Setting up a new 800 watt panel - off grid system, Need some help please :)

darrylgood
darrylgood Solar Expert Posts: 25
Hello Everyone.

I am setting up an off grid system for our cottage. I have sized it out and have determined that we can live comfortably with 800 watts (3 - 265 watt panels) I have purchased only the panels so far and have a couple questions as I'm just a solar amateur at this point in time :)

Does anyone know of a website/link/forum that has directions in setting up a system such as mine?

I believe I should be doing a 24 volt system, is this correct? What is the advantage, what is different from a 12 volt system?

Is a 1600 watt inverter large enough or should I go for the 2500?

How do I determine the charge controller size?

How should my battery's be wired?

Any info would help

Thanks so much everyone!
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Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Setting up a new 800 watt panel - off grid system, Need some help please :)

    Welcome to the forum.

    I guess it's my day to be mean to people. :p

    You're going about it the wrong way 'round. The first thing you need to do is determine your loads, not buy panels.

    The maximum Watts at any given time will tell you how big an inverter you need. The total daily Watt hours will tell you how much battery you need. These two together will tell you what system Voltage you should pick. Here's a piece on system Voltages you should read: http://forum.solar-electric.com/showthread.php?15989-Battery-System-Voltages-and-equivalent-power

    From there you can figure out how much panel you need to recharge the batteries, and what charge controller will connect the two. All the specifications together (including distances involved) will determine what size wire and circuit protection is needed on the various circuits involved.

    So before any more money escapes from your wallet, let's get down to what you need to run and how much power it all will use.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Setting up a new 800 watt panel - off grid system, Need some help please :)

    The reason we ask about loads first is most people under estimate their load and over estimate how much power a solar power system can output. The batteries can "hid" miss-match between solar power and load power for awhile--but eventually it usually end in a prematurely dead battery bank.

    We can size a system based on solar array size or battery bank size--But that is usually a space or cost limitation. It is always better to start with the loads and see what such a system would look like to meet those loads.... Then make adjustments of costs and other issues.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Photowhit
    Photowhit Solar Expert Posts: 6,002 ✭✭✭✭✭
    Re: Setting up a new 800 watt panel - off grid system, Need some help please :)
    darrylgood wrote: »
    .... I have sized it out and have determined that we can live comfortably with 800 watts...

    How did you determine this?

    DId you take into account solar isolation for Winter, willingness to run generator?
    What % of battery capacity are your values based on?

    I ask and several others will likely already ask by the time I post, since 800 watts of array is a very small amount of electric, I guess you don't have many heavy draws, no well pump, likely no fridge, things with motors...

    This forum will gladly help you setup a system, Your in the OFF Grid area, so I assume you will be off grid, No well pump?

    Might read through the FAQ's Here, Lots of information!

    There are some pretty good articals here.
    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.
  • mikeo
    mikeo Solar Expert Posts: 386 ✭✭✭
    Re: Setting up a new 800 watt panel - off grid system, Need some help please :)
    Photowhit wrote: »
    How did you determine this?

    since 800 watts of array is a very small amount of electric, I guess you don't have many heavy draws, no well pump, likely no fridge, things with motors...
    This is just the right amount of solar to run an energy efficient fridge and a couple of led lights. If that is all you have then 800 watts should be enough. Any more power requirements for an off-grid will send you back to the drawing board for a loads evaluation. An 800 watt system will provide an average of about 26 amps into a 12 volt battery system over a 4 or 5 hours of a bright sun day and will peak around 50 amps. You can expect around 2kw worth of power a day year around average when the sun shines, and near zero energy production on cloudy days. With 26 amps average charge rate, a 260 amp hour battery at 20 hour rate would be about right for this system. You could draw a max of around 1800 watts from this system drawing the battery down to 50% state of charge. This leaves no room for cloudy days without running a generator to keep the system charged up. So if you need 3 days of solar isolation, you could only draw around 600 watts per day. As you see, this system does not power much.
  • darrylgood
    darrylgood Solar Expert Posts: 25
    Re: Setting up a new 800 watt panel - off grid system, Need some help please :)

    Hi guys thanks for the response, here is some info

    The only large thing that will be run in the cottage is a small 10 cubic feet fridge, a couple lights, no tv/microwave, just small stuff - radio, maybe laptop ect...

    I have used an online calculator to determine that i need around 1500 - 2000 watt hours per day.

    Yes i will be off grid, no wells or pumps. It will only be used in the summer and we will use propane for cooking and a wood stove for heating.

    We do have a generator if needed.

