New Solar (first time)

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Professor
Professor Registered Users Posts: 5 ✭✭
I’ve been interested in solar for a long time but have never really dealt with any hardware aside from seeing it installed on my mate’s places and such. Luckily though I was gifted some new hardware:
A 24v Growatt 3000 https://www.amazon.com/PowMr-Off-Grid-Inverter-Controller-Battery/dp/B08L7WN5QX/
Six REC Panels https://www.solar-electric.com/rec-solar-rec330np-n-peak-series-330-watt-module.html
As well as a. Combiner box, 2 breakers, and cables.

Husband of a friend passed away and he had these items for a greenhouse, all new. She gave them to me for helping her clean out her house to sell.

So, my mom owns a small coffee farm up on the mountain that has a shack that is in pretty good condition, just no power. She said I could live there if I wanted. I was thinking about setting this up using a couple of the following batteries:
https://www.amazon.com/Lithium-LiFePO4-Overland-Off-Grid-Application/dp/B08P6HH4WK/

I’ve wired small houses before, so that should not be a problem. What I’m wondering is how to connect it “properly”.
It seems like trying to add a breaker box would be redundant, but I guess it would work. Or should I just keep it simple and maybe use an RV style plug?
Permits and such are not an issue here.

I’d like to live here full time. So a small fridge, freezer, 40” TV, satellite internet, and some lights would be a definite.
A washer would be cool too but I do have a generator that could help with that if it’s too much.
The house has a propane stove for cooking, and I can get solar hot water easy enough.
Would a 110 water pump from a catchment be too much to ask or should I go with an RV style and a pressure tank?

Lots to unpack here, but this is the first time I’ve had the chance to get out from under these high rent prices we have in Hawaii.

Comments

  • 706jim
    706jim Solar Expert Posts: 514 ✭✭✭✭
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    I think you will need more battery than two of those. Get a 120 volt pump rather than the 12 volt RV stuff. It will last longer. Fridge AND freezer? You might need more panels if you need both of those.....
    Island cottage solar system with 2500 watts of panels, 1kw facing southeast 1.3kw facing southwest 170watt ancient Arco's facing south. All panels in parallel for a 24 volt system. Trace DR1524 MSW inverter, Outback Flexmax 80 MPPT charge controller 8 Trojan L16's. Insignia 11.5 cubic foot electric fridge. My 30th year.
  • Professor
    Professor Registered Users Posts: 5 ✭✭
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    706jim said:
    I think you will need more battery than two of those. Get a 120 volt pump rather than the 12 volt RV stuff. It will last longer. Fridge AND freezer? You might need more panels if you need both of those.....
    I see I typed it odd… I meant a fridge/freezer, as in your standard combo.
    And 200ah at 24v LifePo4 would really be that low? Perhaps I did my math wrong.
  • Photowhit
    Photowhit Solar Expert Posts: 6,003 ✭✭✭✭✭
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    Professor said:
    I see I typed it odd… I meant a fridge/freezer, as in your standard combo.
    And 200ah at 24v LifePo4 would really be that low? Perhaps I did my math wrong.
    I think you would be fine, I ran a smaller 4.8 cuft fridge on a similar system in my cabin back in 2005-2008. It used about the same as a modern apartment sized fridge freezer. I'd guess in Hawaii you have reasonable sun, though that might depend on which side of the mountain you are on. The fridge alone will use a little over 1 kWh a day, most days you will get some of that directly off the system without depleting you battery bank. I think overcast sky's clear quickly in general on the islands and lithium are efficient at charging.

    You could check https://pvwatts.nrel.gov/
    Be sure the location the use is on your side of the hill!

    Some of the 12v 200ah by Renogy shouldn't be run in series, worth running down manuals or manufacturer's info.
    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.
  • Professor
    Professor Registered Users Posts: 5 ✭✭
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    What about wiring it all in? Should I install a breaker box or just look for an RV style plug setup?
  • BB.
    BB. Super Moderators, Administrators Posts: 33,442 admin
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    Let's start from the beginning... a 24 VD @ 3kWatt off grid AC inverter and 6x 330 Watt solar panels. I guess you are in/around Kailua, Hawaii.

    Sizing a "paper system" to see what to expect/size the battery bank (start with flooded cell lead acid--cheap), start with your location & Solar array.

    Kailua
    Average Solar Insolation figures

    Measured in kWh/m2/day onto a solar panel set at a 69° angle from vertical:
    (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
     

    Picking December as "break even month" (may need a genset during bad weather to keep system operating). The "average" daily harvest is around:
    • 6 * 330 Watt panels (aka 1,980 Watt array) * 0.52 overall off grid system efficiency * 4.84 Hours of sun per Dec. Day = 4,983 WH per day
    Nominally, I suggest a 3,300 WH (3.3 kWH) per day as the minimum amount of energy per day that gives you a "near normal" electrical existence (LED Lighting, Full Size Fridge, small water pump or solar friendly well, laptop computer/LED TV, clothes washer, propane or other fuel for heating/cooking/hot water, etc.).

