help with choosing correct CC and inverter

narrdarr

hello,
im new to solar and this forum. i have a few questions to go long with which CC and inverted should get.
1st thing 1st. My grandfather had got this array used awhile back and pick up some used forklift batteries to use as the BB and we are now ready to start setting it up DYI style.

what i have:
7 36v forklift batteries(sry idk what the amps are, but i can mod these batteries for whatever voltage is necessary)
9 racks
144 panels
16 panels per rack 4x4 series parallel connection(6v, 14.5amp @ 87 watt per panel= 24v, 58 amps @ 1392 watt per rack*)

* i not sure if the the panel will have 9Vmp or not. if so that put a rack at 36v, 38.7 amps @1392 watt.

My racks appear to have some kind of a integrated solid state device, like a bridge rectifier package from what i have been told. which lets higher power to bypass diodes. the question here is why would some of the racks have 1 device and other racks have 2 of these? i would assume once these are connected, i'll be able to see if i get near the 9Vmp mark.
should i set my BB up for 24v or 36?

Goal:
primary:
to be able to be off the grid.(power my house, shop, greenhouse,ect.
secondary:
if possible sell any excess power to the power company.

i know alot of people will want to say just grid-tie you system, buy/sell to the PC and use a the BB as backup, but getting off the grid is more important to us, so if the secondary isn't possible let me know.

i guess that brings me to the title of this topic. which would be the best CC and inverter to get?

thanks and if you need more info/pic/video from me to give a better answer let me know.

p.s
almost forgot
maker:
arco solar inc
model#:
is rahm

Cariboocoot

Re: help with choosing correct CC and inverter

Welcome to the forum.

Wow. That's the sort of mess I'm often asked to sort out.

First of all be assured you probably will not be allowed to sell any excess power to the grid. They are very picky about things like UL certification of components.

Which bring us to your PV. Are you say you have 87 Watt 6 Vmp 14.5 Imp panels? Arco Solar brand leads me to believe these are old surplus from somewhere.

So the first thing you'd need to do is wire up six in series to get a string of panels with Vmp of 36 for charging a 24 Volt system. With a total of 144 panels you'd have 24 strings. If you put them all in parallel that would be a whopping 348 Amps. No single controller would handle that much to be sure.

You can increase the array Vmp further to reduce the current from the combined panel strings but it won't negate that massive output current. Even going up to a 48 Volt system would only halve that and still be more than two controllers can take.

Which brings us to the batteries and the question of how much power do you need? The problem here is you don't know the Amp hour capacity of the batteries, so charging rate becomes guesswork and that is a bad idea. But as far as Voltage is concerned you're better off with either 24 or 48 as 36V is an 'oddball' in the inverter world.

Regardless of what you've got for equipment you first need to figure out how much power in Watt hours you need to supply. Also the peak Wattage with everything that might be used at once and whether or not 240 Volts will be needed (and if so how much). Otherwise you'll be guessing at everything and likely won't be happy with the result.

narrdarr

Re: help with choosing correct CC and inverter

Thanks for the fast response.

Wow. That's the sort of mess I'm often asked to sort out.
Sorry for the mess.

Are you say you have 87 Watt 6 Vmp 14.5 Imp panels?
The panels only tell me 6V 87 Watts. i just used the power formula to find the amps of each panel.


Arco Solar brand leads me to believe these are old surplus from somewhere.

History of the PV is from my knowledge. Is that a company started to use these to sell power to a PC, but Arco Solar ran into a patient issues and the company had to get rid of them. Some guys bought them to power his home, but a week after buying them he got in a motorcycle accident and didn't make it. Then his wife sold them PV array to my grandfather, but she couldn't find the CC, BB(if there even was one), and inverter to go with it. which brings to now.

So the first thing you'd need to do is wire up six in series to get a string of panels with Vmp of 36 for charging a 24 Volt system. With a total of 144 panels you'd have 24 strings. If you put them all in parallel that would be a whopping 348 Amps. No single controller would handle that much to be sure.

The problem with wiring up this way, is that the racks that hold the panels only allow for a 4x4 series parallel setup per rack. Although it appears i can string multiple racks together. Which now that i think about it is probable the purpose for the solid state device things attached to the racks.

Which brings us to the batteries and the question of how much power do you need? The problem here is you don't know the Amp hour capacity of the batteries, so charging rate becomes guesswork and that is a bad idea. But as far as Voltage is concerned you're better off with either 24 or 48 as 36V is an 'oddball' in the inverter world.

Regardless of what you've got for equipment you first need to figure out how much power in Watt hours you need to supply. Also the peak Wattage with everything that might be used at once and whether or not 240 Volts will be needed (and if so how much). Otherwise you'll be guessing at everything and likely won't be happy with the result.

this is a tough one to answer answer as we are always trying to expand on our farm, so we are always going to need more power and yea i'll need 240v for the welder and dryer. i'll put together some numbers and get back to you on our current usage tho.. I'm assuming there is no way to test to see how many amps the batteries are...? if not maybe the best thing to do is sell the batteries and get some with all the information.

so what do think of string the racks together? and how far? (i think i could go pretty far with it.)

Cariboocoot

Re: help with choosing correct CC and inverter

Electrically the panels don't care if they are mounted 4x4. In fact if you have eight panels in series you get 48 Vmp, which through an MPPT controller will be fine for a 24 Volt system (but not enough for a 48 Volt system which actually needs an array around 70 Vmp). So with a 48 Volt system you'd put two of the 48 Volt arrays in series to give you 96 Volts to down-convert via the MPPT. It would work.

If we look at it from a reverse prospective of how much battery the array can support we see:
144 * 87 Watts = 12,528 Watt array. Typical 77% derating gives you 9,646 Watts which could supply about 400 Amps on 24 Volts or 200 on 48. Either of which would require multiple charge controllers (as 80 Amps is about the limit for one). In that case you'd be looking at dividing it into 3 for 4 separate arrays with one controller each. Under those circumstances you can't beat the MidNite Classic line because they are the best for co-ordinating multiple controllers (using their "follow me" function).

At any rate, that would be a massive battery bank. Say 48 Volts (not sure if you can reconfigure your cells for that) because in such a power league you'd want that higher Voltage. You are still looking at being able to charge about 2,000 Amp hours @ 48 Volts. At 50% DOD that would be about 24kW hours of power.

Unfortunately there is no easy way to test the batteries. A forklift shop could possible load test them or at least figure out what model they are and maybe find some specs on them.

Welders and dryers can use a lot of Watt hours in a hurry. So can electric stoves and hot water heaters. Our little house here does 16 kW hours per day with gas stove and no welder (only two people). It's possible this could work.

As far as inverter go you are in the big power bracket: 240 Volts at probably 6kW+ and 48 VDC input. Realistically you'd be looking at an Outback Radian, Xantrex XW6048, or stacked 4kW Magnums. Something in that order.

narrdarr

Re: help with choosing correct CC and inverter

thanks so much for your help Cariboocoot. I've have much better understanding of what i'm shooting for now. If anything thing else comes up i'll post it here. thanks again.

zoneblue

Re: help with choosing correct CC and inverter

First thing id do if you cant find specs for those old pv, is to test Isc and Voc. Take a DMM, and get these values for a few cells and average them. In fact given their history id test them all, write it all up, and toss any that look way out of sync from the median.

From this we can do a "good enough" estimate for Vmp and recomend a charge controller, and string configuration.