarding the inverter. They have lots of models. Just a warning to read the specifications (cut off during original posting).

    Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • yakapo7
    yakapo7 Registered Users Posts: 27 ✭✭
    How do people wire up a 12v 1500 watt inverter?  Are they using 2 gauge or bigger wires?  Or are they using some sort of parallel wires?  (As in two or three wires going to the same terminal)

    It seems like the 24v inverters are way more expensive. 
  • BB.
    BB. Super Moderators, Administrators Posts: 33,433 admin
    For heavy current draws.. Heavy cables in parallel is sometimes done (for example, 2x 4 AWG cables are equal to a single 1 AWG cable--For every doubling cables, it is a -3 AWG drop in equivalent wire gauge).

    There are tradeoffs. More expensive inverter vs cheaper/easier wiring. Generally going with a 24 or 48 volt battery bank, you can use much smaller AWG wiring (and support larger AC inverters and loads).

    12 volts is a real pain in the butt when trying to power larger loads/longer distances from battery to loads.

    For smaller inverters, Victron is exactly the same price for 12 or 24 volt inverters of the same size:

    https://www.solar-electric.com/residential/inverters/off-grid-inverters.html?manufacturer=574

    Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • yakapo7
    yakapo7 Registered Users Posts: 27 ✭✭
    edited September 2020 #15
    I’m going to pick up three 300w panels.  Open circuit voltage is 40v.

    https://www.wholesalesolar.com/9434300/heliene/solar-panels/heliene-300-black-mono-solar-panel

    I’ll use an mppt 45 amp controller which can accept max open circuit voltage of 150v, so I’m ok with three panels in series, right? 

    How do I calculate the gauge of wire I need? Let’s say it’s 25’ - 120v and less than 8 amps. 



  • BB.
    BB. Super Moderators, Administrators Posts: 33,433 admin
    Assuming your 45 amp controller is MPPT with 150v Vpanel input rating... (voltage looks good, but you should always confirm that your 3x panels in series in the coldest weather you plan on--That Voc-cold is less than 150 Volts (I think you are OK--Trust but verify).

    The 45 Amp controller:
    • 3 * 300 Watt panels * 0.77 panel+controller deraings * 1/14.5 volts charging = 47.8 Amps maximum current available in cool/clear days near solar noon
    For MPPT controllers, is is "OK" to over panel... And it will be pretty rare if your 45 amp MPPT controller will "clip" its output (typically a handful of times a year, with a handful of hours). So, that is fine on a 12 volt battery bank (cost effective).

    Your panels are rated at ~33.72 volts nominal (STD conditions), and 9.56 amps per panel, and 10.10 amps Isc (short circuit current):
    • 10.10 amps * 1.25 NEC derating for continuous current wiring+breaker+fuses = 12.625 Amps
    Using the NEC chart for wiring, 14 AWG is the minimum wire AWG I would suggest (based on current):

    https://lugsdirect.com/WireCurrentAmpacitiesNEC-Table-301-16.htm

    Then wire AWG based on voltage drop... At Vmp-array~100 volts, don't need to worry about "too low" of array voltage for controller to charge your 12 volt battery bank. So use the 1% to 3% maximum voltage drop we usually design for (does not waste much electricity, does not cost a bunch of $$$ for an oversized copper cable):
    • 3 * 33.72 volts = 101.16 volts Vmp-array nominal
    • 9.72 Amps Imp-array nominal
    • 25 feet wire run one way (this assumes 2x wire run for out and back). Play with voltage drop calculator:'
    https://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=8.286&voltage=101.16&phase=dc&noofconductor=1&distance=25&distanceunit=feet&amperes=9.72&x=47&y=27

    Result

    Voltage drop: 1.23
    Voltage drop percentage: 1.21%
    Voltage at the end: 99.93

    14 AWG wiring seems like a perfect cost effective fit.

    -Bill

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • yakapo7
    yakapo7 Registered Users Posts: 27 ✭✭
    edited September 2020 #17
    I’ll go with a 24v battery bank, I will use 3 x 8 volt batteries instead of 2 x 6 volt. Should be no risk of clipping. 

    coldest it gets here is around 30 degrees.  40 x 3 x 1.23 = 147

    Thanks for all you help sir. 
  • BB.
    BB. Super Moderators, Administrators Posts: 33,433 admin
    Makes your 12 volt battery bus wiring and wiring to the inverter 1/2 as thick (or less) at 24 VDC vs 12 volts.