    Hope this helps :) Thanks soooooo much everyone
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Setting up a new 800 watt panel - off grid system, Need some help please :)

    You'd be amazed (or possibly appalled) by how much power that "small stuff" actually uses. Particularly the little refrigerator: http://forum.solar-electric.com/showthread.php?12272-Just-how-bad-a-small-frige-is

    What you can expect from 800 Watts of panel is about what mikeo described. I've got 700 Watts on a 24 Volt system with fairly long Summer days and can squeeze about 2.5 kW hours per day from it with a bit of load management. So with your predicted 2kW hours consumption and generator at the ready it should be feasible.

    You might do a 12 Volt system, but with the inevitable load increases you may be happier with 24. As a rule I suggest avoiding 12 Volt unless there is a specific need for that Voltage.

    Those panels probably have a Vmp of 30 +/- though, so they won't work well on a 24 Volt system (cannot configure three of these panels for 24 Volt except all in series: Vmp 90). On 12 Volts you'd put them in parallel and use an MPPT type controller. That would get you a peak charge current around 50 Amps which is fairly good size. It would support 500 Amp hours @ 12 Volts (somewhat difficult configuration to obtain). At 25% DOD that would give you roughly 1.5 kW hours capacity.

    So you have to start looking at trade-offs between equipment available and what you can do with it. For example you might buy four golf cart batteries and get 440 Amp hours @ 12 Volts. You'd have more charging capacity than you need (good for not-so-sunny days) but at 25% DOD your stored power would be 110 Amps hours * 12 Volts or 1320 Watt hours. Panels can supply additional power to that during daylight hours, and/or you could discharge a bit deeper if needed (up to 50% which is 2.6 kW hours).

    Your inverter size would be determined by the maximum combined power draw you expect. In other words if all the loads that would be running at the same time don't exceed 1kW you don't need a 2kW inverter. The refrigerator is probably the worst, as its start-up surge is likely to exceed all the other loads combined.

    Is this starting to make sense to you? :D
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Setting up a new 800 watt panel - off grid system, Need some help please :)

    Roughly, where is the cottage (amount of sun)?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • darrylgood
    darrylgood Solar Expert Posts: 25
    Re: Setting up a new 800 watt panel - off grid system, Need some help please :)

    The cottage is located in south Ontario/Canada on Georgian Bay. I can get a full 8 hours or more of summer sun from the future location.

    Thanks Cariboocoot, slowly starting :)

    Can I get some more info on the difference between a 12v and 24v system also the advantages/disadvantages in wiring them in series/parallel.

    I should also add that we will most likely like to make this this larger in the future to produce more energy, so I should keep this in mind when setting up the current system,

    Thanks :)
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Setting up a new 800 watt panel - off grid system, Need some help please :)

    I don't know if you've read this bit yet: http://forum.solar-electric.com/showthread.php?15989-Battery-System-Voltages-and-equivalent-power

    That's the basics of comparing system Voltages. Although maybe I should add something about the wider variety and availability of <48 Volt fuses/breakers/switches which can make 24 Volt systems easier to wire up.
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Setting up a new 800 watt panel - off grid system, Need some help please :)

    Just as an aside from one who has been there. The question of the fridge is complicated. A good LP fridge is way more cost effective even with low(er) PV system costs, assuming part time use. A good energy star fridge will use as much energy (~500 WH/day) as we use in total. Lp fridges a fairly expensive to buy, pretty easy on Propane. The equation begins to favour a conventional fridge as the use become closer to full time.

    I figure my fridge costs about $1/day to run. To increase the PV (and batteries) to run a conventional might be ~$2000 all in. That said, since we are closer to full time, if I had to do it over again, I would have gone with a bigger PV and a conventional fridge, but if you are really part time, a LP migh prove much cheaper life cycle cost.

    You can often beat the price on a Lp by carefully buying used. I bought a great used Dometic Americana from a Candian rebuilder, with warrantee for under $1000 shipped to Thunder Bay.

    You can also decrease the run time of an LP by adding insulation to the. Ate, and adding fans to the condenser.

    tony

    PS, as has been stated before, all design considerations stem from t he load calcs. Any other method is,, Ready, Fire, Aim.

    t
  • darrylgood
    darrylgood Solar Expert Posts: 25
    Re: Setting up a new 800 watt panel - off grid system, Need some help please :)

    Thanks icarus, we might even decide to keep our old propane fridge, so I do believe that the 800 watt system will be enough for our uses.
  • darrylgood
    darrylgood Solar Expert Posts: 25
    Re: Setting up a new 800 watt panel - off grid system, Need some help please :)

    Can some one please give me a beginners rundown on amps watts and volts and how they all work into the equation. I am starting to get confused :)
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Setting up a new 800 watt panel - off grid system, Need some help please :)
    darrylgood wrote: »
    Can some one please give me a beginners rundown on amps watts and volts and how they all work into the equation. I am starting to get confused :)

