Upgrading to support a Fridge and TV at night.

KalaniKalani Registered Users Posts: 16
For 5 years now I've been good on my 400w 12v system and 2 6v golf cart batteries. Living off-grid and a very simple life in Hawaii, that was more than enough to have a radio, wifi, laptop, lights, and small water pump.

I recently came into a 20k inheritance and am wanting to finally get a reliable car, fix up my 400sqft home, and FINALLY get a fridge and television so I can keep food longer and have cold beer and watch movies on a bigger screen. I haven't had a fridge in over 5 years, and would REALLY love to get a full size one, 16-18 cubic/ft. You have no idea how much fruit/vegetables and pork I lose (I hunt boar) or have to give away.
I know a fridge isn't a big deal to you guys, but it's like a dream appliance to me. Silly thing to dream of I know, but I'm simple - hunt, garden, surf, WWOOF!

I've read what I can read, but sometimes I question what I am reading because things seem to contradict other things.
I was hoping not to spend more than $5k on the system before hitting up Costco for the 201ah 6v golf cart batteries.

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Comments

  • BB.BB. Super Moderators, Administrators Posts: 31,769 admin
    edited June 10 #2
    Kalani, welcome to the forum.

    No problem... We talk about things practically that "meet your needs". I will go through a quick example of a "nominal" design and the Q&A's that needs to be addressed.

    With solar power, you need to find the most efficient appliances/load you can. It is almost always cheaper to conserve vs generate power.

    Look for efficient refrigerator--EnergyStar website is a good place to start:

    https://www.energystar.gov/most-efficient/me-certified-refrigerators/results

    Probably you will get somewhere in the 300 to 400 kWH per year for a full size, simple, refrigerator/freezer with frost free. Things like heated door edges (anti-sweat) and ice makers add energy usage. To figure out Watt*Hours of energy per day--What we use here... Example 350 kWH per year:
    • 350 kWH per year * 1,000 WH per kWH = 350,000 WH per year
    • 350,000 WH per year / 365 days per year = 959 WH per day (hot weather, making ice, fridge uses more power)
    For TV--Look for LED type, and you can find the Energy Star Tag to estimate power usage:

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

    40 Inch LED TV around 35 Watts (guessing):
    • 35 Watts * 5 hours per night = 175 Watt*Hours per day 
    8 amp * 12 volts * 30 minutes per day RV Water pump:
    • 8 amps * 12 volts * 1/2 hour per day = 48 WH per day water pump
    You know that 400 Watts of solar panels (?) runs the rest of your power... Looking at random city in Hawaii:
    http://www.solarelectricityhandbook.com/solar-irradiance.html

    Kane'ohe
    Average Solar Insolation figures

    Measured in kWh/m2/day onto a solar panel set at a 69° angle from vertical / 21 degrees from Horizontal:
    (For best year-round performance)

    JanFebMarAprMayJun
    4.99
     
    5.85
     
    6.24
     
    6.50
     
    6.43
     
    7.37
     
    JulAugSepOctNovDec
    6.53
     
    6.63
     
    6.60
     
    6.11
     
    5.25
     
    4.84
     

    You would get around 4.84 Hours of sun minimum:
    • 400 Watts * 0.52 off grid AC Solar efficiency * 4.84 hours of sun (December daily average) = 1,007 WH per day
    Suggest "plan" on having 50-65% of "predicted power" for base loads (like refrigerator, some LED lights)... You don't want to unplug fridge during a couple days of bad weather--Unlike other loads (radio, TV, vacuuming, etc.)... Although, you could use a backup genset (your choice--Invest in "extra" solar panels, or genset+backup fuel+fuel stabilizer).

    959 WH per day Fridge
    175 WH per day TV
    300 WH per day laptop usage (good size laptop, work from home, etc.)
    150 WH per day LED lighting
    48 WH per day Water pump
    ====================================
    1,632 WH per day (pure guess--More of example of process--You need to pick your energy needs for your life)

    You can get a Kill-a-Watt meter (120 VAC power meter), and there are DC power meters too (Amazon, etc.) and you can better estimate/measure your present loads)...

    I will suggest that 3,300 WH per day (or 100 WH per month) is a good starting point for a "near normal", highly conserving, energy usage (LED lights, fridge, water, washer, smaller laptop, tv, radio, cell phone charger, etc.)...

    Sizing the system:

    Battery bank--A nice system (lead acid--cost effective, good "starter bank"--Lithium Ion LiFePO4 batteries are very nice, but very expensive if you make any mistakes). Enough storage for 2 days of "no sun" and 50% maximum discharge (for longer battery life) is a good start:
    • 3,300 WH per day * 1/0.85 AC inverter eff * 2 days storage * 1/0.50 max planned discharge * 1/24 volt battery bank = 647 AH @ 24 volts
    • 6 volt @ 220 AH "golf cart batteries; 4 x batteries in series (24 volts) * 3 parallel strings (220 AH) = 12 batteries for 24 volt @ 660 AH battery bank
    That is a "reasonable" bank if you want to start with Golf Cart type flooded cell batteries... Good for 3-5 years or so (warm/hot Hawaii weather can age batteries faster vs 6 months in the Canadian cold). Better batteries will usually last longer and you can get different larger AH rated batteries (later discussion).