    Say 1,200 Watt AC inverter and 5 feet of cable at 12 and 24 volts:
    • 1,200 Watts * 1/0.85 AC inverter eff * 1/10.5 volt cutoff = 134.5 amps max current (12 volt)
    • 1,200 Watts * 1/0.85 AC inverter eff * 1/21.0 volt cutoff = 67.22 amps max current (24 volts)
    https://lugsdirect.com/WireCurrentAmpacitiesNEC-Table-301-16.htm

    1/0 vs 6 AWG (approximatly) for 12 vs 24 volt based on current.

    If you have >5 feet of battery to inverter wiring, you are looking at possibly heavier cable to keep voltage drop down (~0.5 volts max for 12 volt vs ~1.0 volt drop for 24 volt system).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • yakapo7
    yakapo7 Registered Users Posts: 27 ✭✭
    edited September 2020 #19
    Fuses, breakers, and grounds...

    Thus far, I’ve only bought three panels. I’m about to buy a victron mppt 100/50 and a victron 1200va inverter.
    Battery bank will be 24v.  Panels will run parallel with three separate cables to the controller.  (That way, I can add three more panels if needed) 

    how many fuses and breakers do I need?  What needs to be grounded and where?  

    Do I need bus bars between the battery and the inverter?  See the image in the next post... 
  • yakapo7
    yakapo7 Registered Users Posts: 27 ✭✭
  • BB.
    BB. Super Moderators, Administrators Posts: 33,433 admin
    3 panels--A question, What Vmp and Imp (and Pmp) are they rated.

    On a 100 volt max input rated MPPT controller, the Vmp-array max is around 70 volts or so (depends on how you get the Vmp of the panels). And Vmp-array around 39 volts minimum for optimal MPPT operation.

    If you have 3 or more panels in parallel, then you need a combiner box with one fuse/breaker per panel (string of panels).

    If you put all panels in series (if you have 3x "12 volt panels"), then you would not need any breakers on the solar input at all. (and if you put 3x more panels in series for 2x parallel strings, still no combiner box+fuses+breakers either).

    Generally, most systems are negative ground--So any electrical boxes/etc. that are metal, should all be run back to the negative bus on the battery bank (chassis ground for charge controller, AC inverter case, etc. too). Also the solar panel frames and metal racking ground should be tied back to the battery negative ground too.

    You can stop here for grounding... But, if you are in a lightning prone area, then you should run a ground rod just outside of the wall of the house or shed. The ground from the array goes down to the ground rod at the base of the array (short, straight run from array to ground rod, looping curves vs "right angle"). Then run a ground wire back to the battery bus (or to the local home ground rod). You don't want to bring the "lightning energy" into the home.

    Then to the battery positive bus. Every wire/cable that leaves the bus should have its own fuse/breaker rated for the maximum current you expect to carry.

    The 50 Amp charge controller has a maximum rating of 50 amps, but if your array is smaller, you can get away with smaller AWG cable.

    Lets say you want 50 Amp rating (may put more panels on later). Then I suggest for chargers (solar, and AC) that you up rate the wiring by 1.25x. Fuses/breakers are rated to blow somewhere around 80% to 100% of the listed current. By increasing the rating for fuse/branch circuit, you will have a more reliable system (battery charging can take 5 or more hours at maximum current--And cause "false trips" for fuses and breakers):
    • 50 amps * 1.25 NEC continuous current derating = 62.5 Amp suggested minimum (nearest even fuse rating).
    Using the NEC table (fairly conservative):

    https://lugsdirect.com/WireCurrentAmpacitiesNEC-Table-301-16.htm

    8 to 6 AWG cable looks OK (see voltage drop calculations below).

    The max current rating for a 1,200 Watt AC inverter:
    • 1,200 Watts * 1/0.85 inverter eff * 1/21.0 battery cutoff = 67 Amps worst case current
    • 1.25 NEC derating * 67 amps = 84 Amp minimum rated breaker/fuse/wiring
    The NEC derating for AC inverters may be a bit on the conservative side--So you may choose to up rate or not (not many folks run their inverters at 100% rated load continuously). 6-4 AWG wiring looks OK (check inverter's maximum AWG connection ability).

    And you also need to worry about voltage drop.

