Larger array vs. larger battery comparison

[894tom]

Small solar system with a battery comparison
I have wondered why someone would spend the extra cash on a true large deep cycle solar battery. I have heard it is a long term savings advantage and I have also heard it is the ability to handle much larger loads. I did a cost analysis of the purchase to see if would make sense to spend the extra money on the better solar specific batterys

[Sunking]

Add 18 panels = (total array size 24 panels @ 4680watts) This array should produce 3.5kw during the worst month of the year in my location.
Battery bank = 48v 510a/h (12v Universal AGM 8D) =$ 4,000 replace 8 x’s (every 3.75 years due to high cycle rate) = $32,000 total battery cost over term*

Hey Tom welcome. Glad you found your way here from the other forum. You have found a really good active forum.

First thing that strikes me is your panel wattage vs minimum daily Kwh production appears to be way off. I believe you live around Albany NY right. Albany receives 2.5 Sun Hours and with your panel wattage and CC combination should produce around 4680 watts x 2.5 hours x .66 efficiency factor = 7.72 Kwh/day.

Secondly if you use 3 Kwh per day and have a 48 volt rectifier requires a 312 AH battery.

Last in the second scenario none of the numbers make since. Panel wattage's and battery capacity need to be matched up. So IMO your analysis is invalid.

But here is the bottom line. A 1 to 3 year battery will cost you around $100/Kwh. A good Surrette 10 year warranty battery that will last 5 to 7 years will cost you $190/Kwh.

[894tom]

I honestly have no idea where I came up with that 3.5kw. I tried to come up with that number again and couldn't . I thought I mixed up my locations and array sizes...but I still could not come up with that number.....ANYWAY.....The concept doesn't change regardless.

The array is oversized because I had extra cash left over from the battery costs in senario #1 over the span of the 30 years. I also used a larger AH battery then needed because I had trouble making up a small A/H 48v bank out of the Surrette batteries. An oversized array and battery bank are only benificial to an overall extended battery bank life.

Speaking of numbers, what specific batteries are you speaking of to come up with your numbers ($100 and $190)? These are my examples.

8- 12v Universal AGM 8D in series/parallel= 510a/h =$6,000.00 = about $4.08 per watt x 8 replacements every 3.75 years (very realistic due to oversized battery capacity and array size) = $32,000 in batteries
12 - 4V Flooded Surrette Battery in series = 524a/h = $7,600 = about $3.30 per watt x 5 replacements considering they would last for 6years. I would be cycling these batteries the exact same as the AGM bank and was giving them a much longer life expectancy than the AGMs. This cost came out to $38,000.......A $6,000 difference.

I bought more panels with that money and applied it to building my array in the AGM senario. The larger array could only stand to improve the life expectancy of the AGMs because even on a cloudy winter day the large array would be charging the battery bank. Remember in Senario #2 the total end cost is the same as Senario#1, I just have a much smaller array I am working with which really wont do much on a cloudy winter day.

[Sunking]

Speaking of numbers, what specific batteries are you speaking of to come up with your numbers ($100 and $190)? These are my examples.

I am speaking to the battery cost of $/Kwh. For example a Trojan T-105 is a 6 volt, 220 AH battery and cost $125. So 6 volts x 220 AH = 1320 Watt Hours or 1.32 Kwh. That works out to $94.69/Kwh.

[894tom]

Gotcha.

But what do you think about this concept? You have not given an opinion on the overal concept of this thread......ie larger array/AGM vs. Good quality solar battery but small array.....from a cost perspective.

[Sunking]

You can get away with a smaller array if you have a generator to bail you out. The real challenge for a properly designed system is in the months of December and January in the USA. That is when you need a generator most of the times. In summer months the panels should generate 2 to 3 times what you need. You just cannot store the excess energy, but you can recover from 2 or 3 cloudy days in a day without using the generator...

[894tom]

Any idea of what kind of kwh would be generated from a 4.6kw array on a cloudy winter day near Albany NY? No one I found gives the minimum wattage their system puts out. In typical american fashion it is all about how big you can go. I am concerned about replacing what was used (3kw) on a cloudy winter day so the minimum is important to me.

[Sunking]

Any idea of what kind of kwh would be generated from a 4.6kw array on a cloudy winter day near Albany NY? No one I found gives the minimum wattage their system puts out.

Well Tom they do, or lat least th equality manufactures, you just have to learn how to extract the data from IV curves. With that said though it is roughly 5 to 10% of normal production turning you 100 watt panel into 5 to 10 watts.

[Mike90250]

On a cloudy / rainy day, I get 100 - 300 watts from a 3,000 watt array.

Solar PV & clouds, are not a good mix.