    To figure out how much solar panels... You have two calculations... First is 5%-13%+ rate of charge... For full time off grid 10%-13%+ is recommended (up to ~20% or so max for FLA batteries).
    • 660 AH * 29 volts charging * 1/0.77 panel+Controller deratings * 0.10 rate of charge = 2,486 Watt array "nominal" full time off grid
    • 660 AH * 29 volts charging * 1/0.77 panel+Controller deratings * 0.13 rate of charge = 3,231 Watt array "typical cost effective" maximum array
    If you are trying for full time off grid and little to no genset use, use December daily Hours of Sun:
    • 3,300 WH per day * 1/0.52 off grid AC system eff * 1/4.84 Hours of Sun per day (December) = 1,311 Watt Array "December break even" average...
    While you could probably get away with a 1,311 Watt array--If you want extra power for bad weather, other loads (adding a Washing Machine, perhaps an Induction cooker, Insta-Pot)--You could certainly justify ~2,486 Watt array--And probably not need a genset and reduce Propane usage (solar hot water?).

    I would suggest an AC inverter (pure/true Sine Wave) in the 1,800 to 3,300 Watt range with a 24 volt @ 660 AH FLA battery bank to run the fridge and possible other loads (washer, induction hot plate, etc.)... You don't want to "oversize" the AC inverter--Larger inverters "waste" more energy...

    MPPT type solar charge controller... If you choose a 2,486 Watt array, the minimum current rating I would suggest is:
    • 2,486 Watt array * 1/29.0 volts charging * 0.77 panel+controller deratings = 60 Amp minimum MPPT rated solar charge controller
    Note the math... I used numbers so you can follow me. In solar anything within +/-10% is "close enough" for solar work (2,486 Watt array +/- 248.6 Watts is about the same).

    The above needs to work for you. And is just a sample of the math and what would be needed hardware wise for a pretty respectable off grid solar power system.

    The suggestion is to "oversize" the solar array if $$$ permit. It will keep your battery bank "happy" during dark days, or when you have some friends over.

    Please feel free to ask questions... Start of a conversation, not the end.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • KalaniKalani Registered Users Posts: 16
    I'll always be limited to what is available on the island, but Lowe's and HD both show a few Energy Star fridges under 400Kwh.
    Panels sell at Mattos in Hilo for about $1 per watt I think, maybe a little more (price of paradise). Anything else I can order online.
    And woah, is that more batteries than I expected! But I REALLY want a fridge man, so it's a price to pay I guess.
    Would there be any advantage for me to go up to 48v on something like this?
  • BB.BB. Super Moderators, Administrators Posts: 31,769 admin
    For this size system, 24 volts would be the minimum I would suggest. 48 volts would be nice--But you need to make sure you find an AC inverter in the size (wattage) and with the options you want.

    Batteries--There are many different options out there... This is a "mid size" system and about the largest I would suggest using "Golf Cart" batteries with.

    You can look at your local battery supplier and see what they have available... For example, there are 2 volt cells that have large AH ratings... A medium priced Lead Acid bank could use 6 volt @ 703 AH -- 4x in series (4 batteries in total, each battery weighs 315 lbs each):

    https://www.solar-electric.com/tr673am6vode.html

    Again, not saying this is "for you"... Just the mix and match game you can play. Depends on how much room you have, can you move 300 lbs batteries, etc... 

    LiFePO4 batteries are getting pretty nice--But they do have their own issues (very expensive, Battery Management System suggested as "near mandatory", suggest that LiFePO4 batteries be "outside" in their own  building/shed)--Li Ion you could probably get away with 1/2 the AH rating and a smaller array...

    Anyway... The above is just a suggested starting point. If you wan to try "smaller", you can look at a 2,000 WH per day system (about 1/3rd smaller). And run closer to the minimum suggested array. You generally have lots of sun in Hawaii--May need a small genset (like a Honda eu2200i) to run your refrigerator during stormy weather a few days a year on a 2-3 gallons of gasoline per day.

    You could even start with a smaller battery bank (1/2 the AH rating)--Again with lots of sun, they will (on average) be pretty well charged.

    The suggested system was just a stick in the sand for discussion... Reliable off grid power for refrigeration/freezer is what take a system from "small" to "midsize". Refrigerators, desktop computers, and such take surprising amounts of energy per day... The "larger" system can probably even run a small microwave for you pretty nicely...

    These are all questions about how you want to proceed. But anything more than 1,000 WH per day and needing power 24x7 (no interruptions due to weather, etc.)... You end up with what looks to be an "over-sized" system. But that is the nature of providing reliable power 24x7. You just cannot shut power down to the fridge/freezer for a few days and keep the food safe/cold.

    A cheaper genset can work pretty nicely too for backup--The standard non-inverter generators are fairly noisy--So that is another thing to think about (neighbors, your own home, etc.).

    I don't want to "use up" your inheritance on solar--Some folks do pretty nicely looking for used panels, less expensive controllers and inverters, even used batteries (such as used forklift batteries)--But these are all things you are signing up for--More maintenance issues, more time monitoring system, etc...

