Please critique my plan / diagram

minisolarminisolar Solar Expert Posts: 57 ✭✭
Hoping I am not making a fool out of myself but how else one learns? 

Please let me know what I am missing and if anyone can maybe show on my wires where things go because I am not 100% of anything really. 

A few notes questions: 

  1. I will prefer 2x 250 watt panels which I think is right at the max of my mppt? If so then can anyone point me where I can find one for not a lot of money? 
  2. Does the Go Power! TS-30 work in my system in terms of max power so I don’t fry it?
  3. Maintenance on the batteries? Any tips on location? Cool? Air supply? https://www.samsclub.com/p/duracell-golf-car-battery-group-size-gc2/prod3590228

  4. Should I get a lightning arrestor? I am in upstate NY. If yes which one and how to incorporate?

  5. Only between batteries I need special cables the rest is just a regular electrical wire?

  6. I prefer 2x 250 watt or 260 watt panels which is right at the max of my mppt right? Should I not go as high? Anyone can steer me to where I can get cheaper panels than the ones I picked?

  7. From the inverter I run a hot and neutral?

  8. Do I need a shunt in my system?

  9. Do I wire batteries directly to rv 12v system or is there anything in between?

  10. Are my fuses good? https://www.amazon.com/Fastronix-Automatic-Reset-Circuit-Breaker/dp/B07NSGVBC1/ref=sr_1_2?dchild=1&keywords=10amp+inline+fuse+breaker&qid=1589512345&sr=8-2

    https://www.amazon.com/InstallGear-Gauge-Line-Fuse-Holder/dp/B01LXO6UWS/ref=sr_1_8?dchild=1&keywords=300%2Bamp%2Binline%2Bfuse%2Bbreaker&qid=1589656348&sr=8-8&th=1


Comments

  • BB.BB. Super Moderators, Administrators Posts: 30,505 admin
    edited May 18 #2
    I still always like to work from your loads... But based on what you have here, I can make some math assumptions (you update the math as needed).

    Solar power does not generate as much energy as most people think... And when you want (for example, 5 hours of power in the evening, that can be a lot more energy overall than a 2 kWatt skill saw running for 20 minutes.

    For RVs, you may, for example, plan on using 50% of the battery energy every day (small system, weekend loads, etc.)... For a cabin, I would be suggesting you use 25% of the power per day--Better for full time off grid vs summer system.

    I will start with a cabin class system (full time off grid for 9+ months a year)--And we can adjust from there.

    First, battery bank 2 days of stored energy  and 50% max discharge for longer battery life (RVs, 1 day storage and 50% discharge can be OK, batteries will age out before they cycle out).
    • 645 AH * 12 volt battery bank * 0.85 AC inverter eff * 1/2 days storage * 0.50 max discharge = 1,645 WH per day average battery loading
    Now for charging, 5% to 13%+ rate of charge is typical... 5% can work OK for summer/sunny weather usage, 10%+ recommended for full time off grid (I think you are building home onsite over the next few years?).
    • 645 AH * 14.5 volts charging * 1/0.77 panel+controller deratings * 0.05 rate of charge = 607 Watt array minimum
    • 645 AH * 14.5 volts charging * 1/0.77 panel+controller deratings * 0.10 rate of charge = 1,215 Watt array nominal
    • 645 AH * 14.5 volts charging * 1/0.77 panel+controller deratings * 0.13 rate of charge = 1,579 Watt array typical cost effective maximum
    So, your present 500 Watt array is pretty much on the "very small size" for your battery bank (based on rate of charge).

    The other calculation is based on where the system will be installed (hours of sun, number of Watt*Hours per day, etc.)... Using PVWatts, fixed array, Watertown NY, facing south, 45 degrees (guessing):
    https://pvwatts.nrel.gov/pvwatts.php
    MonthSolar Radiation
    ( kWh / m2 / day )
    AC Energy
    ( kWh )
    Value
    ( $ )
    January2.69658
    February3.848210
    March5.0211413
    April4.9710312
    May5.2811013
    June5.4410713
    July5.7011413
    August5.4010813
    September5.2810512
    October3.37728
    November3.02648
    December2.26526
    Annual4.36

    I toss the bottom 3 months (winter+genset), and use February 3.84 hours of average sun per day (break even month):
    • 1,645 WH per day * 1/0.52 off grid system efficiency * 1/3.84 hours of sun per day (Feb) = 824 Watt array minimum
    And, the nominal AC inverter should be based on the battery bank AH capacity. For flooded cell lead acid batteries, C/10 for nominal max AC inverter discharge, and C/5 maximum draw:
    • 645 AH * 12 volts * 1/10 hour discharge rate * 0.85 AC inverter eff = 658 Watt inverter nominal maximum
    • 645 AH * 12 volts * 1/5 hour discharge rate * 0.85 AC inverter eff = 1,316 Watt inverter max suggested
    Looking at your basic design, it is not really a "well balanced" off grid power system. The solar array is on the "small size" and the 2k Watt inverter is on the larger size (again for your battery bank). And I really do not know your daily power needs...

    You can do things like use the off grid solar+battery for (quiet time power, such as evenings/nights, and use the genset for daytime power--Like saws and tools).

    I could go on--But I wanted to understand your needs and assumptions before I go down more math equations...

