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Old 25-04-2011, 16:38   #1
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Four Solar Panels - Parallel , Series or Series-Parallel

Hi

Installing 4 x kyocera 85W panels (chose this arrangement due to space availability consideration which would not easily accommodative two larger panels). They will not likely all be seeing the same solar irradiance at the same time. I have chosen not to install them on adjustable mounts and accept the reduced power output.

Using them with Blue Sky Solar Boost 3024 MPPT charge controller with Max input voltage 57V and max 12V current 40 Amps.

the panels have built in blocking diodes. There is about 10 feet of AWG 10 Ga wire from the terminal box to the battery compartment.

Three options for connecting:

1. four in parallel - does not take full advantage of MPPT.
2. four in series - less voltage drop given the lower current in series (likely negligible given the large gauge and relatively short distance i'm using). I wonder about the effects of shading on this arrangement as well. also, i wonder whether this approaches the input-side limit of the charge controller (57V, though it states preferred is 45 V)
3. series-parallel: two pairs of two in series then connected in parallel for a nominal 24V input-side configuration. also uncertain about the effects of shading on this arrangement.

any experience or insightful comments, particularly on problems if one or two panels are shaded, greatly appreciated.

cheers
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Old 25-04-2011, 17:16   #2
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Re: 4 solar panels: parallel, series, or series-parallel

It depends on the chances of shading which on a boat, are usually great.
I'd go with all parallel connections and thick feed wiring.
With a series or series/parallel, you have only slightly more than half output if only ONE panel is shaded, but with parallel, you would have a little more than 3/4 output.

BTW. I love my Bluesky 2512iX MPPT controller.
The only downside is the RF interference on 770khz.
Whenever there's any load, I can't listen to my favorite AM station.
The Bluesky guy kinda shook his head after I listed all my RFI killing attempts.
He agreed it was probably fruitless to try anything more outside of building a Faraday cage for the controller.
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Old 25-04-2011, 17:39   #3
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Re: 4 solar panels: parallel, series, or series-parallel

A clarification about solar panel diodes... If panels have factory installed "By-pass diodes", they should not be confused with "blocking diodes", like the Schottky diodes that I put in my + wire, along with a fuse, at each panel. The By-pass diodes serve to prevent back flow within the panel, not from one panel to another. You may need to call the manufacturer to know what the function of the panel's diode really is. In my case I choose to add blocking diodes, (to panels already equipped with by-pass diodes), in spite of a small V loss, because my panels were far apart, and it is often true than one is shaded when others are not. In my application, I felt this was a good trade off.
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Old 25-04-2011, 17:55   #4
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Re: 4 solar panels: parallel, series, or series-parallel

Quote:
Originally Posted by west coaster View Post
Hi

Installing 4 x kyocera 85W panels (chose this arrangement due to space availability consideration which would not easily accommodative two larger panels). They will not likely all be seeing the same solar irradiance at the same time. I have chosen not to install them on adjustable mounts and accept the reduced power output.

Using them with Blue Sky Solar Boost 3024 MPPT charge controller with Max input voltage 57V and max 12V current 40 Amps.

the panels have built in blocking diodes. There is about 10 feet of AWG 10 Ga wire from the terminal box to the battery compartment.

Three options for connecting:

1. four in parallel - does not take full advantage of MPPT.
2. four in series - less voltage drop given the lower current in series (likely negligible given the large gauge and relatively short distance i'm using). I wonder about the effects of shading on this arrangement as well. also, i wonder whether this approaches the input-side limit of the charge controller (57V, though it states preferred is 45 V)
3. series-parallel: two pairs of two in series then connected in parallel for a nominal 24V input-side configuration. also uncertain about the effects of shading on this arrangement.

any experience or insightful comments, particularly on problems if one or two panels are shaded, greatly appreciated.

cheers
I'm sure you know that they actually put out >20v each, open circuit. I wonder if there might be circumstances (manual cut-off through the controller) that would put you at 80v if in series. Seems like courting trouble.

So option 3 is interesting.

I just wired up a pair (2 x 80w) today in parallel, so you have me thinking. I need only move a few connections to make the change--no wire-pulling.
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Old 25-04-2011, 18:26   #5
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Re: 4 solar panels: parallel, series, or series-parallel

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Originally Posted by thinwater View Post
I'm sure you know that they actually put out >20v each, open circuit. I wonder if there might be circumstances (manual cut-off through the controller) that would put you at 80v if in series. Seems like courting trouble.

So option 3 is interesting.

