I just have some questions

I am about to buy a beginners set of panels and  i want to know if i am buying the right stuff for what i want to do with it. i am trying to make my RV off grid for camping and the web sight will only give me "Individual Run Times"  so if some one would be kind and help me i would really appreciate it.                                                                                                                                                     http://www.earthtechproducts.com/xantrex-powerhub-1800-with-3-panels.html?utm_source=googleshopping&utm_medium=cse&utm_campaign=broi&gdftrk=gdfV25982_a_7c2497_a_7c9183_a_7c1800SG_d_300&gclid=CjwKEAiAws20BRCs-P-ssLbSlg4SJABbVcDpuEy_tvjcz0XrdWTu1A87UB8rAvZQX59ZjOCDIUuVqxoC-EDw_wcB


  • BB.BB. Super Moderators Posts: 26,768 admin
    Seems a bit on the expensive side to me...

    In any case, I would suggest:

    1. Know your loads/power needs.
    2. Paper design a system to meet those needs
    3. Now start shopping for components

    And even for #1, you really need to look very carefully at your power needs. Conservation is almost always less expensive than building a bigger system to run those loads.

    The system you are looking at:
    • AC inverter is way too large (for most people) to use with the battery bank. If you run the inverter at 1,200 Watts, you will drain 50% of your battery capacity in ~1 hour (50% maximum discharge of battery bank gives you longer battery life).
    • Battery Bank is, conversely too small for the AC Inverter if you plan on running more than a few hours
    • Solar panels--Really need more watts for a "balanced system design"--Sort of OK for that battery bank, but really too small if you plan on using a lot of solar power with your 1,800 Watt inverter. And if you run the inverter at ~1,200 Watt load for 1 hour, you would need around 500-600 Watts of solar panel to recharge the battery bank in one day (or a bit less) of "average" sun.
    But--In the end, need to know/understand your loads when designing the system. Average Wattage and peak Wattage (i.e., running a desktop computer 10 hours per day is a lot of power--Lots of solar and a good size battery bank. Running a small well pump or microwave oven for 10 minutes per day, need a larger inverter to handle high starting loads and/or high short term loads--don't really need as large of battery bank for short term loads.

    To learn about AC loads... A very handy and cheap tool is a Kill-a-Watt meter (or other brand). You plug your AC loads into the meter and you can figure out (roughly) your average power (Watts) and how much power you use in 24 hours (Watt*Hours per day). At least, with those type of numbers (and a rough description of your loads/power requirements), we can be a bit more helpful.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • chazchaz Registered Users Posts: 3
    Thanks a lot that helps out some. i will keep shopping around some i just wonted some feedback on that system. 
  • BB.BB. Super Moderators Posts: 26,768 admin
    What are your power needs? Even if that system was a good deal, I am not sure it would perform to your needs or expectations.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • chazchaz Registered Users Posts: 3
    edited January 2016 #5
    Just some lights  a mini frig and a flat screen thats really about it.  also been looking at this one to.                                                              http://www.amazon.com/Grape-Solar-GS-400-KIT-400-Watt-Off-Grid/dp/B009ANH790/ref=pd_sim_sbs_263_1?ie=UTF8&dpID=51yIwHXp1-L&dpSrc=sims&preST=_AC_UL160_SR160,160_&refRID=106ASHH1E9CEMG3XABJ0                                                                                                                                                                                                                                                  with  four 35AH 12V DC DEEPCYCLE SLA SOLAR ENERGY STORAGE BATTERYS 

  • BB.BB. Super Moderators Posts: 26,768 admin
    Have you identified the exact refrigerator you want to run... A typical 120 VAC refrigerator (at least in the US) takes a large starting surge (typically need a 1,200 Watt rated minimum) AC inverter, and take upwards of 800 to 1,000 Watt*Hours per day (quite dependent on "room" temperature too).

    A new LED type flat screen TV is getting quite efficient--But if you have an older one, they can use 5x or more electricity.

    I will take a quick guess and say you want 1,200 Watt*Hours per day (Mini-Fridge, TV, and a few LED lights). And you live near Salem Or.