    Some short answers:
    1. 500 Watts of panels in on the "small side" for your battery bank (unless you plan on running the genset more)
    2. A 30 Amp transfer switch is fine at 120 VAC (~3,600 Watts of 120 VAC)
    3. Lead Acid batteries are "happy" from ~45F to 120F... Colder batteries work fine, but need to be charged if sub zero F. Above 75F, batteries age faster (for every 18F over 75F, is 1/2 the ageing life). Sub freezing FLA and AGM batteries work, just less apparent AH capacity (don't want to discharge too much, or they will freeze).
    4. Lightning arresters are nice on both solar array and AC output from inverter--Need ground rod(s) or ground plate(s) for the lightning to go somewhere: https://www.solar-electric.com/search/?q=surge+midnite
    5. You need heavy cables (and large fuses/breakers) for battery wiring. Need UV resistant wiring if exposed at the array.
    6. Panel pricing--Our host is nice--But shipping can cost a lot (packaging, large panels need to ship by truck--Finding local panels from a local GT solar installer may save money).
    7. Depends on your power needs. A 120 VAC output is Line+Neutral (for PSW/TSW inverters) or (sort of) Line+Line for MSW inverters. A ground with the 120 VAC is nice--But can be avoided if you use GFI outlets and breakers (more discussion needed).
    8. DC shunts (precision power resistors) are very common for Battery Monitors and large Amperage meters. Need more discussion for your needs.
    9. 12 volts is nice for an RV system. Other than using a fuse/breaker to protect your wiring from the battery bank... But if you are looking for >1,800 Watts, a 24 volt (or 48 volt) battery bank and AC inverter makes more sense.
    10. Large Amp fuses and holders are not much cheaper than good quality circuit breakers. Many times, it is nice to use breakers as on/off switches for maintenance...
    -Bill


    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • minisolarminisolar Solar Expert Posts: 57 ✭✭
    Wow Bill. Thank you so much for really looking into it. 

    First, after many people recommended and after the wife and I discussed further - we are now thinking to try and finish up the cabin instead of buying an RV. Having said that, my current cabin is 12ft x 12 ft. I wired it to a standard distribution center (AC) and used to just hook up generator to it for my power needs. 

    This cabin will be used for 2-3 days at a time then no usage for a week or more. Sometimes 2-3 weeks. which is why I thought I can get away with this array. I can go with a higher mppt. 60amp epever is $70 more then bump up to 750watt array. My cabin is very very shaded.... so maybe this whole panels and array is a mistake? I could just hook up the genie every time I go instead. Assuming I do that is my IOTA 30amp charger the strongest I can use? if yes then how long to charge this size bank? If no and I can get a bigger one then what size and how long will that one take? 

    OR I can buy two silly panels and PWM charger along some kind of solar charge monitor to see how much I am getting and do an experiment for a few months this summer and see how much energy I pull? If so can you outline what I will need for that?   

    I did think about 24v system but it seems like the battery bank will be much more expensive or big. 6x 6v 215ah gc batteries at sam's club are $560. If I want same size bank at 24v not only will it cost $1120 but I don't want this monster bank. If I get away from these batteries and go for instead a 12v or 24v batteries then price seems to be even higher but less batteries... 

    In terms of usage, I have a 7 year old excel sheet I made for my usage and a friend of mine looked at it back then and said that I can get away with a 1000w inverter if no microwave and an 1800 if yes to microwave. So I went with this 2000watt magnum.

    I will never stay full time in this cabin and if once in a blue moon I stay there with the fam for a week -I planned to recharge using gennie. 

    Great tip on #10. 

  • BB.BB. Super Moderators, Administrators Posts: 30,505 admin
    If you don't get sun for something like 9am to 3pm per day (especially given it is near "summer" now)--You are not going to get much from solar in a shaded area.

    You have options--Cut trees, install the array in an open area upwards of 100's of feet way is possible... Put the batteries on a cart/trailer to charge in sun, install a bunch of solar panels and use LiFePO4 batteries (Li Ion batteries can charge much quicker vs lead acid). Or, install the solar you can to float/lighting charge the battery bank, and use a 120 VAC charge controller + Genset for power as needed (run the battery bank at night for "quiet power time", and the genset during the day (cooking/water pumping/etc.)...

    Using as little energy as needed from battery bank (LED lighting, cell phone and tablet charging, RV water pump)--And the genset for anything more. 2-4 6 Volt @ 200 AH batteries for a 12 volt @ 200 AH or 400 AH with a ~300 Watt AC inverter--Won't be a bad life (or expensive). Running a Honda eu2000i (or the new eu2200i) on a 1-2 gallons of fuel per day--Not bad. I have used a couple of eu2000i with aftermarket gas caps + fuel hose to pull from a 5 gallon gas can.

    Another poster here was highly suggesting an eu3000i "class" of genset--Not much more fuel usage, but much more capable. (the eu2200i and eu3000i family--Not sure about how to run an extended/external tank).

    The whole solar array question--If not "now", what is planned when the place is finished? Is your plan for solar power with genset backup, or mostly genset+battery bank+a little solar, or bringing in utility power, etc.?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • minisolarminisolar Solar Expert Posts: 57 ✭✭
    Great info here Bill. Highly appreciate it. 

    I have decent clearing about 80ft from the cabin and can hang them about 13ft in the air so I will give it a go there.

    For $300 I think it is worth a shot with those 3x 250 watt panels and see if trees need to be cut or what not. Can you just confirm I can indeed use ti with a 60amp epever mppt? 

    I can pick between two panel types (both poly) -
    cs6p-250px - CANADIAN
    tsm-250pa0s.08 - TRINA

    let me know which is better.

