New Configuration

solaris3000

Hello. all I am setting up my new system and have a few questions.
At any rate I'm a rookie and am only able to start out with a small albeit scalable system to start with..

My battery bank is wired in Parallel.. 900ah 12v

I only have 1 panel rated at 125watts and its 6 feet from the Battery bank.
my Inverter is Xantrex Prowatt SW1000
Charge controller,, None.(waiting for the Rogue) :-(


I only have the single solar panel. Should I reduce the size of my battery bank to keep the AGM 12v batteries in healthy charge state.

My calculations tell me that with a 900ah bank my single panel will require 15 days to bring the bank cells to full charge if the battery bank is discharged to 90%

If I purchase the MPPT controller, will this give me a smaller recharge window than 15 days?




Thanks for your time.
Brian

BB.

Re: New Configuration

Welcome to the forum Brian.

For an AGM battery (and any lead acid battery)--Spending lots of time below ~75% state of charge will sulfate the battery and cause it to loose capacity (and eventually not store enough energy for your needs). Spending even a few days below 75% state of charge is not a good thing.

For a "nice" balanced offgrid system--We like to start with a 5% to 13% of rated battery bank capacity with a 0.77 derating of the solar panels+charge controller... For your bank:

• 900 AH * 14.5 volts charging * 1/0.77 derating * 0.05 charge = 847 watts minimum
• 900 AH * 14.5 volts charging * 1/0.77 derating * 0.13 charge =2,203 watts cost effective maximum

Note: You have a very large battery bank and, ideally, you want a pretty large solar array to "keep it happy".

If, all you wanted to do was keep the bank floating (properly charged while stored), you could go down to 1% rate of charge with solar... This would be, for example, a weekend cabin that is only used during a couple seasons with a generator to recharge during the day, and use the batteries at night. The solar array would be just to keep the batteries floating/charged during non-use. (or could be for emergency backup power system+genset too).

MPPT controllers--If you are in sub freezing weather, you might gain 10-15% extra power from an MPPT controller over a PWM controller. But, this is usually not the best reason for purchasing a MPPT controller.

MPPT controllers are great for running the solar array Vmp>>Vbatt-charging... This allows you to put the array farther from the battery bank and keep the wire gauge smaller. Running a large array with Vmp=17volts with >10' of wire can mean you are in the 8-2 awg, or even larger, guage wire from the solar array.

Before you buy any more hardware, we need to define your needs and system requirements first... Then pick the supporting hardware.

So--do you have any daily usage figures (Amp*Hours or Watt*Hours of load per day?). How much sun do you get (where is the installation)?

For example, assuming you get at least 4 hours a day of "full noon time equivalent sun" (sort of an OK estimate for 9 months of the year for many locations)... We could guess that with 850 watts of panels you could use a maximum of:

• 850 watts * 0.52 derating * 4 hours of sun per day = 1,768 WH per day
• 1,768 WH / 12 volt battery bank = 147 AH per day (or a bit more)

-Bill

solaris3000

Re: New Configuration

Bill Thanks for the help. I have a small entertainment center that I was planning on running via Solar. that draws.


Via Kill a Watt meter data

2 amps
200- 220 watts range

Runs about 5 hours a day. House is facing west half mile from pacific. Problem is that a mountain behind me blocks direct sun until 10am...

City San Diego

regards
Brian

BB.

Re: New Configuration

You are very welcome Brian.

The k-a-w meter also has kWH logging... It would read something like 1.1 kWH over the 5 hour period (assuming 5hours * 220 watts = 1,100 WH = 1.1 kWH).

For Example:

• 220 watts * 5 hours * 1/0.52 derating * 1/4 hours of sun = 529 watts minimum of solar panels

Of course, you should never plan on using 100% of your usable power every day... But that gives you a very rough idea of what you are looking at.

-Bill

solaris3000

Re: New Configuration

It looks like until I can get some additional panels I need to scale things down to keep the batteries in good shape.

So that would be

single 125watt panel
AGM battery 12v 300ah

solaris3000

Re: New Configuration

Hello Bill, I'm creating a diagram of this to better visualize. If I use 4 AWG wires between the Battery and the Charge controller. Should I use fuse block or a circuit breaker of some kind. I have seen some setups where they simply ran the batteries direct into the charge controller, which seems like it could damage the charge controller if the batteries were to short out by something falling across the + and - terminals. I'm just not clear on where to put the fuse protections if needed for my small setup..



much obliged
Brian

BB.

