Did I architect this right ?

3 Posts
Mar 27, 2011 03:29 pm
Did I architect this right ?

I am new to altE and am very pleased with the site and the education available.
I will be purchasing a new solar system and building the system myself, component by component.
The only thing I am unsure about is how I have architected the system.  So please let me tell you what I have sitting in my altE cart and why and then maybe you can confirm if my choices are good.
I want this system to power my refrigerator and freezer, that’s it.  It will be off-grind only.
The only component I own right now is 4 gel 12v 90ah batteries. Everything else is being considered. I know I will need approx 15 batteries for a complete system but this is what I have today.
A friend suggested this solar panel
The charge converter I am considering is:
Morningstar Tristar TS-MPPT-60, 60A MPPT Charge Controller
 And the battery monitor I am considering is
Bogart Engineering TM-2020 TriMetric Meter Battery Monitor
And of course the inverter:
Go Power 1000W GP-1000 12V Inverter
What do you think so far ? acceptable choices or can you suggest something different ?
I picked the Morningstar Tristar cause it has the ability to handle 6 of the solar panels above and it can select the sealed/gel battery.
Also, I would connect the panels in parallel, so the volts would be 17.4 total and the amps would be 780
I just want to be sure before I go and do a cart checkout and then learn later on that I missed something
Your comments are welcome
Columbia, South Carolina
462 Posts
Mar 28, 2011 10:40 am
Re: Did I architect this right ?

Peter, hard to tell without the power demand of the fridge and freezer. How many daily Watts and/or Amps and at what voltage?
3 Posts
Mar 28, 2011 06:30 pm
Re: Did I architect this right ?

The calc I came up with is
Refrig = 1200 watt-hours per day
Freezer = 1000 watt-hours per day

462 Posts
Mar 30, 2011 10:45 am
Re: Did I architect this right ?

Can I assume 120 volts and 5 hrs sun and/or 5 hrs run time?
 So 1200 Wh /( 120v x 5hr)= 2 amps
 or 1200 Wh / 5hr = 240 Watts
 Does the fridge only draw 2 amps?

freezer 1000 /(120 x 5) = 1.7 amps?
  1000/ 5 = 200 Watts

If this is true then the battery stuff and  inverter should be okay.

Then, 130 Watt panel for 5 hrs, around 600 Watt hrs. So to cover your power needs of 1200 + 1000, you would need 4 of the panels. One more to ensure enough power for storage. Current from these 4 panels would be around 40 amps so the charge controller should be okay also. 

99 Posts
Mar 30, 2011 01:28 pm
Re: Did I architect this right ?

The panel you chose is $4.55/W.  I would pick one that is only $2.33/W

Are the watt-hours you specified based on actual measurement or what they're rated for?

1200 + 1000 = 2200 Wh/day

You should assume at least 25% inefficiencies in your system between the solar panels themselves, the wire losses, inverter losses, battery charging losses, etc.  So you'll really need:

2200Wh / 0.75 = 2933 Wh/day

Three of the above linked 225W panels will provide this much power in about 4 and half hours of full sun. 

Also, you're better off connecting the panels in series, as you'll have less line loss at the higher voltage.  Your charge controller will convert the solar input voltage to your battery system voltage.  Double-check your docs on your charge controller to ensure it can handle the series-wired input voltage though.

Likewise, you should series connect at least two of your batteries for 24V and parallel the banks of two.  This would reduce losses between the batteries and inverter and within the batteries themselves, but you'll need a 24V inverter then. 

Your batteries have a total capacity of 4 x 12 x 90 = 4320Wh, but you'll only want to deplete them 50% at most, so you have 2160Wh available.  If fridge and freezer combined use 440W, then you'll be able to run them for approximately 4 hours 55 minutes once the sun goes down assuming your batteries are 100% charged at that time.  If you do not open and close them a lot at night, that should be fine.  But you'll want to watch the battery voltage.  If it gets down to 23V or so, don't open and close the fridge and freezer anymore.  The compressors may trip the inverter otherwise since the load will instantaneously drop the voltage below the cutoff.

BTW, if you intend to always have these off-grid, then maybe you should look into DC appliances instead of AC and eliminate the inverter.
462 Posts
Mar 31, 2011 06:10 pm
Re: Did I architect this right ?

If all works out, and you get the freezer going, make ice while the sun shines. Then put the ice in the fridge to reduce running time.
3 Posts
Apr 4, 2011 01:50 pm
Re: Did I architect this right ?

Thanks guys. I realize I am asking some simple questions (ok they are a little stupid) but I am new to solar systems so thanks for being patient.

I purchased the kill-a-watt meter from here and will use it on each appliance, the fridge and deep freezer for a week each and get some real numbers.
Also I purchased the book:
Photovoltaics: Design & Install Manual
From this site and will do some homework before I come back to this group with another post.

I know, you wanted to suggest that but I got to it on my own Smiley
Little by little this is starting to come together for me.
Thanks again for your opinions.

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