    I did see some used Lithium batteris 12v, 90ah, for sale but not sure how to match a BMS for them? is that simple or a complicated process? 

    In terms of loads I will have: mini split ac (about 350-400watt running), 700watt microwave (we just heat and not cook in it so it work for 2-3 min a dy max), charging phones tablets, power for when propane furnace works, rv water pump, lights, fridge (can run on propane but I rather have it on electricity). I think a 2000watt inverter will serve me well right? 

    I will use this system for 3-4 years for sure but potentially 5 years. I think eventually I will either be all grid or grid ties solar once I build a real cabin there. 


  • BB.BB. Super Moderators, Administrators Posts: 30,505 admin
    I am not in the solar business, so I cannot tell you which brand of panels are better...

    80 Feet for panel wiring... That is getting out there. And choosing the right MPPT type charge controller can be important. Also the right panels and panel configuration... For example, if you have 3 panels with Vmp~30 volts and Imp~8.3 amps, 80 feet out (one way run for this calculator), using a voltage drop calculator for 3 panels in parallel:
    https://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=0.8152&voltage=30&phase=dc&noofconductor=1&distance=80&distanceunit=feet&amperes=24.9&x=40&y=28

    4 AWG cable for 1s x 3p:
    Voltage drop: 0.99
    Voltage drop percentage: 3.30%
    Voltage at the end: 29.01

    80 feet of 4 AWG cable is not cheap.

    If you get a 100 Volt Vpanel input max MPPT controller, you can put 2 panels in series (3 panels in series is too high of array voltage for a 100 volt max controller). And you would probably use 2s x 2p configuration (4 panels total). 80 feet,
    Vmp-array~60 volts, Imp-array=16.6 :
    calculator.net/voltage-drop-calculator.html?material=copper&wiresize=2.061&voltage=60&phase=dc&noofconductor=1&distance=80&distanceunit=feet&amperes=16.6&x=68&y=18
    8 AWG
    Voltage drop: 1.67
    Voltage drop percentage: 2.78%
    Voltage at the end: 58.33

    Cheaper cable, and more power...

    Or you could get a ~150 Volt Vpanel controller (more expensive), and have 3s x 1p:
    https://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=8.286&voltage=90&phase=dc&noofconductor=1&distance=80&distanceunit=feet&amperes=8.3&x=75&y=26

    12 AWG:
    Voltage drop: 3.35
    Voltage drop percentage: 3.73%
    Voltage at the end: 86.65

    Just showing how the array configuration and different controller options can affect costs and how far you can run the cabling.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BB.BB. Super Moderators, Administrators Posts: 30,505 admin
    Your loads--I still do not really understand. The system (750 Watt array) is really too small for the larger loads (A/C, propane fridge on 12 VDC / 120 VAC, etc.).

    Propane refrigerators running on 12 VDC or 120 VAC are very inefficient (generally run on propane, not solar or pick a compressor based refrigerator), and A/C systems draw lots of energy (2-3x more than a refrigerator).

    You are much better off sticking with the solar power system with a smallish battery bank (2 or 4x 6 volt @ 200 AH golf cart batteries and a 300-600 Watt AC inverter or so). A 2,000 watt 12 VDC inverter on a 750 Watt array is just too much of a mismatch. Just run a small solar system for the small loads (LED lighting, phone/tablet charging, RV water pump--Everything else on the genset).

    Li Ion (like LiFePO4--Lithium Iron Phosphate) batteries can be nice. Not cheap, and if you buy individual cells with a separate BMS system--Lots of research to do. There are integrated Li Ion batteries with BMS:

    https://www.solar-electric.com/residential/batteries-battery-storage/deep-cycle-batteries.html?nav_battery_type=537

    If you are seriously interested in Li Ion, there are others here that can help.

    There are other battery chargers--Power Factor Corrected AC input--That are very nice and can run 40 Amps @ 12 volts from an eu2000i genset. The Xantrex TC2 chargers are nice, but not cheap:

    https://www.solar-electric.com/xantrex-804-1240-02-truecharge2-40-amp-battery-charger.html

    Say you have 4x golf cart batteries for a 12 volt @ 400 AH battery bank, and drain it by 50%:
    • 400 AH * 0.50 = 200 AH
    • 200 AH / 40 Amp charging = 5 hours
    • 5 Hours charging + ~4-6 hours "absorb charging" (for lead acid batteries) = ~9-11 hours to fully charge from 50% State of charge
    The above is just a very rough guess... The 50% to 80% state of charge will take ~40 Amps (~3 hours) , and then the battery will hit ~14.75 volts (set point), and then spend ~4-6 hours in absorb, as the battery charges from 80% to ~100% State of Charge as the charging current drops from 40 amps to near 0 amps.

    This is one of the major drawbacks of Lead Acid batteries... Charging from 50% to 100% simply takes a lot of time.

    Keeping the system relatively "cheap" for a remote cabin would be my choice. Only 3-5 years of construction, then "abandon" the solar system for grid power (or keep it for backup power)--You would not want to put too much money into it--And there may be an issue with theft(?). Li Ion batteries (with the right BMS) are pretty close to ideal batteries--But they are expensive (take them back home?--At least they are small/lightweight).

    If you ever wanted an RV--Moving an Li Ion bank into the RV would be a good second life.

    I am still not quite sure what size battery bank you are planning on installing and what loads you expect solar to support...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • minisolarminisolar Solar Expert Posts: 57 ✭✭
    I really appreciate this and look forward to reading your comments. 

