Savannah GA member first time solar user

[mlw19mlw91]

Hello solarpaneltalk members! I'm from Georgia and looking to set up my first solar system. In the past I've owned a diesel car, and experimented with biodiesel setups but was turned off by the now scarcity of waste veggie oil. I think I've made the right choice investing in a solar setup as we get LOTS of good sun down here in the south!
Currently, I have invested in the following:

1. 8 CS6P-235PX solar panels (Canadian solar 235 watt panels)
2. 10 sets of MC4 connectors
3. MC4 crimpers
4. 500 feet 10AWG PV wire

I've bought a cheap 30 amp no name charge controller from amazon and will probably get my solar system up and running this weekend or next with the addition of batteries and a cheapo inverter. I look forward to developing a good system with your help, advice, and experience! I am glad to have found a good forum for solar systems!

[inetdog]

Hello mlw.... and welcome to Solar Panel Talk!

[Sunking]

I've bought a cheap 30 amp no name charge controller from amazon

Get your money back, it is useless. Its going to take a $600 80 amp MPPT controller, and a 24 volt 800 AH $4000 battery to work with 1880 watts of panel wattage.

Surprise!

Additionally you 10AWG is too small.

[me2003]

"Additionally you 10AWG is too small. "

I thought that was the standard for connecting solar panels. 500 ft for 1 run would possibly be excessive
All the mc4 connector wire systems sold are 10 or 12.
I think you need to look at the application in more detail.
What voltage, are you connecting multiple solar panels to a combiner box ...
I have invested a lot in MC4 cables and if they do not work I need to discuss
this with the vendor to return them.

[Sunking]

"Additionally you 10AWG is too small. "

I thought that was the standard for connecting solar panels.

Individually to a combiner sitting right next to the panels, but not for much anything else. 10 AWG is only rated for 30 amps max, but at low voltage distance is extremely limited before losses add up to render the circuit useless and non functional

With 8 panels he has only two configuration options available to him on a 24 volt battery system. 2 x 4 or 4 x 2. That means the feeder will either have 16 or 32 amps of load current. At 32 amps already exceeds # 10 AWG capacity, and at 16 amps he can only go about 10 feet one-way max for 3% loss.

[Sunking]

I think you need to look at the application in more detail.

I don't have to think about it anymore. I did that 30 years ago when I started professionally. After 30 years and doing the same thing over and over again thousands of time I can do it in my sleep with out thinking about it. As soon as I read what the OP wanted know immediately it will not work, no thought required.

Huge Red flag:

1880 watts, 30 amp no-name controller means it will not work period. You should have known that before giving advice. At 1880 watts require brand name MPPT controllers at:

12 volts = 160 amps
24 volts = 80 amps
48 volts = 40 amps.

What the heck is he suppose to do with a cheap 30 amp PWM controller? At best turn his 1880 watts into 500 watts. Is that your advice?

[mlw19mlw91]

Hello guys, and sorry for the poor introduction, typed all of that up while burning up the midnight oil!
to answer some of your questions, reply to concerns, etc.:

Get your money back, it is useless. Its going to take a $600 80 amp MPPT controller, and a 24 volt 800 AH $4000 battery to work with 1880 watts of panel wattage.

Surprise!

Additionally you 10AWG is too small.

thanks for raising your concerns.
the 30 amp controller is temporary pending further decisions on how to proceed, please see my other thread

http://www.solarpaneltalk.com/showthread.php?17974-shopping-for-inverter-charger-any-integrated-smart-packages

wire runs from solar panels will not be very long. Will upload scale drawings when I find them. Last time I checked we were using less than 20 KWH every day. Have since switched every light bulb to LED, ordered (not yet installed) a 20 SEER 1 ton LG ductless mini split systems, insulating house, air drying clothes, considering heat pump water heater, installing pre-insulated PEX and hot water recirc pump, a model that only turns on when it senses demand, ordered energy recovery ventilator for the bath room. Have smart power strips for all major electronic that shut down phantom drain, etc. etc.
Anyways..... how should I choose a battery size? Assuming I should size it to only use the batteries down to 80% state of charge.

"Additionally you 10AWG is too small. "

I thought that was the standard for connecting solar panels. 500 ft for 1 run would possibly be excessive
All the mc4 connector wire systems sold are 10 or 12.
I think you need to look at the application in more detail.
What voltage, are you connecting multiple solar panels to a combiner box ...
I have invested a lot in MC4 cables and if they do not work I need to discuss
this with the vendor to return them.

I was wondering why I could not really find connectors for a larger wire, that makes sense!
I was going to run a wire from each panel to the charger seperately, since it's short runs. panels are nominal 24 volts. Short circuit current from each pannel is 8.46 Amps, optimum operating current is 7.90 Amps.

