Proposed system for off grid cabin

callisto
callisto Registered Users Posts: 2
Howdy folks,

Next year I am hoping to purchase some land and build a small off grid cabin as my permanent residence. I intend to meet my power needs by solar power with a generator back up for emergencies. I have determined that I would be using roughly 3 kwH per day in worst case scenario and have picked parts to build a system I think will suit my needs, with 2 days of back up. I was looking for some feedback on the system, if I have too much one one thing and too little of another, ect ect. All this is still a good ways off, I got plenty of time to get it right.

4 265 watt kyocera panels
4 crown 430 AH 6 volt batteries
Morningstar Tristar 30 amp MPPT
Samlex 1500 watt 24 volt sine wave inverter

I am located in the central region of North Carolina in Zone 4, which I believe means I should expect 4.5 peak hours of sun in the summer and 3.0 hours in the winter time.

Thank you for your input

Comments

  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,731 ✭✭✭✭✭✭
    You really can't have enough solar. How are you going to survive the summer heat? 
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

  • Jay
    Jay Registered Users Posts: 2
    callisto,
    I have almost identical equipment to yours, except
    a 40amp MPPT Renogy Tracer 4240 12/24v (max 800w input)
    4x 205AHr Crown batteries.
    4x Sharp 235w panels 30v  8.6A
    a Cotek SK1500 psw inverter

    Hope to set it up soon.  I will be curious to hear if your system works or not.  I am told by Crown to expect 2460 watt hours/day at 24v to a 50% DOD.  Doesn't seem like much, does it?  That's 205w/hr for 12hrs... to 50% DOD (according to Crown's tech dept)  doesn't sound like much, does it?   Perhaps I should consider 4 more batteries, ya think?  (Cr 205 6v)
     I plan to adjust the mounting angles of the panels to limit my output to 800w (my controller limit) and hook them in series. (8.6amps).  I am in mid- Missouri. Batteries in series also, for 24v at 205AHr.  Would gladly entertain ANY pointers from any users. 

    Thanks

    Jay
  • Jay
    Jay Registered Users Posts: 2
    ps:  I also have two gas generators.  One 6.5kW and the other 1.2kW.  Mostly the larger one for using the well (240v) as needed.
  • zoneblue
    zoneblue Solar Expert Posts: 1,220 ✭✭✭✭
    Hi and welcome to the NAWs forum.
    callisto said:
    I have determined that I would be using roughly 3 kwH per day in worst case scenario
    What will serve you better is knowing a run of the mill average day. The peaks will come out in the wash. For a permanent residence cabin, 3kWh/d is not a bad place to start. This generally allows you to use a fridge, water pumps, washing machine and all the computer toys and lighting that i guy or gal needs. Investing time in a full load analysis on a spreadsheet will pay dividends down the track.
    4x 265 watt kyocera panels
    4 crown 430 AH 6 volt batteries
    Morningstar Tristar 30 amp MPPT
    Samlex 1500 watt 24 volt sine wave inverter
    How did you arrive at these? If you lay out your reasoning we would be better able to comment. As Dave said this system wont cover air conditioning. In general terms that gear gives:

    - a peak charge rate of 1060W/24V or 45A (thus your CC is too small).
    - this is equal to 0.1C (which is a happy battery, 0.1C is the ideal for FLA)
    - your peak discharge rate for that inverter is 1500/0.85/23 or 77A
    - thats equal to 0.18C (again a battery freindly figure, you want <0.25C there).

    Some good things to check, look up the idle/tare on the inverter and CC. Add those into your load budget.
    Note that inverters (and water pumps) theres a very close corelation between what you get and what you pay for.
    But samlex is a good entry level brand.