    After further discussion (sorry for back and forth) my wife and I decided to indeed buy an rv and use it has a cabin (so ti will not be moving - ever) until we build a real system. This could be 3-5 years from now. 

    This means a few things: distance between panels and batteries/mppt will now be about 15ft and the panels will be located in that clearing which has the best shot at the sun. 

    The biggest thing I am confused about here is this balance of the system you refer to. In really general terms, the way I understand it, the larger your solar array the faster it can replenish/charge your batteries. Then the larger the battery bank the more energy you can store to use later. Then the larger your inverter - the more energy consuming items you can run at the same time. 

    That is what I understand as the underlining principal (mistakenly maybe?) which then guides my logic: This is a part time use RV that will not be moved. My part time will probably be 2-3 days stays a week at most with spats of 2 weeks not going there. Therefore I can have a relatively small array as it will have a week or more to recharge my batteries while there is zero usage - nothing will be left on while we are gone allowing the batteries to slowly charge over that length of time.  

    But while I am there for 2-3 days - I will have the ac on (it draws around 350watt - it is super efficient), fridge on, lights, charging phones and tablets, water pump, and small microwave on short runs. These together might require a large amount of power at the same time which a 2000 watt inverter will easily provide. I thought an inverter only pulls as much energy as it needs to provide? And the 2000 watt number just means how much he can provide total at the same time. That is not the case? That is why I chose a 2000watt inverter which can support the few hours a day I will have all the big usage items running together. Furthermore, I thought the magnum has the search option so it sits without using almost any power then when power is called (I turn on the microwave) it kicks in and provides power... 

    Then finally, because of these two factors - a 645ah lead acid bank might be well for me - long charge time without usage and then big usage for short period of time. It will have a week or more to go from 50% (or more - I might boost it before leaving with my generator) to 100%. 

    I went back to your first comment at this thread to try and figure out from your calculations how long will it take a 645ah lead acid bank to go from 50% to 100% on 750 watt solar array assuming no usage ( everything will be left off). I could not figure it out but it seems like it won't? 

    That is my goal - to have a system that can run all these loads I mentioned for 2-3 days straight then fully charge itself over the next week while I am not there and no usage. If 750 watt is not able to recharge during that time then I need to increase it. I either go to 24v or to even higher amp mppt. 

    Also, I am reading that because my usage is sporadic - I should get AGM as they are maintenance free. Along those lines... I have seen on aliexpress a lithium battery, 24v 200ah, for $838 shipped... Assuming I will get 2 of them. Is that a good route? Spooky to spend $1600 on aliexpress. https://www.aliexpress.com/item/4000783289615.html?spm=a2g0o.productlist.0.0.61ae4c7cIGnYOL&algo_pvid=a5dda69e-d572-4aa1-bad7-b699b75a3419&algo_expid=a5dda69e-d572-4aa1-bad7-b699b75a3419-0&btsid=0ab50f4415900294977592048e9dd6&ws_ab_test=searchweb0_0,searchweb201602_,searchweb201603_




  • mike95490mike95490 Solar Expert Posts: 8,761 ✭✭✭✭✭
    Lithium batteries have some cold weather limits, slow charging below 40F.    No charging allowed at all below 33F   So they need to be in a somewhat heated area, but below 100F
    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 ,

  • Wheelman55Wheelman55 Registered Users Posts: 98 ✭✭✭
    I bet that you’ll do just fine. Just live within your solar means during this phase and use the genny as a backup. 

    To figure it all out turn everything into watts.  

    Total watts consumed per day, watts available in your battery bank for daily consumption, watts needed to replenish battery bank, and watts generated from your solar system. 

    Keep in mind that on cloudy days your system might only produce 5% to 10% of what it will in a full sun day. 

    BB will likely give you some detailed thought with numbers. 

    Have fun on this great adventure. 
    Building Off-Grid in Terlingua, TX
    14 CS 370 watt modules. HZLA horizontal tracker. Schneider: XW6048, Mini PDP, MPPT 80-600, SCP. 1 Discover AES 48 volt LiFePO4 battery 130 ah
  • BB.BB. Super Moderators, Administrators Posts: 30,505 admin
    When I talk about a "balanced" system... It is sort of the idea of trying to decide on a VW bug, a 1/2 ton pickup, or a Mac Tractor/Trailer Truck... Yes, you can put a Cat Diesel Engine in a VW with a 5 gallon gas tank, or a VW engine in a Mac Truck with a 1,000 gallon fuel tank. But it is difficult to do, difficult to maintain, and not very cost effective.

    And, it is not really practical to convert a VW bug into a Mac Truck (start small, then grow).

    I will apologize for the word salad below... Solar Power is really all about the details. If this causes your eyes to glaze over--I understand. It is a lot of information to cram into one post... Please ask more questions, or ignore. It is OK either way. -Bill

    I always like to call the battery the "heart" of your system. It is what runs your devices. The solar panels are just battery chargers--Yes, solar panels can help during sunny days/weather... But when you have storms, or a hot afternoon, and still want to run the A/C for a few hours after the sun goes down, it is the batteries that will do that.

    Loads are what drive the overall system design. A "small" system may be something like 500-1,000 WH per day. LED lighting, cell phone charging, RV Water pump, Radio, maybe a small laptop.... A 1,000 WH per day system is ~30,000 WH or 30 kWH per month (look at your "city" electric bill--30 kWH per month is probably "rounding error").

