DIY off-grid system

czyhorse
czyhorse Solar Expert Posts: 42 ✭✭
Let me start off by saying I wish I would have found this forum a month ago...it could have helped save me some time in determining what I needed for my system!

I am attempting to go the DIY route and have purchased the following equipment:

Three (3) Evergreen Solar 195W ES-A-195 panels
Outback FM60 charge controller
Exeltech XP1100 pure sine wave inverter
Midnight Solar Mini DC Disconnect (125 Amp)
2 Outback 60 amp DC breakers for input and output of charge controller

I am getting ready to purchase 4 Rolls/Surrette 6cs-21ps deep cell batteries (683 Ah) for a 24 V system. I'm also considering the 6cs-17ps (546 Ah)

My goals are to power stereo, TV, moderate low-wattage lighting, computer, and possibly a small energy efficient freezer in the future. I did a energy estimate and designed from an estimated 2,000 Watt hr/day electrical need. I wanted to get components that allow me to upgrade panels in the future.

Panels will be roof mounted and approx. 70' away from the charge controller. Charge controller, battery bank, and inverter will all reside nearby in an attached garage.

I have a few questions:

Did I make a mistake purchasing the Exeltech if I want to add more solar panels in the future? I had heard that getting an oversized inverter for your system wasted energy. That's why I went with the 1100 W Exeltech.

Did I size my DC breaker (from battery to inverter) correctly at 125 Amp? I can not find any information anywhere on how to size DC breakers. I used the 60 Amp Outback breakers (between array and cc, and cc and battery bank) because that was what was recommended in the FM60 user manual. Are those sizes appropriate?

Thanks in advance for any response.

Comments

  • RandomJoe
    RandomJoe Solar Expert Posts: 472 ✭✭✭
    Re: DIY off-grid system

    No, I don't think it's a mistake to get that inverter. For a variety of reasons. First, as you mention, larger inverters often have higher idling losses. You can in the future get a larger inverter for more / larger loads, but keep the smaller inverter in use for nighttime standby in case you want to get up and turn on a light or if you have some "always on" loads that are small. (For night standby, when you normally have no loads at all, there are better options - some inverters have "sleep" modes so they drop to a very low current draw until something is turned on for them to power. Don't know if your Exceltech has that.)

    But there's also the "eggs in one basket" issue - the inverter is one of the more complex pieces of a solar system (the other being the charge controller). If it goes down, I'm stuck. But I have a small collection of inverters, so even if the big one goes out on me, I can still keep some lights on or run a computer on one (or more) of the smaller ones.

    Actually, loss of the inverter is more of an issue than the charge controller to me. In a pinch, I can do some quick reconfiguring of my solar panels and just hook them straight to the batteries. I have to keep an eye on them that way, but it works. No inverter means no 120VAC, no way around that.


    The inverter fuse sounds about right to me - it just needs to be able to handle the max current the inverter is going to draw, so be sure you use its surge rating. 125A @ 24V should still be fine unless your inverter has an outrageous surge capacity... Just be sure the wire you use can handle at least 125A. Does no good to put a fuse in if the wire's going to burn up instead! :p
  • Windsun
    Windsun Solar Expert Posts: 1,164 ✭✭
    Re: DIY off-grid system
    RandomJoe wrote: »
    But there's also the "eggs in one basket" issue - the inverter is one of the more complex pieces of a solar system (the other being the charge controller). If it goes down, I'm stuck.
    With many inverters, especially the cheap MSW ones like Walmart and online discounters sell I might agree.

