Stand Alone System powering 3 phase load

[Naptown]

[QUOTE=Sunking;45554]

What about this:

• Array feeding 600V to charge controllers.
• Each controller on separate 48V bank.
• Smaller inverters connected to each bank.
• Combine inverters in panelboard to power load.{/QUOTE]

Yes it would work using consumer grade charge controllers which can go up to 96 volt battery like those made by Midnight Solar. However this is an industrial application which requires industrial solutions and equipment. No offense offered Rich but quit thinking inside the residential box. This system screams 480 volt poly-phase, not 240/120 volt single phase. To do that you need 490 to 600 volt battery voltages.

Hey I never claimed to be an industrial battery guy.

But what was never mentioned or I failed to see it is the actual load in amps on this system.
I saw 90KW a day but is that 9KW over 10 hours 3.75 KW for 24 hours or 90 KW for one hour.
I would imagine it would make a bit of a difference as far as batteries, inverters etc are concerned.

[Sunking]

[QUOTE=Naptown;45556]

Hey I never claimed to be an industrial battery guy.

Sorry Rich I did not mean to offend you. My intention was to redirect your thinking.

When it comes to industrial battery applications we try to limit the string count to 2 parallel strings at most. The justification for 2 strings is mission critical operations for redundancy so we can take 1 string off-line for maintenance if needed. However with 2 strings comes a lot of expense and maintenance issues.

So with that thought in mind try to imagine a 450 Kwh battery capacity with 48 volts. 450,000 Kwh \ 48 volts = 9375 AH. Largest 2 volt cells I know of are 2300 AH or 4 parallel strings. Or use the exact same batteries in 2 parallel strings operating @ 96 volts, or 1 string @ 192 volts. FWIW a 2 volt 2300 AH battery weighs about 280 pounds each and you would need 96 of them or 13 tons and $63,000 worth. That puts your wallet and back in the HURT LOCKER

[Solariser]

Hi. Apologies if I come across the wrong way. I guess I am too used to the traditional residential style stand alone systems and not to keen to turn it into an industrial type system. I was under the impression that it would be cheaper to many lower Ah rated batteries than a few with very high Ah rating??
In addition I am trying to keep as residential as possible to facilitate the ease of sourcing the batteries and charge controllers hence why the approach of splitting it into several battery banks with smaller current rating charger controllers was more appealing. In addition the idea of using three single phase inverters would work if the load was correctly split.
I apologise if I am being ignorant, I design grid tied systems for a living but haven't ventured into the stand alone area before.

[Sunking]

Hi. Apologies if I come across the wrong way. I guess I am too used to the traditional residential style stand alone systems and not to keen to turn it into an industrial type system.

No apologies are needed, no problem here. It is expected if you work in residential systems not to fully understand commercial/industrial systems. They are completely different animals. Here in the many of the state electrician licenses have separate categories for electrical work and you are not allowed to cross. Texas where I am has 11 different electrical licenses. Only a Master can cross from residential to commercial and industrial. But to be a Master requires a minimum of 12,000 billable work hours under direct supervision of a Master Electrician, and 4 years of education.

I was under the impression that it would be cheaper to many lower Ah rated batteries than a few with very high Ah rating??

That might be true where you live but not here in the USA. When figuring battery cost it is done on a Watt Hour capacity cost. Smaller batteries like 12 and 6 volt batteries will cost around $130 to $140/Kwh for a good 10 year warranted battery. While a high capacity 2 volt cell will cost around $110 to $130/Kwh.

The other thing to consider when you start using 6 and 12 volt cells to make large capacity is going to require many parallel strings. With that comes multiple problems and expense. I will not go deeply into the technical problems of parallel strings other than to say cuts the battery life in half which means more frequent replacement cost. The initial installation cost will be much higher because of all the cabling, disconnects, and circuit protection required. It sky rockets both labor and material cost. So in summary using multiple smaller batteries is a Lose-Lose situation.

Do not feel bad 95% of the people who come here are stuck in the same 12 volt box thinking you are in. Most are ignorant that 2, 4, 6, and 8 volt batteries exist. They have never seen or heard of a 2 volt 3000 AH 700 pound battery before unless they have been on a submarine or work with rail roads, mining industry, telephone, or electrical generation utilities.

