Solar Panels - Series or Parallel ?

[sparrowhawk1]

One thing that makes a huge difference is how the panels are orientated. The shadow from the mast is obviously long and fairly narrow. So if the panels are orientated fore and aft the shadow is likely to shade less panels at any given time.

[Fuss]

Originally Posted by sailinglegend

So I repeated the tests the next day and when both panels were connected in Series the output charging current fell to zero with the wrong kind of shadow on just one panel. In Parallel the same shadow dropped the charging current by half.

For my new Solara semi-flexible panels Parallel clearly wins over Series.

I suspect that if I had fitted an extra bypass diode ACROSS each panel there may have been no difference between Series and Parallel connection.

Hmmm.... If in series the charge current dropped to 0 and then in parallel the same shadow dropped the current by half.... then I would assume that you have some sort of bypass diode problem on a panel. can you test them all?

Bypass diodes are what makes the series installation so much more efficient and so I would assume that if you are not getting at worst, similar output results, then you might have a diode problem.

[Cotemar]

I have a solar panel on my bimini and one on my davits. For the different shading issues and different locations it was a no brainer to do parallel wiring to the controller.

[s/v Jedi]

Originally Posted by Fuss

Hmmm.... If in series the charge current dropped to 0 and then in parallel the same shadow dropped the current by half.... then I would assume that you have some sort of bypass diode problem on a panel. can you test them all?

Bypass diodes are what makes the series installation so much more efficient and so I would assume that if you are not getting at worst, similar output results, then you might have a diode problem.

Indeed. His tests were flawed because the bypass diode(s) is(were) blown or missing, or installed backwards. Adding an additional diode over the whole panel is only to optimize things in case a whole panel gets shaded; current would flow through the other diodes without it.

I think I remember that this passing or blocking of current in a series connection was considered a matter of opinion instead of scientific fact. That's where I leave the discussion

So yes, it is possible that all series-array output stops with minimal shading. If that happens, a diode is missing, installed backwards, or smoked. Simple to replace though.

Let me add that my panels had an extra diode installed over the whole panel (in addition to the ones for each section) from factory. I never studied other panels so don't know if this is the norm or not. If you don't have that, it is very easy and cheap to add them and it will optimize array output in shading conditions.

[SeaKing]

I took 12 panels at 50 w each, splitting them into three groups with seperate controllers. The Aurinco panels are 18 volt panels. The panels were wired in parallel to the controllers. I have one group on the port side of the bimini and one group on the starboard, the third is across the back behind the sail. The plan is mostly only one side gets shading leaving the aft and opposite side getting full sun. I am getting 37 amps in full sun.

The three smaller controllers (MPPT) were cheaper than one large controller and if one fails I still have two third of my system up until I can get a replacement controller.

[Thumbs Up]

I use two 185 watt panels through an Outback mppt. I don't think my panels have many (or any) diodes. I originally had them in series and got impressive outputs when both panels were in full sun, but they rarely are. I obtained some schotsky diodes online (it has been awhile and don't remember the details), wired one across each panel and saw no change. I have kept them in parallel ever since and they work okay. My suspicion is that I bought the wrong diodes. Can any of you guys provide a source and specs for the correct type of diodes to add across each panel?

[Thumbs Up]

If I had to do it over I would have bought two smaller charge controllers. This would also allow me to use different types of panels, I got roped into the whole mppt thing which now does me little good since I am running the panels in parallel. The controller does have a lot of settings that I can play with if I get bored and it logs stats for 180 days but I spent more on it than I spent on the two panels!

[colemj]

Originally Posted by Pelagic

Boy... somehow I missed this focused Thread and to disclose, I am a Solar Dummy with little support in the Philippines.

Like so many others, I had assumed from various past articles and sailors advice that if you expected shading then parallel was the best solution and buying panels with the largest VOC for a 24v house bank was recommended.

So I went ahead and committed to buying the following:
4 x Sunpower E20/327 Watt panels…. VOC 64.9
1 x Outback Max 80…. PV Open Circuit Voltage (VOC) 150 VDC absolute maximum coldest conditions / 145 VDC start-up and operating maximum


My large Bimini is now modified and mounts are made for a fixed horizontal installation, but the 4 panels are not mounted or wire connectors purchased yet.

So opportunity for me to wire intelligently based on the (evolving) consensus of others and to order the remaining hardware that is needed.

Attached is sketch and mock-up photos to illustrate that I will always have some shading which is the reality of a schooner

I labeled the panels and obviously S-1 and P-1 will get more mast and aft stay shading at anchor.

Boom at anchor is stored and centered low so not a shading issue but the topping lift still is.

12m wiring run to MPPT in pilothouse from where I show a combiner

(I can place a combiner anywhere)

Nick/Chuck would you still go ALL Series?
1 ... If yes how would you wire this?
2.....Use a combiner or individual panel cables to breaker by MPPT?
3 Then not sure if my one MPPT enough or is it practical to buy a 2nd?

Colejmi…. Your experience suggests 2 x Series in Parallel… then same questions
1.... If yes how would you wire this?
2 .... Use a combiner or individual panel cables to breaker by MPPT?
3 .... Then is my one MPPT enough or do I need a 2nd?

Obviously, any advice is at my risk, but I do need guidance on connectors and cable purchases to finish this off and I trust my fellow CF council over anything I can find in the Philippines.

Thanks in advance.

