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Old 16-06-2014, 13:34   #1
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Noob help please

I am installing solar on a 29 foot Ketch 12 volt system. I am using the cabin roof at this stage to place my panel.I know its not the best spot OK
I have so far purchased a Power Tech 30 amp MPPT controller its specs below
solar array nominal voltage 12 or 24
Max solar array 360watts @12 volts
Max PV 65 volts
Bulk charge (adjustable)13.8 - 14.8 volts
Float Voltage(adjustable) 13.0 - 14.0 volts
Maximum charge current 30 amp
Maximum load current 30 amp
Ambeint temp range 20 -50 Celsius
Efficiency 97%
The question
I have a maximum space of 1640 cm x 990 cm on top of my cabin roof
My thoughts are buy a high voltage panel up to 65 volts and the controller does its job rather than a 12 or 24 volt panel
Is this a good way of thinking
I have been thinking of a LG neon house panel polycrystalline
Remembering I live in Australia we do not have the luxury of choice that the USA have .
My way of thinking is the high voltage panel will produce more power when there is no shading during the day
Can some one focus me on the the right choice please
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Old 16-06-2014, 13:48   #2
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Re: Noob help please

From what I have read here on the forum and other places, which makes me no expert by any means. With the higher voltage panel the charge controller converts the excess voltage into more amperage. Please don't take my word for it, that is just my rudimentary understanding of how the new charge controllers work. There are several threads about solar panels and charge controllers on the forum here, it would be a good idea to run through some of them, they are quite informative, and they can help you ask the right questions to your local vendor.
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Old 16-06-2014, 19:09   #3
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Re: Noob help please

Sorry for a side question, but is your main boom removed? How can you keep the cabin top clear of its shadow? or can you wing it out so far it will not shadow the panel at midday?

Ann
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Old 17-06-2014, 01:41   #4
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Re: Noob help please

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Originally Posted by Ann T. Cate View Post
Sorry for a side question, but is your main boom removed? How can you keep the cabin top clear of its shadow? or can you wing it out so far it will not shadow the panel at midday?

Ann
I wing it out its a 30 foot ketch the mast is forward .this question has nothing to do what I asked to what I asked
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Old 17-06-2014, 02:13   #5
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Re: Noob help please

You're right, I did say it was a side issue. Sorry if it annoyed you.

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Old 17-06-2014, 03:41   #6
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Re: Noob help please

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Originally Posted by Ann T. Cate View Post
You're right, I did say it was a side issue. Sorry if it annoyed you.

Ann
Sorry Anne my apology Im a little tired . But I willexplain and I know where your coming from when you poped the question
My Walker H 28 which I only recently bought is under restoration for the next few years the masts will come off soon I have refurbished the house electrical system and add batteries ( so I can listen to music while I work on the boat) so it wont really have any booms or mast left on it for a while as I will be repainting in two pack and re do all the rigging and sheets so the panel will be fine on top of the cabin . Even when I start cruising my Intension will be finding Isolated places and throw out the pick and enjoy till I run out of food
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Old 17-06-2014, 07:26   #7
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Re: Noob help please

Ok - I wrote this big long post and got carried away - If you just want an answer I would say no more than 24v panel.

If you want to know why, read on...

(BTW - I am not a solar expert - I have just read and absorbed what I have - there may be some factual nuances incorrect)

I have been hesitant to jump in because solar power is "science" and the scientists get picky over the details. But most explanations around are beyond us mortals and the scientists get involved and confuse us even more...

but I will try to make a simple explanation -

First you must understand the Volts X Amps = Watts

So Watts / Volts = amps

These definitions are not science but are for clarity

Volts - consider this as Pressure - the ability of electricity to "push" electrons
Amps = How many (volume?) of electrons I am pushing
Watts - Because it is a formula consider this as "power"

Your battery has about 12.2 volts worth of cells. To push electrons into your battery you need greater than 12.2 volts. You can't just raise voltage to 1,000v and charge your battery in 5 minutes - The battery can only accept electrons so fast or it heats up too much further increasing resistance (resistance is bad) and further deteriorating acceptance. (oh and it will blow up)

Amps are sort of like volume - You'd like to have plenty of volume available so that the battery will accept them as fast as it can.

