Outback fm80 Effeciency factor question

Himins

My Charge controller is pretty busy converting 109 volts, into 14 amps, currantly i only have one string of 3 panels connected. When this project is complete, I have to pick 2 strings of 3, or 3 strings of 2. My panels produce 8 amps and when they are wired in series, the amps they develop remain 8 amps but the voltage can spike to 110 easily. My question, this seems like quite a conversion process and may lose some efficiency...If I wired 3 strings of 2 this conversion process would be radically modified as now the CC only has to convert 24 amps but much lower voltage...Is the happy medium, 16 amps with a higher voltage to play with be more efficient using 2 strings of 3...or would the 24 amps available to the cc be more effecient by stringing 3 strings of 2. I do need this system to be as effecient as possible in CLOUDY conditions....If one is more effecient in cloudy conditions...and the other is more effecient in sunny conditions....I will have to choose cloudy.

gww1

Re: Outback fm80 Effeciency factor question

I can't remember if it is in the charge controller manual or the manual for the inverter but I just saw a chart that showed the conversion percentages for 48 volt system and it seemed that 70 volts was 1or 2% better then 90 volts.
gww

Cariboocoot

Re: Outback fm80 Effeciency factor question

On a 12 Volt system the controller is going to be more efficient with three strings of two in series. We're talking about 5% difference at full power.

Cloudy conditions are irrelevant: panels are current source. When the sun doesn't shine brightly the power drops off no matter what. MPPT will make best use of whatever is there providing the Voltage is above the battery level.

In case anyone is wondering, I have in fact tried this very experiment myself: running higher Voltage string to increase charging ability on cloudy days. I used three 35 Vmp panels in series on a 12 Volt system It did not work. The total system performance improved when the array Voltage was reduced by putting all three in parallel. Cloudy day output was pretty much a wash.

Now I have "the best of both world" using a 48 Volt nominal array (with two parallel strings) on a 24 Volt system. Efficiency averages 82% overall (high elevation helps).

offgrid me

Re: Outback fm80 Effeciency factor question

I would also think it depends on the CC used. I run 430+- volts into a 48v battery and see around 96% conversion efficiency through the cc to the batteries. How far are you trying to send the power from the panels to the CC? This could have an impact on your choice.
Ned

Himins

Re: Outback fm80 Effeciency factor question

Ned, My panels are mounted to an exterior verticle wall, the CC is mounted inside the same wall, i needed 6' of #6awg to reach the combiner box...one foot to the CC. It seems the distance from the CC to the batterys @ 18 ' may be a concern, again, the wire size is #6awg

offgrid me

Re: Outback fm80 Effeciency factor question

I would use three strings of 2 panels for your short run. It seems to me that you are overloading that CC if you are running a 12v system. The panels could put out 1380w which at 12v is 115amp. This wont hurt the CC but you will loose some power. Also if you are using 6awg from the CC to batteries this is a problem. I would use at least 2/0 for this run or you will have too much voltage drop and the batteries will not charge properly.
Ned

Himins

Re: Outback fm80 Effeciency factor question

I thought there may be a little more squeezed out of this system by adjusting the math into the CC. Your experiment is very revealing Cariboo, thanks for the insight. This info will cement my final wiring diagram for the completed project finally. As much as 5% is stunning. Even though only half this system is up right now..it was exciting to see my shadow for the first time yesterday knowing...I am saving money/keeping MY money. For me, it was all about boycotte the local co-op to which I have been a member since 1996, but these fools have turned on their owners by investing in the MOST expensive realestate/remodeling/equipment/salaries/ etc...now we went from the least expensive, to almost most expensive kwh price in only 4 years...My ele bill went considerably higher than my house payment in the winter months. My neighbors, many of them, are paying well over 400 a month for ele in the winter time...
If i had enough money to pay THAT bill, I would also have enough money to buy the entire co-op...s crew them.

Cariboocoot

Re: Outback fm80 Effeciency factor question

1380 Watts on an FM80 will put out 80 Amps of current maximum on a 12 Volt system. That's all. You can't overload it. It's potential would be 88 Amps, but it will just clip that down to 80.
On cloudy days a little extra panel can help a bit.

