Help needed!

BrynBryn Registered Users Posts: 2
Hello all! I’m new here and pretty new to the Solar world and could use some help please. I’ve built a house(1800 sq ft) in central Az and it’s time for power, originally I was going to run grid power it will be pretty expensive around 15k due to my distance from service which I knew before beginning. After doing a little bit of research I am thinking I would rather go solar. I was given 25 New Trina solar panels with the following specs,
maximum power 310 volts,
maximum power voltage 37.0v,
maximum power current 8.38Amps,
open circuit voltage 45.5volts,
maximum system voltage 1000volts.
 I believe I would like to go with a 48volt battery bank and system. My usage would be pretty normal for a house that size with 2 people, fridge, freezer, lights, some tv, phone chargers, some power tool chargers, washing machine, (propane) dryer, evaporative cooler now, but would like to go to a high efficiency mini split ac if possible. So finally on to my questions, how would you recommend wiring my solar panels, ie like 3 in series and 8 series in parallel using 24 panels? Also looking for recommendations for good quality Mppt charger controller, 48volt inverter and anything else you could recommend, of course I’d like to stay as inexpensive as possible but I would rather pay more for stuff that works how it’s supposed to and is going to last. Thank you all for your time!


  • couchsachragacouchsachraga Solar Expert Posts: 84 ✭✭
    Your first step is to better quantify your usage, and then properly size the system for that.  There really isn't any such thing as "typical" usage.  If you want to be off-grid you will likely want to purchase more efficient appliances, bulbs, just about everything as it is cheaper not to have to produce (and store) that power in the first place.  I'll add the system is very likely going to cost more than the 15k it would to connect to the grid you mentioned; the offset is that you won't have an electric bill (just replacing batteries and other systems maintenance).  You may want to contact a local solar firm and see what they would charge for the system to give you an idea what it may all cost and entail.

    I have grid-intertie at my primary residence (all installed by a local solar company; qualified for state incentives that way), and an off-grid set up at a year round camp.  I've very happy with both.
  • BB.BB. Super Moderators, Administrators Posts: 32,019 admin
    Welcome to the forum Bryn,

    As Couchsachraga suggests--You need to figure out how much energy you will need.

    Solar power is not cheap--It can be 5-10x the $/kWH pricing of your utility when you take everything into account (new hardware, new batteries every 5-8 years, new electronics every 10+ years, 25 year life for panels, etc.)... $15,000 for tying to the grid is probably still less than the full up cost of an off grid power system. I agree there is no power bill from the utility--But your costs/maintenance/etc. is not to be forgotten.

    I also suggest that you look at the value of your property if you (or your heirs) ever need to cell the property--Will having power to the property be a value to the buyer (also ability to get loans/insurance/etc. for Grid vs Off Grid properties).

    To just play with some numbers... Lets see what you could expect to harvest based on what we "know" here:
    • 310 Watt panels * 25 = 7,750 Watts of panels
    Figure out the harvest (using Phoenix AZ sun):

    Average Solar Insolation figures

    Measured in kWh/m2/day onto a solar panel set at a 57° angle from vertical:
    (For best year-round performance)

    Use December 4.74 Hours "worst case" average and 6.0 Hours for "summer" best case average harvest:
    • 7,750 Watt array * 0.52 off grid AC system efficiency * 4.74 Hours of sun per day = 19,102 WH per day (December)
    • 19.102 kWH per day * 30 days = 573 kWH per month (December harvest)
    • 7,750 Watt array * 0.52 off grid AC system efficiency * 6.00 Hours of sun per day = 24,180 WH per day (Summer average)
    • 24.180 kWH per day * 30 days = 725 kWH per month (Summer minimum average harvest)
    With off grid power--You cannot count on "using" your average daily harvest... We generally suggest that your "base loads" (lights, water pumping, refrigerator, cell charger, etc.) be 50% - 65% of predicted loads... And on "sunny days" you can add other loads (A/C, shop tools, washer/dryer, etc.).

    More or less--The "average" north American home uses around 500 to 1,000 kWH per month...

    So--It does look "possible" for you to run a home from your 25x solar panels... You have to look at your personal energy needs--This is a highly personal set of choices (and where you live).

    Solar panels, these days, are among the least costly parts of an off grid power system. AC inverters-chargers while not cheap--Are not the most expensive parts. The battery bank, racking for panels, possible AC genset backup, etc... All need to be taken into account.

    For example, say you need a minimum of 10.000 kWH per day (*30 days per month = 300 kWH per month). A typical lead acid battery bank (2 days of storage, 50% max discharge for longer life):
    • 10,000 WH per day * 2 days storage * 1/0.50 max discharge * 1/48 volt battery bank = 833 AH @ 48 volt battery bank
    A  4-8 kWatt AC inverter would work nicely with the above bank...

    This is a good size system--And talking with a knowledgable solar supplier/installer--This would be a lot to bite off for a first time self install.

    Do lots of research, and paper designs before you start buying any more hardware.

    I hope you have done a lot of conservation in your new home build (lots of insulation, Energy Star based appliances, etc.).

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BrynBryn Registered Users Posts: 2
    Thank you Couchsachraga and BB! Very helpful info, after visiting some family I think for this day and age my usage would be fairly low compared to most the world.  When I built the house I did everything with the idea of conserving energy. Thanks again for the info, any thoughts on brands of inverters, to look into, and stay away from? Thanks again. 
  • BB.BB. Super Moderators, Administrators Posts: 32,019 admin
    Do you have an idea of what capacity and system loads will be (real numbers you need the system to meet)? Will the bank be cool (cellar/ground contact can help). Going to use Flooded Cell Lead Acid batteries, or do you want to try Lithium Ion (LiFePO4 or similar)? Lithium cells are expensive, but are about the "ideal battery" and work very well in hot climates--However, they do not really cycle well below ~40F (need to keep bank warm in freezing climates)--And I suggest that you keep the batteries in an unoccupied shed/cellar as Lithium fires, if it ever happens, Lithium fires are difficult to put out and can output some very dangerous chemicals (hydrofluoric acid). And there is the whole BMS (battery monitoring system) choices and understanding how to keep cells "balanced" and not exceed a (roughly) recommended State of Charge range of 20% to 90% or so...

    And there are other options too... Hybrid Inverter+Chargers (AC backup genset or possible grid connection in the future), remote (Internet) monitoring, Integration with Battery Monitor systems (and especially Li Ion BMS units). Costs, available support and replacement parts (most electronics are almost impossible to get factory parts and supports after 5 years end of production). And many lower cost systems, there is little to no support available.

    Once you sized your system needs and looked at integration and other factors--Then you can start looking at the hardware (and revise your choices if costs or other issues cannot be met in the first round).

    Our host, Northern Arizona Wind & Sun does have good products and has their own engineers... So always a good place to look for products (I do not work for NAWS, just a volunteer here). There are also some overseas products that looks very interesting (and lower costs).

    Off Grid Solar is not cheap or easy... And you are your own power company responsible for repairs, updates, and money. 

    I suggest bringing utilty power to a property can be an investment that can add value to a property (a buyer down the road will "value" the utility connection). Known fixed costs and no "surprises". Doing your own solar power system--I suggest you have "extra" money in the the bank (don't take out loans) to build out your system, and have funds available for the inevitable (relatively) major costs to replace hardware every 5-10+ years. And the occasional "oh heck" where visitors/family come by and do something "wrong" (leave major appliances running, take battery bank dead, etc.).

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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