    For a 24 volt battery bank, I would suggest a maximum of 0.1 to 0.2 volt drop from bank to charge conroller:
    • For example: 50 amps @ 5 feet @ 0.1-0.2 volt drop, using a voltage drop calculator:
    https://www.calculator.net/voltage-drop-calculator.html?
    material=copper&wiresize=1.296&voltage=24&phase=dc&noofconductor=1&distance=5&distanceunit=feet&amperes=50&x=45&y=25

    6 AWG cable will give:
    Voltage drop: 0.20
    Voltage drop percentage: 0.82%
    Voltage at the end: 23.8

    And 67 amps for inverter, 1.0 volt max drop, at 5 feet:
    https://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=2.061&voltage=24&phase=dc&noofconductor=1&distance=5&distanceunit=feet&amperes=67&x=46&y=19
    6 AWG:
    Voltage drop: 0.42
    Voltage drop percentage: 1.75%
    Voltage at the end: 23.58

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • yakapo7
    yakapo7 Registered Users Posts: 27 ✭✭
    I bought six 8volt Trojan deep cycle batteries today.  As foolish as it may sound, I thought I could keep them in my home.  I will have to put them in the garage.  The run will be 75-85 feet.  
    Do I need to put the batteries in some sort of insulated box?  The coldest it gets here is about 35F.  My garage might go down to the 40’s.  

    I also ordered a 1500 watt Samlex pure sine wave inverter.  The victron at 1200va was not enough power and the bigger victrons are too expensive.  

    I still have to get a 150v mppt controller.  It will either be victron or Morningstar tristar.  
  • BB.
    BB. Super Moderators, Administrators Posts: 33,433 admin
    Lead Acid batteries do well at colder temperatures (last longer). And if they are not run below 50% or so state of charge, they will take very cold weather without freezing.

    https://www.trojanbattery.com/pdf/TrojanBattery_UsersGuide.pdf
    Freezing Point of Electrolyte
    Specific Gravity Temperature °C °F
    1.280 -68.9 -92.0
    1.265 -57.4 -71.3
    1.250 -52.2 -62.0
    1.200 -26.7 -16.0
    1.150 -15.0 -5.0
    1.100 -7.2 19
    Source: BCI Service Manual © 1995

    Even down to 50% state of charge (SG=1.170), the batteries will not freezer until below 0F.

    Of course, you should keep the batteries charged/floating (or at least unloaded) if "stored" for winter. And cold lead acid batteries do have less apparent capacity:

    https://www.solar-electric.com/learning-center/deep-cycle-battery-faq.html/

    At ~0C/32F, the lead acid batteries will be at ~80% of capacity.

    Some folks in cold climates will keep their batteries in an insulated box to keep them warmer (higher usable capacity). If they are cycling, battery heating is not usually required (if going into a cold cabin, a battery heater may be useful to get batteries >freezing; and of course, the battery box needs to be vented to prevent hydrogen gas buildup during charging).

    -Bill


    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Before you buy, consider getting 4 panels instead of 3.   Wired 2S2P  you get Vmp 80V and a lot more headroom for the cold weather Voc to not kill a 150V controller  with 3 x  Voc 50V  ~ 150Voc  !!!
     And "more power" with solar PV is always good.   Also the MPPT controller will run cooler downconverting from 80V to 28V for charging, than it would 120V to 28V charging.

    Cables, keep inverter - battery cables short, and just run the 120Vac cable the long distance 
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • yakapo7
    yakapo7 Registered Users Posts: 27 ✭✭
    edited September 2020 #25
    mike95490 said:
    Before you buy, consider getting 4 panels instead of 3.   Wired 2S2P  you get Vmp 80V and a lot more headroom for the cold weather Voc to not kill a 150V controller  with 3 x  Voc 50V  ~ 150Voc  !!!
     And "more power" with solar PV is always good.   Also the MPPT controller will run cooler downconverting from 80V to 28V for charging, than it would 120V to 28V charging.

    Cables, keep inverter - battery cables short, and just run the 120Vac cable the long distance 
    I have 40 volt panels.  Do you still think it’s better not to have three in series?  The coldest it gets here is around 35 degrees.  Panels are cheap.  I can get another 300 watt panel for $100 (I know someone with a few extra).  But the wire is expensive and I’d need a higher gauge, right?  It’s about 75’ from the panels to my garage.  However, by going 2s2p, I could get a victron 100v/20a which is half the price of a victron 150/35.  

    Edit...  oh, I can join the two cables from the 2 series before the long run.  I guess, I didn’t understand that part.  What would that look like?  How is it 120Vac?   Would it not be 80v 20a?   Either way, I like your plan better.  For $50 extra cost in wire + $100 for an extra panel, I get 300 more watts.  Plus I save $170 on the controller. 


    I accidentally bought an open box 12v Samlex 1500 watt pure sine inverter. I thought it was 24v.   I can’t return it because I bought it from eBay and I would lose too much in return fees.  I imagine I’ll sell it eventually.