Generally in bulk phase ~14.8 volts is good and as many amps as your system can produce. The battery basically will take only what it can.

(I won't talk about the final stages of charging (float) except to say that it's like filling a pitcher with water. As you get close to the rim you slow down the tap so you can fill precisely to the rim without spilling)

So now onto solar panels. Each cell produces a voltage and an amperage and many, many cells are wired together.

What happens when we wire them together. If we wire in series (plus to minus) voltage is doubled and amps is the same. If we wire in parallel (plus to plus) voltage is the same and amps are doubled.

Think about watts = power. If we double the cells we should double the power. So 12 volt cell and 1 amp capacity

1 cell = 12 X 1 = 12w
2 in series = 24 X 1 = 24w
2 in parallel = 12 X 2 = 24w

So now a trick. Solar cells do not produce power when shaded. So a 12 v panel actually is wired so that under full sun they produce 17 volts typically. Then when some of the cells are shaded the panel is still putting out 12v.

So the smart guys figured it out. If I built circuits that always kept the output voltage at 14.8 when the panel "is producing" 17v I could lower the voltage and get more amps!

This first link shows a couple of graphs that describe another bit and that is the power output is not linear with sunlight - there is a "peak efficiency zone" fancy controllers take advantage of this to find the peak efficiency voltage and keep the panel there.

Solutions - Techniques to Maximize Solar Panel Power Output

So Is more volts better? The downside of more volts is high voltage (big "pressure" makes big sparks if shorted and we humans aren't super tolerant of high voltages). counter intuitively high voltages can "push" amps down smaller wires - that's why home electricity is routed around at 440+ and stepped down near your house.

Likely your choices will be 12/24/48v panels.

Remember - Power is a function of the number of cells which equates to area of the total panel so there is no magic. You can't get a higher voltage panel of the same size as a lower one and magically get more watts. You get lower amps with higher volts.

But the advantage is if the panel gets shaded the likelihood of partial shading won't drop the panel voltage below 14.8v (needed to push into the battery).

You charge controller is rated at

360w @ 12 volts -and-
30 amps

This makes sense

360w /12v = 30a for 12 volt panels

So what if you opt for 24v = Remember there is no free lunch for the same dimension panel half of the cells are wired to the other half in series - there is only so much power (volts X amps) per area square.

So the same dimension panel is likely

360 /24 = 15a

You are in the 75w range for panels

75 / 12 = 6 amps
75 /24 = 3 amps

Remember you want 14.8 volts and max amps. The peak voltages of these panels is likely to be 17 and probably 34.

But your fancy controller will reduce the voltage to 14.8 all the time and maximize the amps. Your 24v panel will be outputting 14.8v (though the charge controller) and putting out around 5 amps - BTW your 12 v panel is also operating at 14.8v and around 5 amps (higher voltage = lower amps)

I would not go higher than 24v - That's just my paradigm. The wire between the panel and the controller will have 34v and that's enough for me.

Also if you think the panel will get 50% shaded than 24v panel should still give you (marginally) a charging voltage (although 1/2 the amps are gone) the 12 volt panel will be outputting 6 volts - not enough to "push" the electrons.

To be honest - If I had a giant battery bank and was pushing towards 30 amps of solar (360w+) I would go for 24v (maybe)

For 75w single panel I probably would go 12v. However that's probably just my paradigm. The MPPT controller probably loves 24v panels.

This next link has articles about maximizing solar output - basically says get an MPPT controller - and dives into some science.

