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CA Traveler

The Western States

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Posted: 08/24/19 01:29pm Link  |  Quote  |  Print  |  Notify Moderator

devildog1971 wrote:

(for 4K I could have put 400 watts or more on the Bigfoot)
No doubt.

As a DIY I paid $1450 for 750W in 2014 for all of the parts including UV wires, aluminum for mounting and SS screws and bolts, etc. This included a high end Morningstar MPPT 60 controller. All panels in series which provides much better shade performance than parallel panels, but that is a whole different topic.


2009 Holiday Rambler 42' Scepter with ISL 400 Cummins
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work2much

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Posted: 08/24/19 01:55pm Link  |  Quote  |  Print  |  Notify Moderator

CA Traveler wrote:

devildog1971 wrote:

(for 4K I could have put 400 watts or more on the Bigfoot)
No doubt.

As a DIY I paid $1450 for 750W in 2014 for all of the parts including UV wires, aluminum for mounting and SS screws and bolts, etc. This included a high end Morningstar MPPT 60 controller. All panels in series which provides much better shade performance than parallel panels, but that is a whole different topic.


For shaded conditions parallel is superior. In series shading one one panel affects all the panels. In parallel it only affects the shaded panel.

The advantage to series connection is that you will have a higher voltage with less amperage. Less amperage means you can run smaller wires with the same voltage drop as parallel with larger cables.

Here is an interesting video showing the difference. Per also has some pretty interesting videos of his Tesla powered RV.
https://www.youtube.com/watch?v=kHafdxzIMh4


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GeoBoy

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Posted: 08/24/19 02:29pm Link  |  Quote  |  Print  |  Notify Moderator

Dog, not to change the subject but how did you make out with the batteries and are you up in Acadia now?

CA Traveler

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Posted: 08/24/19 06:31pm Link  |  Quote  |  Print  |  Notify Moderator

work2much wrote:

CA Traveler wrote:

devildog1971 wrote:

(for 4K I could have put 400 watts or more on the Bigfoot)
No doubt.

As a DIY I paid $1450 for 750W in 2014 for all of the parts including UV wires, aluminum for mounting and SS screws and bolts, etc. This included a high end Morningstar MPPT 60 controller. All panels in series which provides much better shade performance than parallel panels, but that is a whole different topic.


For shaded conditions parallel is superior. In series shading one one panel affects all the panels. In parallel it only affects the shaded panel.
I should have added that serial is superior when the panels have bypass diodes. Virtually all larger panels have bypass diodes. This may not apply to some 12V panels.

My 3 serial panels (90V total) have 3 bypass diodes each. Each diode will bypass 20 cells (10 volts) of my 60 cell panels when there is a shadow on that portion of the panel. So basically I have 9 serial panel sections. When 1 section has a shadow for example the diode causes a short which is 0 volts and passes the full amps of the other 8 sections. So the result is (90V-10V) * 8A (panel Imp) or 8/9 of the panels power.

The same panels in parallel result in 1/3 power loss, hence the voltage is lower than the other 2 panels. The result is the power is 6/9 of the 3 panels vs the serial 8/9 of the 3 panels.

In the past I've posted graphs showing the effect of bypass diodes. It's easy to see the 10V steps with full amps for the given sun condition on leafy shade, hard shade and other types of shade.

From past comments I'm aware that panel bypass diodes with serial panels and shade and not well understood. But with some electrical knowledge and research what I've posted can be verified.

CA Traveler

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Posted: 08/24/19 06:42pm Link  |  Quote  |  Print  |  Notify Moderator

I've seen charging with 7 bypass diodes active or 20V to the controller. Or 2/9 of the power vs 100% with no shadows.

D.E.Bishop

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Posted: 08/24/19 06:44pm Link  |  Quote  |  Print  |  Notify Moderator

CA Traveler wrote:

D.E.Bishop wrote:

CA Traveler wrote:

Could also be the controller or even wiring.

To check the panel: Look up the specs. Then locate the panel wires (not the controller output wires), disconnect one and then with good sun check the voltage which should be very close to Voc (open circuit). Next short the 2 wires and the amps should be close to Isc (short circuit). These 2 measurements are a very good test of a panels performance.


Ok, I don't wish to appear dumb but if he were to short the two wires from the panel, where would he place the meter leads. When shorted it would appear to be a close loop.
I use a AC/DC clamp on ammeter to measure amps, just clamps around the shorted wires. It also measures voltage, ohms, etc. Or use an ammeter on the wires and many meters have 10A capability.


Okay, that I can understand but when you went from an open circuit to a short circuit Using a clamp on sort of slipped my mind.


