Help: Need Solar installation diagram that follows NEC guidelines

• 24,000 WH per day * 1/0.85 inverter eff * 1/48 volt battery bank * 2 days storage * 1/0.50 max discharge = 2,353 AH @ 48 volt battery bank

• 2,353 AH * 59 volt charging * 1/0.77 panel+controller derating * 0.05 rate of charge = 9,015 Watt array minimum
• 2,353 AH * 59 volt charging * 1/0.77 panel+controller derating * 0.05 rate of charge =18,029 Watt array nominal
  
• 2,353 AH * 59 volt charging * 1/0.77 panel+controller derating * 0.05 rate of charge =23,438 Watt array "cost effective" Maximum
  
• 2,000 Watt load * 1/0.77 panel+controller losses = 2,597 Watt array to support day time loads
• 18,029 Watt array (nominal)+2,589 Watt load support = 20,627 Watt array minimum recommended (based on battery AH capacity)
  

Karachi
Average Solar Insolation figures

fm.109 said:

Thank you very much everyone for the replies and BB once again very thorough answer. Though, i do have a few questions (please dont mind if i am acting like a complete idiot lol).

1. Can you elaborate the 2353 Ah @ 48 Volt figure into how we can choose the number of batteries?

• In general, you try to find the AH battery that will support your bank size. You want as few parallel strings as practical for your system... Ideally, you would look for a 2,353 AH @ 2 volt cell, and put 24 of them in series. If you cannot find that, then (for example) a 1,150 AH @ 2 volt cell, 24 in series, then 2x strings in parallel (48 total cells).
• There are lots of drawbacks with a massively parallel battery bank. My suggestion is 1-2 parallel strings are ideal. 3 is workable. More than 3 parallel strings, then you are getting into higher expenses (more cabling, each string should be fused/breakered), more cells to water (24 vs 48 vs 96 vs more--). Gets old watering 96+ cells.
• There are secondary issues too--Getting current to share between strings, a shorted cell can discharge the bank, an open cell can be missed and you now have a string of 23 cells that are not helping your loads, and are slowly self discharging to sulfation, issues of thermal stability (a "hot cell/string" has lower charging voltage, which draws more charging current, gets hotter, more charging current, etc.).
• Not to say that a large number of parallel strings don't work--Just try to avoid them if possible. If you are the type of person that enjoys tinkering/maintenance tasks, it can be done and work well.
  

2. I have read that the manner in which you interconnect batteries affects the charging performance. Is that true?

• Yes--Batteries (and good wiring) has very little series resistance. If you have wiring "done wrong", you can end up with some batteries getting all the charging/discharging current, and others hardly any. Check this link out:
• http://www.smartgauge.co.uk/batt_con.html
  

3. I have read that DC breakers are sized at 1.25 times the needed Amperage; are there any other factors I need to keep in consideration when sizing DC breakers?

• Maximum working voltage. Many smaller breakers/fuses are rated for 32 VDC maximum (or even less). A 48 volt battery bank will charge at 60+ VDC.
• Maximum Amp Interrupt Current. Smaller fuses may only interrupt 10's or 100's of Amperes of current. Even a relatively small Lead Acid Battery bank can output 1,000 Amperes or more into a dead short.
• Average load vs surge load. When working with motors that have large starting current (well pumps, compressors, etc.). You can get "fast or slow blow" fuses/breakers. Motors can take 5x running current when starting--But only for a second or few seconds... Normally, unless you are in an industrial situation, a properly rated fuse/breaker (1.25x max continuous running current as the minimum rated wiring/breaker) should work.
• Breaker orientation. Some breakers have a "THIS SIDE UP" requirement--So the hot arc of switching goes into the arc suppression channel.
• AC vs DC breakers and fuses. They are very different. You can find AC/DC rated devices, but if so, the DC Ratings (working voltage, amps interrupted current) are usually much lower than the AC specs.
  

4. If the input current into the charge controller is so high that one controller can not suffice then how can you add add and interconnect multiple controllers together to cater for the amperage.

• You wire up each controller (panel->controller->breaker/fuse/switch->battery bank) independently. Then attach all the controllers to the same bus bar/stacked battery connection.
• There are higher end controllers that will "sync" their charging cycles (bulk, absorb, float)--But that is really not needed. As long as they are set close to the same voltage/times--They will share the charging reasonably well.
  

5. Since this 48 Volt system needs 59 volt of charging, does that mean I have to interconnect panels in a manner that the controller receives a minimum of 59 volts as input?

• Yes. For a 48 Volt Lead Acid Battery bank, you want the Vmp-array (standard test condtions) to be around 72 volts minimum to allow for hot panels (lower Vmp), voltage drop in wiring, cold batteries (cold lead acid batteries need higher charging voltage). If your Vmp-array is >~80 volt, you should be looking at a MPPT type solar charge controller (for a large system, you will be using a MPPT controller anyway--PWM controllers just are not really handy to use on large systems).
  

6. I have read that not all panels output efficiently which causes problem with mppt of a string. does that mean having mico sized controllers on each panel is better that to have multiple large controllers?

• It is an argument for "micro controllers"... However, that usually only applies to Grid Tied AC systems. Battery based systems do not have "micro controller" configured units available. You can build a GT Micro system that charges a Hybrid/Off Grid solar power system--But you want to do a lot of study/paper design/etc. before you open your wallet. It is not a "simple" system to design and use (although, no reason it could not work).
  

7. is there a reliable wire sizing chart that I could possibly use? i seem to come across conflicting charts at times and not sure which one is true.

• In the US/North America--Code (like the National Electric Code) is the gold standard. It is also pretty conservative on average. Believe me, conservative is good when building larger power systems. Turns out that even following NEC (AC mains or Genset charging a large battery bank) is not always conservative enough.
• Our house wiring, we run a toaster oven for 20 minutes at maximum of ~12 amps on a 15 amp circuit. A well discharged battery bank can run maximum circuit current for 5 hours or more--That can cook "marginal" wiring/fuses/breakers.
• NEC has a bunch of deratings (conduit fill factor, working temperature, insulation type, etc.).. But here is a simple verson of the capacity chart:
• https://lugsdirect.com/WireCurrentAmpacitiesNEC-Table-301-16.htm
• And a much less conservative Marine wiring chart. It will "allow" 2x the current level vs NEC. And "standards", NEC uses AWG vs Marine which uses SAE--SAE wiring is slightly smaller in diameter vs AWG. Be very careful when mixing/matching standards:
• http://www.boatus.com/boattech/articles/choosing-cables-and-terminals.asp
  

8. which batter would work best for solar? AGM or Lithium Ion. Considering that a region has power failure almost every other hour. Is there any informational site that lists down which battery works best for a particular use?

• For now, large Lead Acid Deep Cycle Batteries (aka Traction/Fork Lift Batteries, and other industrial L.A. batteries) are going to give you the best return on your money for a solar/backup power system. Some Li Ion (LiFePO4 chemistry specifically) can give Lead Acid a run for its money--But do a lot more research before spending your money.
• Do no use "Marine" or "Truck" or "Automotive" batteries for deep cycling--If you can avoid it--They do not have near the life of a true deep cycle battery (if you cycle below 85% state of charge, or 15% depth of discharge).
  

For now these questions have been bothering me for so long that I am always confused. I would really appreciate clear answers. Thank you guys for taking time in replying once again.