More panels or more batteries?

[paulcheung]

3500W into a 12V battery bank = 300 amps. That's way too much. 3500W into a 48V battery bank = 73A, that's more manageable.

For battery bank, 5000Wh / 2 (50% DoD) x 5 days autonomy (needed without a genny) x 1.2 temperature compensation (guessing on storage temp of batteries) / 48V = 1250Ah 48V battery bank. (If it was a 12V battery bank, it'd be 5000Ah, just not doable).
.

This don't make sense. 5000/2X5X1.2 /48 is =312.5AH, 12 volts is 1250AH also remember 1250 Ah with 24 hours is around 53 amps. even though 12 volts is not for a house system.

[Mike90250]

the stock answer to this common question is More Panels. Batteries die, panels generally don't

[coinmaster]

Hmmmmm. Most of the stuff I'm powering takes 12v directly, I was hoping to avoid using a converter. If I use more panels all I need to do is purchase more charge controllers to split the current right? More panels would fill up my batteries easier and prevent the need for more battery capacity I would imagine.
If I'm going to forgoe 12v then why not go straight for a 120v battery system and just get lots of panels? The higher the voltage, the less AH I need right?

[inetdog]

Hmmmmm. Most of the stuff I'm powering takes 12v directly, I was hoping to avoid using a converter. If I use more panels all I need to do is purchase more charge controllers to split the current right? More panels would fill up my batteries easier and prevent the need for more battery capacity I would imagine.
If I'm going to forgoe 12v then why not go straight for a 120v battery system and just get lots of panels? The higher the voltage, the less AH I need right?

Yes. A 12V 2000AH battery bank would be 24000 watt-hours, and a 120V 200AH battery bank would also be 24000Wh.
But going above 48V DC complicates the wiring methods for electrical code compliance significantly and the only chargers and inverters you are likely to find for that battery voltage will be designed as components of a UPS system.

And to operate most 120V appliances you would still need and inverter as they would not work directly off DC.

[coinmaster]

If I have to use an inverter or converter in order to get enough power to handle my location then I'm okay with that.
Perhaps a 5000w panel system and a 120v 125AH battery system?

Here's a controller that can handle 120v battery systems http://www.midnitesolar.com/productP...21&sortOrder=4

That leaves me with finding a 120v inverter or converter
What did you mean by going above 48vDC complicates the wiring methods? What becomes complicated?

[Sunking]

If I have to use an inverter or converter in order to get enough power to handle my location then I'm okay with that.
Perhaps a 5000w panel system and a 120v 125AH battery system?

No no no. Al the rules change when you go above 50 volt battery. All wiring including battery wiring have to be made inaccessible. At 5000 watts a you can run a Midnite Solar Classic 150. at 48 volt battery. Then use a 48 volt battery from 700 to 1000 AH. You will NOT be using 12 volt batteries so get 12 volts off your mind. You will be using 2 to 6 volt batteries like a Rolls 6CS25P a 6-volt 820 AH battery. You would need 8 of them.

You should also know you will be replacing those 2600 pound $9000 batteries every 5 years if you treat them with TLC like an expert.

[coinmaster]

Why not just go with 120v so I can spend $2500 in batteries @ 700lbs instead?
http://www.vmaxtanks.com/SLR125-AGM-...ery-_p_38.html

[coinmaster]

No no no. Al the rules change when you go above 50 volt battery

Where do I find these "rules"?

[sensij]

Where do I find these "rules"?

National electric code, published as nfpa 70.

[inetdog]

What did you mean by going above 48vDC complicates the wiring methods? What becomes complicated?

The rules for wire type, protection from damage, access control, grounding, among other things all get more specific, or at least an inspector is more likely to insist that they be followed.

If you accidentally touch 48V DC with dry hands not much will happen, just do not short the system with a wrench, ring, or bracelet!
If you do the same on 120V DC you will definitely feel it and are likely to be injured, even if only from jumping back.

[coinmaster]

I'm used to playing with 100-400v tube amplifiers, if all it is is increased protection standards then I'm not too concerned. It's not like an inspector is going to come out to my inaccessible off-grid cabin anyway.
A 120v battery system seems to be the sweet spot for price, weight, and power.

A 120v battery system at 125ah will store 15,000 wh of power and a 5000w solar panel array will produce 15,000w on a day with 3 hours of sun. Does that sound right?

[Sunking]

A 120v battery system at 125ah will store 15,000 wh of power and a 5000w solar panel array will produce 15,000w on a day with 3 hours of sun. Does that sound right?

No Sir that is not right. You do not know what you are talking about. 5000 watts x 3 hours = 15,000 what hours at the panel output, not 15000 watts. While it is true 120 x 125 AH = 15 Kwh, it takes a 75 Kwh battery to be able to store and use it efficiently and cost effectively. You would burn your batteries up within a week hitting them with 42 amps of current or C/3.One cloudy day and you go dark until after you have a full sun day to recharge. Even if the batteries could handle a C/3 charge current discharging 100% each day and you get 150 to 200 cycles or less than a year out of them. Minimum requirement is 20% discharge per day or 5 day reserve. Only 50% of the energy is usable without significant battery damage.

Secondly to generate 15 Kwh of usable energy per day requires the panels to generate 22,500 watt hours. With 3 Sun Hours means 7500 watt panels, not 5000. As for the battery to yield you 15 Kwh of usable energy per day requires:

12 volt @ 6250 AH
24 volts at 3125 AH
48 volts @ 1562 AH
120 volts @ 625 AH.

Makes no difference how you spin it, that is a 4500 pound battery costing $18,000 day 1 and higher every 5 years replacement. A utility would only charge you $2800 for the same amount of power in 5 years.

[coinmaster]

While it is true 120 x 125 AH = 15 Kwh, it takes a 75 Kwh battery to be able to store it. .

Why?

[Sunking]

Why?

I already explained it.

[coinmaster]

. As for the battery to yield you 15 Kwh of usable energy per day requires:

12 volt @ 6250 AH
24 volts at 3125 AH
48 volts @ 1562 AH
120 volts @ 625 AH.

.

I only need 5Kwh of usable energy per day remember.

I already explained it.

I'm not following the reason.

You would burn your batteries up within a week hitting them with 42 amps of current or C/3

Isn't that what charge controllers are for?

Secondly to generate 15 Kwh of usable energy per day requires the panels to generate 22,500 watt hours

Where are you getting that number?