Author Topic: OFF GRID POWER; various thoughts on...  (Read 519553 times)

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Offline OlJarhead

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Re: OFF GRID POWER; various thoughts on...
« Reply #1175 on: November 09, 2013, 08:57:33 PM »
Installed and set up my TriMetric meter today and after fully charging the bank it read 101% of charge.

THen after 4 hours of running the cabin (watching TV etc) I see it's reading 94% of charge.  I was happy to see this until I saw the voltage was showing 2.4v which according to Trojan is only 60% of  charge.

I'll have to shut down for the night soon so it will be interesting to see if the batteries increase a little in voltage but I'm a little confused by the 94% right now as it would seem that's not accurate unless I'm not understanding the way it calculates the percentage of charge.

Any ideas?

Offline OlJarhead

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Re: OFF GRID POWER; various thoughts on...
« Reply #1176 on: November 09, 2013, 09:00:07 PM »
BiggKidd... the amp-hour rating that is the important one for off grid use is the 20 hour rate. Some batteries are rated at longer or shorter times, such as 100 hour or 5 hour. Hundred hour ratings are higher than the 20 hour. Our batteries are 210 amp-hours at the 20 hour rate.

Oljarhead... same batteries we placed into service summer 2009. Plates viewed through the fillers appear the same as when installed, FWIW. Performance is much the same now as then too. Water them twice a year and maybe equalize three times a year, IIRC  ???   I'd have to look at the log book but that is in the battery enclosure. And I'm not there.

That's great!  I've abused mine more then you but it gives me some hope that they might last another year or more...I might not have to buy the new batteries next year and that would be a big savings....but see my post on the TriMetric because if it's wrong then I can't see living with this small bank that long.  I need to run the calculator again with better data that I now can gather from the meter as that would help me understand the capacity I think.

Offline BiggKidd

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Re: OFF GRID POWER; various thoughts on...
« Reply #1177 on: November 10, 2013, 04:12:55 AM »
sorry I seem to have fallen asleep in the middle of this.   :-[   Long day and another today, can't wait to get back home. Don I'm pretty sure that is the 20 hour rate. But I'll check.

 Thanks

Larry
A hard life only makes you stronger.

 Larry

Offline BiggKidd

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Re: OFF GRID POWER; various thoughts on...
« Reply #1178 on: November 11, 2013, 04:07:57 AM »
Hi Guys,

  Could I get you to look at these panels and give me an opinion?  http://www.civicsolar.com/product/et-solar-et-p672300ww-300-watt-solar-panel and heres a link to the others I am looking at. https://www.renogy-store.com/300-Watt-Solar-Panel-p/rng-300p.htm

 Thanks. BTW those batteries are at the 20 hour rate. Just about ready to order 4 panels and the midnite 150 controler. Do I need a combiner box for this? I figure this will be a good first step.

Thanks
Larry
A hard life only makes you stronger.

 Larry

Offline BiggKidd

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Re: OFF GRID POWER; various thoughts on...
« Reply #1179 on: November 11, 2013, 11:41:13 AM »
Well it turns out the civic solar is out of stock. Renogy on the other hand has the 300 w panels and offers free shipping. So unless I find a reason not to go with them I think thats what I'll order. Still looking for the best price on the midnite solar classic 150. Civic solar has a decent price but wonder if they have it in stock?

Larry
A hard life only makes you stronger.

 Larry

Offline BiggKidd

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Re: OFF GRID POWER; various thoughts on...
« Reply #1180 on: November 11, 2013, 12:20:08 PM »
Do you all use combiner boxes on your systems? How about breakers / fuses on the in / out charging? Finding out there is a lot more to solar than what it took to hook up my harbor freight panels! My DC stuff now has no breakers or fuses. When I was running 12V in the house that had a fuse but since we went all 120 AC haven't used any DC fuses.

 Thanks
Larry
A hard life only makes you stronger.

 Larry

Offline MountainDon

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Re: OFF GRID POWER; various thoughts on...
« Reply #1181 on: November 11, 2013, 02:48:44 PM »
Either of those panels appear okay. 