I just wired up a pair (2 x 80w) today in parallel, so you have me thinking. I need only move a few connections to make the change--no wire-pulling.
Yes, and also interesting is I understand the panels are wattage rated at the output voltage cabability times the output current. So if the output volts is say 22 for discussion, the current for 85 watts is 85/22 = 3.8 amperes. Now reference that 3.8 ampere to the 12 v battery voltage and the delivered wattage is now 12 times 3.8 = 46 watts. Far below the expected 85. Where does the lost wattage go??? Into the regulator as wasted heat.

Foggy
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Old 25-04-2011, 18:34   #6
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Re: 4 solar panels: parallel, series, or series-parallel

series connection is better. Check the specs or call support to find out the absolute maximum voltage allowed. If calling them, explain them your open circuit voltage (find the specs for your panels).

foggysail: time for you to start reading some MPPT controller info. There's good threads right here on CF.

ciao!
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Old 25-04-2011, 19:10   #7
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Re: 4 solar panels: parallel, series, or series-parallel

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Originally Posted by foggysail View Post
Yes, and also interesting is I understand the panels are wattage rated at the output voltage cabability times the output current. So if the output volts is say 22 for discussion, the current for 85 watts is 85/22 = 3.8 amperes. Now reference that 3.8 ampere to the 12 v battery voltage and the delivered wattage is now 12 times 3.8 = 46 watts. Far below the expected 85. Where does the lost wattage go??? Into the regulator as wasted heat.

Foggy
Another loss is battery histeresis; you charge at 14.3v and then discharge at 12.5v (these numbers vary). Also, the rated amperage for an 85w panel is probably ~4.8 amps when charging at ~ 14.4v, or about 70w.

I've always found amps easier to track than watts; the voltage can vary for many reasons, but the number of electrons tends to be a bit more consistant (one in, one out). Perhaps it is easier to consider that an 85w panel is about ~4.5 * 5 = 22.5 AH.
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Old 25-04-2011, 19:10   #8
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Re: 4 solar panels: parallel, series, or series-parallel

Just installed four Kyocera KD185GX-LPU 185 Watt panels. They are wired two series pairs in parallel for 48 volt system. Outback Power FM60 mppt for charge controller. 48 volts keeps them well above battery voltage (even in low light) as the outback is buck only, but not to high as to be less efficient.

46.6 amps midday here in Jacksonville! Yes!

Sv Hold Fast
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Old 25-04-2011, 20:09   #9
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Re: 4 solar panels: parallel, series, or series-parallel

foggy-
"Where does the lost wattage go??? Into the regulator as wasted heat."
Probably not. There are two considerations. If you are using an old fashioned regulator, then yes, it cuts the voltage down and wastes the excess power as heat. If you are using a newfangled MPPT controller, the controller presents the solar panels with a matched output, so the panels keep producing maximum power at maximum voltage and amperage, and there is very little waste. Instead of dumping excess voltage, it uses dc-to-dc conversion to change the excess voltage into extra amperage, resulting in a power loss of typically less than 5%.
This is one reason we measure power (watts) instead of voltage or amperage. The power level can be maintained, when amperage or voltage cannot be. The difference between physics and magic, is that physicists rarely have gorgeous assistants in sequins and tights.
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Old 26-04-2011, 00:21   #10
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Re: 4 solar panels: parallel, series, or series-parallel

Quote:
Originally Posted by west coaster View Post
Hi

Installing 4 x kyocera 85W panels (chose this arrangement due to space availability consideration which would not easily accommodative two larger panels). They will not likely all be seeing the same solar irradiance at the same time. I have chosen not to install them on adjustable mounts and accept the reduced power output.

Using them with Blue Sky Solar Boost 3024 MPPT charge controller with Max input voltage 57V and max 12V current 40 Amps.

the panels have built in blocking diodes. There is about 10 feet of AWG 10 Ga wire from the terminal box to the battery compartment.

Three options for connecting:

1. four in parallel - does not take full advantage of MPPT.
2. four in series - less voltage drop given the lower current in series (likely negligible given the large gauge and relatively short distance i'm using). I wonder about the effects of shading on this arrangement as well. also, i wonder whether this approaches the input-side limit of the charge controller (57V, though it states preferred is 45 V)
3. series-parallel: two pairs of two in series then connected in parallel for a nominal 24V input-side configuration. also uncertain about the effects of shading on this arrangement.

any experience or insightful comments, particularly on problems if one or two panels are shaded, greatly appreciated.

cheers
Definatly not 2, but option 1 and 3 will be close.
I think you will find 1 is best in your instalation.
If you do go with option 3 try to join the panels that will most likely see the same conditions.
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Old 26-04-2011, 19:20   #11
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Re: 4 solar panels: parallel, series, or series-parallel

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Originally Posted by foggysail View Post
Yes, and also interesting is I understand the panels are wattage rated at the output voltage cabability times the output current. So if the output volts is say 22 for discussion, the current for 85 watts is 85/22 = 3.8 amperes. Now reference that 3.8 ampere to the 12 v battery voltage and the delivered wattage is now 12 times 3.8 = 46 watts. Far below the expected 85. Where does the lost wattage go??? Into the regulator as wasted heat.

