Just need a double check on my system setup. (Three 100w panels, 30A MPPT controller)

Hey guys! I pieced together my own little system to have on hand incase of a power outage in my area. It is just meant to run a mini freezer and a few LED lights incase the power in our area goes out for a few days or longer. My list of stuff is as follows....

-1500w 12v Power Inverter
-30A Tracer MPPT Charge Controller
-Two 35Ah 12v Deep cycle batteries run in parallel
-Three Renogy 100w Panels run in parallel

I made a schematic here...

http://s469.photobucket.com/user/MapleBoarder78/media/solar%20stuff_zps4ovu5lsj.jpg.html

As you can see in my diagram, I'm just not sure what size fuses to run on the five fuses with question marks next to them. I have been surfing this forum and others for days and I am finding a bit of conflicting information as the threads I read always have a setup that's a bit different than mine. I'm guessing the fuse between the controller and battery could use a 30A and the fuse between the panels and controller can also use a 30A? But for the three fuses running on the 12 gauge wire from the panels I'm not sure. From what I've gathered maybe 20A fuses on those? Thanks so much for your help!

Comments

  • BB.BB. Super Moderators, Administrators Posts: 29,207 admin
    Welcome to the forum TBK.

    OK, I am going to rain on your parade a bit--But some comments and answers both.

    The fuses for the solar panels, you might find a series fuse rating for them--If you cannot, then a good estimate would be:
    • 100 watts / 17.5 volts Vmp = 5.71 amps Imp (current maximum power)
    • 5.71 amps Imp * 1.25 Isc estimate * 1.25 NEC derating for wiring/fuses = 8.9 amps ~ 10 amps rated fuse/breaker per panel string
    You do not need another fuse/breaker from the array to the charge controller Vpanel input--The three fuses are fine.

    For the charge controller to battery bank, since the controller is rated for 30 amps, then:
    • 30 amps * 1.25 NEC derating for wiring/fuses = 37.5 amps ~ 40 amps maximum (based on 30 amp controller
    • 5.71 Imp * 1.25 * 1.25 = 26.8 ~ 30 amp minimum rating (based on your 3x 100 watt solar panels
    For the AC inverter:
    • 1,500 Watts * 1/0.85 AC inverter eff * 1/10.5 inverter cutoff voltage * 1.25 NEC derating factor = 210 Amp fuse/breaker if planning on 100% continuous inverter load
    Now, the rain.... First, realistically, the size battery bank of flooded cell lead acid batteries needed to power that amount of power would be:
    • 1,500 Watts * 1/0.85 AC inverter eff * 1/12 volt battery bank * 5 hour discharge rate (max recommended discharge) = 735 Amp*Hour @ 12 volt battery bank
    Your 35 AH batteries (12 volts * 2 in parallel for a 70 AH @ 12 volt capacity) would typically be expected to supply a maximum of ~14 amps continuous (for less than 5 hours) or possibly around 28 amps for a few seconds. No where near enough to really run a 1,500 Watt inverter (or standard refrigeration compressor).

    If these are AGM or GEL batteries, they could supply upwards of 140 to 350 Amps for a few minutes--But I would not recommend running them like that (the batteries probably would not last long).

    Another minor issue is the way the batteries are wired--You want to "cross connect" (negative power on one terminal, positive power from the opposite terminal on the other battery) to equalize current (charging/discharging) of the battery pair. More information here.

    A refrigerator is quite a large load. Even a smaller "bar fridge" can easily use ~290 kWH per year or:
    • 290,000 WH per day * 1/365 days per year = 795 WH per day
    A battery bank that can supply that amount of energy for 2 days with 50% maximum discharge (typical full time off grid battery bank) would be:
    • 795 WH per day * 1/0.85 AC inverter eff * 1/12 volt batter bank * 2 days storage * 1/0.50 max discharge = 312 AH @ 12 volt battery bank
    For an R/V or emergency power system, you might go with 1 day of storage instead or ~156 AH @ 12 volt batter bank--But that may have problems starting a refrigeration compressor.

    Also, to charge such a load:
    • 795 WH per day * 1/0.52 typical off grid system eff * 1/4 hours of sun (sunny area ~9 months a year, not winter) = 382 Watt solar array minimum
    Anyway--Just some quick back of the envelope calculations. When you go with a fridge/freezer for an off grid solar system, you go from a "small" to a "medium" size off grid power system pretty quickly.

