Project Thread 1.8kw 24v System

[crxvfr]

I'm getting closer to the brass tacks on one of my systems so I'm starting a thread so any important info that might have to do with the questions I ask will hopefully be in this thread.


Panels:
42 - 70-volt .6 amp 43 watt BP amorphous Millenia panels for 1804 watts
Charge Controller:
Outback FlexMax 80


Question:

Resolved - I bought the Outback 80 amp.

[Mike90250]

Quick answer, just barely. The limit is the output transistor @ 60A. If you can, redo you system for a 48V battery bank, same wattage, but less current ( amps) and less losses in the wires (copper loss)

Your 24V system will RARELY put out nameplate power, plan only on 80% of nameplate mor most times, average conditions. (unless you have a 2 axis tracker). The saving grace is that the MPPT will throttle itself back as trasnistor temps reach high levels, and the s/w will also throttle back at 60A.

[crxvfr]

I bought the 80 amp Outback.

So my question now is about connecting the panels together.

They have 4 leads. 2 positive, 2 negative.

The wires coming out of the panels are small. 18 or so. At .6amp, I could only hook 25 panels together before the amperage gets bigger than the wire coming off the panel is rated for? 25*.6=15 and 18 gauge limit is 16amps? If I soldered two 18 wire's together in parallel, together it's like 32 amps capacity, right?

What I want to do is cut all off all the mc4 connectors, twist and solder both black leads to the negative side of a 12 gauge THHN bus wire, and both positive leads twisted together and soldered to the positive side of a 12 gauge THHN bus wire. OR Solder one of the MC4 connectors onto each of the terminal wire pigtails just made by tying similar colors together, but then, it would go down to 18 gauge for a very short length.??

On a good day I should get 25.2 amps with all panels parallel.

Question
Can I pigtail the terminal wires coming off the panels and solder them to a bus wire? -OR- Can I solder one MC4 on each (2 wire) terminal lead then solder the extra MC4 connectors onto the bus wire so the panels are connected to the bus wire with MC4 connectors instead of having to solder them together after I get them in place? I hope that made sense.

I have pics ( in progress) of the whole system below. Thanks.

I am editing this image instead of pasting several versions of it.
You may have to refresh to get fresh version.

[Mike90250]

1) Man - what a job to check water on all those batteries.
2) What a chore to insure all those parallel connections are equal, even with buss bars
3) I've never seen panels with connectors like that - any paperwork at all to explain how they hook up?
4) the panels are designed for grid-tie high voltage inverters, not for battery charging. Have you checked the string sizer for outback, to see if you can wire 2 panels in series, and stay under the 150V (or whatever the limit is) absolute max voltage.
5) when you cut the factory connectors off, you have voided the warranty.
6) be sure you add fuses, to each string of batteries

I'd even add a remote disconnect, so I could stand outside the battery shed, and pull a rope, and disconnect the whole smoking mess, if something goes wrong. You have way too many small batteries, and too many interconnects.

[Mike90250]

You have a flaw in your battery bank wire connections, you have created a 6V battery bank, not a 24V.

Eventually, a 24V battery @ 1664ah, (39,936KWH) will need a (400KWH) 166A charger, in order to properly charge the batteries, and supply enough current to equalize them. Your solar array is about 1/8 of the needed size for your battery bank, and will only keep up with light loads, and battery self-discharge.

Example, my 48V, 400A bank, (19,200KWH) has a 3KW array (15, 200W panels) which can only feed batteries 60A under best conditions. This is barely the amount needed to charge the batteries properly, and you have 2x the batteries, & 2/3 of the PV, which is a recipe for chronic undercharge and early battery bank death.

[crxvfr]

1) Man - what a job to check water on all those batteries.
2) What a chore to insure all those parallel connections are equal, even with buss bars
3) I've never seen panels with connectors like that - any paperwork at all to explain how they hook up?
4) the panels are designed for grid-tie high voltage inverters, not for battery charging. Have you checked the string sizer for outback, to see if you can wire 2 panels in series, and stay under the 150V (or whatever the limit is) absolute max voltage.
5) when you cut the factory connectors off, you have voided the warranty.
6) be sure you add fuses, to each string of batteries

I'd even add a remote disconnect, so I could stand outside the battery shed, and pull a rope, and disconnect the whole smoking mess, if something goes wrong. You have way too many small batteries, and too many interconnects.

LOL

1) Being uncertain about the battery bank voltage, I rushed thru the battery part of the image last night. I am glad to hear you say I don't need that many batteries.

2) I am no pro, I work with what I have. I don't know what you mean by making all the connections equal. Do you mean resistance?

3 & 4) You are correct sir. See HERE. And yes, I have thought of wiring them in series. I'm open to suggestions.

5) These panels are brand new, unused, but 6 years old. I bought them on ebay for $1 per watt. There is no warranty. It's a Frankenstein project. Beats using a kite and a key in a lightning storm.

