Ready ! - Aim ! - ...

Skippy

Re: Ready ! - Aim ! - ...

BB. wrote: »

And always confirm your array specifications to controller's input capabilities. MorningStar has an array sizing tool which works very nicely for the task:

http://www.morningstarcorp.com/en/strings/calc.php

-Bill "trust but verify" B. :roll:

Thank you for that link, I will be running the numbers A.S.A.P.

Photowhit

Re: Ready ! - Aim ! - ...

Things to think about, where is the 1000 watt load? is that the load on the inverter, as in running a 1000 watts burner for 4 hours? Just so your thinking correctly, the load on the batteries will be greater since a cheap inverter is likely around 85% efficient so the load on the batteries is more like 1200 watts.

Also while you have 650 amps at 24 volts storage, if you load them at just a 1000 watts, or 42amps this is greater than the 650amp hour battery is rated, ratings are based on a 20 hour discharge so your battery will 'act' smaller.(1000/24=@42 amps)

Just things to be aware of and understand...

Skippy

Re: Ready ! - Aim ! - ...

Photowhit wrote: »

Also while you have 650 amps at 24 volts storage, if you load them at just a 1000 watts, or 42amps this is greater than the 650amp hour battery is rated, ratings are based on a 20 hour discharge so your battery will 'act' smaller.(1000/24=@42 amps)

Just things to be aware of and understand...

I like the way you put that .. . and understand... I know alot of this stuff, you can read it, but until you have the problem right in front of you - some of it just don't sink in . . . this will be my first deep cycle battery, so I hope I can baby it . . .
surge from fridge 700 - 800 watts drops to 100 watts
surge from washing machine over 1,500 watts, but then drops down to between 300-500
Only if there is lots of power, (fully charged battery) would I hook up the microwave (1200 watts) or toaster oven (1800 watts).
The only thing that I really HAVE to have on the system is the fridge . . just because I want that solar powered !

I had a look at the morningstar calc. . . . where do you get the last 4 figures from .. . all 4 of the coefficients it won't let me continue without them. . . also, what numbers do I change to wire 3 panels in series ? It's a nice tool, and thank you for pointing it out. . . now to figure out how to use it properly

BB.

Re: Ready ! - Aim ! - ...

For battery voltages, the suggested values are fine (based on your battery bank voltage).

For temperature, pretty much use the near record low temperature (i.e., if you hit 10F in your area often and hit -40F in 1854--Then the number you want is the lowest you would reasonably expect over the last 20 years (and you can turnoff / disconnect the solar array from the charge controller if you expect 100 year loads in the forecast). Otherwise controller can be damaged.

For high temperature, as the system temperature approaches design maximum (and Vmp-array-hot falls below Vbatt-charging), then your system reduces current into the battery bank. If your system limits charging current a few days during a summer hot spell--It does not damage anything (other than not fully charging your battery bank during the afternoon).

Both the above are limits to set the maximum number of panels in series (cold winter morning Voc-array-cold) and the minimum number of panels in series (hot summer afternoon Vmp-array-hot).

The cold is a "hard limit" to prevent damage to the controller. The hot is a soft limit for optimum battery charging (if your summer loads are not high--not the end of the world--If you need A/C, perhaps a big deal).

-Bill

Skippy

Re: Ready ! - Aim ! - ...

BB. wrote: »

For battery voltages, the suggested values are fine (based on your battery bank voltage).

For temperature . . . .

-Bill

Maybe I have had too much beer, or not enough coffee. . . but, was the coefficient answer in there somewhere ? I got the battery voltage, and the temperature min and max - that was fairly easy to figure out. . . but above that - on the calculator , you take the numbers off the back of the panel and type them in on the left side -voc - imp - , but on the right side, you have the nominal operating temp and then all the coefficient numbers below that . . when I click on the little "?", it says its not a required value, but then when I hit "calculate", it won't continue until I put a number in there - and it has to be a minus ?

vmp coefficient
voc coefficient
imp coefficient

BB.

Re: Ready ! - Aim ! - ...

OK... I think you are entering the panel information directly instead of using Brand X YYY watt panel (where they pre-loaded that other stuff)?

• Voc Coefficient = -0.36 %/^oC
• Vmp Coefficient = -0.52 %/^oC
• Isc Coefficient = 0.060 %/^oC
• Imp Coefficient = 0.0066 %/^oC
• For Tnoct use 45^oC or 113^oF.