    Uh, read my signature. That's why I put those two formuli there. :D
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Setting up a new 800 watt panel - off grid system, Need some help please :)

    Here is an Electricity 101 for Boaters:

    http://boatsafe.com/nauticalknowhow/electricity.htm

    On the AC side, it gets a bit more complex (math)--But the basics between AC and DC are the same for a first order approximation.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • darrylgood
    darrylgood Solar Expert Posts: 25
    Re: Setting up a new 800 watt panel - off grid system, Need some help please :)

    Perfect, thanks guys
  • Skippy
    Skippy Solar Expert Posts: 310 ✭✭
    Re: Setting up a new 800 watt panel - off grid system, Need some help please :)
    darrylgood wrote: »
    Can some one please give me a beginners rundown on amps watts and volts and how they all work into the equation. I am starting to get confused :)

    From one new guy to another - your not alone :cry: . . . :p

    I am finding out all kinds of usefull stuff, just reading all the old posts that are on here. . . it takes awhile, and when my eyes start to glaze over from all the technical stuff, I stop and leave it for a day or so. . . but I am still reading !

    I definately agree with the points made here so far, since I ran my batteries down to 60 percent (WAY to low for good battery life) and since it is the middle of winter here,and cloudy ALL the time. . . it took almost 3 days for the thing to recharge back to 100 % with NO LOADS - and another day on top of that, to trigger the green light on the battery monitor. . . so it is very easy to overestimate the amount of power you are going to get out of the panels. . . I am starting to think, that I should "estimate" my panels at about 1/2 of the rated capacity - since I have yet to see anywhere near full output from them . . .
    Good luck on the project . . . :D
    2 - 255W + 4 - 285W PV - Tristar 60 amp MPPT CC / 3 - 110W PV -wired for 36V- 24V Sunsaver MPPT CC / midnite bat. monitor.
    1 KW PSW inverter 24V / 2.5 KW MSW inverter-24V ~ 105 AHR battery.
    3 ton GSHP.- 100 gallon warm water storage / house heat - radiant floor / rad
    9 -220W PV - net meter - Enphase inverters and internet reporting system.
    420 Gallon rain water system for laundry.***  6" Rocket Mass Heater with 10' bed for workshop heat.
    Current project is drawing up plans for a below grade Hobbit / underground home.
    Google "undergroundandlovinit" no spaces.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Setting up a new 800 watt panel - off grid system, Need some help please :)

    The panels+charge controller probably output a good 77% of the "name plate" capacity (sort of like HP ratings for US cars--And better than Horse Power ratings for air compressors :p).

    Add that flooded cell batteries (worst case, older batteries cycled 15% from full) are somewhere about 80% efficient and the typical AC inverter usage is around 85% efficient--You multiply that all together you get around 52% end to end efficiency (solar panel name plate to AC power as measured by a Kill-a-Watt meter).

    So--Yes, the "loses" are near 50% for the system... And you should never plan on using 100% of your power every day (some days there is more sun, others less). And some days you may use 66-75% of your power and others you may use 120% of your power (cleaning/wash day/visitors/etc.).
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Setting up a new 800 watt panel - off grid system, Need some help please :)

    Don't feel bad, guys; some of us have been poking about with electrical circuits for *mummble-mumble* years now. You're trying to get it all in one go, and that's not easy! :D
  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Setting up a new 800 watt panel - off grid system, Need some help please :)
    BB. wrote: »
    You multiply that all together you get around 52% end to end efficiency (solar panel name plate to AC power as measured by a Kill-a-Watt meter).

    I got a good laugh from some YouTube videos with people testing the efficiency of (illegal) plug-in grid tie inverters by dividing the Kill-a-Watt reading of the grid feed by the nameplate power of their panels rather than trying to measure the DC input. Funny thing, it came out around 50%. :-)
    SMA SB 3000, old BP panels.
  • darrylgood
    darrylgood Solar Expert Posts: 25
    Re: Setting up a new 800 watt panel - off grid system, Need some help please :)

    Ok guys thanks for the help, after a LOT of reading I am finally getting a hold on this.

    I will be buying another 270 watt panel, so that is 4 - 270 - 1080 watts total.

    The only thing I am stuck on now is whether I should do a 12v or 24v system. Can my panels do the 24v system? Is the advantage of the 24v system that it can handle a larger load?

    It seems like most small off grid systems that I have read about are 12v, so I'm a little stuck :(
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Setting up a new 800 watt panel - off grid system, Need some help please :)

    These panels with a Vmp around 30 can be used on a 24 Volt system if they are put two in series (Vmp 60) and connected via an MPPT charge controller. So with four panels you'd have two parallel strings of two in series.