Sorry for the long lecture and to the scientists - be gentle...

http://www.sunforceproducts.com/Supp...lectricity.pdf
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Old 17-06-2014, 11:39   #8
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Re: Noob help please

That is a great explanation, much better than I could articulate. Also made things clearer for me. Thank you.
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Old 17-06-2014, 14:30   #9
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Re: Noob help please

Quote:
Originally Posted by Ex-Calif View Post
Ok - I wrote this big long post and got carried away - If you just want an answer I would say no more than 24v panel.

If you want to know why, read on...

(BTW - I am not a solar expert - I have just read and absorbed what I have - there may be some factual nuances incorrect)

I have been hesitant to jump in because solar power is "science" and the scientists get picky over the details. But most explanations around are beyond us mortals and the scientists get involved and confuse us even more...

but I will try to make a simple explanation -

First you must understand the Volts X Amps = Watts

So Watts / Volts = amps

These definitions are not science but are for clarity

Volts - consider this as Pressure - the ability of electricity to "push" electrons
Amps = How many (volume?) of electrons I am pushing
Watts - Because it is a formula consider this as "power"

Your battery has about 12.2 volts worth of cells. To push electrons into your battery you need greater than 12.2 volts. You can't just raise voltage to 1,000v and charge your battery in 5 minutes - The battery can only accept electrons so fast or it heats up too much further increasing resistance (resistance is bad) and further deteriorating acceptance. (oh and it will blow up)

Amps are sort of like volume - You'd like to have plenty of volume available so that the battery will accept them as fast as it can.

Generally in bulk phase ~14.8 volts is good and as many amps as your system can produce. The battery basically will take only what it can.

(I won't talk about the final stages of charging (float) except to say that it's like filling a pitcher with water. As you get close to the rim you slow down the tap so you can fill precisely to the rim without spilling)

So now onto solar panels. Each cell produces a voltage and an amperage and many, many cells are wired together.

What happens when we wire them together. If we wire in series (plus to minus) voltage is doubled and amps is the same. If we wire in parallel (plus to plus) voltage is the same and amps are doubled.

Think about watts = power. If we double the cells we should double the power. So 12 volt cell and 1 amp capacity

1 cell = 12 X 1 = 12w
2 in series = 24 X 1 = 24w
2 in parallel = 12 X 2 = 24w

So now a trick. Solar cells do not produce power when shaded. So a 12 v panel actually is wired so that under full sun they produce 17 volts typically. Then when some of the cells are shaded the panel is still putting out 12v.

So the smart guys figured it out. If I built circuits that always kept the output voltage at 14.8 when the panel "is producing" 17v I could lower the voltage and get more amps!

This first link shows a couple of graphs that describe another bit and that is the power output is not linear with sunlight - there is a "peak efficiency zone" fancy controllers take advantage of this to find the peak efficiency voltage and keep the panel there.

Solutions - Techniques to Maximize Solar Panel Power Output

So Is more volts better? The downside of more volts is high voltage (big "pressure" makes big sparks if shorted and we humans aren't super tolerant of high voltages). counter intuitively high voltages can "push" amps down smaller wires - that's why home electricity is routed around at 440+ and stepped down near your house.

Likely your choices will be 12/24/48v panels.

Remember - Power is a function of the number of cells which equates to area of the total panel so there is no magic. You can't get a higher voltage panel of the same size as a lower one and magically get more watts. You get lower amps with higher volts.

But the advantage is if the panel gets shaded the likelihood of partial shading won't drop the panel voltage below 14.8v (needed to push into the battery).

You charge controller is rated at

360w @ 12 volts -and-
30 amps

This makes sense

360w /12v = 30a for 12 volt panels

So what if you opt for 24v = Remember there is no free lunch for the same dimension panel half of the cells are wired to the other half in series - there is only so much power (volts X amps) per area square.

So the same dimension panel is likely

360 /24 = 15a

You are in the 75w range for panels

75 / 12 = 6 amps
75 /24 = 3 amps

Remember you want 14.8 volts and max amps. The peak voltages of these panels is likely to be 17 and probably 34.

