How tolerent would these panels be with each other?

[crxvfr]

Hi everybody.

I'm pretty sure these numbers are close enough to work ok, but for how long?
Are they too far out of whack to consider?
Could they live together nicely?
Both are Monocrystalline.


185 watt 24 v
Open Circuit Voltage (Voc): 44.5V
Short Circuit Current (Isc): 5.6A
Maximum Power Voltage (Vmp): 36V
Maximum Power Current (Imp): 5.14A

200 watt 24 v
Open Circuit Voltage (Voc) - 45.5
Short Circuit Current (Isc) - 5.56
Maximum Power Voltage (Vmp) - 37.0
Maximum Power Current (Imp) - 5.4

Many thanks.

[Mike90250]

They would work pretty well. Now you just need to find BOTH in stock somewhere.

[crxvfr]

To tell you the truth, I'm trying to match a panel I already have
[as gasps erupt from the audience ]. I was excited to find one with numbers that close considering my existing panel is a 24 volt panel. These panels are readily available, but after I get enough panels in place to make the small morningstar controller I already have hum, I'm hoping then to move up a notch to name brand panels for my next independent system.

BTW, I understand that in a perfect world, they would all match exactly down to the batch and manufacturing date. I also understand that any advice I get from you guys is a gift. If something ever were to go wrong, ...personally, I could never turn around and blame somebody else. I'm catching on slowly and proceeding with baby steps.

Thanks Mike.

[Sunking]

Well Mike you are limiting yourself and not taking advantage of higher voltages. The panels you listed can only be used in parallel, and not in series. You get the best efficiency at higher voltages. For example on a 24 volt battery system you can run up panel voltages to 150 volts DC. Only way to do that is use panels wired in series, you are stuck with parallel.

Edit to clarify. You can use them in series, but power will be limited by the lower Imp rating

[Mike90250]

To tell you the truth, I'm trying to match a panel I already have I was excited to find one with numbers that close considering my existing panel is a 24 volt panel. ............

The panels you listed are a POOR match for a 24V panel. To each other, they aren't bad. connected with a 24v panel, you will loose about 35% of the power of the 36VMp panels.

Tell us what you already have, and where you need to go, and we can advice a whole lot better.

mike90250

[crxvfr]

ok, had to wait to get home for manual

Panels...
Have 24v 200 watt (Voc=45.5) (Isc=5.56) (Vmp=37) (Imp=5.4)
Want 24v 185 watt (Voc=44.5) (Isc=5.6) (Vmp=36) (Imp=5.14) ..actually found many on um, ebay

Have Morningstar Sunsaver MPPT...
System Voltage: 12/24
Rated Battery Current: 15 amps
Rated Load Current: 15 amps
Max Input Voltage: 75 Volts
Nominal Input Power
---12v:200 watts
---24v:400 watts

I would like to use a 24v battery system
...and I would like to add as many 185 watt panels as I can with the 200 watt, if it works decently.

btw mike, for what it's worth, I liked your answer

....so ya mean there's a chance!
(said like in movie dumb and dumber, because when it comes to electronics, I am)

EDIT ADD:
...and just to be clear, they are BOTH 24v panels, which I don't understand because they put out 40+.
...unless I've been duped. The wires could go to anything and his hand is in front of a cell.
It's from someone who has bulletproof feedback on ebay.
I may read thru again and take a guess on things using my own infamous wizardly mathematical skills.

[Mike90250]

OK, 24 V pv system, needs 31V to eq the batteries. So any panel with Vmp over 33V is going to wasted, unless you use a MPPT controller.

Your 2 panels in series, will be over the max input for the Sunsaver MPPT,
so you have to go "Panels in Parallel".

That would give 46-36V feed to the controller (within limits) and about 11A
This seems like a good charging system for a 24V battery, of about 100Ah capacity. Maybe up to 150Ah, I've no idea of your loads.

[crxvfr]

100 amp hours? Really? If I string 4 six volt golf cart batteries together to make 24 volts, I'll not be able to charge them????? If so, I should have gone for the TriStar. It sounds like I will be done with my first system earlier than I anticipated.

