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Old 28-04-2015, 16:06   #16
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Re: Assorted solar panels 20w to 110w

When you wire dissimilar panels in a series array, add the voltage to determine combined voltage of panels wired together. The amperage in series wired panels is limited by the smallest wattage panel.

When you wire dissimilar panels in parallel array you will be constrained by the lowest voltage panel in the string. The amperage in the string is added.

To optimize mixed panels have matched sets on their own charge controllers. The most efficient regulators use the MPPT algorithm.
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Old 28-04-2015, 21:53   #17
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Re: Assorted solar panels 20w to 110w

After spending thousands to install a stern arch that can safely hold 100 lbs of bargain solar panels designed for rooftops, a mast can still shade the panels, making a 300 watt panel a 30 watt panel.
The OP's collection of panels in parallel is best.

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This is what I would do. I would sell that random collection of solar panel on CL for $1.50 per watt, price in a little haggle room so they knocked off a few bucks but you end up at $1.50 per watt per panel. That will net me about $625.

I'd buy 2 x 300 watt panels and mount them on an arch on the stern, away from any shade.I've been buying new panels for as low as 60 cents/watt lately, but let's assume you end up paying 75 cents/watt, so the 2 panels cost you $450, plus tax. Then I'd buy 2 20 amp MPPT controllers for $100 ea and connect each panel to it's own controller. After $625 from the solar panels and about $680 spent on new panels and controllers (plus whatever for cabling, which you'll save a ton on not stringing a bunch of random panels together) you'll be way ahead for just a few $$.

You'll get double the output (very close to 40 amps under ideal conditions), no shading, and it won't look like a hodge podge of "stuff" on your boat, which will help with resale value in the end.
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Old 28-04-2015, 22:03   #18
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Re: Assorted solar panels 20w to 110w

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My understanding is that you should only wire 2 panels in parallel with one controller for each pair of panels. So 6 panels should have 3 controllers. If you have say 6 panels with one controller, the 5 in the sun can damage the one in the shade. That from a solar company web site. It's also the way I've wired my boat. My 2 Optima AGM house batteries are still going strong after 12 years. The Optima starting battery lasted 10.
2 or more controllers can connect to one battery if you want.
If you install bypass diodes to the panels (or buy ones with them) you won't "harm" any other panels. In parallel, as stated above, the shaded panels drops amp for volts, but does not affect the others in the string.

This is the best setup for a sailboat with constant shading from rigging, masts, and booms.

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Old 28-04-2015, 23:16   #19
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Re: Assorted solar panels 20w to 110w

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If you install bypass diodes to the panels (or buy ones with them) you won't "harm" any other panels. In parallel, as stated above, the shaded panels drops amp for volts, but does not affect the others in the string.

This is the best setup for a sailboat with constant shading from rigging, masts, and booms.

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Most panels have built in bypass diodes

And to the guy recommending 2 300 watt panels I would rather have 4 100 watt panels which in the course of a coup,e days will actually produce more use able power due to only loosing at the most 100 watts at a time from shading verses 300 watts at a time with your bugger panels
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Old 29-04-2015, 02:25   #20
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Re: Assorted solar panels 20w to 110w

For those of you who missed it somehow, I specifically stated "away from any shading."

You guys really can't mount those far enough aft so as to prevent shading? Whether you've got a mishmash of 20 watt panels, 4 100 watt panels or 2 300 watt panels, if you're getting shade on your panels you're still wasting your time and money.

As far as those micro MPPT controllers go, I'm not about to spend another $150 for a solution in search of a problem. Buy 300w panels with an MPPT controller per panel and you already have a dedicated MPPT controller per panel.

Let's say you buy a bunch of little panels and you mount them... next to each other, in a row, obviously. Each one has it's little microMPPT hooked up feeding 24v down to the master controller. Why? To maximize power out when shaded. Except where does your shade come from? The boom? Mast? Sail? All linear sources of shade, meaning if it's shading one panel, it's probably shading them all. Even if the shadow only crosses half of each mini panel, you're getting virtually zero output. Looking at cockpit roofs, salon roofs, biminis, etc, the shadow is always going to fall essentially fore/aft, the only question is, how far from centerline are your panels mounted, and how far the shadow is from centerline. The problem is bad enough that I wouldn't bother mounting fixed panels on any roof or bimini.

I wouldn't pull out my drill for 100w panels, much less 20w panels. The rewards aren't anywhere close to the effort. It takes an equal amount of effort and cable to wire up a 20w panel as a 300w panel, with the possible downside that unless you use a nice fat cable, your voltage drop could very well put a serious dent in what little power the 20w panel put out.
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Old 29-04-2015, 06:02   #21
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Re: Assorted solar panels 20w to 110w

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As far as I can find from master volt no it is a pwm controller

SCM40 | Mastervolt Marine

Here is a reasonably good unit at a reasonable price from an american company

Amazon.com: Renogy® Tracer 4210 40 Amp MPPT Charge Controller 12/24V 100VDC Input: Patio, Lawn & Garden

My Tracer charge controller is made in China. Amazon is an American company. Not sure what you were trying to say.