"I travel not to go anywhere, but to go. I travel for travel's sake. The great affair is to go". R. L. Stevenson

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work2much

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Posted: 08/24/19 08:48pm Link  |  Quote  |  Print  |  Notify Moderator

CA Traveler wrote:

work2much wrote:

CA Traveler wrote:

devildog1971 wrote:

(for 4K I could have put 400 watts or more on the Bigfoot)
No doubt.

As a DIY I paid $1450 for 750W in 2014 for all of the parts including UV wires, aluminum for mounting and SS screws and bolts, etc. This included a high end Morningstar MPPT 60 controller. All panels in series which provides much better shade performance than parallel panels, but that is a whole different topic.


For shaded conditions parallel is superior. In series shading one one panel affects all the panels. In parallel it only affects the shaded panel.
I should have added that serial is superior when the panels have bypass diodes. Virtually all larger panels have bypass diodes. This may not apply to some 12V panels.

My 3 serial panels (90V total) have 3 bypass diodes each. Each diode will bypass 20 cells (10 volts) of my 60 cell panels when there is a shadow on that portion of the panel. So basically I have 9 serial panel sections. When 1 section has a shadow for example the diode causes a short which is 0 volts and passes the full amps of the other 8 sections. So the result is (90V-10V) * 8A (panel Imp) or 8/9 of the panels power.

The same panels in parallel result in 1/3 power loss, hence the voltage is lower than the other 2 panels. The result is the power is 6/9 of the 3 panels vs the serial 8/9 of the 3 panels.

In the past I've posted graphs showing the effect of bypass diodes. It's easy to see the 10V steps with full amps for the given sun condition on leafy shade, hard shade and other types of shade.

From past comments I'm aware that panel bypass diodes with serial panels and shade and not well understood. But with some electrical knowledge and research what I've posted can be verified.


The linked video in my post was using 200 watt panels with bypass diodes. Per's results were similar to my own using series vs parallel in panels with bypass diodes. Slightly better with no shade and dramatic worse with shade.

As far as 12v vs. higher voltage panels I haven't found any high voltage panels that are small enough for a truck camper. I can see larger panels with more bypass diodes could be more efficient in shaded conditions but I would still bet that panels in parallel would outperform when there is substantial shading on some panels.

What model truck camper do you have and what panels do you have mounted on the roof that are high voltage? In my search for high voltage panels building my system (would have loved 24v or higher) I came up with none that would fit my roof and I have a large camper.

* This post was edited 08/25/19 01:53am by work2much *

CA Traveler

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Posted: 08/25/19 09:28am Link  |  Quote  |  Print  |  Notify Moderator

I wanted to avoid rooftop shadows and mounted my panels 6" high. Prior to that I started seeking out fellow campers with higher mounted panels and taking pictures of their setup. Done correctly there is absolutely no technical reason for wind or other concerns. That said however posters often think there will be technical problems or want more limited visibility.

My 60 cell 24V panels are oriented side to side, 6" high on the inside and slope 4 degrees to the edge. The edge is visible from the ground. My panel arrangement means no roof top shadows when the sun is above 10 degrees elevation and no shadows at all for some rig orientations. I could have gone a little higher and been above the A/Cs but chose not to. I also decided not to use the 72 cell panels because fore/aft roof access would have been more restricted.

My 42' MH has limited flat panel mounting space and would have resulted in various sized panels to achieve the wattage I wanted. In addition the serial panel cost with MPPT was only $100 more than parallel. Plus the footprint was less and the watts/sq foot was greater for a given wattage.

I don't know how you and the video reached your conclusions and perhaps I'll view the video. But if you dig into the information on bypass diodes you'll find how they operate and why they can provide better serial panel performance.

You'll find that if a hard shadow is across the short axis of a panel then the bypass diodes provide a short for that panel and pass the amps and volts from the other panels. Hence you still have power from the other 2 panels. It's basic electronics involving diodes. Next week I'll try to find my posts and graphs showing the 10V steps on my panels.

I also found a picture of panel mounting above A/C' length wise along both sides by a commercial solar shop in Yuma, AZ. I don't recall the size or panel size as I was interested in the mounting.

CA Traveler

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Posted: 08/25/19 09:38am Link  |  Quote  |  Print  |  Notify Moderator

BTW If you research bypass diodes there are 2 main reasons why they are used.

1. Without bypass diodes shadows on a panel (like a chimney) will cause those cell to overheat and be damaged. Bypass diodes prevent that.

2. At the same time they allow all other panel sections and other serial panels to provide full power based on the light conditions.

pianotuna

Regina, SK, Canada

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Posted: 08/25/19 10:16am Link  |  Quote  |  Print  |  Notify Moderator

The ideal panel would have bypass diodes between every cell. I don't think anyone makes one that way any more.


Regards, Don
My ride is a 28 foot Class C, 256 watts solar, 556 amp hours of AGM in two battery banks 12 volt batteries, 3000 watt Magnum hybrid inverter, Sola Basic Autoformer, Microair Easy Start.

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