Help: Need Solar installation diagram that follows NEC guidelines

fm.109 · February 2016

Hello everyone! I have been on this blog for a long time now and more of a shadow figure trying to learn solar as much as i can. Previously i have asked questions and managed to receive great answers and so I am back again for more!

I am interested in looking at a detailed installation diagram for a solar off grid system. I am trying to learn exactly where, how and why each and every component will be installed. I know it seems like a big ask but i am genuinely interested in knowing this because here in my country we have lots of scams when it comes to system design and its components.

I know a general guideline that is Solar panel > Combiner box > Charge Controller > DC Breaker > Battery bank > DC Breaker > Inverter > AC Breaker > Load

However, i do not know the precise method in calculating all the requirements. if anyone here can post a diagram along with rules and calculation methods, i will be truly thankful to that person.

Hope to hear from you guys soon.

BB. · February 2016

Outback Solar has some very detailed wiring diagrams (different system configurations):

http://www.outbackpower.com/wiring-diagrams

And so does Midnite:

http://www.midnitesolar.com/documentsA.php?menuItem=admin&docCat_ID=4&docCatName=Wiring Diagrams

For sizing, it is much easier (the first time) if we design the system to your (estimated) needs/system sizing. Seeing it done once, will give you a good idea how to design other systems later.

Small system designs are "different" than large system designs (VW Bugs are different than Diesel Trucks)--But the basics are similar.

-Bill

fm.109 · February 2016

Well these are the following items that I would like to have on solar:

1. Energy saver light bulbs: 30 Lights rated at 14 watts each running for an average of 10-12 hours a day
2. Ceiling Fans: 12 fans rated at around 80-100 watts each running for almost all day for 8 months a year
3. Laptops: 5 Macbook Pro
4. Phone Chargers: 5
6. LED TV: 4 TV's; 42 Inch; running for around 8 to 10 hours a day (LED TV with wattage of 70 watts each roughly)
7. One Router

So these are pretty much the items I would like to use on solar.
Hope this much info is adequate.

mike74820 · February 2016

i just did a rough calculation on a ohms law calculator i use and i added up your watts and at 12 volts it says you will need 168 amps. if you ran a 48 volt system you would need 43 amps and hour to run that stuff. you will need a pretty big solar set up to run that stuff

westbranch · February 2016

Scrap that TV and get a low power one, ours is ~ 15W, but smaller and 3 yrs old... otherwise conserve and get a smaller one...

BB. · February 2016

Say you want 2,000 Watt loads @ 12 hours per day... Karachi Pakistan. Just a real Quick rule of thumbs design to get some sort of idea of what you would need.

2,000 Watts * 12 hours per day = 24,000 Watt*Hours = 24 kWH per day = 720 kWH per month (that is tyical sized western home power usage).

Assuming 2 days of storage and 50% maximum discharge (for longer battery life), a typical full off grid system would need a battery bank of:

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

Next, calculate the size of the solar array. First, based on minimum charging rate for battery bank and second based on hours of sun per day. You can use 5% to 13% for typical solar charging of a battery bank--However, for full time off grid, would suggest minimum of 10% rate of charge. And if you are running loads during daytime, you have to add additional solar panels to support daytime loads too:

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)

And then based on fixed array in Karachi, tilted to latitude facing south:

http://solarelectricityhandbook.com/solar-irradiance.html

Karachi
Average Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 65° angle:
(For best year-round performance)

Jan	Feb	Mar	Apr	May	Jun
5.58	6.25	6.41	6.50	6.13	5.74
Jul	Aug	Sep	Oct	Nov	Dec
4.99	4.99	5.80	6.06	5.55	5.38

24,000 Wh per day * 1/0.52 typical off grid system eff * 4.99 hours average Jul-Aug sun = 9,249 Watt array minimum (break even Jul-Aug)

So... The minimum array you could get away with is around 10,000 Watts--And if you want a "robust" system (fewer battery charging problems, longer battery life, and less genset runtime), you could justify upwards of a 20,000 Watt array.

-Bill

fm.109 · February 2016

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?

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

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?

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.

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?

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?

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.

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 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.

BB. · February 2016

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.