It is very easy to experiment, and the wiring configuration does not change anything about your installation. Many panels have two sets of terminals in their junction boxes that allow either series connection on one or parallel on the other. Or, if you run separate wires from each panel, you can just make the series/parallel connection inside the boat as you wish.

Experimentation in your typical conditions will give you the best answer.

Your controller is limited to an OCV of 150V, so you cannot put more than two of your panels in series.

Mark

[ChuckSK]

I just ran a series of simulations with PSpice. 4 Kyocera 130 watt panels were simulated in a series connection and in a parallel-series connection. With no shaded cells both connections produced the same 520 watts as expected. With 2 panels shaded in the series connection the output was 234 watts. With 2 panels shaded in the parallel-series connection the output was 260 watts. The shaded panels were in the same series string.

The outcome is that if shade can block all the panels on one side of the boat, the better solution is the parallel-series connection. The difference in output is caused by the voltage drop across the bypass diodes.

Chuck

[sparrowhawk1]

Originally Posted by ChuckSK

I just ran a series of simulations with PSpice. 4 Kyocera 130 watt panels were simulated in a series connection and in a parallel-series connection. With no shaded cells both connections produced the same 520 watts as expected. With 2 panels shaded in the series connection the output was 234 watts. With 2 panels shaded in the parallel-series connection the output was 260 watts. The shaded panels were in the same series string.

The outcome is that if shade can block all the panels on one side of the boat, the better solution is the parallel-series connection. The difference in output is caused by the voltage drop across the bypass diodes.

Chuck

So can we take it even one step further. For shading purposes only wouldn't it be better to connect all the panels in parallel?

[s/v Jedi]

Originally Posted by ChuckSK

I just ran a series of simulations with PSpice. 4 Kyocera 130 watt panels were simulated in a series connection and in a parallel-series connection. With no shaded cells both connections produced the same 520 watts as expected. With 2 panels shaded in the series connection the output was 234 watts. With 2 panels shaded in the parallel-series connection the output was 260 watts. The shaded panels were in the same series string.

The outcome is that if shade can block all the panels on one side of the boat, the better solution is the parallel-series connection. The difference in output is caused by the voltage drop across the bypass diodes.

Chuck

While I find 56W loss way too much for two diodes (they would flash bang the boat to pieces), it is true that series-parallel would perform a little better. Did you add a bypass diode for each panel in your simulation? If the current is 7 amps and the loss over the diode is 0.6V, then the loss of power is 7 * 0.6 which makes 4.2W. This times two for two shaded panels comes to 8.4W loss, so 260 - 8.4 = 255.8W output, instead of the 234W you found.

Your result is about 6 times as much loss as my math… hmm… I can see 4 times as many diodes, but not 6 times. Maybe the current is higher? Or the diodes have a higher voltage drop? In your simulation, how many bypass diodes were there in the circuit?

However, you should also do the emulation for partially shaded panels. This is where the series connection will outperform the series-parallel connection.

cheers,
Nick.

[sailinglegend]

Originally Posted by s/v Jedi

Indeed. His tests were flawed because the bypass diode(s) is(were) blown or missing, or installed backwards. Adding an additional diode over the whole panel is only to optimize things in case a whole panel gets shaded; current would flow through the other diodes without it....

My panels last year were new - I checked the diodes after your comments then - I am an Electrical and Electronic engineer so do have some idea of what I am doing.

As I said in my post on one of my panels all the cells were shaded and therefore there was no output from that panel. The two built-in bypass diodes in the sections of my panels did nothing, which is why you need an extra Bypass Diode across the whole panel when you want to connect them in series and you have bad shading problems. Your panels do have that extra bypass diode, but as you admit you don't know how many other manufacturers have both bypass diodes to protect the individual cells and ALSO have a Bypass Diode across the output of the panel. As I said if I had fitted an EXTRA bypass diode across each panel then current would have passed via the totally shaded panel and allowed current to flow from the other unshaded panel.

These extra Bypass Diodes are what makes all the difference and will probably make a series connection better than a parallel connection. Your suggestion that these are easy to fit is a bit naive as most here admit to being solar dummies. Ask a dealer what Bypass Diode you need and they will look blankly at you. I have experience of this from one of the largest UK marine dealers!!!!

This is a very very complex area and just saying "series is always better", shows your ignorance. Ignorance isn't what you don't know - it's what you think you know that is incorrect. Sometimes you talk so much nonsense it hurts. We fell out over this issue last year and I was put on your long "ignore list". It's a pity you are now reading my posts again - but I suggest you read the posts properly in the first place.

As others have suggest many times people need to check their series/parallel connections and see what is best for them under all conditions.

[s/v Jedi]

Originally Posted by sailinglegend

My panels last year were new - I checked the diodes after your comments then - I am an Electrical and Electronic engineer so do have some idea of what I am doing.

I am sorry, but as an EE you know that two diodes in series would start conducting on the output of the unshaded panel. Adding a diode over the whole panel will make it better, but only a little bit.

How can you not work out a simple diagram with two or three diodes?

Here you go: the right section has a shaded cell and thus the diode bypasses that whole string of cells. This is electric 101. If that right diode does not start to conduct, it is broken or not connected right.

[sparrowhawk1]

I have 4 12 volt panels. Right now my plans are to parallel two sets giving me 24 volts and then parallel those two sets so I can use just 2 6 gauge wires to my mppt. Can anyone give me a simple schematic to do that? Thanks.

[sparrowhawk1]

And I know the basic way to wire them. But I need help with those diodes.