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solar and battery config with 12/2 wire bottleneck?
#21
In my city - electrical codes for DC 48v (or higher) require red/black wires in metal conduit within the home (in attic, walls, etc) and AC does not (can just run the wire).   I think this might affect DC vs AC 'bias' beyond just wire/amps/voltage.    I've read that this is one of the pros of 'solar panel' inverters - to run AC from panels on roof into attic, you don't need conduit in attic. Codes.... (sigh).
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#22
You dont need your panel voltage to be 1.5times larger just to the most efficient. That is old saying for pwm controlles and cheap chargers. Mine is hvdc and is around 800vdc....
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#23
Wow, lots of useful info. I'm lost AF now, but I'll re-read it again with Google and get up to speed.

However, I did just remember that I analyzed my past electric bills not too long ago to get some usage stats and discovered that depending on the config I go with, I can just barely power the whole home with just solar panels on the garage roof alone! I used as a reference for dimensions (and I guess wattage and budget), Renogy's 24v 300W 10 pack panel kit - I can fit 12 total panels on the garage roof alone (and down the road potentially 12 to 15 more panels on my main house roof). That's 3600W/3.6 kWh (if I go with a 24v system instead of the preferred 48v) and according to my electric bill I'm averaging 2.64 kWh per hour (64 kWh per day, 1977 kWh per month). I said barely earlier because I'm assuming panel efficiency will bring that energy down somewhere between 3.6 kWh and 2.64 kWh and then there's watts lost during the conversion. Of course I know this is only during peak sun hours, but still.

Is my work correct on this? If so, can I push this 24v system down a 12/2 wire if I followed the 240V AC suggestion or the "push DC over the 12/2 instead of AC" suggestion? Of course, that's a $4000 cost for just the panels alone so this is a high end, "do it more right than dirty" option.


P.S. - In case anyone's wondering - my original plan was buy some 100 watt panels used off Craiglist just because I have a spare cheap charge controller and inverter laying around... just because. Then I remembered that 12/2 wire coming from the house and our $250/month electric bill and started taking this a little more seriously
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#24
Time to dig a trench with 10/3 underground wire.
Quick and dirty has just become more complicated

Wolf
DCkiwi likes this post
If 18 X 650 = 2200+mAh then we have power! 
May all your Cells have an IR of 75mΩ or less Smile
Last count as of 8/7/2019
Total Number of Cells Recorded and processed                 6106
Total Cells required for PowIRwall                                   2856
Total Cells ≥2200mAh, ≥80%, ≥35mΩ, ≤75mΩ, ≥4.12V   2694
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#25
(06-08-2019, 03:33 PM)daromer Wrote: Mine is hvdc and is around 800vdc....

Wow 800V is pretty high! Are you worried about PID "potential induced failure" ** - some panel might get this, hopefully not yours!
(** where there's creepage due to the high voltage between the cells & the frames & you get ground faults, some panels here in Australia have had this issue)
Running off solar, DIY & electronics fan :-)
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#26
This is not a project build. Moved to the correct section...
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#27
Okay, so to wrap things up... if I wanted to stick with that 12/2 wire and stay within it's spec and if I have all DC stuff in the garage then I should aim to keep AC pushed under roughly 1800 watts to avoid constantly spiking/peaking and stressing that 12/2 wire??

And there's no consensus that pushing DC instead of AC or pushing AC at 240 volts instead of 120 volts over that 12/2 wire is safe or worth it?

Otherwise, if I did want to go with the high end plan of 12 300 watts solar panels, then I need to dig another trench and run at least 10/3 wire? Should I just run 8/3 instead to future proof things?
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#28
DC is out for the safety reasons above.
With AC you can run the rated current for that cable allowing for buried underground conditions.
You don't have to worry about short bursts for higher current, ie you could easily get double the rated current along it for a few minutes safely before temperature rise started to kick in.
Cables like this are rated for average current & won't blow or melt suddenly.
Suitable breakers should be used in the garage gear anyway to protect the cable.

In reality, will you have more power available in the garage than the existing cable can handle? Probably not :-)
Running off solar, DIY & electronics fan :-)
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#29
Redpacket. Most home owneres here have 300-800HVDC systems on the solar side.
No I dont worry about issues there. That would be like worrying going over the street every time you do that Tongue
DCkiwi likes this post
The Ultimate DIY Solar and build place
YouTube / Forum system setup / My webpage  Diy Tech & Repairs

Current: 10kW Mpp Hybrid | 4kW PIP4048 | 2x PCM60x | 83kWh LiFePo4 | 10kWh 14s 18650 |  66*260W Poly
Upcoming: 14S 18650~30kWh | Automatic trip breakers, and alot more
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#30
(06-08-2019, 03:33 PM)daromer Wrote: You dont need your panel voltage to be 1.5times larger just to the most efficient. That is old saying for pwm controlles and cheap chargers. Mine is hvdc and is around 800vdc....

Eh well shoot me and paint me red. First I did not say "most efficient" I said "For your MPPT controller to work at the best efficiency your solar panel voltage should be at least 1.5 times higher than the nominal battery voltage."

Whether that is an old saying or not you are not really going to charge a 48V battery with a 35V PV string no matter what the controller is whether PWM or MPPT expensive or cheap. 
1.5 times higher is a good starting point and a good rule of thumb especially if you are getting started and remember his original post was "quick and dirty" not expensive and complex.
Also If you consider MidNight Solar Classic 150 cheap which recommends that the  PV input voltage should be at least 30% higher than the highest expected battery voltage then Boy Id like to see your controllers Smile Oh wait I have.

My system runs at 2 to 2.5 times the battery voltage maybe a bit more on occasion and if the OP would put 3 panels in series he would realise that also.
Not all of us can and for that matter of fact want a 800VDC PV array. 

Quote:Redpacket. Most home owneres here have 300-800HVDC systems on the solar side. 
No I dont worry about issues there. That would be like worrying going over the street every time you do that [Image: tongue.png]

Well in Sweden I guess HVDC is common and that is great!! As far as crossing the street oh you bet I'm gonna worry especially if you are on the road and driving. Tongue

Wolf
If 18 X 650 = 2200+mAh then we have power! 
May all your Cells have an IR of 75mΩ or less Smile
Last count as of 8/7/2019
Total Number of Cells Recorded and processed                 6106
Total Cells required for PowIRwall                                   2856
Total Cells ≥2200mAh, ≥80%, ≥35mΩ, ≤75mΩ, ≥4.12V   2694
For Info Google Drive
Not your average Wolf       
            Cool
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