    Your inverter is a good practical size for such a system, it will start most fridges and many pumps. But too small for a standard vaccum cleaner. For a permanent residence do consider going a little more upspec, or plan to upgrade at some point. Upgrading, while not impossible  can be a bit painful because as you see form the above all the parts have to play nicely together.
    I am located in the central region of North Carolina in Zone 4, which I believe means I should expect 4.5 peak hours of sun in the summer and 3.0 hours in the winter time.
    Again peak hours arnet much good to you. You want the average daily sun hours for the 10 sunniest months, and where that has been sourced assuming the proposed azimith and elevation of your array. PV Watts allows you to enter these. Then to get a rough rule of thumb of system production (assuming other system components are up to it).

    - eg, assume PV is 1000Wp. and sun hours are 3
    - 1000W *0.77 * 3 or 2300Wh/day (0.77 is the combined CC and PV derating).

    When you have a better load analysis, and irradiance data you can use bills more detailed model, the above is just ball park.
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


  • WaterWheel
    WaterWheel Registered Users Posts: 375 ✭✭✭
    Callisto,       Having played with a smaller system for years I'd suggest spring for the next size Tristar MPPT controller.      I've run the 45 amp MPPT Tristar for several years on my smaller system with no problems.      You can always easily enlarge your panels or your batteries if needed but if the charge controller proves too small for expansion you're stuck.

    Conext XW6848 with PDP, SCP, 80/600 controller, 60/150 controller and Conext battery monitor

    21 SW280 panels on Schletter ground mount

    48v Rolls 6CS 27P

  • WaterWheel
    WaterWheel Registered Users Posts: 375 ✭✭✭

    ZoneBlue,       I agree that the charge controller needs to be larger, a 45 or 60 amp to allow for some system growth but in my experience while 3 kwh/d is great for lower draw electronics the motors in the washer, well pump, and any fridge larger than a dorm fridge will not be well covered on that smaller power amount.

    my full sized energy star refrigerator  1.25 kw/hrs/day

    my 7cu/ft freezer uses .7 kw/hrs/day

    my 1 hp well pump draws 2000 watts when running

    toaster oven, hotplate, and microwave all draw about 1200 watts     You can always get smaller appliances and cut this draw to about 800 watts so the 1500 watt inverter should work.

    Yes, With the exception of the large well pump you can get everything to run on 3 kw/hrs/day but I suspect Callisto is taking a more minimal approach to the electronics if he can get by on that energy budget.

    Conext XW6848 with PDP, SCP, 80/600 controller, 60/150 controller and Conext battery monitor

    21 SW280 panels on Schletter ground mount

    48v Rolls 6CS 27P

  • zoneblue
    zoneblue Solar Expert Posts: 1,220 ✭✭✭✭
    edited November 2015 #8
    With fridges your ambient is a factor obviously if its running in a room thats 30*C, its got its work cut out. But foo, if you are, or are planning on, running that fridge on solar you might look at the cost benefit of getting a more effcient one. Solar systems are expensive, and fridges are (sometimes) cheaper, thus it may pay to get a low energy one, (most of which come from scandanavia). The target there is sub 1000Wh/d, ideally 6-700Wh/day. And smaller is not always more energy effcient, as it requires thicker insulation. Still itll be twice the cost, so you have to do the math.

    Well pumps can be challenging. You can either run a genset once a week to fill a tank, or spend a bit more money and get one of the RE friendly pumps like the Grundfos multi voltage units. They dont have a start surge, making it easier to run from inverter.

    Regarding appliances, and for that matter, power tools, for all but serious use, most people find that while these are all mid to high power using products, they only run for short periods and their watt hours barely factors in load planning. (work at home excepted). However the smaller the inverter the more mindful you need to be about what you run simultaneously. The wife and i lived here the first year on an 1100W inverter. Through trial and error she found she could run the hairdryer on low only, replaced her iron with an older 1000W model from a yard sale. The juicer and blender worked, power drill, angle grinder, and belt sander, again all ok, but the handheld circular saw wouldnt. The electric kettle wouldnt. And one or two small suprises... like laser printers. They need better then 2kW inverters. But we run all those things on a 3kWh/day load budget well enough. Weve even recently started using one of those mini ovens. That thing heats up so quick you can bake a pie or roast in the mid afternoon on surplus solar, and just warm it at dinner. You get crafty with practice.
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


  • WaterWheel
    WaterWheel Registered Users Posts: 375 ✭✭✭

    Old fridge died last year, before this solar system, so I'm stuck with a newer fairly efficient fridge.         Some things like led lighting I'm willing to pay to switch out, $1400 refrigerator isn't getting swapped anytime soon.