    What I would prefer is a 48v 2000 watt inverter.   Samlex makes a 24v 2000 watt, and a 48v 1500 watt, but no 48v 2,000 watt.  Any suggestions? I’d prefer to buy from a company with a legitimate warranty. I don’t want to wire up a breaker box, so victron is not an option.

  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    edited September 2020 #26
    @yakapo7
    You need to stop to really think things through, want an excellent retailer go to the store of the sponsor of this site, linked above as Store, they can supply all the equipment needed and assist with post sales warranty support, making mistakes is costly as I'm sure you're aware of.

    Building a ballanced system always begins with load demands, followed by the storage needed to support the loads, finally the PV needed to satisfy the battery (storage ) needs. Going off in all directions prior to doing load calculations is a recipe for disaster, in my opinion. Pause rewind and start again, is the best advice I can offer, there are many pitfalls which are far too easy to fall into.

    With all the useful information provided, it really comes down to the fundementals which are all too easy to get wrong, most beginners  overestimate the capabilities of what the system can or will provide, only later to complain why things went wrong, don't fall victim to this as it's common problem. .....Seriously I mean this. Start from the beginning.....the load demands.
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
  • yakapo7
    yakapo7 Registered Users Posts: 27 ✭✭
    edited September 2020 #27
    mcgivor said:
    @yakapo7
    You need to stop to really think things through, want an excellent retailer go to the store of the sponsor of this site, linked above as Store, they can supply all the equipment needed and assist with post sales warranty support, making mistakes is costly as I'm sure you're aware of.

    Building a ballanced system always begins with load demands, followed by the storage needed to support the loads, finally the PV needed to satisfy the battery (storage ) needs. Going off in all directions prior to doing load calculations is a recipe for disaster, in my opinion. Pause rewind and start again, is the best advice I can offer, there are many pitfalls which are far too easy to fall into.

    With all the useful information provided, it really comes down to the fundementals which are all too easy to get wrong, most beginners  overestimate the capabilities of what the system can or will provide, only later to complain why things went wrong, don't fall victim to this as it's common problem. .....Seriously I mean this. Start from the beginning.....the load demands.

    I have 7.68 kWh of batteries.  Max use of 3kwh per day (overestimate).  4 hours of sun in winter.  900 watts of panels, soon to be 1200 watts per recommendation from previous post.   Only critical item is the deep freeze. Everything else can wait for sun.  Even the deep freeze will be ok for a day without power. 

    What am I doing wrong?  

  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    Being the system is for emergency use not full time perhaps it could work if the load calculations are accurate including the inverter self consumption and other losses, I had mistakenly assumed it was for fulltime whole house use, my bad.

    Having the luxury of grid power it would be wise to conduct a test during the worst weather over a number of days to take Murphys law out of the equation, though a generator could supplement any shortcomings should there be any.

     
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    edited September 2020 #29
    Victron makes decent gear, maybe it's in your price point
    https://www.victronenergy.com/inverters/phoenix-inverter-smart

    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • yakapo7
    yakapo7 Registered Users Posts: 27 ✭✭
    edited September 2020 #30
    mike95490 said:
    Victron makes decent gear, maybe it's in your price point
    https://www.victronenergy.com/inverters/phoenix-inverter-smart

    I’ve decided to go ahead and get the victron 24v 3000 watt inverter.  It’s more than I planned on spending, but everyone seems to say they are better quality for a lower price than other high end brands.  

    So my setup will be 

    1200 watt PV 2s2p
    victron 100 50 controller
    Victron 24 3000
    7.68 kWh Trojan battery bank.

    later - 
    Have electrician install transfer switch.

    edit
    the smart ones you linked to are much more affordable.  However they are 230v only.  Victron is supposed to release a 120v version, but no one knows when. 
  • BB.
    BB. Super Moderators, Administrators Posts: 33,433 admin
    Just be aware--More or less the rule of thumb is around 500 Watts per every 100 AH for a FLA @ 24 volt battery bank:
    • 7,680 WH / 24 volt = 320 AH battery bus (@ 24 volts)
    • 320 AH * 500 Watt inverter * 1/100 AH = 1,600 Watts max suggested AC inverter for 320 AH battery bank
    Just rough rules of thumbs--But if you plan on drawing 3,000 Watts from your inverter in the future--It would not be a bad idea to double the AH capacity of your battery bank (3,000 Watt inverter @ 24 volts ~600 AH minimum FLA battery bank).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset