Newbie Putting in Stand Alone System: MPPT Controller, Other Questions

SystemSystem Posts: 2,511 admin
Please be patient with me -- although my husband has an electronics and electrical background (24 years in electronic maintenance with a major hospital, plus several years installing computer cabling, some HVAC experience, plus several years as the electrical dept head at a large Home Depot store), he has never done anything with solar up till now. He's also a licensed ham radio operator, and has built his own ham radio station.


We are retired now, and have a 10 acre farmette where we grow alot of organic vegetables, a peach orchard, a berry patch (strawberries, raspberries and blueberries) and a small chicken operation (13 birds, for eggs and composted manure).


I have no electrical experience, though I do have a tech no-code ham radio license myself. But I am the person who is most comfortable with the internet, hence it is me who posts to forums like this.


Anyway, we're wanting to put in some solar panels to run the lights and fans out at the chicken house. There will be two or three fans on the system, and six 4-foot long T-8 florescent tubes to run off of the panels.


My BIL is giving us two 190 watt solar panels as a retirement gift. They are supposed to be on the way to us as I write this. I don't know anything about them, other than they are 190 watts each, of the polycrystalline kind.


We already have a 2000 watt inverter, a 750 watt inverter and a deep cycle battery. I can get the specs on the battery if it helps.


Anyway, we have several questions and hoping that somebody here might be able to help us plan this all out:


1, What is the best MPPT controller to buy for this system? My husband is not really experienced with solar operations, and he would prefer something that did not require an expert to set up and operate. The more "plug and play" the controller is, the better, to quote my husband.


2, How is the best way to do a ground mounting of the solar panels? We're in a rural area in southwest Tennessee, if that makes a difference.


3, What are the best connectors, wires, fuses, and other miscellaneous things that we will need to set this system up? This will be a stand alone system, as our chicken coop is way off in a field away from any grid based electrical outlet.


4, What other things should we be concerned about as we set about putting this system together and getting it going?


Thank you in advance for your help.

Comments

  • icarusicarus Solar Expert Posts: 5,351 ✭✭✭✭
    Re: Newbie Putting in Stand Alone System: MPPT Controller, Other Questions

    Just as a rule of thumb, off grid PV is only ~50% efficient.

    the first suggestion is to do a load calculation of all your proposed loads in watt/hours and then work backwards to figure out how much PV you need.

    Here is my napkin calculation: Name plate rating/2*4=watt/hours/day WH/D The 2 representing the combined system loses, including wiring loses, charge controller losses, battery charging efficiency, inverter efficiencies etc. The 4 is the average hours of "good" sun one might reasonably expect. (Few people can get (on average) much more!)

    Your 360 watts of Pv might yield the following in a battery based system.

    360/2*4=720wh/day average

    That would be enough to power a 100 watt fan for 7.2 hours, or a pair of 40 watt florescent tubes for ~9 hours.

    The general suggestion is that if you have grid power, you are much further ahead to build a grid tie system rather than a battery based system. Battery based systems are ~2 times as expensive per net watt, and they yield ~ 1/2 the efficiency of a grid system, leaving the net/net cost of power being ~4 times the cost for a battery based system over a grid tie system.

    Hope this helps, and welcome to the forum, feel free to shout with other questions. There are some very sharp folks here who have forgotten more about PV/RE than most of us will ever know.

    Tony
  • BB.BB. Super Moderators, Administrators Posts: 29,706 admin
    Re: Newbie Putting in Stand Alone System: MPPT Controller, Other Questions

    Tenn Powers,

    Welcome to the forum.