    Some things like the clothes washer I run during days with at least some sun and I still use the toaster oven and microwave at night for 10-15 minutes.

    It's good to hear that you and your wife have got your energy consumption that low.

    Conext XW6848 with PDP, SCP, 80/600 controller, 60/150 controller and Conext battery monitor

    21 SW280 panels on Schletter ground mount

    48v Rolls 6CS 27P

  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    foo you might be surprised about that fridge, we bought  a GE this spring and it went to the cabin, uses ~.6Kwh per day, rated at .87.... get out the Kill-a-Watt and check  it out... they are all getting better  as the efficiency standards increase each year....
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • callisto
    callisto Registered Users Posts: 2

    You really can't have enough solar. How are you going to survive the summer heat? 
    AC: I found a window unit that uses 455 watts, figuring it would run the compressor roughly 5 minutes of every 15 minutes I was thinking 455 watts x 0.33 hr = 150wh. The cabin is going to be pretty small 12 x 20, a single room with a loft.

    Jay:

    It doesn't sound like enough at all, from what I've been reading keeping batteries above 70% seems to be the best for their lifetimes.

    Zoneblue:

    I came up with those parts thinking 3 kwh a day with 2 days back up, though looking at it again it would discharge my batteries below a safe limit, so I would have to have a larger bank.

    My largest drawing appliance would be a dorm fridge that would eat about 1.5 kwh/day to run, reading other peoples posts though it sounds like I can find more efficient ones to give me more kw budget.

    I will hunt down that average sun hours for the 10 sunniest months data, thanks for that.

    Thanks for your post. I did not take C ratings into account when putting this together, I'll add it to my notes and go back to the drawing board. Is there a point where I should look at getting more than one charge controller? At that point I would have to run multiple banks of batteries?

    Foolami:

    Thanks for your response. I will definitely step up my charge controller, according to the numbers Zoneblue provided its a requirement anyway. I also completely forgot about powering a well pump, I'll add that to the list.

    Overall it sounds like I need to double up the size of my system to have a comfortable amount of room, if so I'm glad I know now instead of later next year so I can put more money away.


    Thanks everyone for your input!

  • Photowhit
    Photowhit Solar Expert Posts: 6,002 ✭✭✭✭✭
    edited November 2015 #12
    callisto said:
    Howdy folks,

    Next year I am hoping to purchase some land and build a small off grid cabin as my permanent residence. I intend to meet my power needs by solar power with a generator back up for emergencies. I have determined that I would be using roughly 3 kwH per day in worst case scenario and have picked parts to build a system I think will suit my needs, with 2 days of back up. I was looking for some feedback on the system, if I have too much one one thing and too little of another, ect ect. All this is still a good ways off, I got plenty of time to get it right.

    4 265 watt kyocera panels
    4 crown 430 AH 6 volt batteries
    Morningstar Tristar 30 amp MPPT
    Samlex 1500 watt 24 volt sine wave inverter

    I am located in the central region of North Carolina in Zone 4, which I believe means I should expect 4.5 peak hours of sun in the summer and 3.0 hours in the winter time.

    Thank you for your input


    Well, let's start with your needs You figure 3 KWH a day, (we'll look closer at that in a minute.)

    4 - 265 watt Kyrocera panels will produce about 191 watts in Normal Operating Cell Temperatures, NOCT values in pdf.

    http://www.kyocerasolar.com/assets/001/5693.pdf  So 4 x 191= 764 watts during a normal hour, So in your 4.5 hour average day your panels will produce 3438 watts, Looks good, but you inverter is only 85% efficient, so 3438 x .85= 2922 watts. Are you going to use the energy after it's stored? Batteries are only about 80% efficient so 2922 x .8 = 2373 watts (of course you will use energy while the batteries are charged... I just want to give you an idea of what you are looking at...