Re: New Configuration

Fuses/breakers are to protect wiring against too much current (and overheating/fire).

So--in an off-grid system, the high current source is the battery bank. Placing fuses/breakers on the positive "bus" of the battery bank sized for the wire that leaves the + bus connection is the goal.

Fuses don't really protect the charge controller--other than if the controller develops an internal short--the fuse will limit maximum current through the 4 AWG wire and into the box (to prevent the box from catching fire too).

A 900 AH battery bank is capable of 1,000's of amps into a short circuit--so fusing/breakers are very important for safety on your system.

-Bill

solaris3000

Re: New Configuration

Thanks for the detail Bill, Is there a rule of thumb for the Size of fuse to use on the positive side, I understand that the fuse must serve as the weakest link. I just dont want to end up blowing fuses every time the nominal voltage is reached.

Also do think there is any problem if I use a Fused Distribution Block. I ran across these at a Car Stereo Warehouse in San Diego, The fuses were called ANL


Funny thing was that when I tried Home Depo they had no idea what I was talking about. They told me to look for an Electrical supply shop..



Regards
Brian

nsaspook

Re: New Configuration

Here is a link to Blue Sea with a huge amount of DC fuse/breaker types. http://bluesea.com/files/resources/catalogs/sections_2011/circuit_protection_2011.pdf

solaris3000

Re: New Configuration

Many thanks, exactly what I was looking for...

BB.

Re: New Configuration

There are different charts that list "safe" current for wiring... Really depends on where used (i.e., in homes with National Electric Code), packing in conduit, and also maximum AC or DC voltage (fuse/breaker ratings).

This charge is the most optimistic:

American Wire Gauge table and AWG Electrical Current Load Limits

And then there is the NEC tables:

http://lugsdirect.com/WireCurrentAmpacitiesNEC-Table-301-16.htm

For example, look at 14 AWG wiring... The AWG table--upwards of 32 amps maximum. From the NEC table, 20-25 amps... But interestingly enough, there is a (1) which states:

The load current rating and the overcurrent protection for conductor types shall not exceed 15 amperes for 14 AWG, 20 amperes for 12 AWG, and 30 amperes for 10 AWG aluminum and copper-clad aluminum after any correction factors for ambient temperature and number of conductors have been applied.

So--which do you want? 15 amp; 20 amp; 25 amp; 32 amp; for your installation (before you take high temperatures into account).

In the end, think of the wiring leaving the positive bus as a "Star" configuration. each wire that leaves should have a fuse/breaker sized to prevent that wire from overheating (catching fire).

Also, fuses have AC/DC ratings (DC current is harder to "break" and DC rated breakers/fuses are typically larger than AC breakers of the same rating). Also, fuse/breakers have maximum voltage ratings... Typically 32 volts maximum for automotive and boat--But not high enough for 48 volt battery banks.

Also, there is a max AIC (amp interrupt current)--Basically, a lead acid battery has a lot of energy available and can burn up a too small breaker/fuse with excessive current into a dead short.

So--finding the right hardware is not always easy.

Our host has some larger fuses/breakers for RE power:

Midnite Solar System Installation Products
High Amperage Inverter Fuses & Breakers

And others--(search around site).

There are also other vendors like Blue Sea and such that have interesting products too.

-Bill

solaris3000

Re: New Configuration

Great, Info... I'm adding this to my knowledge base so I can refer back to it for reference/education..

I just ordered a Rogue Controller and am reading the PDF manual on it to learn its functions. I like the fact that it has built in logging and a Laptop interface,,



Regards
Brian

solaris3000

Re: New Configuration

Hi Bill, I Hope all is going well..

Have you seen the PDF document for the Rogue controller by chance? Page 24 has a basic wiring diagram that points to a {DC Load Center} It's some kind of junction Box... Is this something I can pick up at Home depot or my local electrical contractor supply? The Rogue does not have the capacity to connect a DC/AC Inverter directly to it so I need to create my own (DC Load Center) or purchase one.


with regard
Brian