Combiner:  They are handy things when it comes to connecting panels together to transmit the power run to the CC. It is possible to cobble something together using off the shelf electrical service panels, etc. The BIG thing to remember is devices like breakers, switches, disconnects, etc. that are made for use with AC current are usually not usable for DC current. Usually.  AC current as it's name indicates alternates directions. Every time it changes direction the current drops to zero as it heads in the other direction. That makes interrupting AC current much easier than DC. Using an AC disconnect on DC will sooner or later reult in the contacts being burned, maybe even welded together.

In case you are not aware DC can create flame arcs if the current is sufficient. Pulling a DC fuse to disconnect an active set of panels for example, can result in getting burned and/or starting a fire. So be careful if making something up from parts off the shelf.

OTOH, Square D  QO and QOC breakers can be used on low voltage DC circuits; 12 or 24. Nothing higher. 

There are also breakers available from golf cart parts that can handle high amperage and high voltage DC loads. Solarseller.com has assorted DC rated breakers.

Breakers / Fuses:   Devices like breakers and fuses must be rated for DC to be safe on DC.  The aforementioned Square D items may not have the DC approval labeled on them but they are okay. But because they may not be stamped for DC an inspector may not pass them. 

I like having a suitably sized breaker just before the input connection  (from PV)  on a CC as well as just after the output connection (before batteries). Suitable means, on a 24 VDC system the breaker voltage should be 37-38 volts or more. The amperage should be equal to the maximum of the PV output or the CC output.

A breaker in the positive line to the inverter is good as is a Type T fuse right at the battery positive. Yes, both; the type T fuse is for catastrophic shorts and the breaker can be used as a disconnect. Many DC breakers are rated for disconnect use; check ther specs before purchase.

Usually equipment made for DC use is much more expensive than for AC use. They need much heavier contacts and not so many are made as AC ones.

Hope that helps.



Just because something has been done and has not failed, doesn’t mean it is good design.

Offline hpinson

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Re: OFF GRID POWER; various thoughts on...
« Reply #1182 on: November 11, 2013, 03:11:25 PM »
The Midnight Solar DC combiners are reasonably priced and have a cutout for their nice MNSPD-600 lightning arrestor.

http://www.midnitesolar.com/products.php?menuItem=products&productCat_ID=9&productCatName=Combiners

Prewired with DC breakers and MC4 connectors (nice) here:

http://www.midnitesolar.com/products.php?menuItem=products&productCat_ID=35&productCatName=Combiners - Pre-Wired

Offline BiggKidd

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Re: OFF GRID POWER; various thoughts on...
« Reply #1183 on: November 11, 2013, 03:41:00 PM »
Thank you again Don.

 Yes when I was using 12v water pump etc I did have a fuse or fuses inline. Since we got away from 12v stuff I haven't. All of our power does run through a standard breaker box.  Yes your answer was very good and concise. The midnite combiner box is what I have been looking at. I am trying to make sure anything I buy at this point can also be used when I switch to a 48v inverter, magna sine 4448. I think I only have one last question for you guys and I'll be ready to order. What amp breakers do I need for running two of the renogy 300 W panels in series then in parallel with two more. Nope just realized two more questions. Can I run just one set of 10 awg cables from the four panels to the combiner (less than 100')?  Do you mount the combiner closest to the panels or the Charge controller?

hpinson, I like that prewired box but with the amp limit I think I will have to go larger.

Thank you all for taking the time to answer my questions it is a huge help!!!

  Larry
A hard life only makes you stronger.

 Larry

Offline MountainDon

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Re: OFF GRID POWER; various thoughts on...
« Reply #1184 on: November 11, 2013, 05:08:34 PM »
Quote
What amp breakers do I need for running two of the renogy 300 W panels in series then in parallel with two more

Look at the specs... Short- Circuit Current (Isc)  =  8.56A.   The panels in series still produce a max of 8.56 amps but their maximum voltage output is doubled; that is the Open - Circuit Voltage (Voc)   46.12V X 2 = 92.24.

The two series strings in parallel will double the maximum amps; Short- Circuit Current (Isc)   8.56A X 2 = 17.12 amps maximum.  The voltage max stays the same, 92.24.

