Solar Choices

[COLINFLTENG]

On my boat one panel gets sun in part of day am pm why parrel works for me

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[jcapo]

This thread and another recent series vs. parallel thread prompted me to real word test series vs. parallel on my boat, again.

I have two 195 watt arrays one on each side of the bimini top. Each array, port and starboard, feeds its own Morningstar 200 watt MPPT controller with a remote monitor panel. Each array is 3 65 watt Kyocera panels. 10ga wiring from each panel runs to terminal blocks in the lazarette where the panels are connected in series or parallel. I did it this way to allow me to test series vs. parallel and to easily take a bad panel out of the array should I need to.

I tested series vs. parallel at the dock in 2010 with one array installed by changing configuration from day to day. This was in Dania, Florida during June when the sun was high and cloud cover was pretty consistent from day to day. This wasn't a true side by side apples to apples test but I was convinced that parallel was best.

So I'm at anchor in Titusville, Florida with zero current and only the wind affecting boat and therefore sun direction. I connected one array in series and the other in parallel. The series array was one on the side with the shortest wire runs, no more than 20 feet depending on which panel in the array. The parallel array would be about 30 feet of wire to each panel. So for the series array there is no more than 60 feet of 10 ga., the series connection is in the lazarette and not up at the panels, vs. 30 feet of 10 ga. for the parallel array. These 65 watt panels are 3.75 amp max. The series array had an additional 250mv or so voltage drop over the parallel array.

I ran this test for a week with varying conditions and sun passage direction. Winds that week were all over the compass. Neither array had a favorable sun position for a significant amount of the time. Some days there would be a 360 degree direction change through the day. I moved the boom off of the gallows to remove its shadow. There is a fourwinds generator at the canoe stern that casts a shadow. The blades were locked down to cast a smaller consistent shadow. The shadow from the spinning blades does make a difference.

Over the week the parallel array produced 360 ah vs. 294 ah from the series array. There was only one day where the series array produced more power and that was only 2 ah.

The Morningstar controller is more efficient with 17 volts input than with 51 volts input. At 25 watts there is a 10% difference narrowing to 4% at full power. That efficiency difference would account for some of difference seen in the test. The additional voltage drop in the series array would account for a bit more. Hard for me to say how much. The voltage drops across the bypass diodes would account for some difference also.

Other things that convinced me to stay parallel. The controller is much warmer. I measured it but I forgot what it was. The controller whistled a bit, transformers I guess. Covering one panel dropped the output to zero. I did not expect that. On this boat parallel works better with these panels, controllers, and wiring configuration.

[sparrowhawk1]

Jcapo thanks so much. I've been spending hours reading about this stuff and theories great. But nothing beats real world testing.

[Siege]

Jcapo, it's nice to hear some real world numbers on this topic as I'm much more interested in actual power production vs theoretical. I need to do more extensive testing on my own boat, but it sounds like you've confirmed what works best for you.

[jcapo]

Originally Posted by Siege

Jcapo, it's nice to hear some real world numbers on this topic as I'm much more interested in actual power production vs theoretical.

Last week here in Titusville we had some decent clear skies for several days. I was getting a bit over 100 ah per day from 390 watts of panels when my batteries were not fully charged. With higher sun angles and more daylight as the year progress production will go up on good days.

The week I tested was 50% cloudy and lower sun angle so the output was less than last week but both arrays had equal sun exposure for the test.

[s/v Jedi]

Originally Posted by sparrowhawk1

Jcapo thanks so much. I've been spending hours reading about this stuff and theories great. But nothing beats real world testing.

I love tests but there are problems with this one:

1. when a panel of the series array is covered, array output drops to zero. This means that a bypass diode is burned out, or missing and this completely kills any benefit from partial shading issues.

2. with small panels like these, how many strings of cells does each one have? Only with multiple strings can partial shading be countered with series connection.

3. the wiring is the same for parallel as for series connection. This kills any advantage that series has over parallel on the subject of cable losses.

4. how can a shorter cable run have more voltage drop? This means that there is a bad contact or damaged cable.

What would help is to change arrays for each setup, i.e. moving parallel to the other side and vica versa. Also, replacing/adding the bypass diodes fixes things.

[sparrowhawk1]

Well there are two ways of looking at it Jedi. series allows you to have less loss or you can save money on smaller wire with the same loss. I'm okay with him paralleling them till the wire gets to the Laseret. I'm mostly interested in effect of shading and I know real world tests are hard to be exact but I always have some shade so I think I'm going to go parallel. The other thing I'm trying to decide is to use 8 10gauge wires 4 8gauge wires or 2 heavier gauge. (4 panels)

[goboatingnow]

I don't see the point of arguing wire size as a justification for series. Wire size is a separate issue to panel configuration

Dave


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[CarinaPDX]

It seems to me that the greatest value of these tests are that they show that a somewhat typical installation doesn't benefit from series/MPPT unless the components and design are chosen to be optimal for that choice. While we may debate about how much of an improvement is possible with series/MPPT I think it is unlikely that it would do worse as long as the entire system was chosen with that option in mind. I have said before that one or another solution is not likely to always be the best choice (particularly when cost is considered), and that a properly engineered system design is the key to success - and I'll stick to it. The details matter, a lot.