    Hopefully, some others here can give you better ideas of setting up a fridge/freezer in the tropics--And what tradeoffs they made for a reliable/less expensive system.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • 706jim706jim Solar Expert Posts: 429 ✭✭✭✭
    You can just look at my signature for a working system configuration. Get at least 2000 watts of panels and 12 GC's and you will be fine.
    Island cottage solar system with 2400 watts of panels, 1kw facing southeast 1kw facing southwest 400watt ancient Arco's facing south.Trace DR1524 MSW inverter, Outback Flexmax 80 MPPT charge controller 8 Trojan L16's. Insignia 11.5 cubic foot electric fridge. My 28th year.
  • KalaniKalani Registered Users Posts: 16
    I spent some time last night thinking about this.
    You mentioned a washer, I had never thought of that. It would be nice to not have to clean clothes by hand anymore.
    When I get back to the island I'll definitely have to look and see how much all of this costs there. I know the flooded batteries cost $100 each at Costco, and the panels are about $1 a watt. I'm so excited about this that it's funny.

  • BB.BB. Super Moderators, Administrators Posts: 31,769 admin
    There are some smaller "portable" or "mini" clothes washers out there (many have two sections, one for wash, a second for spin dry):

    https://www.amazon.com/Best-Sellers-Appliances-Portable-Clothes-Washing-Machines/zgbs/appliances/9709422011

    Again--You are looking for low power appliances for solar.

    Another hint... Don't buy any hardware until you have done a few (at least) full paper designs. There are lots of issues of "matching" the right panels to the right solar charge controller to the right battery bank to the right AC inverter...

    Many people get ahead of themselves and buy a mix of solar panels that don't play with together with the solar charger, etc...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • KalaniKalani Registered Users Posts: 16
    I've been trying to learn more about this so I'm not just going in blind.
    One question - What is the maximum size of a 24v system? Like, how many panels?
    I'm just curious is all.
  • BB.BB. Super Moderators, Administrators Posts: 31,769 admin
    Most "large" residential solar charge controllers max out around 80+ amps of charging current... If you are looking for 10% rate of charge (really the minimum for deep cycle flooded cell lead acid batteries)--That means 10% of 800 AH bank = 80 amp charging current.

    So, I suggest if the bank is over ~800 AH, you should step up to the next size (12 to 24, 24 to 48, etc.)... Note--For the most part, residential solar systems are limited to 48 volts maximum for regulatory/safety reasons (from what I see).

    There are other reasons too... The size of copper wiring for the DC side, and keeping lengths short to reduce voltage drop are other big issue...

    Just for show and tell--Lets say you get a 2,400 Watt AC inverter (I suggest 1,800 Watt inverter is "max" for a 12 volt battery system--FYI)...

    The current draw for 2,400 Watts at 12 volts vs 24 volt bank:
    • 2,400 Watts * 1/0.85 AC inverter eff * 1/10.5 volts cutoff for 12 volt bank = 269 Amperes of current
    • 2,400 Watts * 1/0.85 AC inverter eff * 1/21.0 volts cutoff for 24 volt bank = 134 Amperes of current
    Or about 1/2 the current. Looking at a (simplified) NEC table for cable size vs current:

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

    for 268 Amps a 4/0 or 250 kcmill AWG cable with 90C rated insulation is about the minimum cable diameter:

    https://www.engineersedge.com/copper_wire.htm

    4/0 AWG is  about 0.46" in diameter (copper conductor)... Expensive, stiff, need right parts and equipment to terminate ends...

    134 Amps is around 1 or 1/0 AWG cable with 90C insulation.

    So, just based on current, the 48 volt identical inverter is 1/2 the current so 1/2 the cable costs (copper).

    There is another issue too... That is voltage drop. If you have too much drop, the inverter will shut down before the battery is "empty"...

    For 12 volt system, suggest 0.5 volt max voltage drop for wiring from battery bank to inverter DC input. Say you need 6 foot of cables--Using a simple voltage drop calculator.

    6 feet copper cable (one way run for this calculator)
    0.5 volt drop for 12 volt bus (i.e., 11.5 volts is roughly 50% battery capacity under load to 11.0 volts (PVC conduit, PF=1.0... And most inverters can surge at least 2x power rating for starting surge--which takes us down to 10.5 volts or inverter cutoff--Note inverter cutoff is to protect the inverter, not protect the battery bank from over discharging).

    https://www.calculator.net/voltage-drop-calculator.html?necmaterial=copper&necwiresize=8&necconduit=pvc&necpf=1&material=copper&wiresize=0.4066&resistance=1.2&resistanceunit=okm&voltage=12&phase=ac&noofconductor=1&distance=6&distanceunit=feet&amperes=269&x=62&y=16&ctype=nec

    Result for 1 AWG cable @ 12 volts & 269 Amps

    Voltage drop: 0.48
    Voltage drop percentage: 4.02%
    Voltage at the end: 11.52

    https://www.calculator.net/voltage-drop-calculator.html?necmaterial=copper&necwiresize=4&necconduit=pvc&necpf=1&material=copper&wiresize=0.4066&resistance=1.2&resistanceunit=okm&voltage=24&phase=ac&noofconductor=1&distance=6&distanceunit=feet&amperes=134&x=82&y=19&ctype=nec

    Result for 6 AWG cable @ 24 volts & 134 Amps

    Voltage drop: 0.79
    Voltage drop percentage: 3.29%
    Voltage at the end: 23.21

    Note, in this case, the maximum current rating is the "limiting factor" for AWG calculators (cable getting too hot).