Note that the above electrical numbers are in %/^oC. For use in the MorningStar Calculator, (think) you need to convert them to V/^oC etc... So you have to go back to your panels specs and multiply them out--For example Vmp would be

• 30.2 volts * -0.52 %/^oC * 0.01 Percent conversion = -0.157 V/^oC

And remember to use the "-" sign for the voltage numbers (they go down as temperature increases.

These number should be "close enough" with any good quality silicon crystalline solar panel (I got these numbers from a Kyocera 140 watt panel).

Hope that helps.

-Bill

Skippy

Re: Ready ! - Aim ! - ...

So it wasn't the hangover . . .;)

Skippy

Re: Ready ! - Aim ! - ...

I kinda cheated a bit, I looked up mitsubishi panels, and the very bottom one has the last didgets of - 210GA6 - while the panels I am looking at have the last didgets of 218G6 - now, ass-u-ming, that the 210 (GA6) is the wattage for the first panel, and the panels here are 218 (g6), I entered that into the equation, instead of doing all the math. I get a read warning bar saying "exceeds maximum power ratings" . . . ummm isn't that what "overpaneling" does ?

Even if I do all the math, I already know that I am "overpaneling" this thing . . . so . . .

BB.

Re: Ready ! - Aim ! - ...

Yep... Over paneling (within reason) should be Yellow (or some other orangish/salmon color) in that there is nothing that will "break".

It should be an "informational warning" that some days/conditions the MPPT charge controller may "clip" the output a bit.

My handy (non-vendor approved) method is:

60 amp controller * 14.5 volts charging * 1/0.77 panel+controller derating = 1,130 Watt "max cost effective array"

Of course, this is just a very rough number and installation issues can push the numbers one way or another (very cold winters vs hot/humid/poor visibility weather). But nothing that will "break" a system.

-Bill

Skippy

Re: Ready ! - Aim ! - ...

BB. wrote: »

In general, an over loaded good quality AC inverter should just "shut down" if there is excessive current/power draw and/or low (or high) battery bus voltage.

Will yours? I have no idea.



Is this a TriStar MPPT charge controller (they mix things up because there is an almost identical looking PWM version of the controller)? If so, yes you should be fine (you will need a series fuse/breaker--around 15 amps?--per string of panels (typically in a combiner box).

You did not mention the voltage of the battery bank--Assuming 24 volts (based on the probably Vmp-array of ~60 volts--too low for 48 volt bank), my suggestion is the max cost effective size of array for an MPPT charge controller would be around (nothing happens if the array is larger--just the MPPT limits output current to 60 amps in the middle of the day more often):

60 amps * 29 volts batt charging * 1/0.77 panel+controller derating = 2,260 Watt max cost effective array...
-Bill

I think you got your numbers mixed up there, I believe you quoted 14 Volts charging for a 12 V system . . . this will be a 24 V system, like you mention above - but now that we are getting into the numbers a bit more, and I do have to buy everything yet, I may just switch it to 48 V same controller, and it can handle the power . . . and leave the number of panels where it is . . 1962 watt array on a 48 V battery . ..hmmm how many A/H do I need . . .
Is there a thread on here somewhere with examples of your math ? I could really use it ..:D I had it here a while ago, and figured that this array would be at the upper limit of the 650 A/H battery at 24 V . . . if I stayed with the 650 AH battery, but upped it to 48 Volts, how would the array fit then ? I gotta go looking for that darn formula again. . .

Cariboocoot

Re: Ready ! - Aim ! - ...

1962 Watt array @ 77% efficiency = 1510 Watts.
Divide by 12 Volts = 126 Amps
Divide by 24 Volts = 63 Amps
Divide by 48 Volts = 31 Amps
(Factor differences caused by rounding.)

I use system nominal Voltage as a minimum battery Voltage under load, where you'd expect to see the most current needed for battery charging only. Above that the current usually drops off, except for supplying concurrent loads. This way the current rating is roughly 10% of the battery capacity. No adjustments for system Voltage efficiency are made, even though they exist. It gets you in the ballpark.

So on 48 Volts that array could probably charge a set of 320 Amp hour L16's, for example.

BB.

Re: Ready ! - Aim ! - ...

