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Old 03-12-2012, 13:28   #16
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Re: Solar panels - Large or Small?

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Originally Posted by SURV69 View Post
If I remember right newer solar panels(depending on type), are much more forgiving about shade.
Solar panels have not improved much in terms of their shade tolerance. Most panels of the same type are fairly similar, but the number of bypass diodes does make a slight differance. The better panels have 8 or so.
There are also some difference with temperature tolerance etc comparing the NOC wattage of different panels rather than the STC wattage can be useful as the NOC data is collected under more realistic conditions.
Amorphous panels are quite a bit mode shade tolerant than other types, but need to be much larger for the same output.


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I'm even considering very small panels(5 watts or so), to be dedicated to recharging d, c, AA, AAA and small(6-7ah), batteries for inside LED lighting.
This will be less efficient than connecting the panel to the normal house bank and using a 12v battery charger. The good battery chargers are very efficient and models are available that will charge almost any battery from a single AAA to an 18v lithium battery.
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Old 03-12-2012, 16:33   #17
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Re: Solar panels - Large or Small?

The smaller 5 watt panels are portable, while the larger more permanently attached panels are not.

This means that for certain things(such as charging small batteries and such), the small panels can easily be moved to the best location(for the sun), while the permanently attached panels might be "stuck" in the shade for one reason or another.

The 5 watt units can even be used on a dinghy or on shore . . . easily.
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Old 03-12-2012, 17:22   #18
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Re: Solar panels - Large or Small?

I have the newer type of panels, and partial shade is still problematic.

I like system redundancy, and therefore opted for two 130-watt panels rather than a single large one. There's a gull in my neighborhood who opens mussels by dropping them on hard objects. Some day he'll drop one on a solar panel. If it's my panel he experiments with, I'd just as soon he break a smaller one.
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Old 03-12-2012, 18:21   #19
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Re: Solar panels - Large or Small?

The higher voltage panels with mppt makes the beat combo imo in reducing the effects of partial shading.
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Old 03-12-2012, 19:07   #20
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Re: Solar panels - Large or Small?

This is a no brainer...go with the higher voltage, actually the higher the voltage the better with an mppt controller. I have 36 volt panels and with the mppt contoller the amperage to my house bank is doubled almost always!!!!!!! I have seen up to 35 amps out to the bank from two panels that are rated at a max of 8 amps each into the controller.
In summarry from my experience and real life results: High voltage equals higher amperage with mppt charge controller which equals higher efficiency.
Go for the biggest panels with the highest voltage that you can fit on your boat. You will not regret it. If you would like to discuss further send me an email.
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Old 03-12-2012, 19:30   #21
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Re: Solar panels - Large or Small?

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This is a no brainer...go with the higher voltage, actually the higher the voltage the better with an mppt controller.
The effeciency is almost the same, but for most controllers it drops off slightly as the panel voltage rises significantly above the battery voltage.

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I have 36 volt panels and with the mppt contoller the amperage to my house bank is doubled almost always!!!!!!!
As it should be.
If the voltage conversion was 100% efficient a panel operating at 36v should put in 2.5 x current into a battery at 14v. The gain sould be higher still at lower battery voltages.
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Old 04-12-2012, 06:38   #22
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Re: Solar panels - Large or Small?

Based on past threads I thought there would be more input for this question.

Does the higher voltage of the larger panel really make much difference as to maintaining performance when shaded? Seems I've read that the shading performance really comes down to the percentage of the panel that gets shaded and it effects the panel output as a percentage of rating. Wouldn't that hold just as much regardless of the voltage (assuming the output voltage is still above battery voltage)?
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Old 04-12-2012, 11:28   #23
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Re: Solar panels - Large or Small?

Don, as I understand it the physical array in the panel will make a difference in shade tolerance, and that array is partly constrained by the voltage choice.

Let's say you have two columns of actual cells in the panel, each column producing "12" volts at ten amps. The panel is either going to be wired with the two columns in series, or in parallel. If they are wired in series, the panel produces 24v@10A, but if the are in parallel the "same" panel produces 12v@20A.

Now the question is, what happens when a shadow falls across any cell(s) in JUST ONE COLUMN? If the two columns were wired as one 24v array, you just lost the entire output. If the two columns are wired as 2x12v arrays, the one in shadow goes offline, but the other column keeps producing. (Assuming there is a blocking diode, so the one can't pull down the other.)