    However, the Exeltech inverters are almost bulletproof. We have never had a single failure of one in the 10+ years we have been selling them (not counting things like lightning hits and other such physical damage). As far as I know, they are still the only small inverter approved for military use in Iraq and Afghanistan.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: DIY off-grid system

    Starting with your existing panels: Use the PV Watts website, use 1 kW of solar panels (1,000 watts, unfortenatuly the smallest array value allowed), use Indianapolis, Indiana, use derating = 0,52 overall system efficiency (off-grid with AC inverter) gives us:
    "Station Identification"
    "City:","Indianapolis"
    "State:","Indiana"
    "Lat (deg N):", 39.73
    "Long (deg W):", 86.28
    "Elev (m): ", 246
    "PV System Specifications"
    "DC Rating:"," 1.0 kW"
    "DC to AC Derate Factor:"," 0.520"
    "AC Rating:"," 0.5 kW"
    "Array Type: Fixed Tilt"
    "Array Tilt:"," 39.7"
    "Array Azimuth:","180.0"

    "Energy Specifications"
    "Cost of Electricity:"," 7.3 cents/kWh"

    "Results"
    "Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
    1, 3.18, 52, 3.80
    2, 4.14, 61, 4.45
    3, 4.44, 69, 5.04
    4, 5.15, 75, 5.48
    5, 5.73, 84, 6.13
    6, 5.84, 79, 5.77
    7, 5.92, 82, 5.99
    8, 5.67, 80, 5.84
    9, 5.20, 72, 5.26
    10, 4.70, 71, 5.18
    11, 3.07, 45, 3.29
    12, 2.37, 37, 2.70
    "Year", 4.62, 806, 58.84

    That gives a 1,000 watt of solar panel system ~ 37-84 kWhrs per month average output. Take the top 9 months and we get ~61 kWhrs minimum per month (month #2 or February). You have 3x195 watts of panel = 585 watts total... So:
    • 61 kWhrs per month per 1k watts of panels * 0.585 kW * 1/30 days per month = 1.2 kWhrs or 1,200 Watt*Hours per day
    So, you are a bit light on the number of solar panels to meet your load requirements for 9 months of the year.

    Assuming the highest voltage of 48 volt bank, you would need 4 Evergreen panels in series to have a minimum Vmp=58volts at 95F. Your controller would support up to 5 modules in series (Voc=124vdc at 14F). 6 panels in series is pretty close to the absolute maximum voltage of 150 VDC (Voc=149vdc at 14F).

    But you are planning on a 24 volt battery bank, so 3 panels in series is just fine.

    You have a 70' run from the panels to the controller/battery shed--So, you would probably want to run the three panels in series (3 panels in series is fine for 24 or 12 volt battery banks). That will allow you to run much smaller gauge wire (and/or heavier wire with less losses) when running the array at Vmp at the higher voltage.

    You do not need a circuit breaker at the input of the charge controller... It is input protected. If you put, for example, the three Evergreen 195 watt 17 volt panels in parallel, you should have a fuse/breaker of 15-20 amps (check the spec. sheet for Series Protection Fuse rating) in series which each panel (protect a shorted panel from over current by the other two panels).

    However, if you run all three in series to the MPPT Charge Controller, you don't need any fuse/breaker at all.

    For the output of the FM 60--you should follow the manual's instructions. Normally, for a standard breaker/fuse, you would use wire+fuse rated at 1.25 the operating current (safety factor). So 1.25x60a=75a minimum. Round up to the next standard breaker/fuse of 80 Amps (IIRC).

    In the case of the Outback Breakers, they have ones that are rated to operate at rated load. So check the specifications for the 60 amp breaker you are using and see if it is rated to operate at 60 amps. Wire should still be rated to operate at 80 amps.

    Now, the above 60 amp rating is the maximum output from the charge controller... But it also depends on the battery bank voltage. For example, if you have a 12 volt battery bank (charging at 14.4 volts, the maximum current (without safety factors and losses) would be:
    • 3*195 watts / 14.4 volts = 40.625 amps
    So, a 60 amp circuit is certainly practical for a 12 volt battery bank.

    If you had a 24 volt battery bank, the maximum current would be 20 amps. A 48 volt bank would be 10 amps maximum. 60 amps is overkill, but perfectly OK and great to do if you plan on adding more panels in the future.

