Check my plan?

Re: Check my plan?

What voltage/Amp*Hour battery bank?

-Bill

Re: Check my plan?

Are you going to set this up as a 24 or 12 volt battery bank?

Some basic rules of thumb... Batteries should be charged around 5% to 13% rate of charge:

• 4x 6 volt * 225 AH * 1/0.77 panel+charger derating * 0.05 rate of charge = 351 watts of solar panels minimum
• 4x 6 volt * 225 AH * 1/0.77 panel+charger derating * 0.10 rate of charge = 701 watts of solar panels good sized array to flooded cell battery
• 4x 6 volt * 225 AH * 1/0.77 panel+charger derating * 0.13 rate of charge = 912 watts of solar panels rough cost effective maximum solar array

You panels:

• 4x 175 watts = 700 watts

So--you are right smack dab at the "sweet spot" for charging for your flooded cell battery bank with your array.

In theory, you could go 2x larger with the battery bank--but I would recommend you try it out as is for the moment.

Larger battery banks can take you through more cloudy days--but they also take longer to recharge. The longer your battery bank sets below ~75% state of charge--the faster it will sulfate (as the batteries lose AH capacity)... Basically, you would like to get your bank recharged above 75% state of charge within 1 day... Setting for days/weeks/months below ~75% state of charge is bad--and a small array + large battery bank means it will take longer to recharge your bank.

Do you have an idea of how much solar/battery power you would like to use (per day, Amp*Hours at what voltage or Watt*Hours, AC/DC or what)?

Your 35.20Vmp panels are just about right for charging a 24 volt battery bank with a less expensive PCM charge controller...

However, if you have long distances from the Array to Charge Controller/Battery shed (~20 feet or more) or want to eventually install a larger array--you may want to look at a MPPT controller.

If you don't plan on adding more panels soon--I would not push the MPPT controller purchase (2-3x more expensive). 10 years is "forever" in solar PV equipment--and I would plan on replacing controllers, inverters, battery chargers (electronics) after about 10+ years of use (it can get very difficult to find spares and people to repair old electronics in general).

-Bill

Re: Check my plan?

If you have less than three parallel panel strings, you do not need any combiner box/fuse/breakers on the solar array.

When using AC switches on DC circuits--you should check the DC rating (if any) of the switches... DC current is much more difficult to interrupt (DC sustains arcs much better than AC). Since you will not be using the solar panel disconnect very much--you probably good get way with an AC disconnect...

And, I made a mistake typing up my previous reply--I intended to say you could have a 2x larger battery bank with your current array--Not a 2x larger array with your current battery bank.

-Bill

Re: Check my plan?

bobdog wrote: »

did i miss something here or isn't the battery bank 450 amps at 12 volts? 2 batteries in series to make 12 volts and then each string paralleled to make 450 amps.

tim

sprintman wrote: »

initially the battery bank would be 4 225amp hour 6v golf cart batteries. This set up is going in a vacation cabin. When I retire in 10 years would like to upgrade to the largest possible battery bank.....What would that be?

Tim, you got everything right--Just need to call it 450 Amp*Hours to get the right units.

Is your question my math?

• 4x 6 volt * 225 AH = 5,400 Watts*Hours of stored energy

That can be re-written as (2x 6 volt batteries in series, then two 12 volt strings in parallel):

• 2x 12 volt * 225 AH = 5,400 WH

Still the same "amount" of stored energy.

People usually use AH when talking about battery banks--but Watt*Hours is sometimes easier because we don't have to keep asking what voltage as we do the math...

-Bill