[Mike90250]

100 amp hours? Really? If I string 4 six volt golf cart batteries together to make 24 volts, I'll not be able to charge them????? If so, I should have gone for the TriStar. It sounds like I will be done with my first system earlier than I anticipated.

Batteries have a 1-2% self discharge rate. Flooded batteries also need a certain amount of charge current, to bubble and stir the electrolyte, and prevent it from "stratifying" . You also must have enough current to recharge a discharged bank, before it sulphates. So the general guideline is,for the minimum, 5-10% of the batteries capacity, for the charger. If all you have are light loads, you could go a bit larger, but will be unable to equalize the bank without a generator to supply the EQ power.

Say you have a 300AH battery bank, and somehow, it's down to 50%. That's 150AH, plus 20% recharge losses (180ah) that have to be replaced, and you have about 11A to do that with. That's about 17 hours, and a day only has 4-5 good solar recharge hours in it, so you are looking at over 3 days to recharge, and no loads allowed at that time. After 24 hours, the sulfite crystals on a discharged battery begin to harden, and permanent sulphation sets in.

So, that's the reason for my logic.

[Sunking]

crxvfr,

Sounds like you have a mismatch between what you want and what you have so far. It is a typical rookie mistake, especially for off-grid battery systems.

For off-grid systems you have to know how much energy you need to use in a day vs your location. So let's say you need 3000 watt hours in a day.

Well the batteries are simple as they remain constant regardless of location. Battery Amp Hour capacity = (Daily Watt Hours x 7.5) / Battery Voltage. so in this example (3000 wh x 7.5) / 24 volt battery = 937.5 Amp hour battery.

What does change is the solar panel wattage and charge controller sizes. Those 2 depend on your physical location, solar panel voltage, and controller type (shunt or MPPT) The solar panels have to be capable of replacing all the energy used in a day on the shortest winter days, plus system losses incurred. If you use a shunt controller you can expect to loose 50% of the power generated at best, and 66% with a MPPT controller. With me so far?

Let's take two example demonstrating location differences with a MPPT controller using the 3000 wh example OK? Let's use Tuscon AZ, and Madison Wisconsin as location examples. Tuscon receives 5.6 Sun Hours in December, and Madison gets 2.6 hours.

So in Tuscon using all the losses and a MPPT controller the solar panel wattage needed = 3000 wh / .66 / 5.6 = 811 watts, round up to say 820 watts. Charge controller = Solar Panel wattage for a MPPT controller = solar panel wattage / battery voltage = 820 watts / 24 volts = 35 amps, so a 40 Amp or more charge controller will work

Now in Madison things are quite different and much more expensive. For a solar panel wattage you need 3000 wh / .66 / 2.6 = 1748 watts, round up to 1750 watts. For the charge controller you will need 1750 watts / 24 volts = 73 amps so you would need a 80 amp controller.

Location and charge controller type means everything my friend for a given amount of energy. If you live in a gloomy place like Seattle or Portland with a winter insolation of 1.2 hours, you are SOL. Madison WI is no good place either compared to Tuscon.

[crxvfr]

crxvfr,

Sounds like you have a mismatch

Sunking, your advice is never lost on me. I'm sure your high watt answers are already burning thru the night all across america. I'm just weird and do lots of things my own way. ( I have been sowing reference material for myself see? )

This will not be the first rookie mistake I will make. I anticipate them which is why I am going to build several independent systems. This is my first one (that I am putting together) which requires a total of not much at all. ( still have to buy a killawatt - has been out of stock locally ) ...Router, clock, modem, maybe a laptop or a small light. Once I get this in place, more of what you guys tell me will make more sense. I'll be able to apply stuff I learn here and watch the results. (I learn much better by doing)

[userdavid77]

I am seeking a good used solar panels around North Carolina that we can purchase at a reasonable price. We are hoping that someone can help us in installation too. Both of us are disabled so and are trying to get away from the grid. Can anyone help or give advice? Thanks!!


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[Mike90250]

craigslist or ebay are good sources for used panels. Beware of buying stolen ones, all panels have serial #'s on their stickers, if they are "obscured" the panels may be "hot" and when tracked down, can be reclaimed by owners. And there is no real good way for the consumer to test the panels to verify if they are indeed, good.