    First, you need to size the battery bank for your daily load (treating this like an full time off grid cabin--Design Rules of thumbs). A good start is to size your battery for 2x of "no sun" and 50% maximum discharge (for longer battery life):
    • 1,200 Watt*Hours of AC power * 1/0.85 AC inverter eff * 1/12 volt battery bank * 2 days storage * 1/0.50 max discharge = 471 AH @ 12 volt battery bank
    Next, we also need to double check the size of the battery bank and starting load. Guessing a minimum of 1,000 Watt starting load (refrigerator compressors are >600 Watts of starting load). Will use C/2.5 hour discharge rate for Flooded Cell batteries (cheaper and more rugged). You have AGM in your example system, which do very well at surge current (C/1 or even better):
    • 1,000 Watts * 1/0.85 inverter eff * 1/12 volts * 2.5 max surge current = 245 AH minimum @ 12 volt battery bank for starting surge
    So, in this case, 471 AH is the minimum battery size (using conservative off grid cabin rules of thumb).

    Next, we want to size the solar array. Two different calculations. First, based on the size of the battery bank, and second on the amount of sun you get in a day.

    Sizing for battery bank. 5% to 13% rate of charge is good for solar... 5% is good for weekend/seasonal usage. and 10%+ is good for full time off grid usage:
    • 471 AH battery * 14.5 volts charging * 1/0.77 panel+controller derating * 0.05 rate of charge = 443 Watt minimum array
    • 471 AH battery * 14.5 volts charging * 1/0.77 panel+controller derating * 0.10 rate of charge = 887 Watt nominal array
    • 471 AH battery * 14.5 volts charging * 1/0.77 panel+controller derating * 0.13 rate of charge = 1,153 Watt "cost effective" array
    Next, we size the array on the average amount of sun you have and the seasons you use the system. For example, say Salem OR, fixed array:


    Average Solar Insolation figures

    Measured in kWh/m2/day onto a solar panel set at a 46° angle from Vertical:
    (For best year-round performance)
    Jan Feb Mar Apr May Jun
    Jul Aug Sep Oct Nov Dec
    Toss the bottom three months (use a genset/AC Mains as bad weather backup), and we get February average of 3.35 hours of sun per day (break even, on average, month):
    • 1,200 WH per day * 1/0.52 typical off grid system eff * 1/3.35 Hours of sun per day = 687 Watt array minimum
    So, for this estimated system + location, your solar array should be >687 Watts to run without a genset ~9 months of the year (average weather conditions). If this was a full time off grid system, I would suggest 887 Watt minimum array.

    So, looking at the above estimates--What do you think? Does this system sound like it meets your needs, or did I make some mistakes in my guesses?

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • westbranchwestbranch Solar Expert Posts: 4,827 ✭✭✭✭
    If you can wangle it, get a Kill-A-Watt meter and measure the actual 24 hr draw of the fridge you want, negotiate with the vendor if you can to have it plugged in  for a say.  That should get oyu in the ball park. 
    We got a GE 18 cu ft fridge last spring and were very  happy in that it used about 65% of the posted annual consumption on a daily basis.. including the start up surge
    Don't just assume that a small fridge will use less power than a larger one.. measure it if you can...

    previous post

    Well we got the new GE fridge off the truck and leveled etc. THE BIG moment was when we turned on the power and waited for a SQUEEL from the inverter as it took on the surge expected to run the fridge. Expectations were for a start up surge load> 3000W....

    Fridge GE Model GTE18GMHDRES 319 kWh Canada/ 358kWh US Stated capacity 17.5 Cu. ft

    on the Canadian side of the label the unit is rated as a TYPE 3 18.4 Cu ft, we saw the Sears sticker listing it as a 15.5 cu ft...

    Powered by a Cotek 1500W, 24V inverter.

    I watched the WBjr Live Data via the Local App and saw it read 38.8 A for a second (@ 27.5V = 1067W) and then drop to ~ 15A and slowly drop to the other daytime loads level before it shut off to cycle again later...

    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, Hughes1100 Sat Modem
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
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