But your fancy controller will reduce the voltage to 14.8 all the time and maximize the amps. Your 24v panel will be outputting 14.8v (though the charge controller) and putting out around 5 amps - BTW your 12 v panel is also operating at 14.8v and around 5 amps (higher voltage = lower amps)

I would not go higher than 24v - That's just my paradigm. The wire between the panel and the controller will have 34v and that's enough for me.

Also if you think the panel will get 50% shaded than 24v panel should still give you (marginally) a charging voltage (although 1/2 the amps are gone) the 12 volt panel will be outputting 6 volts - not enough to "push" the electrons.

To be honest - If I had a giant battery bank and was pushing towards 30 amps of solar (360w+) I would go for 24v (maybe)

For 75w single panel I probably would go 12v. However that's probably just my paradigm. The MPPT controller probably loves 24v panels.

This next link has articles about maximizing solar output - basically says get an MPPT controller - and dives into some science.

Sorry for the long lecture and to the scientists - be gentle...

http://www.sunforceproducts.com/Supp...lectricity.pdf
Thank you so much I would like to say one thing when this controller is used as 24 volts the watts are increase to 720 max
What a few have done is wired there 12 volt panels in parallel producing 24 volts then the controller if you batteries are 12 volts .
There theory is if shading occurs the voltage will be above 12.
This was the reason I thought perhaps use a 45 volt panel when shading ahappens the shade reduction will be above 12 volt.
I have only time for a quick read . I will read you input throughly tonight
Thank you
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Old 17-06-2014, 18:17   #10
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Re: Noob help please

Quote:
Originally Posted by HG02 View Post
Thank you so much I would like to say one thing when this controller is used as 24 volts the watts are increase to 720 max
What a few have done is wired there 12 volt panels in parallel producing 24 volts then the controller if you batteries are 12 volts .
There theory is if shading occurs the voltage will be above 12.
This was the reason I thought perhaps use a 45 volt panel when shading ahappens the shade reduction will be above 12 volt.
I have only time for a quick read . I will read you input throughly tonight
Thank you
Volts X Amps = Watts
Watts / Volts = Amps
Watts / Amps = Volts

Watts can only be increased by getting a bigger panel - The controller cannot make more watts.


The controller is rated in amps - how much "volume" can I put through and watts "@" volts (= amps)

This controller for example -

360w @ 12 volts (= 30amps BTW)

If you wire 2 X 12V panels in parallel you still only have 12v output but you have doubled the amps.

If you wire them in series you double the volts but the amps are the same.

BTW - I had forgotten about Compass Marine - This guy has some excellent articles and he really puts things in basic terms. Worth a read.

Seems he doesn't recommend going over 17v for a small boat system. I would disagree only if I expected partial shading a lot - Note, A 24 volt panel is no magic - when shaded output is seriously affected - however you still have a better chance of producing a (minimal) charge voltage.

Installing A Small Marine Solar System Photo Gallery by Compass Marine How To at pbase.com
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Old 17-06-2014, 18:37   #11
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Re: Noob help please

Quote:
Originally Posted by HG02 View Post
Thank you so much I would like to say one thing when this controller is used as 24 volts the watts are increase to 720 max
Oh - BTW - You are not wrong here... You can put 720w @ 24 volts through your charger

360 / 12 = 30
720 /24 = 30

However the 720 watt X 24 panel will have twice the area of the 360w X 12 volt panel.

BTW - that would be a huge array.

Consider a 75w X 12v panel is roughly 2 feet by 4 feet. 8 square feet.

360w @ 12V would be 38 square feet of panels. 4 feet X 9 feet?

In 24v the panels would be something like 76 square feet!
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Old 18-06-2014, 11:28   #12
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Re: Noob help please

The panel Im looking at is 1640 x 1000 cm its 300 watt around 32 volts from memory
Its the exact size Im looking for. Its probably not as marine friendly as some but I think it will do for now LG Mono X neon 300 watt
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