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Old 29-04-2015, 06:28   #22
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Re: Assorted solar panels 20w to 110w

Most cruisers buy solar panels on the basis of dollars per watt. Unfortunately we are not interested in watts at “solar noon” but rather watt hours per day. The solar noon rating assumes 1000 watts per square meter irradiance @ 25 degreeC. Poly-crystalline panels typically are 14-15% efficient and will loose the majority of out-put with a 3” hard shadow across cell rows. Mono-crystalline panels are typically 19-20% efficient and average about a 45% loss with a hard shadow across cell rows. Maxion Cells (mnfd by SunPower) are over 20% efficient and loose less than 7% with a 3” hard shadow in any direction. High efficiency panel surface area can be reduced by over 40% and still provide the same level of daily production performance as a Poly. Panel value is a function of daily production by the square footage required, not solar noon rating. Always ask for the efficiency rating.
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Old 29-04-2015, 07:50   #23
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Re: Assorted solar panels 20w to 110w

Bob, your point about managing to fit in more watts with more efficient panels is well made, although with very large panels like the Sunpower series their sheer size can make it difficult to use all the available space in some installations.

I am surprised by the differences in shade tolerance you quote, particularly the 7% for the Sunpower panels. Perhaps it was a faint shadow? Do you have a reference for this?

Sunpower panels consist of 96 separate panels in a 12x8 configuration. A 3 inch shadow lengthwise will effect 12 cells or 8%. A diagonal shadow will be worse.

The real problem is shaded cells represent a high resistance which affects the output from other cells linked in series that are not covered by a bypass diode. This will increase the impact of the shading enormously , but even if we look at the actual cells affected by the shadow it will be over 7% which makes the number very hard to understand.
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Old 29-04-2015, 08:06   #24
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Re: Assorted solar panels 20w to 110w

My lil 2 x100 watt windy nation panels with cheap Chinese pwm controller always has my battery bank fully charged by solar noon they are mounted on either side of the boom on the hard dodger got less $ invested than some of the panels others say you need and less than the mppt controller some say you need partial shading from about 4 pm PST lowers my output from 10 amps to about 6 amps I have a no shade window of about 6 hours and a partial shade of about 4 hrs on either side of that so in my 12- 14 hours of total output we get about 70 to somewhere just over 100 ah input per day I run the fridge and water maker in the afternoon once the batteries are full haven't needed any other charging source since install in February.
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Old 29-04-2015, 08:21   #25
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Re: Assorted solar panels 20w to 110w

We did our own testing to confirm other independent tests for land based applications Kyocera, Solarworld, Mage and SunPower. Steve Dashew has also done extensive testing for his FPB boat line, which he now builds with arrays recessed in the decks. The "shadow" was a 3" wide piece of 1/4" ply laid directly on the panels. Several companies incorporate Maxeon Cell "seconds" purchased from SunPower with similar efficiencies. On applications where space is limited and daily shadow events are normal mono-crystalline panels will always be the best watt-hour/sqr ft/dollar value, especially panels with Maxeon cells. Much of the performance gain is from the conductors being a copper printed circuit board with a matrix of conductors on the back of the cell rather than the traditional strip across the face.
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Old 29-04-2015, 09:11   #26
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Re: Assorted solar panels 20w to 110w

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We did our own testing to confirm other independent tests for land based applications Kyocera, Solarworld, Mage and SunPower. Steve Dashew has also done extensive testing for his FPB boat line, which he now builds with arrays recessed in the decks. The "shadow" was a 3" wide piece of 1/4" ply laid directly on the panels. Several companies incorporate Maxeon Cell "seconds" purchased from SunPower with similar efficiencies. On applications where space is limited and daily shadow events are normal mono-crystalline panels will always be the best watt-hour/sqr ft/dollar value, especially panels with Maxeon cells. Much of the performance gain is from the conductors being a copper printed circuit board with a matrix of conductors on the back of the cell rather than the traditional strip across the face.
Bob welcome may i ask a question. your posts here and on another thread on refrigeration are very good and spot on it seems so my question is what service provider do you represent?
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Old 29-04-2015, 09:15   #27
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Re: Assorted solar panels 20w to 110w

Bob, I must be misunderstanding something. A 3 inch wide strip covers up more than 7% of the surface area of the panel. Plywood would block virtually all the light.

A solar cell that is in shadow develops a very high resistance. This means the output of cells connected in series with the shaded cell (and not covered by a bypass diode) are affected as well. Thus the output is reduced far more than the percentage area of shadow would indicate. This has been one of the fundamental problems that has influenced solar output on boats.

If I understand correctly with Sunpower panels you have measured the loss to less than the area of panel that has been covered .
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Old 29-04-2015, 09:49   #28
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Re: Assorted solar panels 20w to 110w

The cells are 5" wide, the hard "shadow" is 3". I appreciate your skepticism, there should be a lot more of it in our industry, that's why we do empirical testing. I'm not qualified to provide you with an academic response, only that the 2" cell surface remaining beyond the shadow still has wattage to contribute. The unique difference being the printed copper circuit board conductor laminated under the cell. Sorry to be short, need to get back to work.
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Old 29-04-2015, 10:22   #29
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Re: Assorted solar panels 20w to 110w

I've always liked Sunpower for their efficiency, but I had no idea that they had superior performance while partially shaded. Even more reason to go with a larger, higher quality panel.
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Old 29-04-2015, 11:48   #30
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Re: Assorted solar panels 20w to 110w

There are many applications where one SunPower 250 watt panel at 61.4" x 31.4" won't fit, but certainly doesn't make sense to use the much cheaper Kyocera 245 at 65.4" x 39" when it's production per day, shadowing aside, is going to have at least 2 hours per day more production. On the other hand, Kyocera is a well made poly-crystalline panel that has withstood the test of time and is one of the few companies manufacturing narrower panels (KD140 watt 59.1" x 26.3"). Many monohulls are constrained by dimensional issues and do not have the option for higher efficiency panels. The "roof top" industry is what drives this market, at least we get the benefit of economy of scale, 20 years ago we were paying 3 times the cost per solar watt/hour.
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