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steve-b

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Joined: 07/09/2011
Location: Canada
Posts: 11

Posted: 02:00am 21 Nov 2011

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I am going to make a new solar panel from 54 6x6 polies.
The voltage will end up being 27volts.

Is this OK for charging a 12v battery?
I'm thinking that 27v is not enough for a 24v battery???

Thanks,

Steve.

yahoo2

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Joined: 05/04/2011
Location: Australia
Posts: 1166

Posted: 08:42am 21 Nov 2011

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Hi steve,
there is not a lot of solar stuff going on on the forum at the moment, it would be great if you could post a few details as you go along. lot of people have tried home made panels with mixed results.
have you read the oztules home made panels blog on the projects page, the original of this is on fieldlines.com and is starting to get a few posts of others having a go. If you read oztules stuff you will see that the limiting factor is finding sheets of tempered low iron glass that will fit what you want to make. Once it has been toughened it cant be cut.

VOLTAGE
A panel of any voltage can be hooked to a battery if the panel voltage is lower than the battery voltage (like it could be on a hot day, cloudy day,morning, dirty panel etc)it wont charge and if is a higher voltage then the battery's internal resistance will hold the voltage at whatever the battery voltage is, at that state of charge. so for a 12volt wet lead acid battery it could be between 11.5 volts and 14.8 volts 15.5 at the most. Any power that the panel is capable of producing at a higher voltage eg 27 Volts is lost.

Fortunately the world has moved on from the old days and some smart young whipper snapper invented the Maximum Power Point Tracking controller (MPPT)these hold the panels at the point it produces its maximum amps and feeds the battery a lower voltage. So now we only have to fit panels or banks of panels that match the maximum volts and amps of the controller.Most commercial panel manufacturers produce a spec sheet with graphs and details showing the max power voltage and all the other relevent stuff. Nominal Operating Cell Temperature, etc.

Now some braniacs have improved that again and there are MPPT controllers that can reduce much higher voltages with minimal losses, have a snoop around morningstars website and have a play with the panel string calculator using their tristar MPPT 45 and you will get the idea.

I have never done it myself but I imaging it will involve a lot of practice, skill and perseverance to produce a good panel. I'm thinking it would pay to buy way more than you need and sort them by quality and use the poor one to practice with.

cheers Yahoo

I'm confused, no wait... maybe I'm not...

steve-b

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Joined: 07/09/2011
Location: Canada
Posts: 11

Posted: 07:50pm 21 Nov 2011

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Thanks for the info.

I have read the page you are referring to, and have put it to practice on a couple of smaller panels i have built in the past... works great.
I will have to look into a MPPT charge controller. The controller im using now is a home built 555 based controller. I found the circuit diagram for this controller on this site.http://www.mdpub.com/Wind_Turbine/
As far as glass goes, My uncle owns a glass, and mirror business in my city. I get it very cheap through him.
The panels i will be doing this time are using 6x6 cells 46 of them to give me 185 watts, and 23 volts. I was going to do 54 cells, but if its going to be wasted, then...

Just wondering how you pasted the links in your reply?
When i try to do it, it doesn't seem to work. I don't see an "attachment" or anything on this page to help me.

Thanks again for the prompt reply.

Steve.

yahoo2

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Joined: 05/04/2011
Location: Australia
Posts: 1166

Posted: 12:00am 22 Nov 2011

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POSTING A LINK
its this button in the reply box toolbar

it starts some javascript, that opens a box to type the words that go in the post, then press OK. the next box is to paste the link. the only trick is it needs the HTTP bit on the front. take notice of the link you copy, if it's there, just paste over the top of the one in the box, if it's not hit the right arrow key to unhighlight it and get the cursor then paste.

If the glass is not low iron there is some loss to factor in possibly dropping the voltage, if you look at the edge low iron will have a clear tint, not green, on a thicker piece of glass its easy to see, I guess you know that having relatives in the biz.