6) Fuses and disconnects, ....yes, in abundance. I will ask about where and how to install fuses after I get the rest ironed out.


Thanks.

I'm just a hillbilly, installin' solar panels.
I'm not treating this like an investment for my house.
I'm treating it like a hobby or something to do.
I'm sure there will be much you can join me in laughing at.
I'll upload pics as I get things done.
Right now, I'm still busy hanging 2x6 carport rafters to place the panels on.
Even though this is just for fun, and a learning experience,
I don't want it to blow up at the git go.

Again, I appreciate your guys input.

I will fix the image to make 24v but still unsure about amp hours. Baby steps.

EDIT ADD:
I revised the image.

[crxvfr]

You have a flaw in your battery bank wire connections, you have created a 6V battery bank, not a 24V.

Don't give up on me yet. I fixed the image, the lazy way for now, (you may need to refresh the page to see the newer one) but it will change again.

I will have more battery questions when I get there, but they will be the last thing I buy.
I do know I am going to buy ten.
Two of them are going to be used with a 24 volt, 200 watt panel I have so this project will start with two groups of 4 6v batteries in series, 12+12@416ah.

Since you've been so nice to help me learn, I thought I'd show you what I have going on.
Below is a picture of the first rib of a carport hanging over my truck.
There will be 15 more, spaced just right so the panels lie in a groove. That one is just in place temporarily to scribe a line.

A cat decided to jump onto my ladder just as I took it.
My ladder is 7 years old and made out of 2x4's and 2x2's.
Most people won't climb it. The thieves won't steal it.
I love my ladder.
And yes, its propped up in the back of my truck so I can make it to where I need to be.

I'm kind of impressed with myself. My back is so bad, I can't look up, but I've managed, by myself, to get 10 foot 2x8's, 10 foot 2x4's and 12 foot 4x4's in place, sometimes twelve feet above the ground. And since I can't look up, I have to be at least a couple feet higher than what I'm working on. I have to make two lasso's, hang the wood in them, and tighten each side, going back and forth until its ready to screw it in place.

There is a kennel to the left. I built it before getting into solar. Funny, the very reason I was procrastinating about doing a carport was because the roofing isn't cheap. Sure went the other way with that one.

And yes, I live in Hooterville. Ha. I bought my house with a personal loan! Got the deed but paying a whopping $245 a month on the personal loan. In a year, that will be paid off and and hopefully I will have some cheap electric bills. This is my 401. I may be disabled, and even though I still work, I don't expect to see any substantial Social Security or 401k left when I need it.

I may stop here. 12x30 feet for a mere 1800 watts is pretty ridiculous.



I guess the jury is still out on the connections question.

I wish I knew what you meant (Mike) when you said "insure all those parallel connections are equal".

....and still wondering if I can string all 42 panels together parallel.

Look below where it says nominal voltage (battery charging).
It says you have to have a 48v battery but this was before MPPT, right?

BP Solar, formally Solarex, Millennia 42 Watt silica amorphous solar panels.
MST-43
Maximum power (Pmax) 43.0W
Voltage at Pmax 71V
Current at Pmax 0.616A
Open-circuit voltage (Voc) 101V
Short-circuit current (Isc) 0.787A
Guaranteed minimum Pmax 38.7W
Nominal voltage (battery charging) ............. 48V ..............
Maximum system voltage .............. 600V ..............

[Mike90250]

I wish I knew what you meant (Mike) when you said "insure all those parallel connections are equal".

Meaning the resistance to each battery MUST be the same, or they will charge unequally. here is a nice write up on batteries in parallel.

http://www.smartgauge.co.uk/batt_con.html

....and still wondering if I can string all 42 panels together parallel.
Look below where it says nominal voltage (battery charging).
It says you have to have a 48v battery but this was before MPPT, right?
Voltage at Pmax 71V

If you run 71V panels lower than 71V, you will WASTE the power. Wired thru a conventional (PWM) charge controller to a 48V battery bank, you will only get about 60% (1102w) of the nameplate (1836w) wattage.

An MPPT controller will preserve nearly all the wattage your panels are capable of, which is about 20A at 55V (normal charging voltage for a 48V bank)

[Jenn Nelson]

Just bought a bunch of the same panels!

So I just bought 60 of the exact same panels, and am putting them into one of my 3 outback flex 80's. (I have 3, but one is not being used so I wanted to fill it up.)

Did ja ever figure out how many of these you could connect in parallel?

[Sunking]

Well this is a 4 year old thread. The tech is antiquated. Use a Midnite Solar Classic 15 controller.

[Jenn Nelson]

Well this is a 4 year old thread. The tech is antiquated. Use a Midnite Solar Classic 15 controller.

Well, we have a 7 year old system, so this thread is relatively contemporary!