    Add a full size Energy Star rated refrigerator, more water pumping, Microwave, LED TV, perhaps a small fan--And you are looking at near 3,300 WH per day. That is a (3.3 kWH per day * 30 days per month = ) 100 kWH per month electric bill... The typical North American electric bill is around 500-1,000 kWH per month.

    Add A/C, more electric cooking, etc... And 10,000 WH per day. Or 3,000 kWH per month (a full electric home with A/C in Texas during the summer).

    For system design, there are two major load issues to determine. The total daily energy budget (Watts*Hour per day) and peak loads (Microwave, refrigerator starting, big well pump, etc.). And you need to look at both to determine the basic solar power system requirements.

    Typically loads that run many hours per day--They require a larger battery bank (like a larger fuel tank, to go longer distances between fill-ups).

    And you have the peak loads. A standard refrigerator runs around 120 Watt compressor, but needs >600 Watts starting, and ~600 Watts to run the internal defrost heaters once or twice per day. A microwave needs around 1,200 to 1,500 Watts for 10 minutes per day. A well pump--That can get scary (>4,000 Watts starting for a "solar unfriendly" pump).

    Solar Power (off grid battery based) is expensive... I suggest around $1.00 to $2.00+ per kWH -- That is about 10x the cost of most people's utility power in the US. Conservation (most efficient appliances, least amount of use, etc.) is a first step. And, the less you are there, the more expensive solar power becomes (a large system used on weekends--There are lots of time the system is not running and harvest is lost--Which makes $/kWH costs even "higher"---Not there, generated power is lost).

    And batteries are expensive... 645 AH @ 12 volts--In genset/gasoline equivalent:
    • 645 AH * 12 volts = 7,740 WH of stored energy (~6x 6 volt @ 215 AH "golf cart" batteries)
    • 7,740 WH * 0.50 maximum typical discharge = 3,870 WH of useful energy (the size of your "fuel tank")
    • Honda eu2000i running ~400 Watts * 10 hours per 1 gallon fuel tank (round numbers)
    • 400 Watts * 10 hours per tank = 4,000 WH per tank
    • 4,000 WH per 1 gallon tank of fuel is ~ 4,000 WH per gallon
    Your ~$600 Golf Cart battery Bank can store about the same amount of useful electrical energy as 1 gallon of gasoline at $2-$4 per gallon.
    • $600 of batteries / $3.00 per gallon gasoline = 200 Gallons of gasoline
    • Use ~2 gallons of gasoline per day to run the RV...
    • 200 Gallons of gas / 2 gallons per day = 100 Days
    • 100 Days / 2 day trips = 50x two day trips (use a 5 gallon gas can per weekend).
    • Get a cheap 3.5 kWatt genset to run your power tools when needed (saws, compressor, etc.). Yes, more fuel, but only when you need the power. Use the small Honda for charging tool batteries, running LED work lights, etc. and the RV rest of the time. Use solar+battery for 24 hour per day loads (lights, cell charger, RV water pump, etc.).
    • Replace Golf Cart Batteries every 3-5 years.
    What to use a $1,600+ @ 200 AH Li Ion battery bank--The numbers look even worse.

    Note: Here is one guy that had a largish Propane Fridge and measured the 120 VAC usage--5 kWH per day (5,000 WH per day):

    http://www.beginningfromthismorning.com/refrigerator/

    His old full size home fridge used 2,000 WH (2 kWH) per day.

    Lets look at the loads...
    • Inverter based A/C system: 345 Watt A/C * 12 hours per day = 4,140 WH per day, maybe around 1,000 Watts starting(?)
    • Full Size energy Star refrigerator: 120 Watts * 0.50 duty cycle * 24 hours per day = 1,440 WH per day (>600 Watt starting/defrost heaters load--And RV propane fridge running on 12/120 VAC should be "bigger" WH consumer)
    • RV Fridge (full size RV propane): ~5,000 WH per day
    • RV Furnace: 8 Amps * 12 volts * 12 hours per day * 0.50 duty cycle (?) = 576 WH per day
    • Laptop: 30 Watts * 5 hours per day (news/entertainment) = 150 WH per day
    • RV Water pump: 8 amps * 12 volts * 1/2 hour per day = 48 WH per day
    • RV Lightning (guess): 4x 9 Watt LED lamps * 5 hours per night = 180 WH per night
    • Cell Phone: 3 AH * 3.7 volt battery = 11.1 WH per day (smart phone, USB charger)
    • Microwave (full size): 1,500 Watts * 10 minutes per day * 1/60 minutes per hour =  250 WH
    Some loads are always there (refrigerator, lightning at night, cell phone). Others are dependent on needs. A/C -- Only needed during hot sunny weather (lots of solar). Refrigerators use more power in hot weather (good for solar).

    A 750 Watt array during summer will produce around:
    • 750 Watts * 0.52 AC off grid system eff * 5.0 per day (summer in Watertown) = 1,950 WH per day
    • 6x golf cart batteries ~3,870 WH of useful energy
    • 2 * 1,950 WH of solar + 3,870 WH of stored battery energy = 7,770 WH of energy "available" for 2 day trip
    So--If you want to use your 750 Watts of solar panels, plus the stored (useful) energy in your battery bank for a weekend trip (leave batteries at 50% state of charge at the end of the weekend, and let solar recharge for next 5 days--It could work... But you will have to choose what loads and how much to run them. And if you want to run all the loads (A/C, propane fridge, etc. off off solar), you probably will need a bit of help with the genset too.