    So, 4,983 WH per day is actually not a bad solar array for you. Using that number to size the rest of system. Basically 2 days of storage and 50% max planned discharge (a Lithium Ion bank could be 2/3rd or 1/2 the size of Lead Acid--But that is a discussion for the next posts):
    • 4,983 WH per day * 1/0.85 AC inverter eff * 2 days storage * 1/0.50 max planned discharge * 1/24 VDC battery bank = 977 AH @ 24 volt battery bank
    That is a pretty large battery bank... If your daily loads do not need this much energy--Going with a smaller battery bank will save you money (smaller bank, smaller bank to replace every 5-8 years or so, etc.).

    Like to have 10% to 13%+ rate of charge for full time off grid battery bank (confirm or update assumptions for solar array):
    • 1,980 Watt array * 0.77 array+controller deratings * 1/29.0 volt charging * 1/0.10 rate of charge = 526 AH @ 24 VDC nominal
    • 1,980 Watt array * 0.77 array+controller deratings * 1/29.0 volt charging * 1/0.13 rate of charge = 404 AH @ 24 VDC suggested minimum battery bank
    Because you have lots of sun (even in winter)--You can go with a much larger battery bank... But a 404-526 AH @ 24 VDC battery bank would be a good choice too (minimum rate of charge for full time off grid).

    If you look at 3.3 kWH per day as a "minimum" for a small/efficient home, a suggested battery bank would be:
    • 3,300 WH per day * 1/0.85 AC inverter efficiency * 1/24 VDC batter bank * 2 days storage * 1/0.50 max planned discharge = 647 AH @ 24 VDC battery bank
    Because you have lots of sun, perhaps you could go with less than 10% rate of charge with your present array--But for Lead Acid batteries, 10% minimum rate of charge is suggested by battery mfg.:
    • 647 AH * 29.0 volts charging * 1/0.77 array+controller derating * 0.10 rate of charge = 2,437 Watt nominal array 10% rate of charge for 3.3kWH per day system on Lead Acid batteries.
    What will 3.3 kWH per day system run (some random numbers)?

    24 VDC R/V diaphragm pump: https://www.solar-electric.com/aquatec-550-series-m378-24-volt-booster-pumps.html
    • 1,200 WH per day full size refrigerator (a small fridge may be 800+ WH per day)
    • 24 VDC * 4 amps (average?) current * 1/3 hours per day (20 minutes) = 32 WH per day water pumping
    • 30 Watt laptop computer * 10 hours per day = 300 WH
    • Clothes washing machine 1,000 WH per day (per guess)--Run during sunny weather
    • 5 * 13 Watt LED lights * 5 hours an evening = 325 WH per day
    • 15 WH per day USB phone charger
    • 1,200 Watt Microwave * 1/4 hours per day (15 minutes) = 300 WH per day
    • 1,200 + 32 + 300 + 1,000 + 325 + 15 + 300 = 3,172 WH per day
    Just an example of how to work out your loads... You should use a Kill-a-Watt or similar meter for your 120 VAC loads and there are DC WattHour meters you can measure your DC loads with...

    You can see how your loads, amount of sun, and such drive the sizing your system. I suggest that you size the system assuming flooded cell lead acid batteries--And then figure out the sizing and other issues (battery management system for Li Ion and such) for the Li Ion battery bank (LiFePO4 batteries are almost ideal for solar power systems--But can be expensive and usually BMS is almost a requirement to prevent damage to your battery bank (over charging/over discharging, running near/below freezing temperatures, etc.).

    Circuit breakers are there to protect the wiring... Fuses also work--But Circuit Breakers are nice to use as on/off switches too (turn off to service equipment, turn off inverter when you are away traveling, etc.). You need to size everything first (voltage, current, etc.) per branch circuit to know what you will need to do.

    For example, standard 14 AWG wiring is rated for 15 amps. Your 3,000 Watt inverter:
    • Inverter AC output = 3,000 Watts / 120 VAC = 25 Amps (if you use 14 AWG to lights/outlets, you need 15 amp breakers per circuit)
    • Inverter DC input = 3,000 Watts * 1/0.85 AC inverter eff * 1/21.0 volts battery cutoff = 168 Amp minimum branch circuit wiring and breaker
    Your charge controller:
    • 1,980 Watt array * 0.77 panel+controller * 1/29.0 volts charging = 53 suggested minimum MPPT type solar charge controller
    • 60 amp charge controller * 1.25 NEC derating for continuous charging = 75 Amp round up to 80 Amp rated branch circuit wiring and breaker
    24 VDC can be a "handy" working voltage for your battery bank. There is a fair amount of "stuff" out there that runs from 24 VDC... RV type water pumps and even LED lights. If you ever plan on a larger system (>2,400 to 3,600 Watt AC inverter), you might want to look at starting with 48 VDC battery bus. Higher voltage, lower current in wiring, less voltage drop, lower wiring costs less, and and easier to route.