    What you really need to do is get a Kill-a-Watt type meter and measure you AC loads (and pick very efficient loads--conservation is your friend). For a system design, you really need to start with your loads/power needs. Then define a battery bank that will support those loads. Lastly define a solar array that keeps both the battery bank and the loads "happy".

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • TheBlueKnightTheBlueKnight Registered Users Posts: 5
    Bill, absolutely superb response. Thank you very kindly for taking the time to make such a detailed response. I had a few more questions but you already answered them in your response! :thumbsup:

    I'm gonna head down to the store and get three 10A fuses for the solar panels and a 35A fuse for between the charge controller and battery bank. I'll also increase my battery bank and make sure to cross connect them. Thanks again! :)

    Edit*
    I have a kill-a-watt meter and my mini freezer is using about 500WH per day which is surprisingly close to the energy rating of the manufacturer (190,000kwh a year estimation).
  • BB.BB. Super Moderators, Administrators Posts: 29,207 admin
    You are very welcome.... Let us know how it all works out.

    And just to be clear, the above are based on rules of thumbs that give quick and pretty reliable/conservative answers. If you have specific needs, there are "other solutions" possible (AGM or Lithium type rechargeable batteries) that can give other results (engineering a solution gives way more options than most people are ready for).

    However, for price/performance, the generic rules of thumbs and flooded cell batteries are hard to beat.

    Price/Performance/Reliability -- Pick any two to optimize.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • TheBlueKnightTheBlueKnight Registered Users Posts: 5
    Hi guys! I just finished up the whole set up and tested it. Everything turned out great thank the Lord! Very happy with the set up and will work great for me when the power goes out here in an emergency. Here is a price list of the project...

    Sonic-animated.gif

    $135 100w Renogy Solar Panel
    $135 100w Renogy Solar Panel
    $135 100w Renogy Solar panel
    $120 1500w Power Inverter
    $168 Tracer 30A MPPT Charge Controller
    $64 Mighty Max 35Ah Deep Cycle 12v Battery
    $64 Mighty Max 35Ah Deep Cycle 12v Battery
    $64 Mighty Max 35Ah Deep Cycle 12v Battery
    $45 35ft 8 Gauge Wire
    $50 Misc. Nuts/ Bolts/ Wood/ Connectors ect...
    $980 Total

    So basically it was a grand for the entire system. It has been running my 4 cu. ft. chest freezer in my garage. The inverter also has ports to charge our iphones/ipad plus an extra outlet for running a 10w LED light or two in the house which uses a nominal amount of power in the scheme of things (only used a few hours before bed after it gets dark). When the freezer kicks on it peaks at about 323w for about two or three seconds then runs at a steady 88w. Inverter barely gets warm throughout the day, charge controller doesn't even get warm at all. Batteries and wires stay cold.

    When the sun rises, light begins to hit the solar panels at about 7:10AM. By 12:15PM the charge controller indicates that the battery bank is fully charged. The batteries of course keep running the freezer through the night and at about 6:15AM right before the panels begin charging the battery bank is at it's lowest level which is 12.4v (I believe this means the battery bank is at about 75-80%?). Then at 7:10AM the panels start charging again and by noon the bank is again fully charged, wash, rinse, repeat.

    Thanks again for the help on this forum, can't express how thankful I am for the advice. Take care everyone, here are some pics...

    Setup in the garage :thumbsup:
    FullSizeRender_zpsde485y2r.jpg

    South facing panels (they get full sun light from 7am-4pm)
    FullSizeRender2_zpss8owoinc.jpg

    The Freezer in the garage (we got it for $138. )
    FullSizeRender3_zpsvnim6cee.jpg






  • BB.BB. Super Moderators, Administrators Posts: 29,207 admin
    Looks nice... A suggestion or two...

    Try to keep +/- wires running next to each other where possible (use tie wraps or similar). This keeps electrical noise down/electrical interference (like lightning) from getting into yours system (i.e., the wires are not near as good of antenna when run in parallel, rather than "loops").

    The AC cord--Can you run that over the door and not on the floor?

    The green wire grounding--If you have lightning in the area, try to use 6 AWG copper wire (insulated or not). 6 AWG seems to be the smallest wire that does not routinely vaporize if there is a direct strike (from what little I have read).