The V-drop on 18' of 6 AWG at 80 Amps is enormous: nearly 10%. To get that down below 3% you'd need to use massive 0 AWG wire. That won't fit in the FM80's connections so you'd have to do some short splicing. Could you move the batteries to within 6 feet? Do you really need 80 Amps output? That's good for 800 Amp hours. Don't know how many times I've said that if you need that much stored power capacity you should be going up in system Voltage.

westbranch

Re: Outback fm80 Effeciency factor question

AS an alternative use Niels Voltage drop calculator and try different lengths (distances) from the combiner to the CC to the battery.
The sections with the lower amperage's and higher V will lose less 8) than the way you have it now...

Himins

Re: Outback fm80 Effeciency factor question

I've got to question the 80 amps with only 3 @ 8 amp panels here Cariboot...I get to choose 8/16/24 amps total, not sure how you arrived at 80, perhaps i'm dumber than i thought. When I have 3 stings of 2 in the combiner box...I should be at 16 amps, and roughly 60v of panel per string, full sun.
If I COULD get 80 amps...I think I would sit on my front pourch and fry ants with it like our ancestors.

Cariboocoot

Re: Outback fm80 Effeciency factor question

Himins wrote: »

I've got to question the 80 amps with only 3 @ 8 amp panels here Cariboot...I get to choose 8/16/24 amps total, not sure how you arrived at 80, perhaps i'm dumber than i thought. When I have 3 stings of 2 in the combiner box...I should be at 16 amps, and roughly 60v of panel per string, full sun.
If I COULD get 80 amps...I think I would sit on my front pourch and fry ants with it like our ancestors.

Not with three of the panels; with all six 230 Watt panels.
Half the panels = half the current.

offgrid me

Re: Outback fm80 Effeciency factor question

Remember, you have low amps and high volts going into the CC that is converted into higher amps and lower volts to the battery bank. Per your first post 8 amps at 110volts would be converted to 73.3 amps at 12 volts. This is one of the benefits of an mppt CC.
Ned

Cariboocoot

Re: Outback fm80 Effeciency factor question

8 Amps @ 110 Volts is unlikely out of three 230 Watt panels, since that would be 690 Watts not 880. Probably peak current in to controller is 8 but not at peak Voltage 110 (which probably reflects Voc not Vmp).

What would be expected from three is a maximum around 44 Amps to the batteries from the charge controller (@ 12 Volts).
These panels are probably Vmp 30 with a Voc of 38 X 3 in series: 114 (pretty close to 110). But they will not be putting out their maximum current ( 7.6 to 8 amps) at that Voltage.
(7.6 Imp * 30 Vmp = 230 Watts).

Got to get the numbers in the right order under the right conditions or else they don't make sense.

vtmaps

Re: Outback fm80 Effeciency factor question

Cariboocoot wrote: »

Don't know how many times I've said that if you need that much stored power capacity you should be going up in system Voltage.

Himins, I see from your signature that you have eight 12 volt batteries. If these are hooked up in a 12 volt system you are headed for big problems. That is massively parallel. Please read: http://forum.solar-electric.com/showthread.php?14674
With eight batteries in parallel you should have a fuse on EACH battery. You will need a DC clamp ammeter to monitor the current flow in the individual batteries. When the currents in the individual batteries diverge you will need to disconnect the diverging batteries and try to charge them individually. If you don't disconnect the diverging batteries in time, they will ruin the other batteries. If you have flooded batteries you have to monitor the specific gravity of 48 cells and maintain their electrolyte levels. If your batteries are AGM you have even bigger problems because AGM batteries are even less suitable for parallel configurations than flooded batteries.

Cariboocoot is correct: you really need to be at a higher system voltage. We've seen this pattern before: someone starts with a 12 volt system and tries to grow it. They paint themselves into a 12 volt corner. Finally they abandon solar or upgrade to a sensible system. The sooner you make the transition the less expensive will be the lesson learned.