I was just showing how the equation works... I need you to do some of the math too (I keep telling my kids this--Just a minute, I need to yell at one of them to do their math homework.... :roll:

The difference between 12 volts charging and 14.5 volts charging... 14.5/12=1.21x larger solar array

Most people tend to charge their batteries in the 13.5 to 14.5 volt range--So it "allows" you to use a 21% larger solar array on the XX amp output.

Any math that is within ~10% probably will not even produce measurable differences (between all of the variability of equipment, conditions, etc.).

Remember that X,000 lb$ of batteries will store the same amount of energy--whether wired for 12/24 or 48 volts..

• 400 AH * 12 volts = 4,800 WH
• 200 AH * 24 volts = 4,800 WH
• 100 AH * 48 volts = 4,800 WH

So, the first question you asked was about a 1,962 watt solar array on a 24 or 48 volt battery bank. First, there is the 5% to 13% rate of charge:

• 1,962 watt array * 1/29 Vbatt charging * 0.77 panel+controller losses * 1/0.05 rate of charge = 1,042 AH @ 24 volt bank maximum
• 1,962 watt array * 1/29 Vbatt charging * 0.77 panel+controller losses * 1/0.10 rate of charge = 521 AH @ 24 volt bank nominal
• 1,962 watt array * 1/29 Vbatt charging * 0.77 panel+controller losses * 1/0.13 rate of charge = 401 AH @ 24 volt bank sort of maximum cost effective battery bank

The same solar array on a 48 volt bank, just divide the above AH numbers by 2.

..if I stayed with the 650 AH battery, but upped it to 48 Volts

So, what do you mean by "upped to 48 volts"? Do you mean to rewire it to a 325 AH 48 volt bank--Then it does not change any of the power calculations for loading/charging.

But going to a 48 volt bank allows the Charge Controller to "manage" a 2x larger wattage solar array.

And you would need a different AC inverter (48 volt input).

If you were to go with a 650 AH @ 48 volt battery bank, you would have to buy 2x more batteries (or buy 2* more expensive larger batteries), and you would need to have 2x the solar array, support 2x more loading, etc.

-Bill

Skippy

Re: Ready ! - Aim ! - ...

Cariboocoot wrote: »

1962 Watt array @ 77% efficiency = 1510 Watts.
Divide by 12 Volts = 126 Amps
Divide by 24 Volts = 63 Amps
Divide by 48 Volts = 31 Amps
(Factor differences caused by rounding.)

I use system nominal Voltage as a minimum battery Voltage under load, where you'd expect to see the most current needed for battery charging only. Above that the current usually drops off, except for supplying concurrent loads. This way the current rating is roughly 10% of the battery capacity. No adjustments for system Voltage efficiency are made, even though they exist. It gets you in the ballpark.

So on 48 Volts that array could probably charge a set of 320 Amp hour L16's, for example.

Thanks for the reply guys.
I will admit Cariboocoot, I was/am kinda confused with this :
Divide by 12 Volts = 126 Amps
Divide by 24 Volts = 63 Amps
Divide by 48 Volts = 31 Amps
I realize the battery voltages are for different battery banks, but the amps ? I am going to guess and say that dividing the wattage of the array with the battery voltage gives you usable amps at that voltage ? correct ?

I redid the math, and was not sure I did it right in the first place, so I redid it again. . .
I see where I went wrong on my calculations.
so using the formula:
1962 watts *1/29 for 24V batt charg * 0.77 losses * 1/0.08 rate = 651 AH @ 24 V

Is an 8% rate acceptable ? What is the "ballpark" figure that I should aim for ? I have not bought any parts for this thing yet, but , I have asked the guy to set aside 9 panels, but hold off on ordering the CC for now. . .

I thank you for walking me thru this

Cariboocoot

Re: Ready ! - Aim ! - ...

Yes: Watts divided by Volts = Amps.

I de-rate the panels first, to give the effective Watts available for charging:
1962 (panel rating) * 0.77 (efficiency) = 1510 Watts.

Now the Voltage varies on output depending on the SOC of the battery. I pick the nominal Voltage as that is about the lowest you want to see on the system (roughly analogous to 50% SOC) and I'm usually checking for charging ability. So 1510 Watts / 24 Volts = 63 Amps (rounded).

Usual caveat that your actual results may vary due to the number of factors that enter into it in the real world. But this is generally close enough for judging if you've got the right panels/controller/batteries to work.