    Do you want to use a relay that switches between AC Mains and AC Backup power?

    PowerMax PMTS-30 Automatic Transfer Switch

    Use the transfer switch during winter (poor sun)--Run the freezer from utility power, and fail over to backup power if the utility power goes away.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • TheBlueKnightTheBlueKnight Registered Users Posts: 5
    Thanks Bill. I will definitely run the AC cord somewhere where it won't get tripped over. That transfer switch looks awesome for the price. I like the idea of it switching automatically over.
  • littleharbor2littleharbor2 Solar Expert Posts: 1,318 ✭✭✭✭
    I'm curious as to why you are running your 3-12 volt panels in parallel with your Tracer MPPT CC? Seems like it is defeating the purpose of having an MPPT controller in the first place. Series wiring your panels would negate having to fuse 3 parallel wired panels as well.

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric, 700 ah @24 volt AGM battery bank. Plenty of Baja Sea of Cortez sunshine.

  • JohannJohann Solar Expert Posts: 240 ✭✭✭
    Sams club has 6 volt 215 Ah batteries for $84. So for $168 total , for 2 batteries in series, you could had doubled your batteries capacity.
    You have 2 different kind of panels with 2 different kind of specs.
    Your 100D and 100P panels have 2 different specs.
    100D = Vmp 18.9 volts, Imp 5.29
    100P = Vmp 17.8 volts, Imp 5.62

    You should always try to use panels with the same specs or you will have additional losses.

    You have done a very nice job.
  • BB.BB. Super Moderators, Administrators Posts: 29,207 admin
    The panel ratings should be "good enough for solar work"... I don't see any big issue with the relatively small differences in Vmp/Imp ratings. There is about a 9% difference--10% or less should be fine. 5% or less is pretty much perfect match.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • TheBlueKnightTheBlueKnight Registered Users Posts: 5
    I'm curious as to why you are running your 3-12 volt panels in parallel with your Tracer MPPT CC? Seems like it is defeating the purpose of having an MPPT controller in the first place. Series wiring your panels would negate having to fuse 3 parallel wired panels as well.

    I'm pretty new to this so I wasn't aware I should have done them in series. Running them in parallel seemed to work out excellent though. Very happy with everything. :thumbsup:
    Johann wrote: »
    Sams club has 6 volt 215 Ah batteries for $84. So for $168 total , for 2 batteries in series, you could had doubled your batteries capacity.
    You have 2 different kind of panels with 2 different kind of specs.
    Your 100D and 100P panels have 2 different specs.
    100D = Vmp 18.9 volts, Imp 5.29
    100P = Vmp 17.8 volts, Imp 5.62

    You should always try to use panels with the same specs or you will have additional losses.

    You have done a very nice job.

    Ah, I was unaware of the Sams Club deal on batteries. the reason one of the panels is different is because I got an awesome deal on it.
  • WillBkoolWillBkool Solar Expert Posts: 35 ✭✭
    Nice little system you have there. I read somewhere that you shouldn't mix mono and poly panels in the same array, something about the different characteristics of the cells. I've mixed my mono and poly panels together too, with no apparent problems. Maybe one of the more experienced people here can chime in.
    670 Watts, 4 Evergreen 120 watt, 1 Eoplly 190 watt; M-Star 15A MPPT; 6 105 AH AGM Configured to [email protected]
    Cotek 1500 watt/24v
  • LesVos98LesVos98 Registered Users Posts: 8
    WillBkool said:
    Nice little system you have there. I read somewhere that you shouldn't mix mono and poly panels in the same array, something about the different characteristics of the cells. I've mixed my mono and poly panels together too, with no apparent problems. Maybe one of the more experienced people here can chime in.


    I have as well. There are some out there that say you should keep all your panel wattages the same too, but I have a mix of those as well (4 x 100w and 1 x 200w) and it also works just great..

    Also what I have found is that if you look for a forklift battery company, they refurbish the old batteries (normally every 3-5 years the companies that use them get new ones) and you can get them relatively cheap. They are 2v cells so you can size your battery bank to any size very easily. Mine were 500 + amp hours so I got 6 for a 12v system. (they even gave me a warranty for 5 years) which worked out way better than a sealed system for me.

    Trying to go GREEN
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