Round 17.12 amps up; 20 amps would be a good breaker size.  The voltage rating of the breaker should be the max Voc, 92.24 x 1.25 x 1.25 = 144.125 VDC.  So 150 - 165 volts would do.  That voltage is very close to the maximum the Midnight 150 can handle.

~~~~~~
Quote
Can I run just one set of 10 awg cables from the four panels to the combiner (less than 100')?  Do you mount the combiner closest to the panels or the Charge controller?

Combiner is placed close to the panels, that saves wire.  There would be two series wired sets that complete their parallel connection in the combiner. Then one pair (positive and negative) that go from the combiner to the charge controller, with the positive passing through a breaker/disconnect before the charge controller IF the distance from the combiner to the CC is too great to make it convenient to just rely on the breaker disconnect at the combiner.

10 AWG is fine for the usual distances from panels to combiner. 

What would the distance from combiner to CC be?  I can run my calculator to see what wiring sizes would be best.

Just because something has been done and has not failed, doesn’t mean it is good design.

Offline BiggKidd

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Re: OFF GRID POWER; various thoughts on...
« Reply #1185 on: November 11, 2013, 06:56:19 PM »
Don,

  Thank You  I had come up with 20 amp. But didn't have the formula to back it up, just seat of the pants reckoning. I am not sure on the distances yet watching the sun as the winter progresses to get the best location. It will be mid dec. before everything is delivered and ready to mount. It will be less than 100 ft though, may be as little as fifteen. If I could go five hundred the panels would go on top of the hill. I am sure more trees will have to come down. Its a good thing too. I know people who have no trees and hate it. I have to many trees, but still love them. Just thinning some for other projects.   :)  Boy its nice getting answers that make since. The people who are in solar sales need classes I think. Most of the techs likely know their stuff but the sales staff ..................................

  You all have a nice night.

 Larry
A hard life only makes you stronger.

 Larry

Offline MountainDon

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Re: OFF GRID POWER; various thoughts on...
« Reply #1186 on: November 11, 2013, 08:39:47 PM »
FYI, with 4 panels as described, in series/parallel

maximum voltage drop of 2%, #4 awg = 145 feet
maximum voltage drop of 3%, #4 awg = 218 feet

maximum voltage drop of 2%, #6 awg = 92 feet
maximum voltage drop of 3%, #6 awg = 136 feet

maximum voltage drop of 2%, #8 awg = 58 feet
maximum voltage drop of 3%, #8 awg = 87 feet

maximum voltage drop of 2%, #10 awg = 37 feet
maximum voltage drop of 3%, #10 awg = 55 feet

maximum voltage drop of 2%, #12 awg = 23 feet
maximum voltage drop of 3%, #12 awg = 35 feet

G/L
Just because something has been done and has not failed, doesn’t mean it is good design.

Offline BiggKidd

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Re: OFF GRID POWER; various thoughts on...
« Reply #1187 on: November 12, 2013, 10:08:11 AM »
Don thats some great info. Thank you. I will likely use 10 awg even if its a bit of overkill going less than 30 ft which looks like my distance. Now wholesale solar is trying to work up a better price on their panels since I told them last night I was planning to go with the renogy panels.  d*

Can't wait to see what they come up with.

 Larry
A hard life only makes you stronger.

 Larry

Offline BiggKidd

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Re: OFF GRID POWER; various thoughts on...
« Reply #1188 on: November 13, 2013, 04:52:35 PM »
Guys,

 I bit the bullet today and ordered 4 of those Renogy 300w panels. After I go by the bank tomorrow I will order the classic 150 and breakers etc. This should be a fair start to our adventure in real solar power.

  Thanks to all who helped with my questions.

 Larry
A hard life only makes you stronger.

 Larry

Offline BiggKidd

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Re: OFF GRID POWER; various thoughts on...
« Reply #1189 on: November 14, 2013, 08:28:52 AM »
Finally got all my stuff ordered. After the bank shut my card down thinking it was fraud.   [cool] At least they are watching out for the customer.

  Don,

 I was hoping to barrow some more of your fountain of knowledge.  :)  Trying to make sure we can use all the same stuff once we switch to 48 v and more panels. Also just really realized just how big this bank of panels is going to end up.  [shocked]  What is the formula for figuring wire size. I would like to be able to continue using the same wire when we switch to 48 volts I am thinking we will end up maxing out with panels on each controller. But I am not sure at this time how many amps thats going to be. So many numbers!

  The midnite 150 controller looks to be most effecent (sp) around 70-100 volts going in. So should we keep them in pairs or step up to sets of three in series for a 48 volt system?

  UGG Old dog new tricks!  d*

 Larry
A hard life only makes you stronger.

 Larry

Offline MountainDon

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Re: OFF GRID POWER; various thoughts on...
« Reply #1190 on: November 14, 2013, 03:38:28 PM »
Quote
What is the formula for figuring wire size.
Not a formula exactly, but a calculator. The one I use is an electrical design program on my computer. There are some online ones. Here's two...
1.  http://www.nooutage.com/vdrop.htm
2.  http://www.windsun.com/Hardware/Voltage_Calc.htm

As current flows along longer and longer wires there is more drop in the voltage measured at the far end. Ideally we'd keep that to 2 or 3% maximum; less is best. When figuring for wires from PV panels to the CC use the Vmp voltage figure and the Imp maximum power amperes.


On selecting a charge controller. Maybe you are aware already, but be sure to allow for the cold weather voltage spikes that occur with PV panels. There should be a safety factor. The best / safest method is to use the Voc figure for the panels. If 2 panels are in series multiply the Voc by 2. Then multiply the Voc total by 1.25 and multiply by 1.25 again. The result should be lower than the maximum input voltage for the CC being looked at.

The amps should of course be under the CC max amps rating. Same for the wattage.

Also as for how many panels in series.... from a post above....   The panels in series still produce a max of 8.56 amps but their maximum voltage output is doubled; that is the Open - Circuit Voltage (Voc)   46.12V X 2 = 92.24.   take that 92.24 x 1.25 x a.25 and we get 144 volts. That is close to but still under the 150 max volts for the MN150. So stop at 2 panels in series. Series groups can be wired in parallel; 2, 4, ...  panels. But I did not check the wattage limit so check that.  This is why MidNight makes the 200 ans 250 models.

Midnight has a online sizing tool...
http://www.midnitesolar.com/sizingTool/index.php

Just because something has been done and has not failed, doesn’t mean it is good design.

Offline BiggKidd

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Re: OFF GRID POWER; various thoughts on...
« Reply #1191 on: November 14, 2013, 04:31:14 PM »
Thanks Don,

  Midnite also states in their owners manual that they produce more watts at lower incoming voltages. It looks like 70-100 volts is best through out their chargers. I need to find the manual again and link it. The salesman kept saying to put three in series but that doesn't fly. I think the reason most go with the higher voltage units is because of the distances involved. Thanks for the links, I will save them. You know I am not a well educated person but seem fairly lucky a grasping most of this stuff.

  http://www.midnitesolar.com/pdfs/classicManual.pdf

Copied from page 11 of the linked manual.

For example: if you are using a Classic 250 and 48v battery bank, the maximum continuous output power based
on 25 degree C ambient is 55 amps when using a PV array that yields a Maximum Power Voltage of 180 volts. The
same set up using a bit higher voltage modules that result in a 200V Maximum Power voltage will result in only 53
amps. Although 55 to 53 amps is not a significant change, it does give you the idea that all things being equal, lower
voltages are a bit more efficient.

  I tried to copy the graph but it wouldn't work, pages 10 and 11.

  Larry
A hard life only makes you stronger.

 Larry

Offline BiggKidd

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Offline BiggKidd

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Re: OFF GRID POWER; various thoughts on...
« Reply #1193 on: November 14, 2013, 05:34:55 PM »
Using the data sheet here :
 https://www.renogy-store.com/300-Watt-Solar-Panel-p/rng-300p.htm
 for the panels and the string size here :
http://www.wholesalesolar.com/products.folder/controller-folder/MidniteClassicChargeController.html#MidNiteClassicStringSizingTool
for the controller If I plugged all the numbers in right then 16 panels 8 parallel strings of 2 @ 48 volts battery bank should give me the best bang for the buck. Would you agree?

   Thanks
Larry
A hard life only makes you stronger.

 Larry

Offline MountainDon

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Re: OFF GRID POWER; various thoughts on...
« Reply #1194 on: November 14, 2013, 05:54:09 PM »
using a low temperature of -22 F  and a high of 104 F that seems to work on a 150.   I'd say good!
Just because something has been done and has not failed, doesn’t mean it is good design.

Offline BiggKidd

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Re: OFF GRID POWER; various thoughts on...
« Reply #1195 on: November 15, 2013, 03:53:11 AM »
Thanks Don,

  It has never gotten that cold here and we have seldom seen 104 either. Thanks for double checking my numbers.  [cool]
Amazingly the panels have already shipped.

Did you see what I was talking about the lower voltage for the incoming PV? When figuring wire size what voltage do I use for the PV? Its seems like a dumb question but . I'm thinking 75 volts since if I understand this correctly the mppt is going to try and hold the panels at the optimum charging level. Jeez there's still so much I am not sure of.

  I also think you for taking the time to share your vast solar knowledge.

Larry
A hard life only makes you stronger.

 Larry

Offline upa

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Re: OFF GRID POWER; various thoughts on...
« Reply #1196 on: November 15, 2013, 05:23:07 AM »

  Trying to make sure we can use all the same stuff once we switch to 48 v and more panels. Also just really realized just how big this bank of panels is going to end up.  [shocked]  What is the formula for figuring wire size. I would like to be able to continue using the same wire when we switch to 48 volts I am thinking we will end up maxing out with panels on each controller. But I am not sure at this time how many amps thats going to be.


I am away for a few days and the conversation picks up again, how exciting :D Larry if you are planning to upgrade to a 48v system in the future, now is an excellent time to consider your wiring infrastructure as presumably you are going to bury your 30ft run from the PV combiner to the CC and nobody likes to dig wire trenches more than they have to. While the suggested 10 gauge run would be sufficient for the four 300 watt panels in the suggested series /parallel runs it won't be sufficient for 12 panels(3600 watts) assuming you wanted to max out your single 80 amp CC at 48 volts in the future. You are going to be pumping out much more amps(~ 50)and at that distance and assuming 2 panels in series x 6 paralleled runs your going to need at least 6 gauge wire(2.4% voltage line loss).

Incidentally the following pdf http://lib.store.yahoo.net/lib/wind-sun/PV-NEC-V-193.pdf is an excellent primer on the topic, it will likely answer most of your questions

Offline MountainDon

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Re: OFF GRID POWER; various thoughts on...
« Reply #1197 on: November 15, 2013, 06:40:37 AM »
I suggest that using the Vmp voltage would be about right as would be using the Imp current.

upa makes a good point about sizing the longer runs of wire to be suitable for the future expansion.

The paper upa pointed to is good. Wiles, the author is an expert in the field of PV and the electrical code. He's been involved in PV for many years.
Just because something has been done and has not failed, doesn’t mean it is good design.

Offline BiggKidd

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Re: OFF GRID POWER; various thoughts on...
« Reply #1198 on: November 16, 2013, 01:21:14 PM »
Thanks Upa , Don,

Had to go out of town should be back home sunday night or monday.  Yes I surely want to be able to use the wire once I make the switch to 48V. Now that I have had time to sit back and think about how big this is going to turn out looks like I'll have to move some (most) things. Including the battery building. Still thinking about the best way to go.

More tomorrow or monday.

 Larry
A hard life only makes you stronger.

 Larry

Offline considerations

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Re: OFF GRID POWER; various thoughts on...
« Reply #1199 on: November 17, 2013, 06:18:15 AM »
The folks at Midnight Solar are super smart and helpful. I called them anytime I needed help with sizing breakers, decifering wiring diagrams, wire sizes, as nauseum. They did not laugh or get irritated, not once. They are super....I say if you are not absolutely sure. Just call them...it is actually fun to has a conversation and hang up knowing what is required. I would have been much more uncertain about my system expansion this summer without them.

 

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