I'd like to thank Jedi for providing a lot of those details regarding series installations - this has been a good learning experience.

Greg

[sparrowhawk1]

Okay I just re checked my 2 percent loss charts. The 8 gauge doesn't cut it. So it's either 8 10 gauge wires or 2 4 gauge wires. I'll let cost deside but I kinda like that idea of four independent panel wiring.

[jcapo]

Originally Posted by s/v Jedi

I love tests but there are problems with this one:

1. when a panel of the series array is covered, array output drops to zero. This means that a bypass diode is burned out, or missing and this completely kills any benefit from partial shading issues.

I tried two panels. I guess both are bad.

2. with small panels like these, how many strings of cells does each one have? Only with multiple strings can partial shading be countered with series connection.

It looks like two but I could be wrong.

3. the wiring is the same for parallel as for series connection. This kills any advantage that series has over parallel on the subject of cable losses.

True but I am not going to rewire to prove that parallel works better on my boat with my panels and controllers.

4. how can a shorter cable run have more voltage drop? This means that there is a bad contact or damaged cable.

Never said it did. The series connection has shorter individual cables from each panel to the lzarette but when connected in series in the lazarette the effective length is longer.

What would help is to change arrays for each setup, i.e. moving parallel to the other side and vica versa. Also, replacing/adding the bypass diodes fixes things.

Maybe next year. I'm happy.

[nimblemotors]

I would prefer a heavy wire, it is hard to think of a more reliable piece of equipment than a wire, other than not having one at all, as in wireless.

[s/v Jedi]

Originally Posted by sparrowhawk1

Well there are two ways of looking at it Jedi. series allows you to have less loss or you can save money on smaller wire with the same loss. I'm okay with him paralleling them till the wire gets to the Laseret. I'm mostly interested in effect of shading and I know real world tests are hard to be exact but I always have some shade so I think I'm going to go parallel. The other thing I'm trying to decide is to use 8 10gauge wires 4 8gauge wires or 2 heavier gauge. (4 panels)

You can't "paralleling them till the wire gets to the Laseret". You either connect panels in series or in parallel.

What matters is the resistance value of the circuit (wire, connections, crimps etc) as expressed in Ohms and the current that runs through the circuit expressed in Amps. The voltage drop is this resistance x current.

You can't have more voltage drop with shorter cables unless there is something wrong, or the amperage is higher.

[s/v Jedi]

Originally Posted by jcapo

I tried two panels. I guess both are bad.

Yep, both are bad. Or they are missing. Or the panels are from the pre-diode era.

It looks like two but I could be wrong.

Sounds okay. This means you could have tested the partial shading which is what it is all about. It is known 100% that a fully shaded panel has no output. That such a panel needs a bypass diode when connected in series so that the circuit doesn't break. But only the series connection can produce power with partial shading when the shade does not touch every string of cells in the panel.

True but I am not going to rewire to prove that parallel works better on my boat with my panels and controllers.

There's no need for that as the way it is wired kills part of the advantage of series connection and thus is optimal for your parallel connection already. In other words: your parallel wiring works better for parallel connections. Makes sense

Never said it did. The series connection has shorter individual cables from each panel to the lzarette but when connected in series in the lazarette the effective length is longer.

Not unless you used bundles of wire as jumpers. Just count the total length of wire used: the one with less length must be the one with less voltage drop when the panel current is equal.

Maybe next year. I'm happy.

[sparrowhawk1]

Originally Posted by s/v Jedi

You can't "paralleling them till the wire gets to the Laseret". You either connect panels in series or in parallel.

What matters is the resistance value of the circuit (wire, connections, crimps etc) as expressed in Ohms and the current that runs through the circuit expressed in Amps. The voltage drop is this resistance x current.

You can't have more voltage drop with shorter cables unless there is something wrong, or the amperage is higher.

Not sure I understand you. if you have two 12 volt panels with four wires running to the laseret( at this point it can be considered parallel,to me anyway) then you connect the positive of one panel to the negative of the other and you have 24 volts. Which is why what you said earlier makes sense,- for that length you lose the benefit of series in the wiring. And correct me if I'm wrong but the savings would be only having to run two wires with an adition of a small jumper at the panels, instead of 4