Individually to a combiner sitting right next to the panels, but not for much anything else. 10 AWG is only rated for 30 amps max, but at low voltage distance is extremely limited before losses add up to render the circuit useless and non functional

With 8 panels he has only two configuration options available to him on a 24 volt battery system. 2 x 4 or 4 x 2. That means the feeder will either have 16 or 32 amps of load current. At 32 amps already exceeds # 10 AWG capacity, and at 16 amps he can only go about 10 feet one-way max for 3% loss.

going less than 25 feet on the longest run. Didn't consider a combiner earlier, is this something you recomend I look into?

Huge Red flag:

1880 watts, 30 amp no-name controller means it will not work period. You should have known that before giving advice. At 1880 watts require brand name MPPT controllers at:

12 volts = 160 amps
24 volts = 80 amps
48 volts = 40 amps.

What the heck is he suppose to do with a cheap 30 amp PWM controller? At best turn his 1880 watts into 500 watts. Is that your advice?

what are the industry standards for de-rating? 30 amps times 24 volts, basically was hoping for 720 watts of power.

[Sunking]

going less than 25 feet on the longest run. Didn't consider a combiner earlier, is this something you recomend I look into?

Required by electrical codes, and you have missed a whole lot of the.

what are the industry standards for de-rating? 30 amps times 24 volts, basically was hoping for 720 watts of power.

Not sure of your question so I will guess what you mean. First requirement that must be met is NEC tables 310.17 and 310.17. Cable amp capacity has a few variables, like cable cross sectional area conductor type, insulation type, ambient temperature, and number of conductor in a raceway. But that is only half of it. NEC could care less if your system works or not. It is not their job to worry about that as it is not a How To book. NEC is only concerned with life safety and property damage. NEC has no design requirements like how much voltage drop you should incur o rnot incur. That job belongs to the designer. There is a reason utilities do not use low voltage because losses are too high and it is too expensive. Voltage loss is critical in low voltage systems.

For example lets say you need a 30 amp circuit with 25 feet one-way direction. NEC has not problem if you use #10 AWG as it is safe, but at your voltages you will loose 9% of your power between the panels and charge controller. Same circuit at 120 volts you only loose 2%. Design goal is 2% or less loss and to run 30 amps 25 feet one-way with 36 volts pushing it requires a # 4 AWG conductor. You go from loosing 3.25 volts down to .7 volts. That is a very significant difference and a very expensive one at that.

If you are referring to charge controllers what you need to know is with PWM Input Current = Output Current, and with MPPT Output Current = Panel Wattage / Battery Voltage.

Now put that in practice with your panels and 12 volt battery configuration. With PWM you must wire the panels in parallel. That means you would need a 65 amp controller because with all the panels in parallel 8 x 8 amps = 64 amps. OK 64 amps in, and 64 amps out. Do the math. You have a total of 1880 watts, generation 64 amps into a 12 volt battery = 64 amps x 12 volts = 768 watts with 1880 input. Wow you just lost 60% of your power, and to run 64 amps between panels and controller 25 feet with require 2/0 copper cable. Go price that out.

Do this with a MPPT controllers and we can wire your panels 4 in series in parallel with the same. Now our current is down to 16 amps between panels and controller. On the output of the controller we have 1880 watts / 12 volts = 160 amps. You would need 2 very expensive 80 amp charge controllers. So at this power level 12 volts is out of the question. Use 24 volts and we now have 80 amps and only need one expensive controller instead of 2, and a heck of a lot smaller wire between panels and controllers. # 10 AWG would work in this case.

So you need to stop and completely rethink things because everything you thought or assumed is wrong and will cost you several thousand dollars to correct on top of a 1000% rate increase in electricity going off grid. If you go through with this, you will learn the hard way, with a lot of lost money.

Good Luck and do your homework.

[mlw19mlw91]

Required by electrical codes, and you have missed a whole lot of the.



Not sure of your question so I will guess what you mean. First requirement that must be met is NEC tables 310.17 and 310.17. Cable amp capacity has a few variables, like cable cross sectional area conductor type, insulation type, ambient temperature, and number of conductor in a raceway. But that is only half of it. NEC could care less if your system works or not. It is not their job to worry about that as it is not a How To book. NEC is only concerned with life safety and property damage. NEC has no design requirements like how much voltage drop you should incur o rnot incur. That job belongs to the designer. There is a reason utilities do not use low voltage because losses are too high and it is too expensive. Voltage loss is critical in low voltage systems.

For example lets say you need a 30 amp circuit with 25 feet one-way direction. NEC has not problem if you use #10 AWG as it is safe, but at your voltages you will loose 9% of your power between the panels and charge controller. Same circuit at 120 volts you only loose 2%. Design goal is 2% or less loss and to run 30 amps 25 feet one-way with 36 volts pushing it requires a # 4 AWG conductor. You go from loosing 3.25 volts down to .7 volts. That is a very significant difference and a very expensive one at that.