    I am sorry to throw a "wall of numbers" at you... But that is what is needed to design a "workable for you" solar power system. And the more you go to the "corner cases" (more loads than the solar panels can supply in 1 day, using 50% of battery capacity at end of two days, etc.)--It can work, but you need to manage your system usage even closer to make sure you don't "fall off the corner" (dead battery bank, need new batteries after a few summer weekends).

    Don't worry if this is "too much"... I understand that all of the math and numbers are hard to follow--And I am sort of randomly pulling numbers out of the air too based on my guesses--Which may or may not reflect your actual energy needs/usage.

    If you are committed to an RV--You can get the RV without solar, use a Kill-a-Watt and/or DC AH/WH meter to do some tests at home (when plugged into utilty power) and see how much energy you really use... Then you will have hard numbers, and a better idea of what you need for your comfort--And can make better decisions (solar, genset, propane/120 VAC, etc.) for you. You can also get an AC+DC Current Clamp DMM (they start at ~$50, make sure it is AC+DC Current Clamp capable, many are AC only clamp DMMs) to better understand and debug your DC power systems:

    https://www.amazon.com/s?k=kill+a+watt+meter&ref=nb_sb_noss_2 (120 VAC energy meters)
    https://www.amazon.com/s?k=dc+ah+wh+meter&ref=nb_sb_noss (DC AH/WH energymeters)
    https://www.amazon.com/gp/product/B019CY4FB4 (Mid priced AC+DC Current Clamps DMM)

    You might also rent an RV (or several) from major companies, or even Airbnb equivalent (owner/renter RVs):

    https://duckduckgo.com/?q=rent+personal+RV&atb=v122-1__&ia=web

    And see what works best for you guys.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • minisolarminisolar Solar Expert Posts: 57 ✭✭
    Bill this is excellent stuff. I really appreciate it. 

    I know that from a math stand point I am better off completely running off my generator. I agree 100%. But... I will be happy to pay extra to be in the beautiful quiet, clean aired, deep woods - in serenity and peacefulness than to save some money and listen to my Honda. I have no problem letting it run for a few hours to charge but having it accompany me throughout my weekend in the woods - no way. 

    "So--If you want to use your 750 Watts of solar panels, plus the stored (useful) energy in your battery bank for a weekend trip (leave batteries at 50% state of charge at the end of the weekend, and let solar recharge for next 5 days--It could work"

    This paragraph is for me a great take away here.

    point taken - I will get a compressor efficient fridge (any rec?).

    I always like to think worst case scenario... 

    Let's say I do this and after a few months realizes that I either hit the 50% too early in the weekend or that it isn't able to fully recharge during the time I am gone. 

    By then I already committed to a 60amp mppt and 12v inverter. 

    So can't go to 24v or increase array without either changing the inverter or the mppt. 

    Do you see any other way in this scenario? 

    Only other ways, that I know of, to do things now are either to plan a 24v from the get go or get an even bigger mppt and array now. 

    Cost of going to 24v while keeping same ah is about $1100 for battery bank. Then I can still get the 60amp and bump up to 1500 watt array Then I have to be the owner of 12 batteries which doesn't seem to be fun... (question - if going to 24v then I need 24v panels? I can't just wired them to 24 like with batteries? 

    Or I can buy an 100 amp mppt (!) for an additional $184 over the 60amp, keep the 12v system and go up to 1250 watt array.... 

    So dollar for dollar staying in the 12v is much cheaper for me. But will this be unsafe due to such high amp on 12v? 

    Btw, I read that agm batteris have a high discharge rate vs sealed? That is true? I am going with agm regardless as I will not be around to maintain the sealed lead ones anyway. 

    Thanks wheelman. Honestly the main thing I don't know much about yet here is the wiring. What connects to what and how. 


  • BB.BB. Super Moderators, Administrators Posts: 30,505 admin
    You are very welcome Minisolar,

    Going backwards through your last post..
    • http://2manytoyz.com/ -- His website has lots of detailed photos, and how his installation evolved (lots of DYI), 1/2 down the page
    • AGM batteries do support higher surge/drain... Some even C/0.5 (30 minutes)--Of course, 30 minutes to "dead" is not usually useful for off grid solar
    • High current wiring on 12 volt solar is usually "just expensive" (lots of heavy/difficult to work with/expensive copper cable/fuses/breakers), not explicitly dangerous. And, as you see, expanding a maxed out 12 volt system is also difficult (more charge controllers/more expensive charge controller, wiring already near max, etc.). Your are on the cusp of a 24 volt system being a better choice. You can find some 24 VDC LED bulbs, 24 volt RV water pump, etc... Or as the system get bigger, just running the AC inverter 24x7 and efficient 120 VAC loads is not bad.
    • Most charge controllers are 12/24 volt capable, and many are 12/24/48 volt capable. They are rated on output current... Same 60 amp controller on 12 vs 24 volt battery bank and supported array:
    • 60 Amps * 14.5 volts charging * 1/0.77 panel+controller derating = 1,130 Watt array (suggested max) on 12 volt battery bank
    • 60 Amps * 29.0 volts charging * 1/0.77 panel+controller derating = 2,260 Watt array (suggested max) on 24 volt battery bank
    • Yes, you are correct, 12 to different battery bus voltage, need a "new" AC inverter. MPPT controllers generally support 12/24 or 12/24/48 volt battery bus without changes (there is the whole discussion of reconfiguring battery banks and solar array based on components selected--For another post--Details matter).
    • It is difficult to grow a system (especially >2x more harvest) without major changes/redesign.
    • I try to avoid making recommendations. I just don't have enough experience across "everything" to make suggestions (other than, to a degree, the more you spend, typically the better the product).
    Regarding refrigerators... There are some 12/24 VDC options out there these days--And seem to be getting more popular and less expensive. Here is one that is ~520 WH per day at 25C:

    https://www.homedepot.com/p/Unique-6-0-cu-ft-170-l-Solar-DC-Top-Freezer-Refrigerator-Danfoss-Secop-Compressor-in-White-UGP-170L-W/306705246?MERCH=REC-_-pipinstock-_-309208349-_-306705246-_-N