--vtMaps

Himins

Re: Outback fm80 Effeciency factor question

I am clearly if not carelessly/dangerously, out of my league here. I am not ignoring your case by any means, I am reading/re-reading every post you have submitted here. I am missing one or more very important safty issues as well. All of these issues will be addressed and solved but for some reason, I have a gap in some of the math in this whole process...I may have to pose a new question and start a new thread if I can not locate the info by searching the threads already here.
I am not in a corner as of yet, as my total expendrature has been the very little money I've had available(not much). While I do have a 12 v inverter, I will invest into a 24 or larger inverter some time mid-spring.

It may be easier to quantify what I do know...then work backwards. My killawatt meter shows a draw of 220 watts of power, when my wood furnace blower, tv, one light, and computer is running at the same time. So, now the obvious question, how many amp hrs' do I need to provide, how many 12v batterys are required to provide this currant draw, then...how many panels should I install on this system to maintain a safe and balanced level of currant to this farm. I did not purchase these batterys, they started out as junk and were donated. Reducing the number of batterys in this system appeals to me. I have made the assumption based upon my budget, my new battery will be made from GC 6v from a box store...this is not my optimal system, it is the most I can afford. I am not healthy enough to be more than self employed currantly and am not on some government program...so its out of pocket. I do have the killawat 4460 installed so I can track how much energy is being consumed...but this needs to be interpeted for me into real numbers that quantifies my needs here...I have just invested in the basics...panels, wire, combiner box, inverter, and CC...I need to sort these items out, then purchase a battery, and a more practical inverter.

I have read every single page on the smartgage website multiple times, it just now appears i have somehow overlooked an obvious safty issue. I am self employed so I will make every hour needed to correct this problem part of my FULL time employment!

I do have on site, enough stranded copper wire to resolve the wire size reaching from the CC to the battery...some 300 feet of #10 stranded soldered together can give me an overall wire size of anything I choose except the very last 4 inches or so into the CC. Untill I completely understand and resolve these possible safty issues...the battery remains in a steel shed away from the old farm house, and that distance remains at 18 feet for now...it will be addressed with multiple strands of #10 soldered together into a single strand. (unless/untill someone offers better advice).

Should I drop down to 4 12v batterys parallel this morning?

vtmaps

Re: Outback fm80 Effeciency factor question

Himins wrote: »

I do have on site, enough stranded copper wire to resolve the wire size reaching from the CC to the battery...some 300 feet of #10 stranded soldered together can give me an overall wire size of anything I choose

Are you saying that you will put multiple strands of #10 in parallel to make a single, thicker wire? If so, don't do it. That is VERY VERY dangerous!
--vtMaps

Himins

Re: Outback fm80 Effeciency factor question

Message recieved vtMaps, I will not build a wire from strands.

Cariboocoot

Re: Outback fm80 Effeciency factor question

Here's a thread that I think clearly defines the differences in system Voltages and the whys of using one over another: http://forum.solar-electric.com/showthread.php?15989-Battery-System-Voltages-and-equivalent-power

Now can anyone explain to me why I keep forgetting that thread, especially since I created it? I know: Anno Domini. :roll:

niel

Re: Outback fm80 Effeciency factor question

himins,
it isn't quite that simple to say this draws this so what do i need. there are factors of time involved here too. what if you do a day on the pc and don't put the other items on or you need all items on, but they aren't on constantly such as your furnace blower. the max power draw is good in determining the wattage size of an inverter, but does not reflect what will be needed over time. we usually reference to the needs in a typical 24hr day.

i am curious why there's no refrig listed among items needed to be run as that's usually on everybody's list?

Himins

Re: Outback fm80 Effeciency factor question

5.62 kwh in 102 hours, Don't know how to interpet this. This ofcourse does not include the inverter @ .8 amp draw according to the manual, go power 600w psw. I have not used the furnace blower during this time as iit has been mild but cloudy since the panels were installed. About refrigeration...I have a walk in for 8 months per year ...my back pourch, then in the summer months I have to walk to a home made frige in my well house, a chest freezer conversion using my flow and swamp cooler arrangement. It keeps meat good for 7 days, havn't tryed any longer.

inetdog

Re: Outback fm80 Effeciency factor question

Himins wrote: »

...I have a walk in for 8 months per year ...my back pourch, ...

Isn't that technically a walk-out refrigerator? :-)