Anything that is wired in series will have a restriction around the weakest cell which will derate that string. If it is bad, it will heat the previous cell in line and that further derates it. Can be a real problem in hot climates with long strings of grid tied panels.

Quote 6x6 cells 46 of them to give me 185 watts, and 23 volts.

Is this a typo? more likely nine cells by five strings = 45 cells. Is that open circuit volts?

I guess that will give you a Pmax voltage of less than 18 volts at 1000 watts/square metre of sunshine, then the question is how much sun do I need to stay above the battery voltage? If you live in a spot where the clouds brew up in the early afternoon??

??

there are voltage boosting controllers around, I don't know the limits of these things,bit hard to comment on them.

I watched a bloke trying to get the wax off some untabbed cells a few years ago, that was enough to put me off the whole idea.

Yahoo

I'm confused, no wait... maybe I'm not...

steve-b

Newbie

Joined: 07/09/2011
Location: Canada
Posts: 11

Posted: 02:04am 22 Nov 2011

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The cells are pre-tabbed. Their is no wax on them
I meant to type 48 cells... 6 rows of 8. This will give me 185 watts ,24 volts.

I was going to do a 54 cell panel. This is the maximum amount that will fit in the frames i have. This will give me around 213 watts, and 27 volts.
Im new to this as you probably have guessed by now. Im not sure how i should wire the panels together when im finished them...series, or parallel.
I want to run a 24 volt battery charging system, so i will need to join at least two of them in series. I will have 4 in total, again im just not sure if i should go for the 185, or 213 watt???
I am going to buy a MPPT controller (60 amp).
I can use the controller i made for my wind turbine.
555 controller

Hey it worked.

Thanks.Edited by steve-b 2011-11-23

neil0mac
Senior Member

Joined: 26/12/2009
Location: Australia
Posts: 210

Posted: 02:58am 22 Nov 2011

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yahoo2 said

If the glass is not low iron there is some loss to factor in possibly dropping the voltage, if you look at the edge low iron will have a clear tint, not green, on a thicker piece of glass its easy to see,

Question on the 'clear tint'. Is the colour of the glass a only a problem if the rays are not striking it square to the surface, but all the light will pass through otherwise? If so, what is the critical angle of incidence?

yahoo2

Guru

Joined: 05/04/2011
Location: Australia
Posts: 1166

Posted: 09:04am 27 Nov 2011

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Steve, what you decide is ultimately your call, while the mathematics may be black and white, setting up a solar array is always a juggling act to find a solution that will produce power under a wide variety of conditions for a large number of years. Most installers and owners don't expect to change inverters or charge controllers or rewire the panel strings to raise the voltage as panels degrade, so margin for error in these systems is the name of the game. The best setups are built by people with an eye for detail for both equipment and location. I don't know enough about what you are doing to make any recommendation.

neil0mac said Is the colour of the glass a only a problem if the rays are not striking it square to the surface?

Iron Oxide is an impurity in the calcium carbonate and sodium carbonate supplies used to make glass and it is quite good at absorbing light at the lower end of the spectrum, all that is happening when you look at the edge of the sheet is you are looking through a longer column of glass that means more iron oxide in the light path.

The average yum cha solar cell can only lever an electron loose with 600 nM (orange) to 900 nM (very dark red) light and that is right in the range of what the iron ion is blocking,a bit like titanium oxide does with UV light in sunscreen.More expensive high tech cells are doped or seeded with atoms like gallium that assist shorter wavelengths of light to eject the electrons. I believe low Iron glass is made from remelted offcuts and the iron is chemically replaced with a more reactive less light absorbing metal oxide.

The angle of incidence reflection/refraction thing works with a change in glass density. Optical fiber works on this principal. AFAIK the angle between air and glass where there is an increasingly rapid drop in lower spectrum light transmission due to misalignment is from 20 degrees (-4%) to 50 degrees (-40%)????

cheers Yahoo
No hex fee for the physics lesson

edit: grammar
Edited by yahoo2 2011-11-28

I'm confused, no wait... maybe I'm not...

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