If you are referring to charge controllers what you need to know is with PWM Input Current = Output Current, and with MPPT Output Current = Panel Wattage / Battery Voltage.

Now put that in practice with your panels and 12 volt battery configuration. With PWM you must wire the panels in parallel. That means you would need a 65 amp controller because with all the panels in parallel 8 x 8 amps = 64 amps. OK 64 amps in, and 64 amps out. Do the math. You have a total of 1880 watts, generation 64 amps into a 12 volt battery = 64 amps x 12 volts = 768 watts with 1880 input. Wow you just lost 60% of your power, and to run 64 amps between panels and controller 25 feet with require 2/0 copper cable. Go price that out.

Do this with a MPPT controllers and we can wire your panels 4 in series in parallel with the same. Now our current is down to 16 amps between panels and controller. On the output of the controller we have 1880 watts / 12 volts = 160 amps. You would need 2 very expensive 80 amp charge controllers. So at this power level 12 volts is out of the question. Use 24 volts and we now have 80 amps and only need one expensive controller instead of 2, and a heck of a lot smaller wire between panels and controllers. # 10 AWG would work in this case.

So you need to stop and completely rethink things because everything you thought or assumed is wrong and will cost you several thousand dollars to correct on top of a 1000% rate increase in electricity going off grid. If you go through with this, you will learn the hard way, with a lot of lost money.

Good Luck and do your homework.

so a combiner is a bunch of DC circuit breakers? I was planing on using a fuse block. Does code dictate where this combiner must be placed? Why don't I just place it inside my house within one foot of my inverter and/or mppt charger?

[inetdog]

so a combiner is a bunch of DC circuit breakers? I was planing on using a fuse block. Does code dictate where this combiner must be placed? Why don't I just place it inside my house within one foot of my inverter and/or mppt charger?

A DC combiner is actually just a place where a bunch of low current DC wires come together to be attached to a common higher current wire to go the rest of the way to the CC or GTI.
If you have more than 2 strings you need to have one fuse OR breaker per string. If you have one or two strings, the fuse of breaker must be at or below the "Maximum Series Fuse" value on the panel nameplate.
For convenience, many people like to use breakers so that they can control and isolate individual strings for testing and maintenance.
If you use either fuses or breakers, make sure that what you use is rated for DC!
Fuses and especially breakers are often rated to interrupt AC only, or to be good for a far lower system voltage when DC is used.
Do not try to open a panel string that is carrying current by pulling a fuse!
Also, FWIW, there are very strict NEC rules on the circumstances under which panel DC output wires are allowed to run inside the house (including attic and wall spaces.) The most common installation will put it closer to the panel just to reduce the number of wires that have to travel a long distance to get to the combiner.
Some two string installations do wire directly to two input terminal sets on the GTI or CC, but that is a limiting case.

[Sunking]

so a combiner is a bunch of DC circuit breakers? I was planing on using a fuse block. Does code dictate where this combiner must be placed? Why don't I just place it inside my house within one foot of my inverter and/or mppt charger?

Amy fuse or breaker has to be installed as close to the source as possible, otherwise you defeat the purpose having long runs of wire unprotected. Same with batteries the OCPD is installed right on the battery post. Install down stream and all you got is a big fire.

[mlw19mlw91]

I was planing on using the inline MC4 fuse holders (as seen here: http://amzn.com/B00MHDYTIM and putting fuses in right off my solar panels. I was then going to combine feeds from each panel in a fuse block near the battery charge controller and/or inverter. I've since been convinced to go with breakers. I thought the fuses off each panel would be a good idea as they could potentially prevent any damage to the panels, should, say, wires somehow get crossed between the panels and the combiner. Is this overkill or necessary and proper?

I've been looking for a good book to show the most proper way of setting up my solar system and was considering the following: Solar Electricity Handbook - 2014 Edition http://amzn.com/1907670394
opinions?

[SunEagle]

I was planing on using the inline MC4 fuse holders (as seen here: http://amzn.com/B00MHDYTIM and putting fuses in right off my solar panels. I was then going to combine feeds from each panel in a fuse block near the battery charge controller and/or inverter. I've since been convinced to go with breakers. I thought the fuses off each panel would be a good idea as they could potentially prevent any damage to the panels, should, say, wires somehow get crossed between the panels and the combiner. Is this overkill or necessary and proper?

I've been looking for a good book to show the most proper way of setting up my solar system and was considering the following: Solar Electricity Handbook - 2014 Edition http://amzn.com/1907670394
opinions?

That is a good book that shows you the basics of solar pv systems. I think it is good reference material and worth the cost.