    In other cases, if for example you had 12 feet or more cable run, then you may need heavier cable because of excessive voltage drop...

    Notice because of 1/2 the current and 2x more voltage drop for 48 vs 24 volt system... The wire gauge (because of voltage drop) is about 1/4 the size... Just an example of why we send higher power circuit energy at higher voltages... We can use ~5-6 AWG gauge smaller diameter wire at 2x higher voltage.

    Also note, there are similar calculations for wire from Charge Controller to Battery bank maximum voltage drop. In this case, we want the charge controller to have "accurate" voltage measurements of the battery voltage. This usually helps get the battery bank charged as fast as possible (i.e., want to know if battery is at 14.75 or 14.70 volts for 12 volt bus).

    The typical max voltage drop for charging circuit is:
    •  12 volt: max 0.05 to 0.10 volt drop charging
    • 24 volt: max 0.10 to 0.20 volt drop charging
    • 48 volt: max 0.20 to 0.40 volt drop charging
    It is the "little things" like this that are some of the reasons you want to do paper designs first--And get all of the details "right" before you buy equipment/wiring/etc. and put everything together. And why we start with some "simple" rules of thumbs when starting a system design... It makes getting "close" pretty quick and easy.

    Some other interesting factoids... Jim's system above--1/2 of his array is facing South East, the other 1/2 is facing South West... This is really helpful for Lead Acid battery banks... They need "time on charge" to fully recharge... A "virtural tracking array" (split like this) harvests the sun over more of the sky... There are "physical trackers" which many people still use... One or two electric actuators and some simple tracking hardware can increase harvest too. It is a play between more $$$ on panels (1/2 and 1/2) vs fewer panels but a more complex/expensive tracking system. Both work well.

    I used the NEC based wiring ampacity chart above... The real NEC (national electric code) handbook has a not more information--Not bad to have if you are going into details.

    The NEC ampacity ratings are fairly conservative... There are Marine wire gauge vs current ratings which are less conservative--But I suggest sticking with NEC.

    Another derating... The NEC assumes random current (toaster for 5 minutes, oven for 1/2 hour, etc.)... For battery charging, there is an NEC derating for continuous current flow... Gym lights (dozen lights, on 12 hours a day) and battery charging (charging at full rated current for 5+ hours after heavy over night use, or after a day or two of stormy weather).

    For example, the 60 Amp charge controller, I would suggest the NEC derating here. It is 1.25x "larger" circuit, or only 0.8x of rated capacity... The wiring gets hot, and circuit breakers are designed to "not trip" at 80% of rated capacity, and will trip at >100% of rated capacity... To prevent false trips on charging:
    • 60 amp charge controller * 1.25 NEC continuous current derating = 75 amps -- Round up to 80 Amp wiring and breaker ratings
    The the first time through the design cycle--Yea, it will seem like a pain. That is why suggest that we take this in steps (from general back of the envelope sizing, to equipment choice, to actual interconnects)... Do the back of the envelop first--To design a system that should meet your needs--And you can roughly cost major components (panels, racking, charge controller, inverter, battery bank) and confirm it is in your price range... Then accept/modify... Finally the details on paper designs.

    Also--Remember that batteries (FLA in Hawaii) have a 3-5 year "useful life" (for golf cart/inexpensive batteries). And electronics typically last about 10+ years maximum.

    You will need to save money in your bank account for future maintenance, and when the occasional "oh heck" stuff happens (friends stay at your place and run the battery bank "Dead"--Which usually means a new battery bank).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BB.BB. Super Moderators, Administrators Posts: 31,769 admin
    It is best to estimate/measure your loads first... And figure out the back of the envelope hardware needs (pricing, availability).

    It is like picking a vehicle... Motorcycles, cars, light pickups, vans, Semi-Trucks all have their uses... But need to get in the "class" of hardware/solar power system you need... You are moving from "motorcycle" to "light pickup" (again, quick rules of thumbs). 10 amp solar charge controller vs 80 amp charge controllers--Big difference in capabilities, options, and configurations (and costs).

    One other issue... It is (usually) pretty difficult to "up size" (or even "down size") a solar power system by a factor of 2 or more... A 3,300 WH per day system can be upped to 5,000 or 6,000 WH per day maybe...

    If you "know" that you will be at 3,300 WH per day for the "life" of your system (5 years for battery bank, 10+ years for solar chargers/AC inverters/etc.) then 24 volts will be fine...

    If for some reason you think you will go "larger" in the future, starting with a 48 volt system--Expansion will be easier in the future...