As a rule net 5% of capacity is minimum peak current for charging batteries. Net is after load allowances (any current draw while charging). As such if you target 10% and get somewhere between 5 and 10 it will work. If you have weather issues like short daylight or more clouds you'd want to increase the array size to improve the charging.

Skippy

Re: Ready ! - Aim ! - ...

Thank you Cariboocoot.

I have just been told by my "battery guy", that it is not reccommended to run a fridge off of batteries. I pointed out that I will have a 650 AH battery with a matching array , for the fridge and the washer, and other loads as I can fit them in, but was told the "general rule" is to not run the fridge off batteries, as the start up surge will kill the batteries. . . I should seriously think about getting a propane fridge instead. . . running the washer is not an issue, but the fridge is a no-no . .

What do you guys think of this ? I do agree, that if I were to be in the market for a new fridge, I should look into getting a more apropriate "off grid" model fridge, but since I have a brand new fridge - with an extra 2 inch of insulation all around, I don't see a problem with running it off the batteries .. . I would think the washer would draw more of a start up surge than the fridge ? What do you guys think of the "general rule" ?

westbranch

Re: Ready ! - Aim ! - ...

He is right ...to a point. It all depends on the system voltage, the lower the system voltage the harder on the bank to supply the startup amps. So a higher voltage means less amps pulled at startup...

What system voltage are you going to use?

Cariboocoot

Re: Ready ! - Aim ! - ...

Well I've been running a refrigerator off batteries since 2008 and it hasn't had a problem yet. So I can't agree with him.

For what a propane 'frige costs these days you can buy a lot of batteries.

Skippy

Re: Ready ! - Aim ! - ...

I am still planning on going with a 24 V system . . . So 9 - 218 watt panels - wired in groups of 3 (ready to be delivered) - to a 60 amp cc (waiting to be ordered) - to a 650 AH battery (have a place that I can order - buy them and pick them up). then to an inverter (sales depot is 2 hours away - but can order it in)- still tossing around the upper limits of that one either a 1,500 watt or 2,000 watt unit. . .

The guy I am talking too about the batteries, is the forklift guy from work, NOT the store where I can order them . . the subject came up on "good deals" . . . like 2 - 12 V - 350 AH gell cell batteries - only a year old - brand new-never used . . 200 $ each . . garanteed for 1 year... apparently, gell cells can sit for long periods, and not be effected. . ya right. . .

I have also been told that I should go with 12 - 2 V cells . . they would be better than 4 - 6 Volt cells . . .

Thats about all the advice he gave me, any comments ?

Skippy

Re: Ready ! - Aim ! - ...

Cariboocoot wrote: »

Well I've been running a refrigerator off batteries since 2008 and it hasn't had a problem yet. So I can't agree with him.

For what a propane 'frige costs these days you can buy a lot of batteries.

Thank you for the vote, I kinda thought about the saying on this forum - "everybody is an expert".
You have a fridge that is actually running on batteries - I think I will listen to YOUR advice. .

Cariboocoot

Re: Ready ! - Aim ! - ...

Yes: see my sig?
232 Amp hours @ 24 Volts and it runs a 16 cubic foot refrigerator without a flicker. Four 6 Volt flooded cells in series. It can also start my 3.5 HP air compressor without any problem.

GEL's are not recommended for RE use because they are very picky about Voltage and current. Also there is no way to check the SG.

2 Volt cells tend to be much more expensive per Watt hour than 6 Volt ones because of the difference in production volume.

People who know a little bit about electricity are more dangerous than those who know nothing.

westbranch

Re: Ready ! - Aim ! - ...

OK, some numbers... a 1500W inverter at full rated out put will pull 62.5 A.. or ~10% of your battery capacity.
If Marc's much smaller bank can provide, so can yours.

Your fridge is plugged into a 15A breaker at home, 15 x 110 v =~ 1650A, that is the max it can pull for an extended time before the CB trips. What you need to know what the surge draw is. Do you have a K-o-watt meter? it might be able to show it but it is momentary...

hth

Skippy

Re: Ready ! - Aim ! - ...

Yup. The k.o.w meter says 700 for a split second. . . I have already proven, that I can run the fridge on my cheapie - miss labeled -700 watt inverter . . it does run the fridge. . . I just thought I would bounce this latest advice off of you guys and see what you have to say. . . me personally, I don't think I will be buying a load of 2 V batteries off this guy. . . . and I think a 650 AH battery at 24 V is a BIG battery. . . so I should be o.k. on that side.