    I would go 24 Volts if there is no need for 12 VDC to supply particular loads.
  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Setting up a new 800 watt panel - off grid system, Need some help please :)
    darrylgood wrote: »
    Ok guys thanks for the help, after a LOT of reading I am finally getting a hold on this.

    I will be buying another 270 watt panel, so that is 4 - 270 - 1080 watts total.

    The only thing I am stuck on now is whether I should do a 12v or 24v system. Can my panels do the 24v system? Is the advantage of the 24v system that it can handle a larger load?

    It seems like most small off grid systems that I have read about are 12v, so I'm a little stuck :(

    Some of the concerns:

    1. If you have a bunch of 12 volt appliances and lights, of the sort that would come pre-installed in an RV for example, then you may have no good option but to go with 12 volts. A mixed 12/24 volt system does not work. So lets start by assuming that all of your loads will be AC or that you will get 24v DC appliances.

    2. If you will be using more than about 1200 watts peak (100 amps at 12 volts into the inverter), then it would be much better to go with a 24 volt system. Especially if you cannot easily mount the inverter right next to the battery bank, the smaller wire size you can use and still get low power losses from the cable resistance argues in favor of a larger system.

    3. Look at your battery bank configuration. If you will need 4800 watt-hours of capacity to service your loads while not going too deeply into the battery capacity (~ 1Kwh per day in that example), then at 12 volts you will need to find 400 AH batteries of some voltage and put them in series. (Avoid putting batteries in parallel if you can.)
    If you instead use 24 volts, you can build your battery bank out of 200 AH batteries. If you go all the way to 48 volts, you can use 100 AH batteries in series.

    Now going back to your particular hypothetical case:
    A. With 1080 watts of panel, you should have at least an 800AH FLA battery bank at 12 volts to avoid trying to push too much charging current into the batteries at once.
    But at 24 volts, you only need 400 AH in the individual batteries. At 48 volts, only 200 AH. The energy storage stays the same, but since you cannot make up your bank of cells lower than 2 volts each, you have more options to choose the combination of voltage and AH for the individual batteries the higher your system voltage is.
    B. For the other constrains, look at your actual peak power loads and the size inverter you will be using to service them. Motor starting is usually one of the limiting factors requiring a higher inverter wattage rating even when the running power is low.
    SMA SB 3000, old BP panels.
  • darrylgood
    darrylgood Solar Expert Posts: 25
    Re: Setting up a new 800 watt panel - off grid system, Need some help please :)

    Great, thats what I thought, first thing I have gotten right to far :)
  • darrylgood
    darrylgood Solar Expert Posts: 25
    Re: Setting up a new 800 watt panel - off grid system, Need some help please :)

    Thanks inetdog, very helpful!!!!!
  • darrylgood
    darrylgood Solar Expert Posts: 25
    Re: Setting up a new 800 watt panel - off grid system, Need some help please :)

    Great, and for the 24v system, How would I wire my batteries, lets say I have 6 12v batteries.

    Thanks again
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Setting up a new 800 watt panel - off grid system, Need some help please :)
    darrylgood wrote: »
    Great, and for the 24v system, How would I wire my batteries, lets say I have 6 12v batteries.

    Thanks again

    No, lets say you have four 6 Volt batteries and put them all in series. :D
    Battery system Voltages: http://forum.solar-electric.com/showthread.php?15989-Battery-System-Voltages-and-equivalent-power

    If you use six 12 Volt batteries you end up with three parallel strings of two in series (like the attached pic but three strings instead of two) and the issues of equal current sharing come up.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Setting up a new 800 watt panel - off grid system, Need some help please :)

    Not sure I understand that drawing, but the panels would be wired the same as the batteries above: create two strings with two panels in series (+ to -) then parallel the positive and negative outputs of the two strings.
  • darrylgood
    darrylgood Solar Expert Posts: 25
    Re: Setting up a new 800 watt panel - off grid system, Need some help please :)

    Great, everything makes sense :) If I was to have only 4 12 v battery's though, I would wire them exactly as in your diagram correct?
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Setting up a new 800 watt panel - off grid system, Need some help please :)
    darrylgood wrote: »
    Great, everything makes sense :) If I was to have only 4 12 v battery's though, I would wire them exactly as in your diagram correct?

    Either that or the "diagonal wiring" method #2 from the Smart Gauge page: http://www.smartgauge.co.uk/batt_con.html
  • darrylgood
    darrylgood Solar Expert Posts: 25
    Re: Setting up a new 800 watt panel - off grid system, Need some help please :)

    Wouldn't that only keep the 12v? Maybe i'm missing something