    Solar panels and solar charge controllers--They are pretty re-configurable... An 80 Amp solar charger will support a 12/24/48 volt battery bank very nicely... And each step up in bank voltage supports a larger array:
    • 80 amps * 14.5 volts charging * 1/0.77 panel+charger deratings = 1,506 Watts "max suggested cost effective" array @ 24 volt bank
    • 80 amps * 29.0 volts charging * 1/0.77 panel+charger deratings = 3,013 Watts "max suggested cost effective" array @ 24 volt bank
    • 80 amps * 58.0 volts charging * 1/0.77 panel+charger deratings = 6,024 Watts "max suggested cost effective" array @ 48 volt bank
    Note, this is the same 80 amp MPPT solar charge controller configure to 12/24/48 volt battery banks... Higher bank voltage, larger array supported with same hardware...

    But for AC inverters--They are designed to work at one DC input voltage--12 or 24 or 48 volts... If you jump from 24 to 48 volts, you would need a new inverter...

    However, say you start at 48 volts with a "small" inverter (say 2,400 Watts)... You could add to the solar array and more batteries... keep the "small" 48 volt inverter and add a second inverter (or second larger inverter)--So keep your original "smaller" AC inverter investment.

    Note that solar panels have been "evolving"--Sometimes it can be difficult to find "matching" panels 2-3 years down the road (used to be 140 Watt panels where "big panels"--now we have >300 Watt panels, the many of the other "mid sized" panels are out of production).

    It is difficult to "future proof" a solar power system... It is the cost of being your own utility (more equipment, your money).

    But if you are thinking of going bigger later... Two options... Look hard at 48 VDC battery bus and AC inverter... Or what many of done is give the smaller system(s) away to friends (or sell, if you can--Craig's List many times does not let people "sell batteries")....

    Full of grid solar--Make sure you do not empty your bank account... You need emergency money for living and maintaining your system.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • KalaniKalani Registered Users Posts: 16
    So that's why I keep seeing people say, "I wish I had started with a 48v to begin with". I was wondering how it all worked out, just couldn't figure it out.
    For me though, I don't think I'll ever have the loads those people will. Standard fridge, washer, tv, internet, lights, fan, water pump. Only thing I could think of in the future would be a small chest freezer but that's just me dreaming now that the bug is in my ear.
    I have a 3000W Honda generator, used it before I got the solar. Tossing that into the mix I think I will be a happy camper on a 24v system.
  • BB.BB. Super Moderators, Administrators Posts: 31,769 admin
    Adding a freezer... Roughly that is adding something like 1,000 WH per day. Maybe design your solar/battery side for 4,000 WH per day, and a 2,400 Watt minimum AC inverter--And you will be OK at 24 volts:
    • 4,000 WH per day * 1/0.85 inverter eff * 1/24 volt battery bus * 2 days storage * 1/0.50 max discharge = 784 AH @ 24 volt battery bank
    Still within the "rule of thumb" design... So should be OK. You could always add more panels and batteries later--If needed.

    You need to really total up your loads... If you want 24x7 internet with a standard cable model--You could be looking at another 400 WH per day... Add a fan, another 200 Watts * 8 hours = 1,600 WH per day (if you get a cheap 120 VAC box fan)...

    This "little additions" can really add up quickly. You are (I would guess) in a really sunny climate (on average)--You don't want shading of the solar array (north side of mountain, tall trees, nearby buildings, or even overheat wires/ropes/etc.). Almost any shading of direct sun can "kill" the output of a solar panel/array (like 50% if shaded).

    One reason to stay with 24 volts--You can get reasonably priced RV/Marine fresh water pumps and let those run on 24 (or 12) volts...

    https://www.solar-electric.com/aquatec-550-series-m378-24-volt-booster-pumps.html

    They will not last as long as a 120 VAC pump... But they are less expensive.

    Once you get to a larger system (like the 3,300+ WH  per day system)--You probably will be leaving the AC inverter running 24 hours per day--So a 110 VAC pump is certainly something to think about (no brushes as in most low cost DC pump motors):

    https://www.solar-electric.com/aquatec-550-series-m528-115-volt-booster-pump.html

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • PhotowhitPhotowhit Solar Expert Posts: 5,590 ✭✭✭✭✭
    So I live with a large 24 volt system, 4000 watt array (I have another 1600 up but not connected until I replace the battery in the next couple years.) I use a forklift battery for my current large system not sure they can be had reasonably there and you likely wouldn't need as large a system unless you wanted air conditioning.

    I have had a smaller system, that I used for 4 years with just 4 golf cart batteries, and I ran a counter height fridge on when I wasn't trying to run an air conditioner during the summer. I get less sunlight than you do, but outside of summer the ambient temperature is also lower.

    The cabin system was 1600 watts of array, 4 golf cart batteries (could support 8) and a 1800 watt pure sine inverter. This worked for me and the fridge likely drew near what the current energy star apartment size fridges you've seen use. If your typical stormy/overcast day has some bright light, you could likely get by with a somewhat smaller system. I would encourage you to use no more than 2 strings of golf cart batteries, and if you wanted to use 8 golf cart batteries, consider going ahead and doing a 48 volt system.

    FWIW - the current Danby fridge a similar model currently uses 331 kWhs a day. I think mine was 3.8 cu ft and this one is 4.7.

