question,, which is better when looking at solar panels.??

looks like i'm going to be spending time on the "12v side of life" for a bit. thanks for the link.

why does this **** have to be so convoluted. I want to put 3 195watt 24volt panels on my camper to charge a couple of batteries at 12volts.

this is like obama care on steroids.. :) nohedident..

2oldman wrote:

carl2591 wrote:
they say one thing and other places say other things.. who is correct??

It is tricky...at first.

Notice in the specs it says "Nominal system voltage" of 12,24, 36 or 48. That's important.

1200w of solar @ 24v = 50amps, but, maximum battery amps is 45. How they can say that? It is because 1200w of solar will almost never put out 1200w, it will be somewhere around 1000 on a really good day. So that equates to 1000/24 or 41.6 amps AT 24 VOLTS to the batteries.

1200w of solar @ 12v = 100 amps (ok, maybe 80). You can't put that on 12v batteries unless you want to lose half your amps to heat and possibly destroying the controller, hence the 600w rating AT 12 VOLTS.

This is why, when you start getting up in power you need to look at running higher voltages. Myself I run 100+v of panels and I have a 48vdc battery bank. Higher voltage and lower amperage perform more efficiently and don't require thumb-sized wire.

If what I just said went over your head, spend some time with this: 12v side of life.

Someone may correct anything I've said here, but this is my understanding of it.

Don - yes, your 30A MPPT won't handle 2*24V in series because of low input voltage. I meant a "proper" 30 MPPT ;)

carl2591 wrote:
they say one thing and other places say other things.. who is correct??

It is tricky...at first.

Notice in the specs it says "Nominal system voltage" of 12,24, 36 or 48. That's important.

1200w of solar @ 24v = 50amps, but, maximum battery amps is 45. How they can say that? It is because 1200w of solar will almost never put out 1200w, it will be somewhere around 1000 on a really good day. So that equates to 1000/24 or 41.6 amps AT 24 VOLTS to the batteries.

1200w of solar @ 12v = 100 amps (ok, maybe 80). You can't put that on 12v batteries unless you want to lose half your amps to heat and possibly destroying the controller, hence the 600w rating AT 12 VOLTS.

This is why, when you start getting up in power you need to look at running higher voltages. Myself I run 100+v of panels and I have a 48vdc battery bank. Higher voltage and lower amperage perform more efficiently and don't require thumb-sized wire.

If what I just said went over your head, spend some time with this: 12v side of life.

Someone may correct anything I've said here, but this is my understanding of it.

carl2591 wrote:
the tristar 45 amp controller being able to handle nominal solar input of 1200 watts at 24v.

They mean - with 24V battery bank.

http://tinyurl.com/jmb5zyy

on this site in the description area it show the tristar 45 amp controller being able to handle nominal solar input of 1200 watts at 24v. so how the hell do you figure out what to use..

they say one thing and other places say other things.. who is correct??

confused

Hi Almot,

Careful. My Blue Sky 3024di will not handle 400 watts of panels unless I use nominal 12 volt panels, which kinda sorta defeats the purpose of going MPPT. I can do 300 watts @ 33 volts input to the controller, allowing 125% for cloud effect. I'd hate to let out the magic blue smoke.

I think the next generation of Blue Sky can do more wattage, but they want a bunch of money for an upgraded chip. There is also zero warranty on the chip unless they do the installation (for a service fee, of course). So the answer is "it depends on the MPPT controller".

The rule of thumb for MPPT is the greater the input voltage the lower the efficiency of the controller. Magnum, with their new PT-100 claims 99%. I think my blue sky is only 96% when I do 33 volts input.

While voltage drop doesn't matter much for PWM installations, it does matter for MPPT because MPPT takes volts and processes them into amps. I would aim at 1% or less voltage drop from panels to the controller. So yes, wire size really does matter. I managed to squeak to about a 1% loss by using 33 volts of input, but my real reason for going MPPT was that panel cost per watt was $5.50 at that time, so I purchased MPPT to extract every watt I could. Today with panel prices as low as $0.28 cents per watt, I'd most likely use a fully featured PWM controller.

Hear Hear on "doing it right the first time".

Almot wrote:

Wrong again.
It's about wattage, not number of panels. 30A MPPT is enough for 450-480W array. Jack is correct, +400W is easier to do with 24V panels. Makes sense installing 2*230 or 2*240. High-volt panels need to be of close voltage, installing 195W now and adding 250W later would be a bad idea. One thing that Jack doesn't mention is that solar should better be done right the first time - cheaper and simpler.

There is nothing to "size" from roof to controller with few high-volt panels in series. Wire is the same MC4 #10, for a single 195W or 2*240W or even 3*240W. this is the beauty of high-volt panels - low amps, thin wire. The only thing that is changing is the wire gauge from controller to battery - beefier wire for bigger total wattage.
I have a feeling this is going to be a very long thread.

KD4UPL wrote:

The Blue Sky SB3024iL (a great controller by the way) will only accept 57 volts on the input.

I wanted to say this but it seemed like too much info. To fully utilize the benefits of thin cable with 2*24V panels, they need another controller, with voltage input limit 100V.

They didn't tell what total wattage they wanted with 5 panels. I "suspect" that number 5 appeared as a result of misconception, 30A controller divided by 5.4A panel current. But this is not how it should be calculated.

With planned 2*6V GC batteries they don't need more than 500-600W array anyway.

It would be difficult to make 5 panels work even if a 30A controller would handle that. (Which it won't).
The amp ratting of an MPPT controller is it's output rating. Multiply that by the battery voltage for an approximation of how many watts you can hook to the input.
The reason 5 panels won't work well is that if you hook all 5 in series the voltage will likely be too high for the controller but you can't evenly divide 5 panels into two strings.
The Blue Sky SB3024iL (a great controller by the way) will only accept 57 volts on the input. This is likely only enough for 1 panel in series. You didn't say what the panel's Voc is but I will guess it's over 30 volts. Whatever the Voc is it will rise in cold weather. Panel rating are given at 25 degrees Celsius. As the panel gets colder the voltage rises.
If you want a large array like 5 195 watt panels (5 x 195/ 12v = 81.25 amps.) I would recommend something like the Outback FM80. It's input voltage range will allow for 3 or possibly 4 panels in series. So, you could do 1,2,3,4, or 6 panels.

carl2591 wrote:
I sorta see where the higher voltage panels, even with the lower amps, are most likely the better choice.

There is no "even" here. More watts = more energy harvested for all your uses. Grasp this idea. Don't worry about low amps of high-voltage panels, they use MPPT controller that converts high volts into high amps.

carl2591 wrote:
higher voltage = smaller wire = less weight = lower cost for wire

Now you got it.

carl2591 wrote:

the charge controllers at 30 amps are able to handle 5 total panels if i decide to add a couple more in the future so everything will be sized for 5 panels from roof to batteries.

Wrong again.
It's about wattage, not number of panels. 30A MPPT is enough for 450-480W array. Jack is correct, +400W is easier to do with 24V panels. Makes sense installing 2*230 or 2*240. High-volt panels need to be of close voltage, installing 195W now and adding 250W later would be a bad idea. One thing that Jack doesn't mention is that solar should better be done right the first time - cheaper and simpler.

There is nothing to "size" from roof to controller with few high-volt panels in series. Wire is the same MC4 #10, for a single 195W or 2*240W or even 3*240W. this is the beauty of high-volt panels - low amps, thin wire. The only thing that is changing is the wire gauge from controller to battery - beefier wire for bigger total wattage.
I have a feeling this is going to be a very long thread.

What is the budget?