    Now lets look at your battery bank, 4 - 430 amp hour batteries is a pretty good size bank. We normally suggest, as do battery manufacturers) a 10 - 13% charge rate. Your 24 volts at 430 amp battery bank would like 43-55 amp charging rate. Your array will only produce 31 amps normally, and no more than 30 through your chosen Charge Controller.(764/24)

    Now Loads, Not going to be practical to run an AC unless you do some very careful figuring, and watch you system.

    I will not say it can't be done, but you will have to be realistic, and think every thing through. I ran a small window unit on a 1000 watt array. The array wasn't my most limiting factor, I only used 4 golf cart batteries. A small window unit is designed for about a 10x10 room. How much space are you going to AC?

    Think every thing out in advance. Build in the shade! Use very thickly insulated walls (mine were 6") insulate the floor very well and the roof. Consider a high peeked roof, this has good and bad things...

    I ran my AC for 4-6 hours maybe a bit more at times, The duty cycle of the compressor was very high while cooling the cabin down the first hour then backed down to 50-30%. The well insulated cabin held the cool in to make nights comfortable. I didn't have the storage capacity to do much more. As I added panels growing the system to about 1600 watts, I was able to run the AC during the day once my batteries reached Float.

    I separated my cooking and bathroom into another building, since both required heat, composting toilet.

    I used an 1800 watt inverter, I still am using it today in a larger place. It will run a vacuum, and they make very good 10 amp vacuums now, but if you fridge kicks on while your cleaning... Always nice to have a bit more capacity. I planned to, but left my job, and now I've been living with in the energy budget, so it's not a big deal.

    Trying to run a fridge as well as an AC will also tax your system. Right now panels are cheap. I'd shoot for a larger array, more inline with your battery bank's needs, in fact I would suggest 'over paneling' so that you don't have to worry on marginal days.

    Good luck... someday I'll figure out this new forum software and put the photo in with my text....

    My cabin was 10 x 16... Sleeping loft for winter...

    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.
  • zoneblue
    zoneblue Solar Expert Posts: 1,220 ✭✭✭✭
    edited November 2015 #13
    I came up with those parts thinking 3 kwh a day with 2 days back up, though looking at it again it would discharge my batteries below a safe limit, so I would have to have a larger bank.
    Your muddling some concepts there. What i recomend is defining your base loads. These are things that are more or less non negotiable, non timetable. When i say we live on 3kWh/d thats our baseloads. Our system on a sunny day around the equinoxes is capable of producing around 11kWh/d, but it cant do that that often. But year round it will produce 3kW/day on all but about 5 days of the year. Production over and above the base load is considered surplus and you can use that to run aircon, pump water, heat water or use your imagination. Thats how i designed it, because we dont like generators and our climate allows us to get away without one. So you need to understand your local climate, in order to say whether you do or dont need a genset. Or how often you need it. Those in the wintery north find them much more important, and if you have to invest in one, and keep it running then you may as well factor it into your design. Its that that allows you to bin the winteriest months from your irradiance figures.