Now in a real panel of larger wattage, there may be three, four, six strings of cells. Again, if they are in parallel, and there are blocking diodes, you only lose the string that has a shadow across it. Where a higher-voltage panel is going to have more cells in series, so any shadow area is going to kill more of the whole panel.

Just a thought, and AFAIK it depends on the physical layout and the presence of diodes, which may or may not be used in different panels. And if there's a mighty oak that sahdows the entire panel every afternoon..."nevermind".
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Old 04-12-2012, 12:48   #24
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Re: Solar panels - Large or Small?

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Don, as I understand it the physical array in the panel will make a difference in shade tolerance, and that array is partly constrained by the voltage choice.

That makes sense, thanks for powering the light bulb in my head
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Old 04-12-2012, 13:35   #25
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Re: Solar panels - Large or Small?

Calder and Bruce Schwab recently did some testing and found 24 volt panels to be more shade tolerant even factoring the need to then convert. I personally have used 4 19V panels of around 70 watts each with great success on two different boats. I doubt I will buy anything larger than maybe 90 watts panels for my new boat.
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Old 04-12-2012, 15:38   #26
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Re: Solar panels - Large or Small?

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I'm using Motec 240's and the Midnite Solar MPPT. The controller is head,shoulders, and even a couple more inches over the others ie Morningstar, Xantrex, etc.
I can get Midnites for 625+ shipping. Can also get pv panels for around 1.12 a watt.
Where do you find space for all that on the boat you've listed on your avatar?
BTW, I purchased a Midnite Solar 150 for my home's solar array for $608.95 here:

MPPT Solar Charge Controllers from Outback, Apollo, Morningstar, Solar Boost, BZ - Midnite Solar MPPT Charge Controller CLASSIC 150

They know their stuff, too.
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Old 05-12-2012, 09:28   #27
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Re: Solar panels - Large or Small?

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Originally Posted by senormechanico View Post
Where do you find space for all that on the boat you've listed on your avatar?
BTW, I purchased a Midnite Solar 150 for my home's solar array for $608.95 here:

MPPT Solar Charge Controllers from Outback, Apollo, Morningstar, Solar Boost, BZ - Midnite Solar MPPT Charge Controller CLASSIC 150

They know their stuff, too.
Panels are GOING to be mounted on the stern , custom davit type solution. Working on that right now with my bro-in-law. Ok, just beat my source up, 150's for 605.00 only for Sailneters though! (like anyone else reads this)

Anyone whos interested in the Midnite:
The instructions are very straight forward and will teach you a lot. Download the pdf. This device is really cool especially with the two sets of auxiliary contacts that can be used for virtually limitless things, like hot water elements, laptop charging, etc, etc.
This thing is unlike anything else on the market , xantrex, morningstar, outback.
Every aspect of the charge cycle can be adapted and set for whatever chemistry battery you're using.
You don't have to buy an extra display just to have one, and can have a remote display on any computer.
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Old 05-12-2012, 10:28   #28
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Re: Solar panels - Large or Small?

Being engineringish, I went with two 12V panels. I decided that a single panel did not give enough redundancy. Plus using 12V (well 17V) panels allows me to hard wire them when (not if) the controller fails. and still get full amps.

Shadows on the panels will drastically reduce charge current.

Solar Blvd [url=http://www.solarblvd.com/]/url] Has good prices on panels, Their Solar Cynergy panels are about equal to the KYOCERA. I've one of each and and only difference is the frame gauge on the solar cynery panel is a little lighter. Both are marina rated.
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Old 05-12-2012, 11:14   #29
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Re: Solar panels - Large or Small?

" Plus using 12V (well 17V) panels allows me to hard wire them when (not if) the controller fails. and still get full amps."

Nothing beats redundancy.<G>

Seriously though, I like the idea. I've seen too many silicon critters go belly-up when you need them and expect all the MPPT controllers will spontaneously combust when the Mayan calender ends [sic] or find some other way to make life inconvenient at some point.
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Old 05-12-2012, 12:31   #30
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Re: Solar panels - Large or Small?

I actually put a bypass switch on the wiring to bypass the controller. It also is useful when using the SSB to cut down on RF noise. Plus its a poor girls battery equalizer
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