Foggy

I am adding a correction to my post of yesterday because there were questions regarding power losses made by a couple of members. The regulator may or may not dissipate large sums of power. One should understand what it is they are purchasing and ask about total efficiencies.

In my opening statement I started with " is I understand the ". Well l want to jump to regulators and again, I will caution that I am not expert in solar although I do have a professional background dealing in electrical circuits.

There are generally speaking two basic types of DC voltage regulators; the first is the older series regulator....and for that matter, it is a less expensive regulator. Series regualtors essentially act like variable resistors so the the voltage output remains constant a a predetermined level. The second style is the so called switch mode. Switch modes are currenlty designed using pulse width modulation and also flybacks combined with pulse width modulation

A switch mode regulator chops the voltage so that it can be passed through a transformer, rectified and regulated. This stye is very efficient except at low voltages because the power semiconductors have their own voltage drops that consume energy. But efficiencies of over 80% should be expected in the 12v range. The circuit's transformer can be designed to any voltage range so it is easy to match a high to a low or a low to a high voltage. The way regulation is maintained is usually done by varying the pulse width but I think a deeper technical discussion is inappropiate. Most folks only want to know "does it work?" not "how does it work?"

NOw of course there are other voltage regulation schemes but those are beyond the level our descussion.

I hope this post clarifies my post made yesterday.

Foggy
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Old 26-04-2011, 19:24   #12
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Re: 4 solar panels: parallel, series, or series-parallel

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foggy-
". The difference between physics and magic, is that physicists rarely have gorgeous assistants in sequins and tights.

GEEZ, I love that line!!!! OH--- and neither do electrical engineers.

Foggy
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Old 26-04-2011, 19:54   #13
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It's amazing how much confusion exists here. The first point about photovoltaics is that unlike many power sources they have a non linear power curve for a given sunlight.

Hence the voltage current relationship is not linear across the range of panel voltages ( unlike a good battery for example). Hence specified at max power output doesn't mean that the panel produces that power at a lower voltage.

A 100 watt panel at 20 will be specified as producing 5 amps. It's doesn't not mean at a less optimum voltage oh say 10 v the panel under the same sunlight will produce 10 amps. The curve isn't linear .

That's why MPPT was invented to optimise the maximum point on the VI curve for a panel.

Mppt is a impedance matching process in effect. It's most easily achieved by using a switch mode buck or buck/ boost psu .

Of course mppt is only useful if you battery can accept the power the panel produces at the mppt point

Solar panels cannot be rated in AH the term is meaningless for a panel .

Dave
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Old 27-04-2011, 03:53   #14
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Re: 4 Solar Panels: Parallel, Series, or Series-Parallel

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It's amazing how much confusion exists here.
Indeed... I gave up. People don't know MPPT but post wrong info anyway, completely ignoring MPPT principles and our comments to read & learn, while showing they indeed don't know how these controllers work.

Also, how can anyone advise parallel panels? Is it better to waste energy?!

cheers,
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Old 27-04-2011, 10:20   #15
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Re: 4 Solar Panels: Parallel, Series, or Series-Parallel

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Also, how can anyone advise parallel panels? Is it better to waste energy?!
No its not better to waste energy we are trying to get the most efficient system for the OP.

Nick the problem with any series connection of solar panels is that a well shaded solar cell will conduct no current. It doesn’t matter how many cells downstream are producing loads of power, or if you have a MPPT regulator, one cell connected to another in series that’s deeply shaded means there is no power produced.
To help compensate solar panels have bypass diodes that effectively divide the panel into different sub panels and full shade is rare, but there are major power reductions in series connections, if one panel is shaded. MPPT does not fix the high resistance in a completely shaded panel.
Low current is low current MPPT or not.


In domestic solar systems all panels tend to be similar, shaded on in sun. For a boat this is not true in many installations it is not unusual for individual panels to be experiencing very different conditions.
Parallel connection removes these problems, but as the MPPT regulator cannot boost the solar panel voltage it does limit the gains from MPPT at low voltages.
Weighing these factors is not easy. MPPT models for panels in different conditions become very complex.
To dismiss the often sensible option, on a boat, of parallel connection (or some panels in parallel some in series) as
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showing they indeed don't know how these controllers work.
Is simplistic, naïve, or just wrong.
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