    Pretty similar fridge in propane:

    https://www.homedepot.com/p/Unique-6-cu-ft-Propane-Top-Freezer-Refrigerator-Dual-Power-in-White-Propane-110-Volt-UGP-6C-SM-W/313500447?MERCH=REC-_-pipinstock-_-309208349-_-313500447-_-N

    Either of the options above save running a large(r) AC inverter 24 hours per day, and the 12/24 VDC compressor has (typically) almost no surge power over the ~52 Watt running load. The propane fridge is spec'ed at ~1.1 lbs of propane per day (25C).

    A DC fridge is probably the best bet here... Makes the overall solar system much smaller and cheaper.

    People also have converted Chest Freezers into Chest Refrigerators that get down towards 250 WH per day... But they can be a pain to use (vs a standard upright fridge and access to food stuffs).

    But to be honest, if you want to run an A/C system off solar--That is a lot of energy right there--And adding a full size/standard 120 VAC refrigerator is not going to be the major load here.

    I understand that you don't want to run the genset in a beautiful/quiet setting--That is the part you have to decide on (not me typing 3,000 miles away)...

    Me, I suggest a good size (or even oversized) solar array that can run your daily loads (with margin to spare, through the seasons). And a "smaller" battery bank that you can run to the limits. Trying to run a large battery bank (and loads) with a small array--You may end up just spending too much time managing the system and possibly having a shortened battery life.

    If you want to take the time (and $$$) to learn about and install a Li Ion battery bank--A large array + "minimum" battery bank AH capacity--Works well. Li Ion batteries are much more capable of high charging current/faster charging times/high surge current output vs FLA or even AGM.

    Hopefully, some others can chime in here too... I just have not done what you are planning, and I am probably getting a bit out of my depth here to make specific choices/recommendations. Also, you have to define your loads, then design the system. Getting an RV, running it at home for a few days/weeks with Kill-a-Watt and DC metering to see how much power you need--Will give you a much better idea of the scale of your power needs.

    Other questions like tilted array or flat to roof RV solar panels, etc. ... Being farther north, these questions/issues can also make good size changes in the calculations.

    There are a lot of personal choices that need to be made, and juggling of requirements. No "one right answer".

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Wheelman55Wheelman55 Registered Users Posts: 98 ✭✭✭
    Go as simple as you can for now. Whatever you put in now will not be right for your cabin. You will be spending this money at least twice:)

    We now have a very nice 5,000 watt array on a single axis tracker, with all Schneider electronics and lithium battery. 

    Up until now we got by on all 12 volt DC using a ZAMP 180 watt folding panel/w-15 amp controller. 

    The ZAMP setup allowed us to keep two 12 volt battery banks charged, run two ARB DC fridges, one fan, two iPhones, two tablets, two headlamps, one laptop. We did use the Honda gennies when cloudy. 

    The folding panels got us through until we could get a proper system in place. 

    Once again, I recommend doing something simple for now. Use what you already own and don’t get complex. That way you can spend more of your resources (time, money and labor) on building your cabin. 

    A wise man told me that “not too many people get to build their own house and their own solar system...make sure that you enjoy the process”. 

    Best. 
    Building Off-Grid in Terlingua, TX
    14 CS 370 watt modules. HZLA horizontal tracker. Schneider: XW6048, Mini PDP, MPPT 80-600, SCP. 1 Discover AES 48 volt LiFePO4 battery 130 ah
  • minisolarminisolar Solar Expert Posts: 57 ✭✭
    edited May 23 #15
    Going back to this idea maybe: Because it is hard to know my loads and usage which then sets my solar array and so on - how about I don't get any panels or charger yet but do buy a battery bank and just go with the generator there. Charge the batteries fully, which will take a few hours, then use bank over the few days we are there. If needs a boost in the middle fine and just to be safe - charge the them fully before I go. Then once I figure out my usage I can really get the right charger and array. 

    (I think wheelman will like this super simple idea)

    Questions: 
    1. How long will it take to charge with my generator, 30amp iota charger, and six AGM 12v batteries that have 105ah each? 
    2. What kind of battery monitor should I get? I just need to know my state of charge really...  
    3. I think the magnum inverter I am buying has a low voltage automatic shut off but that it is factory set too low and will harm batteries. Anyone knows if I can set that setting to protect my batteries? if not, then anything I can buy that will kill power from batteries if goes too low? 
    4. I would like to leave a few things running while I am away if possible: mobile hotpot (Franklin rm850) and a wyze cam. Wyze cam input is 5v 1amp. and franklin is the same. So assuming these will be feeding directly from batteries while I am away for a week or two. Is it possible to do so on my bank and not risk draining batteries? they'll run 24/7. 
    5. "AGM batteries do support higher surge/drain... Some even C/0.5 (30 minutes)--Of course, 30 minutes to "dead" is not usually useful for off grid solar". Couldn't really understand what that means... I know you said that if I had GC batteries I can only use 50% of their rated ah so 600ah for example - gives me 300ah. AGM has a higher percentage which allows for more usage?
    6. to plug my generator to the IOTA I am assuming I will buy an extension cord, cut the female side, connect that to my IOTA cahrger, then plug the male side to my generator correct? Assuming I will keep generator 25-30ft away - does a 10/3 extension cord good or do I need bigger? 