    Now, to the inverter. I will do some generic calculations. Assume minimum battery voltage of 10.5 volts (dead 12 volt battery) and inverter is 80% efficient with heavy loads. 1,100 watt inverter:
    • Amps = Power/Volts = 1,100 watts * 1/10.5 v * 1/0.80 eff = 131 amps at on 12 volt bank
    For a 24 volt bank, the voltage would be double and the current will be 1/2:
    • Amps = Power/Volts = 1,100 watts * 1/21 v * 1/0.80 eff = 65.5 amps at on 24 volt bank
    Remembering that you need a 125% safety factor for wire and fusing:
    • 65.5 amps * 1.25 = 82 amps minimum
    You can run heavier wire and round the fuse/breaker up to the next higher value of 100 amps. Check the inverter manual--it should tell you the recommended DC input breaker/fuse rating (100 amps or 125 amps probably).

    Generally a good rule of thumb is ~5% to 13% of a battery banks rated Amp*Hours (at 20 Hour Rate)... So the rough battery bank capacity range supported by 585 watts of solar panels at 24 volts would be:
    • 585 watts * 1/24 volt bank * 1/0.05 = 488 Amp*Hours Maximum
    • 585 watts * 1/24 volt bank * 1/0.13 = 188 Amp*Hours Maximum
    So, at this point, the battery bank you are thinking of supporting of 546-623 AH would be very nicely supported by 2x your current panel farm... You would need a backup battery charger to properly charge and equalize a bank the size you are proposing.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • czyhorse
    czyhorse Solar Expert Posts: 42 ✭✭
    Re: DIY off-grid system

    So it sounds like everything may work out...that's great! Thanks for your replies.

    I will plan on dropping the 60Amp breaker coming in to the charge controller.

    I am a little confused about the need for a backup charge controller for the Surrette batteries... Could you go into a little more detail about why another one is needed?

    I plan on using this system for grid power outages and occasional light use. Is there a problem in oversizing the battery bank Amp-hours? I understand that if I used the system heavily for many days in a row that recharging could be a problem, but I am afraid that a lower Amp hour battery bank will not be as upgradeable...
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: DIY off-grid system

    Backup charge controller in the sense that you will need an alternative energy source to get your batteries back up to charge (and/or fully equalized).

    Typically that is a 120/240 VAC to 24 volt DC charger that is powered from your home's AC wiring and/or a back AC genset.

    Lead acid batteries operate best from ~75-90% state of charge.

    If they are over charged (>100%) the positive plates will fail and you will use lots of battery water (or ruin sealed type batteries). The batteries should be brought over >90% state of charge at last once a week.

    If the batteries go below 75% state of charge and stay there for days/months--they will sulfate and die a quick death (months-year)

    If the batteries are cycled often below <50%, they will not last as long. If they are stored below 50%, they will sulfate and die.

    If the batteries are discharged below <20% State of Charge, you run the risk of "cell reversal" which will kill the cell/battery pretty much immediately.

    Having an additional charging source (beside the solar array) will help you keep your bank healthy.

    Other recommendations, a good temperature compensated hydrometer and a Battery Monitor.

    Take a read through the battery FAQ's:

    Deep Cycle Battery FAQ
    www.batteryfaq.org

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • RandomJoe
    RandomJoe Solar Expert Posts: 472 ✭✭✭
    Re: DIY off-grid system
    Windsun wrote: »
    However, the Exeltech inverters are almost bulletproof. We have never had a single failure of one in the 10+ years we have been selling them (not counting things like lightning hits and other such physical damage).

    Impressive! :) But even then my "security gene" wants a backup. And maybe even a backup to the backup! :p Wouldn't be such an issue to me, except the event that caused me to eventually put the whole system in to begin with was sitting in the cold and dark for two days after an outage. If my online inverter gets zapped by lightning, I still have a backup! :cool:
  • RandomJoe
    RandomJoe Solar Expert Posts: 472 ✭✭✭
    Re: DIY off-grid system
    czyhorse wrote: »
    I plan on using this system for grid power outages and occasional light use. Is there a problem in oversizing the battery bank Amp-hours? I understand that if I used the system heavily for many days in a row that recharging could be a problem, but I am afraid that a lower Amp hour battery bank will not be as upgradeable...

    That's roughly what I do with mine. Primary purpose for existing is to keep the fridge cold / lights on / computer or ham gear going during an extended power outage. It's also a fun hobby to me, and I otherwise use it to a lesser degree on a daily basis. The ham bench has been off-grid for most of a year now, as well as a small computer. More is soon to be added once the new panels get installed (hopefully over Christmas break) doubling my solar power from 540 to 1080W.