    Regarding your questions... The issue is that solar PV power, especially off-grid power, is quite expensive to install/maintain--even if "free". So, we usually recommend the following steps:
    1. Conservation: Lots of conservation--Choose low power fixtures, minimum amount of power required for the operation, etc. It is almost always less expensive to conserve vs building a larger system to power your loads.
    2. Look at running utility power from you home/outbuilding to the chicken shed. Utility power is almost always less expensive and more reliable if on the property vs an off-grid system. If you still want to do significant amount of solar power, a Grid Tied system (solar panels+GT Inverter) tied to your utility power can be a reasonable investment (and in high cost states like California, can actually save you money). But GT Power requires building permits and utility approval.
    3. Next, know your loads. Measure the AC loads with a Kill-a-Watt meter (peak watts, average watts, Watt*Hours). Most people tend to under estimate their loads. Look at alternatives to Off-Grid battery/inverter supplied power... For example, can you run the fans directly off of a solar panel and DC fan motor? The fan will only run when the sun is up--but that may be enough for your needs. It will be much less expensive than powering from solar panels + charge controller + battery bank + inverter (direct solar will be about 1/4 the cost vs doing it with off-grid power).
    4. To design the Off-Grid system, we need to know your rough location (major city/state), and how much power you will need (above step). Also, since this is solar, you may need a back up power source (like a small generator, to charge your batteries during bad weather). Note that most people overestimate how much power they can get from an off-grid solar system.
    As a quick example, say your location gets 3 hours of "full noontime sun equivalent" in the winter and 5.5 hours int he summer. A typical off-grid system with battery+inverter has a maximum efficiency of ~0.52 -- the useful power out the AC Inverter for a 2x 190 watt = 380 watt set of solar panels:
    • 380 watts * 0.52 * 3 hours of sun per day = 592 Watt*Hours per day winter
    • 380 watts * 0.52 * 5.5 hours of sun per day = 1,087 Watt*Hours per day in summer
    Using the PV Watts program, we can show what a 1,000 watts of solar panels (sorry, 1kW is the smallest the program will use--just multiply by 0.380 or whatever your panels will be for smaller systems) will produce for Memphis Tenn:
    "Station Identification"
    "City:","Memphis"
    "State:","Tennessee"
    "Lat (deg N):", 35.05
    "Long (deg W):", 89.98
    "Elev (m): ", 87
    "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:"," 35.1"
    "Array Azimuth:","180.0"

    "Energy Specifications"
    "Cost of Electricity:"," 6.9 cents/kWh"

    "Results"
    "Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
    1, 3.93, 62, 4.28
    2, 4.54, 64, 4.42
    3, 5.34, 81, 5.59
    4, 5.78, 81, 5.59
    5, 5.80, 81, 5.59
    6, 6.01, 80, 5.52
    7, 6.10, 83, 5.73
    8, 6.29, 87, 6.00
    9, 5.21, 71, 4.90
    10, 5.53, 81, 5.59
    11, 4.10, 59, 4.07
    12, 3.48, 54, 3.73
    "Year", 5.18, 884, 61.00

    You can see 1 kW of panel for an off grid system will produce an average of 54-87 kWH per month.

    Anyway--even though you have existing hardware (inverter, batteries, etc.)--you may not be able to use them. Inverters can be inefficient or not matched to your battery bank voltage (12, 24, 48 volt), MSW vs TSW (modified square wave vs true sine wave) inverter (MSW may cause problems with some loads), battery bank size (too small of battery bank will not store a few days of sun, too large of battery bank and the solar panels may not keep them charged), etc...

    So, what can you power with 592 Watt*Hours of 120 VAC per day... Say your system is:
    • 6x 40 watt florescent fixtures = 240 watts
    • 2x 40 watt fans = 80 watts
    • 592 Watt*Hours / (240+80 watts) = 1.85 hours per day (winter average)
    And, during stretches of bad weather--you may get 1/2 to 1/10th that amount of power. So, you have the choice of using almost no power, or using a backup power source.

    Anyway, I will stop typing here.

    Observations? Questions?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • AntronXAntronX Solar Expert Posts: 462 ✭✭
    Re: Newbie Putting in Stand Alone System: MPPT Controller, Other Questions

    You don't need to use inverter at all. Buy 12V DC compact fluorescent (CFL) light bulbs and largest 12V computer cooling fans you can find. Here is example of 12V CFL for $18 a piece. Look for warm white color, don't get cool white - the light from those is too harsh. You can use Rogue MPPT 30A controller to charge your battery, or if $300 price tag is too high, you can get by with cheaper PWM controller and lose some efficiency.

    Panels can be mounted on the ground using few pieces of unistrut. Your husband should be familiar with those. The trick is to figure out best mounting angle. That's how I mounted my panels, take a look at few pictures here.
  • nsaspooknsaspook Solar Expert Posts: 396 ✭✭✭
    Re: Newbie Putting in Stand Alone System: MPPT Controller, Other Questions
    AntronX wrote: »
    Panels can be mounted on the ground using few pieces of unistrut. Your husband should be familiar with those. The trick is to figure out best mounting angle. That's how I mounted my panels, take a look at few pictures here.

    Maybe we should have a unistrut mount gallery.

    http://farm5.static.flickr.com/4070/4673089827_455ff0ee2c_b.jpg
    http://farm5.static.flickr.com/4037/4673713880_9e266226aa_b.jpg
  • AntronXAntronX Solar Expert Posts: 462 ✭✭
    Re: Newbie Putting in Stand Alone System: MPPT Controller, Other Questions

    Yea, maybe we should have one. Unistrut reminds me of old metal erector set, just on a little larger scale for grownups.
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