Take a look at this thread--Has lots of pointers to other sources of information:

http://forum.solar-electric.com/showthread.php?5556-Working-Thread-for-Solar-Beginner-Post-FAQ

Hope this helps.

-Bill

zoneblue · February 2016

Sounds like you need to be budgeting, roughly 80K for that system. Do have funding for this, it sounds like some kind of educational or office facility. Is there no grid at all there?

oil pan 4 · February 2016

You should have included how much money you can spend on this.

Get a copy of NEC 2014. Big changes between 2011 and 2014 as far as solar stuff goes.

westbranch · February 2016

and 2016 is coming in too, very soon... more costly devices...

t00ls · February 2016

I have heard that there are some big changes to the NEC in 2016 as far as renewable energy goes...some for the better...thank goodness

while it doesnt apply to some offgrid folks......some will want to follow NEC for insurance purposes

lets face it...in the past ...the NEC gave some stupid rules for renewable systems.....these changes are supposed to address some of the more stupid ones

YehoshuaAgapao · February 2016

Midnite Solar employs a person who has a major input to NEC changes for PV. Since one of their guys is a significant contributor to NEC changes, they get an automatic head start when it comes to making products that comply with it and it offers them short-term monopolies or near-monopolies on such products (arc-fault protection and system rapid shutdown/disconnect on the DC/PV side).

But for the DIY person (or in my case only DIYed the engineering / plans part) installing off-grid or installing in a place that does not have inspections for solar, using this will at least make sure your wires don't burn or that you don't lose too much to wire resistance (especially between charge controller and battery) this set of calculators work great (the site sells electrician certification classes but the calculators are free without hassles):

http://www.electriciancalculators.com/

Oh also, most electricians (and many engineers and inspectors) don't pay attention to ambient temperature adjustments or adjustments due many current-carrying wires within a conduit (such as wires from 4 strings of solar panels sharing a conduit right on the roof to reach a combiner box that the electrician wanted to install in the shade, which makes sense - sun-struck things have much shorter lives). These calculators make it easy to pay attention to those things. Not only you actually achieve the excess safety margin that the NEC aims to achieve (because they know some things will be overlooked or corner-cut), but you also get less losses especially when your wires are running for 50, 100, or more feet.

For firefighters - they run on a rule of thumb - if they don't think it safe to enter an area (batteries and energized PV), they just let it burn. Part if not most of the reason of the rapid disconnect bit in the NEC 2014. My system cannot comply with NEC 2014 without major changes because the combiner boxes are installed about 2/3 of the wire-travel distance from PV to charge controller. So even if I bought Midnite Solar's birdhouse disconnect kits, it wouldn't help because they shutdown at the combiner box, which are normally installed very close to the PV source. My system splices each string to #6 and takes the #6 through the attic to the combiner box and then it comes out of the combiner at #2

Vic · February 2016

YehoshuaAgapao said:

Midnite Solar employs a person who has a major input to NEC changes for PV. Since one of their guys is a significant contributor to NEC changes, they get an automatic head start when it comes to making products that comply with it and it offers them short-term monopolies or near-monopolies on such products (arc-fault protection and system rapid shutdown/disconnect on the DC/PV side).

But for the DIY person (or in my case only DIYed the engineering / plans part) installing off-grid or installing in a place that does not have inspections for solar, using this will at least make sure your wires don't burn or that you don't lose too much to wire resistance (especially between charge controller and battery) this set of calculators work great (the site sells electrician certification classes but the calculators are free without hassles):

http://www.electriciancalculators.com/

Oh also, most electricians (and many engineers and inspectors) don't pay attention to ambient temperature adjustments or adjustments due many current-carrying wires within a conduit (such as wires from 4 strings of solar panels sharing a conduit right on the roof to reach a combiner box that the electrician wanted to install in the shade, which makes sense - sun-struck things have much shorter lives). These calculators make it easy to pay attention to those things. Not only you actually achieve the excess safety margin that the NEC aims to achieve (because they know some things will be overlooked or corner-cut), but you also get less losses especially when your wires are running for 50, 100, or more feet.

