System Review?

[SM-Viper]

Hi all! Im looking for some input on my system to verify my set-up before I get too much more involved in the rest of the "final" build. Any review or input would be greatly appreciated.

I have been at this for about six months now with a very limited budget. Six months is not a long time, but it's been kind of an obsession with me and I'm having a lot of fun with it.  This is a small system, (to start). Off Grid backup power. I currently have 2 Renogy 100D 100w panels connected in series to a MS Kid, (love it), to 2 "Deka" GC10 6v 215 AH deep cycle batteries in series for 12v. I have an AIMS 1500w inverter (which will be replaced eventually).  My plans are to be able to run my garage heater, (where the RE system lives), run a full size refrigerator to keep food cold when needed and possibly my home gas furnace if necessary. Also some DC lighting in the garage. Not a lot of power, and not all of this will be running at the same time. My intentions are to get two more of these same panels and connect them in series-parallel and be able to bring the batteries back up to full charge in a day from no more than 40%-50% DOD.

I'm working on the MS 125 DC Disconnect box with breakers for the PV, CC, DC, and GFP along with the 125A inverter breaker. I'm using 2/0 battery cables to both the inverter and batteries. The distance is not more than 3ft. I'm using a Deltec 500A shunt with a WBjr attached. I have a Soladeck combiner to place on the roof in the spring, and the distance to the Kid is not more than 30 ft.  I do not have a ground rod yet. At some point in the distant future, I would like to have a 24v battery bank and 4 60 cell panels in series-parallel (instead of 36 cell), and would like to complete the current design with that in mind (wire sizing) future upgrade.

Panel Specs:

Renogy 100D 100w solar panels
VMP 18.9v
IMP 5.29A
Voc 22.50v
Isc 5.75A

* How important is a battery box for me at this stage? I saw some others saying it was important "Post Haste".

* Is this series-parallel the best configuration for the panels with the Kid?

* If I drive a ground rod, the GEC should connect to the ground bus in the DC Disconnect, right?

I really can't think of anything more I need to do to complete the system.  Thanks in advance, and thanks for this forum!

[xsnrg]

Greetings.  Solar is addictive and fun isn't it?  Reading your description, I came to the spot where you said heat garage, after saying 12v and 2 6v batteries.  Even with your upgrade to 24v and expanded battery capacity, heating a garage is a tall order for even a large system.  If you were just using it to run a fan on a reznor that is burning LNG or something like that, then okay...  I think a good learning step that doesn't cost a lot that everyone should go through is to just run some lights overnight, all night.   Oh, wait, that is the step I ran through... I had a lot of experience with UPSes before I started playing with solar, so knew ahead of time how long long an Ah would last under a set load.  The numbers, and then the experiment confirmed.

Your setup seems fine, but realize it is small.  Moderate your expectations like-wise.  A simple example of a 50w bulb at 12.5v is a 4A draw.  If we run that bulb for 12 hrs, we have 48Ah usage.  This would draw your battery down to about 80% SOC, which is a good stopping place for battery health.  Where I am at, I get about 8 hrs of sun exposure now on a good day, and not all of those hours are capable of generating good current, so that same bulb would have to run 18 hours from battery in my case.

On the panel side, you can get about 80% of rated wattage out of them (I have 3 of the same panel you have).  That means under great conditions, 3 panels gives me about 240W.  They produce at this level for only a couple hours per day with a fixed mount.   We can go further into the math of charging the battery back up, but with two panels, you will see about 10A of charging current at peak.  With 6 hrs of good sun, you might get 50Ah back into the battery bank.  All this is assuming my latitude since I don't know where you are at.  I am at about 41N.

Not mentioned above, not all days are good sun, wiring and CC are not without their own losses, batteries don't charge back at 100% efficiency (you need more power put into them to get them topped off, and even more the closer you are to full, etc.  All that, and it is still a lot of fun any time you can remove a load from the grid

Jim

[SM-Viper]

Thanks Jim. That all sounds like what I came up with as well. Btw, the heater is a Reznor NG heater that only takes about 85 watts when it runs and it doesn't run much, (Ohio).  I'll be able to know a lot more about the system capabilities once I get the dc disconnect box and the wbjr hooked up and running. Thanks for the input.

-S

[SM-Viper]

Hi all!

Not surprisingly, I am experiencing enormous sag in my small 12v 215ah system when I try to start my refrigerator. It will only start the frig properly if I fire it up with the power up of the inverter. I know this sag is typical, but I would like to know if anyone has any ideas of how to reduce or offset it with my system. I'm pretty sure that I need to upgrade the size of the interconnect wire from 4GA to 2/0, (I bought the 2GA before I know better). Any advice here would be greatly appreciated.

[Westbranch]

Larger wire will definitely help as will a bigger battery bank  and possibly a larger inverter

[SM-Viper]

I currently have a 2000w mod-sine inverter. It seems to be handling it okay, but it think this is more of a battery issue than anything else. Agree?

[Westbranch]

Sorry, I just went by your text,

small

threw me,  forgot to look  at the sig line but no mention of inverter ,  Yes more battery and more PV are in order, it sounds like 'normal' voltage sag

[Vic]

SM-

Yes,  you should use large gauge wire, especially on 12 V systems.

AND,  Modified SQUARE WAVE inverters can be very hard on motors,  may even damage motors in time.  Treat yourself to a real Pure Sinewave Inverter.   And,  if you really need more than 1,000 watts at times,   perhaps plan on a 24 V system soon.

Furthermore,  That is a HUGE inverter on a relatively tiny battery,  and so on,  just to pick on you some more.  Good Luck,  Have Fun,  so  on.   Vic

[SM-Viper]

We buy. We learn. We buy. Got it. That's what I thought too. Thanks all for the input!

[Robin]

I think you have a battery problem. Please describe your sag.

[SM-Viper]

When the frig tries to start it draws 45 to 75 amps and pulls the battery voltage down to 11.8v. Usually doesn't start befor the motor "resets" and has to try again. It does start eventually. Should only be about 840w max. Think I need 24v battery bank to run this?

[xsnrg]

Are you measuring the voltage of the battery across the battery terminals at start up, or across the inverter?  As discussed, 4ga wire will drop voltage when the amps get high and distance increases.  Not sure I understand though, in your opening post,  you had said

I'm using 2/0 battery cables to both the inverter and batteries[

.  That should be large enough in short length runs from battery to inverter.  Where did the 4ga sneak in?  Also, what is the resting voltage of your battery bank when when you are seeing the drop to 11.8? 

[SM-Viper]

Sorry if I wasn't clear. The interconnect cable for my 2 6v 215ah batteries is 4ga. Everything else is 2/0 cable. Approx. 6 ft from battery to inverter.

The resting voltage is 100% doc at 13.0v after sunny day.

The voltage I saw was from the inverter meter and the kid. There was a small difference as the inverter meter is probably not as accurate.

[Westbranch]

All the cables from the main Inverter disconnect to the battery , THROUGH the (2) batteries and back to the inverter MUST be of the same size....That is your problem! 

That 4 Ga. can not allow as much amperage as the 2/0, it probably get very hot, no where near as warm as the 2/0...

Also the fridge will draw upwards of 5 times the rated wattage of that appliance, all motors are alike in that surge draw...

[SM-Viper]

Yea, that's what I thought. Thanks for the input. I'll probably replace that 2ga wire tomorrow and try again. If no luck then, I'll just have to wait to run that frig when I'm able to upgrade the system to 24v.