    Cabin system with original 1000 watts of array, circa 2004/5;
    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.
  • KalaniKalani Registered Users Posts: 16
    Wow, you guys really do have all the answers!
    I honestly thought that being able to run all that stuff was going to be out of my reach, pretty much forever. When I'd talk story with people at the beach in Hilo or Kona who had solar, their systems were like $20k. But they also needed Air Conditioning
    Fortunately for me I'm at a higher elevation, rarely reaches higher than 80 up here, usually in the mid-to-high 70s with nice cool nights... and the awesome trade winds.
    I don't think I've ever seen an electric forklift on the island, even at the big box stores they are propane. Even if they existed here, too many locals with families working in those places would have digs on those - just the way it is here.

    Golf Cart batteries are always in stock at Costco, usually at $99 each, and I've seen them on sale for $70 each. Seems to be what most people use out in the country here.

    I've got time. I'm on the mainland for another 6 weeks. And when I get back I'll have to do a bit of work-trade to do for the guy looking after my place while I'm gone.

    Who knows! I get real power at my place and my girlfriend might want to stay over more often! :)
  • KalaniKalani Registered Users Posts: 16
    Photowhit said:
    I would encourage you to use no more than 2 strings of golf cart batteries, and if you wanted to use 8 golf cart batteries, consider going ahead and doing a 48 volt system.

    Out of curiosity, why is that?
    Do more strings cause more problems?

  • PhotowhitPhotowhit Solar Expert Posts: 5,590 ✭✭✭✭✭
    Kalani said:
    Photowhit said:
    I would encourage you to use no more than 2 strings of golf cart batteries, and if you wanted to use 8 golf cart batteries, consider going ahead and doing a 48 volt system.

    Out of curiosity, why is that?
    Do more strings cause more problems?

    Yes, in general the more strings you have the more difficult it becomes for them to share the load and charging. What's really hard to explain is that it's a slow damage, so everything will appear to work right but the uneven distribution wears on one string and then the other is brought down to it's level.

    You can read more about how to make the best wiring to maintain as even a resistance as possible here;

    SmartGauge Electronics - Interconnecting multiple batteries to form one larger bank


    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: 31,769 admin
    Another issues for Flooded Cell Lead Acid batteries is the number of caps to remove to check electrolyte levels and measure specific gravity...

    24 volt system with 1x string of large batteries = 12 cells to check
    24 volt system with 2x string of mid size batteries = 24 cells to check
    24 volt system with 3x string of mid size batteries = 36 cells to check
    24 volt system with 4x string of smaller batteries = 48 cells to check

    From working with parallel computer power cables (lots of 5 volt and 3.3 volt cables from board to board, etc...). Personally, I just did not see the multiple parallel cables and connectors as very reliable...

    I had (very expensive) test gear that had something like 5 parallel cables/connectors for +5 and zero volts... And one at a time a cable connection would turn brown then blacken, and another would start--Sort of "unzipping".

    One would think it was a "bad/dirty/loose" connection that was causing problems... But it was actually the "best" connections that failed first...

    Why? Math! (again).

    One of the equations we use is V=I*R or in this case I=V/R... If you have x parallel connections, and one has a better connection and/or a bit shorter cable--R is smaller I for that connection/cable is higher (I=V/R --- Smaller R, higher I).

    Another equation is Power=I^2 * R... Classic formula for a resistor or heating element... Notice that I is "squared"... In this equation, if you get 2x higher current (I), you get 4x more heating (I^2)... So the "better connections" tend to get hot and overheat first--Even though the have a bit lower lower resistance.

    That is my story--And I am sticking with it....

    I personally try to suggest that 2 or 3 parallel strings is a good max limit... More strings, more cells to water, more connections to make, and you should have a fuse/breaker per string to protect against short circuits (such as a wrench falling on the battery bank). When you have a bunch of parallel batteries and one connection goes "open" or one cell goes "open"--It is really hard to see with simple voltage monitoring.

    The bank with 4 parallel strings only loses 1/4 capacity... So in normal operation you may not see a "weak current path"... With one string, an open cell/connection, things stop right away.

    Also, it seems that having more cells in a bank--There are simply more things that can go wrong--So reliability may be an issue.

    There others that like 2x parallel strings of batteries--Especially for remote cabins/locations. If a cell/battery fails in one string, they can run the other string (with reduced loads) until they can replace the bad cell/battery (or whole bank, if near end of life anyway.

    The founder of the forum (started long before I came here) said that in his experience that he was fine with multiple parallel strings of batteries--They lasted fine and where not a big issue to manage (from his experience selling batteries).

    So, you can argue the question from both sides... 

    Then you have Tesla with 100's to 1,000+ 18650 cells (or larger) in their packs. Loss of one string--Not a big issue. Also no "water levels" to check with sealed Li Ion batteries (lots of complex battery monitoring and safety circuits/engineering going on though).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • KalaniKalani Registered Users Posts: 16
    While I'm just asking questions out of the blue...
    What are your guys' opinions on those personal wind turbines?
  • BB.BB. Super Moderators, Administrators Posts: 31,769 admin
    edited June 11 #19
    Me... I think "small wind" is not very helpful--And can be expensive if done right... So--Starting from there:

    I suggest that you get your battery+solar system working well--Look at a gasoline or other fuel backup genset (if needed). And finally, if you still want to try it--Wind.