For firefighters - they run on a rule of thumb - if they don't think it safe to enter an area (batteries and energized PV), they just let it burn. Part if not most of the reason of the rapid disconnect bit in the NEC 2014. My system cannot comply with NEC 2014 without major changes because the combiner boxes are installed about 2/3 of the wire-travel distance from PV to charge controller. So even if I bought Midnite Solar's birdhouse disconnect kits, it wouldn't help because they shutdown at the combiner box, which are normally installed very close to the PV source.

Y....A....., regarding the part about MidNite, Where is the data on this?

Seems disparaging to me, without some concrete, verifiable reference to this.

Otherwise, why not remove it? Thanks, Vic

halfcrazy · February 2016

YehoshuaAgapao said:

Midnite Solar employs a person who has a major input to NEC changes for PV. Since one of their guys is a significant contributor to NEC changes, they get an automatic head start when it comes to making products that comply with it and it offers them short-term monopolies or near-monopolies on such products (arc-fault protection and system rapid shutdown/disconnect on the DC/PV side).

I assume you are referring to me? I have almost no influence over NEC, BUT I do set on a lot of task groups of manufacturers and installers who try to make the new codes make a little more sense. This does not give MidNite any monopoly as ANY manufacturer can participate in these task groups. At the end of the day all we do is make a proposal that gets submitted to the "Code Making Panel" they are the ones that decide what goes in NEC. All the task group info is public knowledge as is the proposals made to the panel so rest assured MidNite is not creating any monopoly here. The good news is EVERYONE reading this can also make proposals to the panel as well.

Ryan

halfcrazy · February 2016

westbranch said:

and 2016 is coming in too, very soon... more costly devices...

I should also point out that NEC releases a new code revision every 3 years so the next release is in 2017. And yes there are a lot of changes, one of the biggest is module level shut down for the fire service. And also for the record that new rule was driven SOLELY by the fire service. Lots of new grounding stuff coming down the road as well as some new rules for disconnects

BB. · February 2016

Remember, many of these codes and standards started by insurance and industry to make things safer--And for common point of reference across the US (originally). They did not pop out fully formed by a government commission.

http://www.mikeholt.com/nec-history-and-purpose.php

"Let The Code Decide"

ANYONE who has anything at all to do with the electrical industry is familiar with this slogan of the International Association of Electrical Inspectors "Let the Code Decide". Not so commonly known is the history of the Code - the National Electrical Code - or how, and by whom, it is written. It is felt that the following brief discussion may be of some interest. We must go back over seventy years (remember this was written in 1950) to find the original ancestor of what we now know as the National Electrical Code. This document was published in October of the year 1881, by the New York Board of Fire Underwriters, under the title "A Standard for Electric Light Wires, Lamps, etc."" To give an idea of how much water has flown over the dam since 1881, this set of rules, exactly as originally promulgated, follows:
NEW YORK BOARD OF FIRE UNDERWRITERS

No. 115 Broadway, New York October 19th, 1881

The New York Board of Fire Underwriters at a meeting held this day, adopted the following standard for Electric Light Wires, Lamps, etc., subject to future additions.
Wires to have 50 percent excess of conductivity above the amount calculated as necessary for the number of lights to be supplied by the wire.
Wires to be thoroughly insulated and doubly coated with some approved material.
All wires to be securely fastened by some approved non-conducting fastening, and to be placed at least: 2 1/2 inches for Incandescent lights, and 8 inches for Arc lights from each other, and 8 inches from all other wires and from all metal or other conducting substance, and to be placed in a manner to be thoroughly and easily inspected by surveyors.
When it becomes necessary to carry wires through partitions and floors, they must be secured against contact with metal or other conducting substance in a manner approved by the Inspector of the Board.

Distributed power--Whether solar panels or large banks of batteries--Is not a simple task to make for a "safe" installation.

-Bill

YehoshuaAgapao · February 2016

Here are pics of my system. Near the bottom are my DIY drawings that were submitted to SRP (not the city though - Mesa and Gilbert AZ do not do inspections for grid-tie solar)

http://www.pbase.com/greatinca/solar&page=all

Dave Angelini · February 2016

Whatever the current revision of the NEC is, the counties in my state of California can use whatever version year that they feel they have the expertise on. The last I looked Mariposa county was at 2012 and probably still is.

Help: Need Solar installation diagram that follows NEC guidelines

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KarachiAverage Solar Insolation figures

Karachi
Average Solar Insolation figures