  • Wheelman55Wheelman55 Registered Users Posts: 98 ✭✭✭
    edited May 23 #16
    Mini.

    Answer to #1. For every 30 amp hours removed from the batteries, your 30 amp charger will take one hour to replenish. 

    With six 12 volt 105 AH batteries you could take out 300 amp hours, which would take 10 hours to charge, plus whatever extra time the Iota charger takes to run it’s charging cycle. 

    Answer to #6 is yes on the 10 gauge cable. 

    Consider living in a 12 volt world for now. 

    We started with two 6 volt 220 ah Trojan batts in series and charged them up with the Honda. Did this for two years. 

    We let the disconnected batteries sit (after a full conditioning charge) over the summer. After 5-6 months the batts still had 12.5 volts when we returned. They’ve used little water. 

    Using the Honda worked well, however once we added the folding solar panels our world improved. On full sun days our batts are 100% SOC and it is quiet. :)




    Building Off-Grid in Terlingua, TX
    14 CS 370 watt modules. HZLA horizontal tracker. Schneider: XW6048, Mini PDP, MPPT 80-600, SCP. 1 Discover AES 48 volt LiFePO4 battery 130 ah
  • PhotowhitPhotowhit Solar Expert Posts: 5,173 ✭✭✭✭
    minisolar said:
     - charge the them fully before I go. Then once I figure out my usage I can really get the right charger and array. 

    "AGM batteries do support higher surge/drain... Some even C/0.5 (30 minutes)--Of course, 30 minutes to "dead" is not usually useful for off grid solar". Couldn't really understand what that means... I know you said that if I had GC batteries I can only use 50% of their rated ah so 600ah for example - gives me 300ah. AGM has a higher percentage which allows for more usage?
    Unfortunatly, The way flooded lead acid batteries work, this wouldn't work well. Flooded batteries will take 13-15% of their capacity up to about 80%, them they accept charging at an ever reduced rate until it gets down to 1-2% This can take some time. 
    AGM batteries have a different charging profile and can be quite different from each other. Some will charge close to 95% before reduction (from what little I know about them @Marc Kurth might be able to shed some light on this) So they might be a better option for this senario.
    Answer to #1. For every 30 amp hours removed from the batteries, your 30 amp charger will take one hour to replenish. 
    Only up to 80-85%, then they will reduce their acceptance of current with the flooded batteries you have.

    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
  • minisolarminisolar Solar Expert Posts: 57 ✭✭
    Photowhit said:
    minisolar said:
     - charge the them fully before I go. Then once I figure out my usage I can really get the right charger and array. 

    "AGM batteries do support higher surge/drain... Some even C/0.5 (30 minutes)--Of course, 30 minutes to "dead" is not usually useful for off grid solar". Couldn't really understand what that means... I know you said that if I had GC batteries I can only use 50% of their rated ah so 600ah for example - gives me 300ah. AGM has a higher percentage which allows for more usage?
    Unfortunatly, The way flooded lead acid batteries work, this wouldn't work well. Flooded batteries will take 13-15% of their capacity up to about 80%, them they accept charging at an ever reduced rate until it gets down to 1-2% This can take some time. 
    AGM batteries have a different charging profile and can be quite different from each other. Some will charge close to 95% before reduction (from what little I know about them @Marc Kurth might be able to shed some light on this) So they might be a better option for this senario.
    Answer to #1. For every 30 amp hours removed from the batteries, your 30 amp charger will take one hour to replenish. 
    Only up to 80-85%, then they will reduce their acceptance of current with the flooded batteries you have.

    Thank you fro the info. I am now hunting for 6v AGM so I have less parallel. Didn't realize that issue of how it slows like that. If I can get a 95% then I am good though... I will try to find out. I'll send Marc a message

    IOTA offers this to control the charging speed specifically for AGM:  . https://www.iotaengineering.com/IQ/#!/detail/IQ-AGM

    I wonder if it can help?
  • BB.BB. Super Moderators, Administrators Posts: 30,505 admin
    Regarding "30 minutes to dead"... I am trying to say that there are batteries that do this (AGM, GEL, some lithium Ion)... Typically a UPS system (keep a computer room running until the computers can safely shut down, or until a genset can start and warm up).

    For off grid homes, typically you draw a smallish amount of continuous power, but for many hours per day. So, you need a large battery bank (and solar array) to supply all of that energy. And these large battery banks for storage, typically have enough "surge capacity" for most needs.

    For example... A few typical loads for a home:
    • Microwave: 1,500 Watts * 20 minutes per day * 1 hour/60 minutes per hour  = 500 WH (large power draw, not much energy usage because only used a fraction of an hour per day)
    • Desktop computer: 300 Watts * 10 hours per day = 3,000 WH per day (medium load, but on many hours per day)
    • Laptop computer: 30 Watts * 10 hours per day = 300 WH per day (small load--conservation saves energy/money)
    • Refrigerator: 120 WAtts * 24 hours per day * 0.50 duty cycle = 1,440 WH per day (and ~1,000 Watt compressor surge--24 hour per day appliance with smallish load, takes lots of energy because "always on").
    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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