[Solariser]

Very interesting indeed, I had not heard of a battery which had that high an Ah rating. Don't you need many of these if you were to work with higher DC voltages in the 500V region??

[Sunking]

Very interesting indeed, I had not heard of a battery which had that high an Ah rating. Don't you need many of these if you were to work with higher DC voltages in the 500V region??

All the time for the last 33 years.

I do a lot of work in Telephone and Data Centers. Telephone offices use -48 Vdc plants up to 10,000 amps and we use a C&D MCT-II 4000 batteries. They are 2 volt, 4000 AH, 720 pound cells.

Data centers use very large scale UPS systems up to 2 Mw and they use battery voltages of typically of 490 Vdc producing 480/270 3-Phase. They use a smaller version 2 volt AGM battery, 245 of them in series that float at 575 volts. They are only designed to give about 10 to 15 minutes at full power. Just long enough for dual 2 Mw diesel generators to come on line and take over.

[Naptown]

[QUOTE=Sunking;45563]

Sorry Rich I did not mean to offend you. My intention was to redirect your thinking.

When it comes to industrial battery applications we try to limit the string count to 2 parallel strings at most. The justification for 2 strings is mission critical operations for redundancy so we can take 1 string off-line for maintenance if needed. However with 2 strings comes a lot of expense and maintenance issues.

So with that thought in mind try to imagine a 450 Kwh battery capacity with 48 volts. 450,000 Kwh \ 48 volts = 9375 AH. Largest 2 volt cells I know of are 2300 AH or 4 parallel strings. Or use the exact same batteries in 2 parallel strings operating @ 96 volts, or 1 string @ 192 volts. FWIW a 2 volt 2300 AH battery weighs about 280 pounds each and you would need 96 of them or 13 tons and $63,000 worth. That puts your wallet and back in the HURT LOCKER

No offence taken.
My thought was to split this up into 3 strings of batteries with 3 inverters (Single phase feeding a balanced 3 phase panelboard to combine.
What I was driving at was what is the Maximum draw on the item(s) that are to be run that need the 90KWH a day.
Not talking batteries here Just inverters.

[Solariser]

The maximum draw from the load, given that the load is 10KW with the ac voltage of 230V will give a nominal load current of 43A.

[Solariser]

Yes I do but hesitate to answer because it is obvious you do not understand batteries or basic electrical concepts.

The battery capacity required is 450 Kwh period. If you were to use say 12 volt batteries rated at 900 AH it will take exactly 42 batteries at what ever voltage you configure them as:

12 volt: 42 in parallel = 42 in series @ 504 volts.

How did you calculate the Kwh value you mentioned??

[Naptown]

How did you calculate the Kwh value you mentioned??

That's simple
daily KWH load x 5
To get max life out of a battery you only want to discharge 20% on a daily basis.

Ok now that it has been established that the load is 10 KW and running for 9 hours a day.
Will these be daytime hours or at night.
What is the nature of the load Motors, resistance, lighting

[Solariser]

Well it may be daytime or night time usage...

[Solariser]

Hi. Please correct me were possible. I want to allow the batteries to discharge by 30% every day and therefore my battery Kwh required per day will be 300Kwh. (Value obtained by multiplying 90Kwh x 100/30 = 300Kwh)

Now if I were to use 12V batteries of 750Ah rating I would need 34 batteries in series. Correct???. As the 34 batts in series would give 408V
and that means that I get approximately 408V x 750Ah = 306Kwh (Not taking into account that the actual value will be less due to different discharge rates)

Now if my array is 30KW peak how do I go about sizing my charge controller?? I know it will need to be able have 408V in its output charging range but how do I rate it for the current?

[Sunking]

Now if my array is 30KW peak how do I go about sizing my charge controller?? I know it will need to be able have 408V in its output charging range but how do I rate it for the current?

Assuming you design the controller as MPPT, Amps Panel Wattage / nominal battery voltage. So 30,000 watts / 408 volts = 74 amps.

[Solariser]

Ok. So do I then need to tailor the module string arrrangement based on that value of current rating??

[maple flats]

Basically, it sounds like you need to enlist the services of the appropriatly licensed solar engineer. While it is good to understand this in concept, it is definately not a do it yourself project!