    Oversizing the battery bank is good - gives you extra reserve, should there be many cloudy days. But only if you are able to keep it charged! In my case, I had 660AH at 12V. I only used about 10% per day, which my 540W of panels could *easily* replace often by 1PM. However, they are also right at the bottom end of the "desired charge current range" for a bank that size. Ideally I'd hit 10% or so (66A) but 540W is only (theoretically) 38A and realistically I only hit 30A on sunny days. Closer to 5%, about the very lowest you want to go or it gets really hard to keep the bank going. Doubling my array will get me closer to that 10% "ideal".
  • czyhorse
    czyhorse Solar Expert Posts: 42 ✭✭
    Re: DIY off-grid system
    BB. wrote: »
    Backup charge controller in the sense that you will need an alternative energy source to get your batteries back up to charge (and/or fully equalized).

    Typically that is a 120/240 VAC to 24 volt DC charger that is powered from your home's AC wiring and/or a back AC genset.

    Does anyone have any brand names/model recommendations/ size of charger I should be looking at?
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: DIY off-grid system

    Xantrex had a nice TC (True Charger) line--but it has been updated with the TC-2 line--which appears to be having problems shipping (no stock anywhere?).

    Our host sells Iota Chargers which are a very good line.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • czyhorse
    czyhorse Solar Expert Posts: 42 ✭✭
    Re: DIY off-grid system

    I read NAWS recommendations for battery charger sizing and they recommend 15% to 30% of your battery amp hour capacity. If my battery amp hour capacity is 683 A-h:
    683*0.15=102

    The largest charger Iota makes is 40 amp (in 24V) and retails for hundreds of dollars. Am I better off just buying another solar panel? Or would I be better off by getting a supplemental modified sine wave inverter w/ built in charger...like Xantrex TR1524?

    Also on wire type I was planning on using stranded TTHN size 2/0 to run from the array to the charge controller (approx. 70 ft). I was thinking of using welding cable for the wiring in the Midnight Solar Mini DC disconnect box where flexibility could be an issue. Will I have any issue with the breakers or the charge controller's mechanical lugs in securing this wire? I thought I read that mechanical connections were not a good choice in securing welding cable...I think I read the optimal connection was soldering.
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: DIY off-grid system

    In short, it is always advantageous to have more PV, but in reality, you really need to have some other way to charge to make up for any solar shortfall, so you really need a genny/shore powered charger. While 102 amp is the optimum size, smaller to some degree will work, as long as you are prepared to run the genny longer. You can always parallel two together.

    I realize that they are not cheap, but consider the cost of a battery charger relative to the cost of the battery bank. What did you pay for ~600Ah of battery @ 48 vdc? Will you spend several hundred dollars to quadruple it's lifespan? You've got ~$4000 worth of batteries, two 15 amp Iota 48 vdc charges would be ~$600. Sounds like a pretty good trade to me.

    Tony
  • czyhorse
    czyhorse Solar Expert Posts: 42 ✭✭
    Re: DIY off-grid system

    That being said, do you think I would be better off getting a dedicated battery charger or a modified sine wave inverter w/ charger (Xantrex TR1524)?
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: DIY off-grid system

    My plans for my 48V bank are for 3 possible sources.
    1) Iota charger via 2KW 120Vac genset ( Iota DLS-54.4-15: 48 volt 15 a )
    2) 1.5KW PV array
    3) XW internal charger via 4KW genset @ 240VAC

    Only #3 is "approved" but the other 2 should keep it 95% charged. Just have enough "toys"
    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 ,

  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    Re: DIY off-grid system
    czyhorse wrote: »
    I read NAWS recommendations for battery charger sizing and they recommend 15% to 30% of your battery amp hour capacity. If my battery amp hour capacity is 683 A-h:
    683*0.15=102

    The largest charger Iota makes is 40 amp (in 24V) and retails for hundreds of dollars.

    True...BUT...