4 - 6 volt batteries sounds a whole lot better than buying a whole bunch of 2 V.

Thanks again for the advice. I have picked up the building permit for the "solar shed", and have started construction. . . I will drop in and keep you guys updated as I go. 8)

Good thing is, one way or another, this darn fridge IS going to go off grid !

Photowhit

Re: Ready ! - Aim ! - ...

Skippy wrote: »

... and I think a 650 AH battery at 24 V is a BIG battery. . . so I should be o.k. on that side.

....4 - 6 volt batteries sounds a whole lot better than...

Where are you finding 6 volt 650 Amp hour batteries? Sounds a bit odd to me .

Cariboocoot

Re: Ready ! - Aim ! - ...

Photowhit wrote: »

Where are you finding 6 volt 650 Amp hour batteries? Sounds a bit odd to me .

He probably won't.
However, Surrette makes 6 Volts in 683 Amp hours ($1,000 each). Some other similar sizes may be available from Trojan or Crown.
More likely he will be running two parallel strings of lower Amp hour L16 size.

Photowhit

Re: Ready ! - Aim ! - ...

Cariboocoot wrote: »

However, Surrette makes 6 Volts in 683 Amp hours ($1,000 each)....
More likely he will be running two parallel strings of lower Amp hour L16 size.

Kinda why I asked, and quoted him, since he's saying "4 - 6 volt batteries" I wanted to be sure he's calculating his amp hours correctly...

Skippy

Re: Ready ! - Aim ! - ...

Cariboocoot wrote: »

He probably won't.

Your right. They don't make batteries in that size. .

Here is what I have so far. . . Panels have been delivered - 9 panels - 50 lbs a piece. . . 77 cents a watt.

Attachment not found.

Progress on shed . . .

Attachment not found.
Attachment not found.
Attachment not found.
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Walls are ready to be stood up and nailed together :
Attachment not found.

One question for you guys. . with a 1,900 watt array, should I worry about making a tilting array mount ? - is it worth the solar gain in the middle of winter ? It would keep the snow off - having the array tilted up more. . .

What do you guys think ? tilt or no tilt ?

Cariboocoot

Re: Ready ! - Aim ! - ...

When do you need the power the most?
If it's in Winter you need to set them for that optimum angle. If it's in Summer, different angle. If it's year-round you can either adjust the angle twice or four times a year or split the difference with a Spring/Fall angle. That is what I do as there is no usage in Winter and Summer has plenty of sun.

If these are all the panels you've got you'll definitely want them tilted high to shed snow in Winter. Otherwise you supplement them with some vertical panels to make sure the batteries get some charg or spend a lot of time clearing snow the hard way.

Those who leave near the Equator have it made in this respect.

Skippy

Re: Ready ! - Aim ! - ...

Cariboocoot wrote: »

When do you need the power the most?

Those who leave near the Equator have it made in this respect.

Thank you for the reply.

Just thought I would ask, since I am still in the planning stages of this build, I can design and build a tilting rack. That is why the shed is built with 2x6's . . they can hold the weight of the racking as well as the panels.

Skippy

Re: Ready ! - Aim ! - ...

So here is what i have managed to put together so far . . . Panel mounting steel is 1/4 inch thick angle iron 1.5" x 1.5" and the rack up-right posts are 1 inch square tube (see attached pics ) . The whole unit is bolted down with 10 - 2.5 " lag bolts on the bottom frame , and 4 lag bolts on the top frame. The lag bolts go thru a rubber gasket, thru the steel roof, then into the 2x4's underneath. 3 different settings . . . Winter- spring- and summer . . . Comments ? Suggestions ? Me, i am wondering if i should put threaded rod thru the entire roof, and anchor it inside. This will hold 3 of my panels sideways. Two more frames to build.

inetdog

Re: Ready ! - Aim ! - ...

Skippy wrote: »

Me, i am wondering if i should put threaded rod thru the entire roof, and anchor it inside.

The only issue I see is what the wind uplift will be on the panels and racking. Using a through bolt or threaded rod with washer and nut should be able to sustain a higher upward force on each attachment that a lag screw would, and it will keep that strength better even if the 2x4 deteriorates or splits at the hole.

But if the calculated holding force of the lag screw is great enough, then there should not be a need.

FWIW, the bolt will be less affected by missing the exact center of the member than a lag screw would.