    Remember that AC inverters take energy just being on and no loads. A mid to larger inverter may take 20-40 Watts "just turned on" (Tare Losses)... If you run the inverter 24 hours per day. Example:
    • 30 Watts * 24 hours per day = 720 WH per day
    On a small system--That is almost another 1/2 refrigerator load (or 100% of a small fridge load). If you do not use the inverter 24x7 (24 VDC fridge, DC for lights, water pump, etc.)--You can save significant amount of energy.

    If, however, you will be running the inverter 24x7--Then using 120 VAC loads "everywhere" is usually the better choice. AC appliances are getting pretty close to DC appliances in efficiency--And tend to cost much less (and can last longer--especially things like RV water pump with "brushed motors" (maybe 2,000 to 5,000 Hours between brush changes) vs AC Induction motors. But for something like water pumping, and 20 minutes per day... 2,000 hours / 0.33 hours per day = 6060 days or ~16 years (diaphragm will probably need replacing before the brushes).

    Anyway... Some math/modeling of your system. Lots of choices and the detailed designs start once you pick the hardware. Your thoughts?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Professor
    Professor Registered Users Posts: 5 ✭✭
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    BB. said:


    Anyway... Some math/modeling of your system. Lots of choices and the detailed designs start once you pick the hardware. Your thoughts?

    -Bill
    Unfortunately I already have the hardware. The AIO Growatt unit is limited to 2000W of solar input.
    Perhaps I should look at what this setup will provide, and then model my life around it.
    $2,000/mo for a one bedroom rental makes one evaluate their life.

    I understand now the reason to have a breaker box, don't know how I brainfarted on that one. I might need to hire that part out unless it's easy to do. I assume I don't need a main? Any good diagrams on that kind of setup?
  • Photowhit
    Photowhit Solar Expert Posts: 6,003 ✭✭✭✭✭
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    I think the Growatt has an integrated charge controller.  And you say it's a 24 volt system inverter. 
    If you haven't bought the lithium batteries yet, you might consider golf cart batteries. In the states, they are about $100 for an inexpensive 6volt 215 Ah battery plus a core charge. Likely places to find them  at that price here are Sam's club and Costco, They don't like to be drawn down past 50% but can be taken down to 20% state of charge once in a while. 

    The biggest part for you will be adapting to life with a limited energy capacity. Everything that you want to do that involves heavy draw energy should be done during the day time with some support from your array. Things like washing laundry are possible and generally fine during sunny days, but create demands on your system when using energy from the battery bank.

    ONce the sun sets you should be doing reduced energy things. Also evaluate the energy everything uses. As Bill eluded to, things like Laptops instead of towers. Figure out how much energy your satellite internet uses, and your TV if an older model. Also figure out energy saving feature on your TV many have them. I've had a progression of TV's a 22" flat screen LCD which used about 40 watts, then a 39" LED lit that used about the same and now a 55" that uses a bit over 50 watts in energy saving mode. Some use4X the energy and more!!!
    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.
  • Professor
    Professor Registered Users Posts: 5 ✭✭
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    Yes, the Growatt is an AIO (charge controller, charger, inverter)… All In One.
    Costco has golf cart batteries for about $110 each, and I considered them, until someone here locally turned me on to those LifePo4 batteries. Even though they are from China, he has had his for 3 years now and they are going strong. With a 200A BMS and 200ah for about $900 delivered each I thought these would be better than the Golf Cart ones… and I wrong? What am I missing if so?
    I know this is new to me but I thought I had a grasp on the batteries.
  • Photowhit
    Photowhit Solar Expert Posts: 6,003 ✭✭✭✭✭
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    If they work, they should be a good value, I live where I want my batteries to be able to charge when below 35 degrees. My system lives outside. The 4 of the golf cart batteries would give 1.5 times the storage of one of the lithium batteries and cost about half as much, If you make a mistake they are pretty resilient. They would require some maintenance.

    The life span, I would expect from the golf cart batteries would be 4-5 years. My cabin with a fridge and running an air conditioner during the summer ran on a single string of 4 of golfcart batteries. But I was already experienced at living off grid on solar electric. The air conditioning was just enough to sleep, NOT 24/7. I started with a 1000 watt array for the air conditioner and added an addition 600 watts of array when I added a fridge. I removed the fridge the last year of service as the batteries were showing signs of some reduction of capacity. The batteries were drawn down to 20-30% State of Charge every day over the summer. Also understand I built the cabin to air likely NOT an option for your shed. 6" well insulated walls, 8+ in floor and ceiling, small 10x16. but it was a large demand. The batteries were a year old when I installed them and lasted 4 summers/5years total. No generator backup... condition,


    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.