    (already mentioned by Icarus in passing but I wanted to clarify)

    You *can* use more than one. In the situation you described, it looks like three of the Iota 40a@24v chargers would do the trick. And yes, they will play nice together.

    It's not a cheap solution, but it is a proper one.
  • SolarJohn
    SolarJohn Solar Expert Posts: 202 ✭✭
    Re: DIY off-grid system

    I just wanted to add that I love my Exeltech 1100 watt inverter. I've used it everyday for the past three years without a single problem. I power a chest freezer, sometimes a refrigerator/freezer, and more. When the power fails, I power a TV or radio, and have none of the interference I had with my MSW inverter. The only household appliances I can't use with the Exeltech are my Washer and Dryer. It just can't quite overcome the motor starting surge I guess. If I ever buy a bigger inverter I'll keep the Exeltech as a backup. I have a picture of my system here:

    http://solarjohn.blogspot.com/

    John
  • wild01
    wild01 Solar Expert Posts: 100 ✭✭✭
    Re: DIY off-grid system

    you had already mentioned that you would like a backup inverter jik

    so If I were you I would get a msw inverter charger that will cover your charger needs and provide you with a backup inverter. you can get a quality one for less than a grand.

    if this is to steep for your budget, look for a used 24v forklift charger, these will meet your needs nicely and are built far tougher than pv products (not that pv products aren't tough, just forklift chargers are designed for extremely heavy industrial use) but will usually require 3 phase power, high amp (100+)will require 440 3 phase.

    also 15-30 percent is a good rule of thumb for smaller systems, but is a little overkill in a battery as large as what you're describing. (overkill isn't a bad thing, it's just overkill)
  • czyhorse
    czyhorse Solar Expert Posts: 42 ✭✭
    Re: DIY off-grid system

    Just an update: I decided to go with the Iota 24v, 40A charger w/ IQ smart charge controller.

    I have most of my components delivered already and I'm getting geared up for the really fun part...putting it all together!

    My batteries have not arrived yet (Surrette 6 CS 17, 546 Amp/hr), and I was wondering if I can hook the Iota charger up to them to keep them fully charged until I get this whole thing put together.

    Does anyone here own a charger like this, and is it safe to leave hooked up to the battery bank for extended periods of time?
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: DIY off-grid system

    One way I have automated my maintenance charging of batteries (for example, cars that don't get driven much) is to use a 120 VAC lamp/utility timer and set it to power on, for example, one hour per day. That way I can keep a maintenance charge on the batteries without over charging (which many AC chargers tend to do if they do not have a good float setting).

    Then I don't have to remember to plug the charger in once or twice a month for a day's worth of charging.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • RandomJoe
    RandomJoe Solar Expert Posts: 472 ✭✭✭
    Re: DIY off-grid system

    An Iota with EQ4 should be just fine left on the battery bank. It will step through the stages of charging until finished, then drop to float. I'd measure that float voltage and make sure it meets with the manufacturer's recommendations, just to be sure. (Only major thing the Iota doesn't have is a temp sensor, so it won't adjust voltages for battery temp.)

    I leave mine on periodically. My off-grid system was put in primarily for backup in power failures, so if nastiness is forecast I'll switch on the charger. Sometimes I forget (or the weather stays gloomy for a week at a time) and I'll leave the thing on for quite a few days. Once it hits float, it never goes anywhere else.

    I just found on the Iota site that the IQ4 does a weekly EQ if it hasn't gone through the charge cycle in 7 days. Hm, may not care for that... Unfortunately (so far) I haven't found any info on how long / what voltage. I remember the (lame) instruction sheet I got with it didn't say much if anything about that...!
  • Robin Gudgel
    Robin Gudgel Registered Users, Solar Expert Posts: 58 ✭✭✭✭
    Re: DIY off-grid system

    60 amp panel mount breakers from OutBack or MidNite now fit in the MidNite MNDC125. That box used to only accept din rail mount auxilliary breakers, but now can accept either style. You can save a little money by going with the 63 amp din rail breakers though.
    The PV disconnect breaker is intended to protect the wiring, not the charge controller. If you wire with 6AWG wire, then a 63 amp breaker is the correct choice.