    We dont really do days autonomy any more. That was when solar was expensive, and lead less so. These days we have the reverse situation, and instead we design battery systems around the optimum charge rate. If you work with something near 0.1C, that generally means, a) that you can recharge your bank in a single sunny day, and b) that you run a 25% DOD daily cycle range, which is considered optimum value for battery life. Working that back to days autonomy that works out at 2 days, because we assume 50%DOD is really as low as you want to go, except on rare occasions. But that doenst mean that the lights go off on the third day. For one thing theres always some solar output, and you dont use all your power at night, and you can manage discretionary loads like laundry. Wait for better weather. The longest nasty spell we had was 5 days. And we survived it just fine.
    My largest drawing appliance would be a dorm fridge that would eat about 1.5 kwh/day to run, reading other peoples posts though it sounds like I can find more efficient ones to give me more kw budget.
    Always start with conservation, its cheaper to not use power than produce it.
    Is there a point where I should look at getting more than one charge controller? At that point I would have to run multiple banks of batteries?
    Systems do tend to come in intervals dictated by charge controller size. As the decent ones are around 80 Amps, at 24V that means multiples of 2kW. At 48V multiples of 4kW etc. You can run parallel charge controllers into one battery bank, but each CC has its own array. Weve hit you with a fair bit, take your time, read here each week for a couple of months and it will all start to make sense. The learning curve is part of the territory.
    I found a window unit that uses 455 watts, figuring it would run the compressor roughly 5 minutes of every 15 minutes I was thinking 455 watts x 0.33 hr = 150wh.
    Mind your units, 455W, at a one third duty cycle (realistic?) is 455W / 3 * 24h or 3650Wh/day.
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,731 ✭✭✭✭✭✭
    We do days of autonomy because where we live (southwest US and similar) does not require a generator. It is just conformance to requirements of the owner. Just another point of view. 
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

  • zoneblue
    zoneblue Solar Expert Posts: 1,220 ✭✭✭✭
    Sure Dave, but you dont just increase bank size willy nilly anymore right? The PV is lifted to match.
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,731 ✭✭✭✭✭✭
    edited November 2015 #16
    I do like willy nilly, I admit that. The truth is that the L16 400 ah and the L16 1,100 AH that I mostly use have really not changed price at all in 10 years. Sometimes they go up a little and sometimes they go down. I have friends your way and I know the pricing is different.

    The real point is that you look out the window and live within your resource. I call it the the 4 to 40 mentality. Live on 4 KWH or run an electric oven, condition space, and pump a 2" stream of water straight up a several hundred feet using 40 KWH. 
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

  • zoneblue
    zoneblue Solar Expert Posts: 1,220 ✭✭✭✭
    edited November 2015 #17
    Well i know we all love solar, but there are plenty of folk who are saying that PV is not sustainable. With the decline of oil, the resulting complexity of our industrial base will necessary decline to the point that we cant support the complex manufacturing processes to build solar, even though theoretically they do have a positive energy return on energy invested. Thats the theory, Nicole Foss is one such advocate for this argument. I dont think theres any way to know for sure, whether we will make some other energy breakthrough before such a thing plays out. Mean time we make a call and say well maybe 4 is better than 40?

    But i do agree on the window thing. Mollison always said that if what you see out the window is cows and cabbage, then thats what you eat.

    In practice here is yesterdays day in the life around here. The top orange curve is the house load in DC watts. Breakfast spikes. Slow cooker in the morning, vacuum at noon, garden watering in the afternoon. Fridge cycling, inverter off at night. Several computers and stereo most of the day, movie and lights at night. Shutting down at 10.30. 4.7kWh CC production.



    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,731 ✭✭✭✭✭✭
    Very well balanced in many ways! I like the part of the stereo on most of the day.
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

  • draines
    draines Registered Users Posts: 17
    Kind of off-topic zoneblue...but what is the monitoring program/output source you use to track your system? I really like this output format! Thanks in advance!
  • zoneblue
    zoneblue Solar Expert Posts: 1,220 ✭✭✭✭
  • softdown
    softdown Solar Expert Posts: 3,812 ✭✭✭✭
         A couple more experienced posters already said it....but this is the time to panel up for many reasons. Batteries are historically expensive while panels are historically dirt cheap. I'd double your panel array. You already acknowledged the need for a larger charge controller. You can also convert a newer model chest freezer into a hyper efficient refrigerator by installing a thermostat that allows it to run at fridge temperatures....40F is a good baseline. Bacteria likes to grow at temps over 40F.
         And brace yourself for several "what the hell just happened" days. Solar power arrays seems to do mysterious things at times. I'm figuring it will take a few years to know what is causing what. Using a little 12 volt system did very little for my knowledge it would seem.
         Reading solar books is pretty useful for beginners. Apparently there are no good intermediate books. This board is usually  exceedingly helpful. You are off to a great start...congrats.
    First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries