Author Topic: OFF GRID POWER; various thoughts on...  (Read 560831 times)

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Offline rick91351

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Re: OFF GRID POWER; various thoughts on...
« Reply #925 on: October 03, 2011, 09:05:52 AM »
I like the idea of the controller, inverter sheltered in the house but I sort of don't like the idea of the batteries located there.  Especially in the basement but then I am a real novice at solar.  Do not claim to know anything about it.  Best left to MD, Sparks and JarHead.  But I have been around those huge storage batteries a lot from trucks to locomotives most of my life.  I have really got a lot of respect for them, their storage potential and their gases.

Could you locate a lean to storage for them on the exterior of the cabin of out of the way?  
Proverbs 24:3-5 Through wisdom is an house builded; an by understanding it is established.  4 And by knowledge shall the chambers be filled with all precious and pleasant riches.  5 A wise man is strong; yea, a man of knowledge increaseth strength.

Offline Squirl

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Re: OFF GRID POWER; various thoughts on...
« Reply #926 on: October 03, 2011, 09:23:23 AM »
Doc,

I am putting my off grid stuff in a separate shed for two reasons.

1. I want to have the batteries and electrical away from the house for safety/fire issues.
2. The building inspector wants me to have it away from the house for safety/fire issues.

If you have an MPPT charge controller wire them in series where ever you put the panels.  I was told that even in low sunlight this makes sure your array voltage is above your battery bank voltage. 

Offline glenn kangiser

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Re: OFF GRID POWER; various thoughts on...
« Reply #927 on: October 03, 2011, 09:36:00 AM »
I am running over 100volts  to my Morningstar and I agree with the above.  Higher voltage is less line loss.
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Offline AdironDoc

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Re: OFF GRID POWER; various thoughts on...
« Reply #928 on: October 03, 2011, 11:48:55 AM »
Running them in series seems a great idea to always be over the threshold voltage. Unfortunately, my Chinese controller accepts up to 40 V and has an output of 12 or 24V. I suspect 55V (2 x 27.5V) may fry it. Batteries away from the house seems a good option too because of off-gassing, etc. Someone I heard of (here on CP.com?) keeps their batts in a deck box with windowed top for warming. I do already have a 250ft coil of 12-2 UF wire. On the other hand, if I got two more panels, I'd have line voltage into the house AND a major boost to my system. A good controller costs nearly as much. This is getting interesting.

Offline MountainDon

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Re: OFF GRID POWER; various thoughts on...
« Reply #929 on: October 03, 2011, 12:38:00 PM »
That would fry it, yes.  One thing to keep in mind as well, especially in locations that experience winter low temperatures is to be absolutely certain to design for the possible voltage spikes that cold temperatures initiate. The safe thing, and the NEC thing, is to multiply the Voc  (open circuit voltage, not the maximum power voltage) of the panel(s) by 1.25 and then by 1.25 again. (1.56 for those who like single steps). That will cover the coldest temperatures. I have mentioned this before but it does bear repeating. The maximum voltage rating of the charge controller must be greater than the result of that math problem.

For those who have or are considering an Outback controller they have an online tool that has temperature adjustments. Handy tool and interesting to look at even if Outback is not the unit of choice. I believe Xantrex has a similar tool.

« Last Edit: October 03, 2011, 12:51:52 PM by MountainDon »
Just because something has been done and has not failed, doesn’t mean it is good design.

Offline MountainDon

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Re: OFF GRID POWER; various thoughts on...
« Reply #930 on: October 03, 2011, 12:48:05 PM »
Batteries simply need to be in an properly vented air tight enclosure if in or near the house or other outbuilding. This can be done and batteries can be in the basement. The hydrogen will rise and dissipate rapidly from a properly designed, sloped top box.

It is also key to not have any sources of possible sparks in the enclosure. No switches, no relays, no breakers or fuses. In fact no electronics at all just to protect them from battery acid fumes.

When placing batteries and inverter at a distance from the building that is being powered size the AC conductors appropriately for the highest amperage use. Depending on distances and AC  amperage designed for the wires for AC may have to be about the same size as for the DC current. Run the numbers through a good voltage drop calculator.

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

Offline MountainDon

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Re: OFF GRID POWER; various thoughts on...
« Reply #931 on: October 03, 2011, 12:57:41 PM »
BTW,  27 VDC at 7.5 amps on 60 feet of #10 copper wire comes out to a 4.03% voltage drop on my calculator. That's a tad high IMO.
Just because something has been done and has not failed, doesn’t mean it is good design.

Offline AdironDoc

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Re: OFF GRID POWER; various thoughts on...
« Reply #932 on: October 03, 2011, 04:00:09 PM »
BTW,  27 VDC at 7.5 amps on 60 feet of #10 copper wire comes out to a 4.03% voltage drop on my calculator. That's a tad high IMO.

Thanks, Don. Now were I to house the equipment beside the panels, and run line voltage to the cabin, would the 60ft of 12-2 wire be an issue?

Offline MountainDon

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Re: OFF GRID POWER; various thoughts on...
« Reply #933 on: October 03, 2011, 04:19:42 PM »
PV module specs please: Vmp and Imp Maximum power volts and amps.

Assuming 27 volts is Vmp, the 200 watt rating makes the Imp 7.4
60 feet, #12 copper wire = 6.35% voltage drop. Too high IMO. I try to aim at no more than 3%.  Mine calculates to 1%.


OOPs I miss thought that. It's for AC, thanks Rob. 

Yes the current load desired is a must know.

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

Offline Rob_O

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Re: OFF GRID POWER; various thoughts on...
« Reply #934 on: October 03, 2011, 04:22:01 PM »
Thanks, Don. Now were I to house the equipment beside the panels, and run line voltage to the cabin, would the 60ft of 12-2 wire be an issue?

Depends on the load...

Voltage drop = current * resistance

.0016ohms/foot * 60 feet * 20 amps = 1.92 volts or about 1.6% of 120V

How much power do you need?
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Offline MountainDon

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Re: OFF GRID POWER; various thoughts on...
« Reply #935 on: October 03, 2011, 04:39:43 PM »
My calculator* indicates 60 feet, 120 VAC, 20 amps, 12 gauge copper = 4% voltage drop which is considered okay for AC circuits. (two conductors)




* EDR,   http://www.edreference.com/
Just because something has been done and has not failed, doesn’t mean it is good design.

Offline AdironDoc

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Re: OFF GRID POWER; various thoughts on...
« Reply #936 on: October 03, 2011, 05:56:36 PM »
I'd have to do an energy analysis of all my planned items and consider the amperage if they were all to be turned on at once. Main players, a 120V pressure pump rated max 1A, 800W microwave and a refrigerator rated at 1Kw daily. Aside from that, up to ten 13W CFLs. The highest draw is at the moment the pumps start and the compressor starts, yes? Am I to calculate the flow if they all started simultaneously? That comes to around 8 amps. Add 2 amps more for assorted possibilities like clocks, radio, etc. So 10 amps over a 60 foot run of 12-2.

Offline Rob_O

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Re: OFF GRID POWER; various thoughts on...
« Reply #937 on: October 04, 2011, 02:55:43 PM »
My calculator* indicates 60 feet, 120 VAC, 20 amps, 12 gauge copper = 4% voltage drop which is considered okay for AC circuits. (two conductors)

* EDR,   http://www.edreference.com/

I forgot to calculate for the total length of the circuit (120 ft)  d*  Your thing seems to be derating by ~20% as well
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Offline Native_NM

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Re: OFF GRID POWER; various thoughts on...
« Reply #938 on: October 10, 2011, 11:54:21 AM »

Grid-tie panels down to $1.25/watt.  Panel is the CSI CS6P-225P 225w. 
New Mexico.  Better than regular Mexico.

Offline OlJarhead

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Re: OFF GRID POWER; various thoughts on...
« Reply #939 on: October 10, 2011, 12:42:24 PM »
For those who were interested in my Battery High Voltage Disconnect alarms and reset on my system I did a test these last two weeks.  I turned off the inverter and shut everything down so the only load on the system was a 12vdc fan in the compost unit.

And the alarm continues.

Very strange -- I have been unsuccessful in getting morning star to respond to my queries also...so they are no help at all.

Offline Native_NM

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New Mexico.  Better than regular Mexico.

Offline MountainDon

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Re: OFF GRID POWER; various thoughts on...
« Reply #941 on: October 13, 2011, 04:44:38 PM »
Well at least GE is a known name, unlike the failed startups here.

I guess I wish them luck. 
Just because something has been done and has not failed, doesn’t mean it is good design.

Offline OlJarhead

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Re: OFF GRID POWER; various thoughts on...
« Reply #942 on: October 14, 2011, 11:24:52 AM »

Interesting...GE is going up against China:

http://finance.yahoo.com/news/GE-to-build-large-solar-panel-apf-1072600519.html?x=0&sec=topStories&pos=4&asset=&ccode=

Doubt it very much....but perhaps...just remember that GE's Jeffery Imelt is Obama's buddy and GE didn't pay a dime in corporate taxes last year...hmmmm

Offline AdironDoc

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Re: OFF GRID POWER; various thoughts on...
« Reply #943 on: October 17, 2011, 04:37:30 AM »
So fellas (and ladies), a few posts back I was waffling on whether to place a small shed beside my panels, put everything in it and run line voltage from the panels or, run 27V into the cabin and do it there. Seemed there would be much less voltage loss doing it at the panels. I've decided to run 27V over the 50ft into the basement. It will allow security for my controller, inverter, batteries etc. and whatever increase in wire gauge needed to offset voltage loss is made up by not needing to build or buy a shed.

I've used the voltage loss calculator and see the outcomes for combinations of gauges and number of conductors per phase. The question in my mind at this point is, how much loss is acceptable? At 27.5V, the difference between a 2% loss and 1.5% loss is several gauges of wire and maybe a few hundred bucks.


Offline MountainDon

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Re: OFF GRID POWER; various thoughts on...
« Reply #944 on: October 17, 2011, 12:46:03 PM »
Chances are you'll never "see" the difference between a theoretical 1.5 or 2.0%


How many PV modules; Voc, Isc?

Has the equipment been bought yet?  

Are you stuck with running the 27.t volts? Much better efficiency wise to be able to series the PV modules, but that requires matching the charge controller to the maximum voltage from the modules.

Also, if in the future you wanted/needed more power from the modules, how would that be achieved? If you go larger on the wire now, then it may be easier to add modules in parallel.  ???

« Last Edit: October 17, 2011, 01:01:27 PM by MountainDon »
Just because something has been done and has not failed, doesn’t mean it is good design.

Offline AdironDoc

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Re: OFF GRID POWER; various thoughts on...
« Reply #945 on: October 18, 2011, 12:09:08 AM »
Thanks for the reply, Don. Panels are Sun 200W 33.2 Voc, 27.5Vmc. Everything is bought. Unfortunately, the MPPT Controller handles up to 40V so I can't run them in series. With my 2 Panels in parallel, I'll buy whatever gauge I can stuff into a 1" conduit. I was thinking to run between 2 to 4 conductors depending on price and ease of pulling. I was shooting for a 1.5% loss. 50ft run means 100ft circuit. I suppose there will always be voltage losses of some extent. How much is acceptable, I don't know.


Chances are you'll never "see" the difference between a theoretical 1.5 or 2.0%

How many PV modules; Voc, Isc?

Has the equipment been bought yet?  

Are you stuck with running the 27.t volts? Much better efficiency wise to be able to series the PV modules, but that requires matching the charge controller to the maximum voltage from the modules.

Offline Tickhill

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Re: OFF GRID POWER; various thoughts on...
« Reply #946 on: October 18, 2011, 01:11:44 AM »
I am sure you have thought about this already but also pull in an extra 14 AWG wire or other small diameter rope for future pulling needs, identify it on both ends. Always keep a spare in the pipe!
"You will find the key to success under the alarm Glock"  Ben Franklin
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Offline Squirl

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Re: OFF GRID POWER; various thoughts on...
« Reply #947 on: October 18, 2011, 04:29:37 AM »
Just curious, but have you done a solar site survey?  By the looks of the picture the trees are very tall and semi close to the house.  Based on my view from the photo, a roof mount would probably give you the maximum power throughout the year.  Which direction is south in the photo?  It looks like the spot of the proposed panels is next to the tree line.

Offline MountainDon

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« Last Edit: October 18, 2011, 09:28:18 AM by MountainDon »
Just because something has been done and has not failed, doesn’t mean it is good design.

Offline AdironDoc

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Re: OFF GRID POWER; various thoughts on...
« Reply #949 on: October 18, 2011, 09:25:13 AM »
Just curious, but have you done a solar site survey?  By the looks of the picture the trees are very tall and semi close to the house.  Based on my view from the photo, a roof mount would probably give you the maximum power throughout the year.  Which direction is south in the photo?  It looks like the spot of the proposed panels is next to the tree line.

Squirl, thanks for the reply. Southern exposure is clear but gotta trim those trees back when I'm up there next. I don't want any limbs falling on the panels. I dragged the rack more or less to true south using a declination chart and propping the legs up, adjusted it to around 40 degrees. All trees in front of the panels are down from "10am to 3pm" sun, but I'll need to take some more along the creek for the later afternoon sun. I thought of roof mounting but the cabin's roofline faces southwest, and the steel roof has no pinchpoints like running seam variety. I'd need to drill and mount bonafide racks with tilts. As I've planned it, come winter, I'll just turn the clips, lift out the panels and put them in the cellar. I'll be happy with sun from 10 to 4. I'm up every other weekend, so, batteries have 12 - 14 days to charge between uses.

Tickhill, extra wire's a great suggestion. Not just for pulling, but also for power to any future sheds, outdoor needs, etc.

Start of a solar rack made of 4x4s. Faces south at 40 degrees tilt. Will be braced with turnbuckles. Firring strips on top so panels drop right into place with clips that turn over the lip of the panels.

 

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