    Wind turbines themselves, are relatively inexpensive. The cost is (typically) in the concrete base and tower--As you need to be, at least 30' high, and at least 10' over any up wind obstructions. If you want to really get good wind, 90+ foot tall tower.

    Then there is the cable, lightning protection (if an issue in your area), charge controller/dump loads, and maintenance (take the turbine down once a year for inspection/lubrication/etc...

    "Good" turbines have several methods to shut down in high winds... Furling (turning away from wind), mechanical brake, electrical break, feathering blades, etc...

    Many of the inexpensive HAWT (horizontal axis wind turbine) units seem to have mixed results on how well they work in wind... Pretty much, you need more that 12 MPH wind to get any useful energy. And most peak out around 25 MPH or so. To be useful, the area where the turbine is mounted needs to be "miserably" windy (trees are "flagging" from prevailing winds, light lawn change blows around, etc.).
    .
    And don't even bother with Vertical Axis Wind Turbines (VAWT). They are outright scams (in my humble opinion). Your frequently seen them mounted on buildings/roofs/as "green art works", etc.

    This is actually a device that a Do It Yourself build is probably better than 99% of the off the shelf units out there. Place turbine away from home/occupied areas (turbines are usually noisy when wind blows; blades and entire nacelles have been known to fall off, don't mount to building--Noise into framework, and flexing hard on buildings).

    This is a post from ~12 years ago with links:

    https://forum.solar-electric.com/discussion/comment/77299#Comment_77299

    Again... There have been folks that like their turbines... But I would suggest that you look at any local installations, and see if you can get daily/monthly harvest numbers over at least a year's operation (Watt*Hours per month at least).

    My 2 cents, add more solar panels, and a backup genset (propane, diesel, gasoline, etc.--Propane stores well. Diesel and gasoline need additives and should be recycled every year--Diesel has issues with water--Algae can grow at the water/diesel interface).

    -Bill "not wind" B.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • KalaniKalani Registered Users Posts: 16
    Thanks again Bill "not wind" B. :smiley:
    I can see the Pakini Nui Wind Farm from my home. Was showing family some pics on my phone of my coastline view and it made me wonder... I'm always wondering things.

    Considering that I already have a good reliable Honda generator, there's no need to not plan on using it for additional power if needed. I've noticed some inverters also act as chargers from generators, most don't. Looks like the more "professional" ones do though.
    Right now just enjoying looking through all this stuff and daydreaming. I saw those Outback FP1 centers - they have those at Mattos in Hilo too! Wonder if they have chargers built in.
    Yup, just reading, learning, and dreaming a bit. You have no idea how big of a thing this is to me. Never thought I'd ever have "real" power at my place.
  • 706jim706jim Solar Expert Posts: 429 ✭✭✭✭
    Wind = a great idea that isn't. Vibration, imbalance, worn out bearings, out of balance blades, noise, tower height and dismal power output in anything short of a gale.

    Did I mention noisy?
    Island cottage solar system with 2400 watts of panels, 1kw facing southeast 1kw facing southwest 400watt ancient Arco's facing south.Trace DR1524 MSW inverter, Outback Flexmax 80 MPPT charge controller 8 Trojan L16's. Insignia 11.5 cubic foot electric fridge. My 28th year.
  • KalaniKalani Registered Users Posts: 16
    706jim said:
    Wind = a great idea that isn't. Vibration, imbalance, worn out bearings, out of balance blades, noise, tower height and dismal power output in anything short of a gale.

    Did I mention noisy?
    These are exactly the things I'm reading about it too.
    Good to know there are forums like this to help people like me.
    Really am appreciative to you guys.
  • BB.BB. Super Moderators, Administrators Posts: 31,769 admin
    There are lots of different combinations of hardware out there these days... Our host (Northern Arizona Wind & Sun) stands by their products... So, if you want to see what "good hardware" looks like (and NAWS has good pricing with engineering support), I suggest you start there/here (I am purely a volunteer here as is pretty much everyone else here--I and NAWS, when we talk, it is mostly about the forum software and such).

    They do ship products--But to Hawaii--As you know--That is "different" in so many way$.

    The Schneider, Outback, Midnite, MorningStar, etc. are higher end products. They also have some other lower cost products Samlex/Cotek... And Victron which seems to be on the leading edge of Bluetooth and other "interesting" hardware.

    Yes, you can buy an AC inverter+separate battery charger or an integrated AC inverter/charger... Inverter-Chargers--The internals have very similar design and parts (enough parts to make an Inverter--Change the microprocessor code and add a few pieces, and you have an inverter-charger).

    You can argue and integrated unit is less parts, can be more sophisticated (AC Battery Chargers are either "brain dead" simple, or are more complex, and more expensive). Integrated units can have some pretty sophisticated functions that can be really neat.

    One example is "generator support" mode... Say it is night and you are running the genset to run your home. It is a "smaller" genset (say 2kWatt). And you have a 4 kWatt inverter-charger... Your program the inverter-charger to only draw 1.8 kWatts from the genset and enable "generator support"... You are buzzing along in your home running some lights and a washing machine while charging the battery banik... And you decide to cook dinner on a hot plate and/or run a well pump... The loads go well over 1.8 kWatts that the genset can supply--And the inverter-charger stops charging and instead starts taking battery energy to run the cook top and well pump (supporting genset output). Once the pump has filled the cistern and your done cooking--The loads drop back down, and the inverter-charger starts battery charging and supporting your LED lights and laptop... (with electric start gensets--Inverter-charger can have AGS automatic generator start controller).

    And/or you can look for an inverter/solar charge controller/or integrated system that can connect to the Internet or Cell Phone--And you can monitor/control your system when you are not home--Or get alerts so that you can ask the friend to drop by and start the genset before your freezer thaws....

    This stuff is very nice... But also complicated to setup and (sometimes) to maintain/debug... And you usually have "more options" with larger systems... Not going to see much of this on a 1,000 WH per day system (300 Watt inverter+Solar) vs a 6-12 kWatt inverter system that is 20+ kWH per day.
    Suggest you get the basics first (estimated power usage, hours of sun per day for your location, needs like 24x7 for fridge+freezer, other loads when sun is up such as washer, electric cooking, backup genset battery charger for your size of genset)...

    Once you know the "class" of system you need (power/function wise)--Then you can starting window shopping for hardware... And see if 24 or 48 volt battery bus make a difference for you, features and options, etc.

    If you are going to maintain your own system (recommended for 3.3 kWH per day system like yours)--You want to keep it simple and straight forward. Even adding something like AGS (automatic generator start) just adds all sorts of wild and wonderful ways things can fail.

    The KISS (keep it simple s......) principle usually applies here. Manual genset for emergency backup will get you what you want...

    A system that will run your refrigerator for 2 months unattended while you are on the mainland... That is another discussion. It is one of those things--A simple system will work, until it does not. A notification and you can call a friend to look at the issues may help (is he going to replace all 12 of your batteries if the bank was taken "dead"--You would have a very good friend). An integrated AGS... Runs until out of fuel, engine oil goes low, overheats, or a nearby lighting strike took out the AGS controller...).

    I help here to get folks started in solar and, to the best I can, try to answer questions, along with the many other folks here. If you are looking for a sophisticated/larger install (I don't thing you are)--Then that is why professional engineers and consultants are there to help you out.

    The first system you install--You will feel like you are drowning in the surf/surge. The third or more systems--You will be surfing (and learn your limitations).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • KalaniKalani Registered Users Posts: 16
    Don't get me wrong here, I have no plans for all that automagic stuff. I just found something "new" and decided to learn a bit about it, and I am one of those people who learn by asking questions about what they read. I don't have unlimited internet access at home like I do here right now, so I'm taking advantage of it. I might get a little pestering with this, but that's because I won't have the access/time to do this when I get back home. But believe me, when I say I appreciate your quick and (extremely) thorough replies, I really mean that.
    I like my simple life, I just want creature comforts - the things most people just take for granted; running water with pressure, clean clothes on demand, cold beer!!
    It'll probably be more than 6 months before I can even get around to any of this stuff anyhow. And I'm sure I'll be annoying with more questions about water pumps, battery maintenance, etc.

  • BB.BB. Super Moderators, Administrators Posts: 31,769 admin
    edited June 12 #25
    Not frustrated at all on my side either... I am usually the guy that gives too much information (and gets kicked under the table by my wife).

    If you want to get an idea what is out there--You can cruse through the FAQ thread (sorry--really just a collection of "interesting posts" thread) Pages:

    https://forum.solar-electric.com/discussion/4426/working-thread-for-solar-beginner-post-faq/p1

    It does touch on many different subjects and links to further research (some "link rot" too--I try to fix when I find them).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • KalaniKalani Registered Users Posts: 16
    Yeah, you posted a link that lead there earlier and I have been going through there - not understanding a majority of what I'm reading, but I'm trying.
    This stuff gets so much more complicated than my 400W Renogy kit.
  • BB.BB. Super Moderators, Administrators Posts: 31,769 admin
    Try to stay at the 50,000 foot level... Just what the basic function of a black box is... And how it connects to other black boxes in the system. You need to keep that overall landscape in your mind as go through the system design (and later on, debugging).

    Then when you dive into one of the boxes (such as programming a charge controller)--You can relate how "local changes/configurations" and such fit into the over all system.

    Electronics, software, and related hardware--It is just amazing at times what can be done these days.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • KalaniKalani Registered Users Posts: 16
    BB. said:
    Try to stay at the 50,000 foot level... Just what the basic function of a black box is... And how it connects to other black boxes in the system. You need to keep that overall landscape in your mind as go through the system design (and later on, debugging).

    Then when you dive into one of the boxes (such as programming a charge controller)--You can relate how "local changes/configurations" and such fit into the over all system.

    Electronics, software, and related hardware--It is just amazing at times what can be done these days.

    -Bill
    Was this meant for another thread?
  • BB.BB. Super Moderators, Administrators Posts: 31,769 admin
    I was just suggesting when browsing through the FAQ to not go "lost in the details" the first time through...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • KalaniKalani Registered Users Posts: 16
    Oh, well allow me to take my foot out of my mouth. :smile:
  • BB.BB. Super Moderators, Administrators Posts: 31,769 admin
    No problem.

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