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Solar - parallel or series?


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I thought I understood this but perhaps not well enough...

 

Two blokes from a marine electrical company are fitting solar panels to a neighbour's boat near me. One of them who says he's a proper marine electrician is adamant that they should be fitted in parallel because the potential disadvantage of lower output morning and evening is mitigated by the fact that the max output voltage of the 2 panels he's installing is about 50v (I think mine are 47v) so they will always put out enough voltage to initiate charging via the MPPT. He also said that the MPPT has to work harder to regulate high voltages on series systems, but I'm not sure why that's a disadvantage apart from the controller getting a bit warmer?

 

The disadvantage of series connection is of course that if one panel is shaded the whole array goes down. I can see that as a good argument for multiple panel systems but I've only got 2 panels, plus the 2 panels he's installing are only 200w each whereas mine are 455w each therefore wouldn't the combined amperage of mine require thicker solar cables to the MPPT if wired in parallel? He said no but I'm not sure he's right (my solar cables are 6mm2 over about 5m one way). He also said that the combined voltage of my panels means I should have fitted a properly rated 12v isolator. Fortunately I did!

 

I know this has been discussed on other solar threads but I'm still unclear...

Edited by blackrose
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You only want to have enough panels in series to get a high enough voltage above the battery voltage for the MPPT controller to work, this depends on the controller -- don't forgot to use the maximum battery voltage and minimum panel voltage. Once you have this more strings/panels can be added in parallel -- if there are a lot of panels it's worth considering having separate MPPT controllers for each bank to maximise power when partial shading happens, also several smaller controllers can sometimes be cheaper than one big one. But also with multiple panels one higher-voltage lower-current MPPT can be cheaper than a lower-voltage higher-current one. Having said that. most boats (OP included) don't have enough panels to worry too much about all this... 😉

Edited by IanD
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Ok thanks. When I was installing my panels the consensus on here seemed to be to connect in series so that's what I did. I just wondered if given the high max voltage output of my panels, would I have benefitted more or had fewer disadvantages connecting in parallel?

 

Or is it 6 of 1, half dozen of the other?

Edited by blackrose
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4 minutes ago, blackrose said:

Ok thanks. When I was installing my panels the consensus on here seemed to be to connect in series so that's what I did. I just wondered if given the high max voltage output of my panels, would I have benefitted more or had fewer disadvantages connecting in parallel?

 

Or is it 6 of 1, half dozen of the other?

 I have 2 x 295W panels, originally in series, but changed to parallel, partly because of the shading issue, and partly because the lower voltage meant that I could use a particular breaker/switch, which I think had a limit of 50V.

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Just now, Richard10002 said:

 I have 2 x 295W panels, originally in series, but changed to parallel, partly because of the shading issue, and partly because the lower voltage meant that I could use a particular breaker/switch, which I think had a limit of 50V.

I have 4 x 250W in two arrays. Up until recently each 2x2 were connected in series through separate Tracer controllers. I found the controller very slow at tracking to the full voltage when connected in series, so connected one array of 2x2 in parallel. This one now appears to perform slightly better than the series connected panels.

 

I expect later in the year though, when the sun is lower in the sky, it may be the other way around.

 

I think I saw somewhwere once of a configuration using switches that would allow manually changing between series connected panels and parallel. It struck me at the time to be a very good idea, though it is possible I dreamt it.

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12 minutes ago, rusty69 said:

I have 4 x 250W in two arrays. Up until recently each 2x2 were connected in series through separate Tracer controllers. I found the controller very slow at tracking to the full voltage when connected in series, so connected one array of 2x2 in parallel. This one now appears to perform slightly better than the series connected panels.

 

I expect later in the year though, when the sun is lower in the sky, it may be the other way around.

 

I think I saw somewhwere once of a configuration using switches that would allow manually changing between series connected panels and parallel. It struck me at the time to be a very good idea, though it is possible I dreamt it.

Switching between series and parallel will mean a more expensive MPPT controller, since it has to be rated to cope with 2x voltage (series) and 2x current (parallel). Also there doesn't seem much point, the panel voltage for maximum power output doesn't change much with light level, it's mainly the current that alters... 😉

Edited by IanD
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Thanks, that's interesting. Yes of course it's not just morning and evening when you need adequate voltage to initiate charging, it's over the whole of winter too.

 

I have no shading issues at my mooring which to be honest is where the boat is 95% of the time and I'm 95% off grid and the panels/controller perform brilliantly. In April I didn't use any shore power and that's including running a washing machine a couple of times/week. Even over winter I only switched over to shore power occasionally. I guess if I do end up mooring somewhere where the panels are shaded I'll have to think about changing over to parallel, but I'm assuming fully shaded panels in parallel perform no better than they would connected in series? So it's only partial shading where paralleled panels which operate independently have any benefit over series?

Edited by blackrose
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2 minutes ago, blackrose said:

Thanks, that's interesting. I have no shading issues at my mooring which to be honest is where the boat is 95% of the time and I'm 95% off grid and the panels/controller perform brilliantly. In April I didn't use any shore power and that's including running a washing machine a couple of times/week. Even over winter I only switched over to shore power occasionally. I guess if I do end up mooring somewhere where the panels are shaded I'll have to think about changing over to parallel, but I'm assuming fully shaded panels in parallel perform no better than they would connected in series? So it's only partial shading where paralleled panels which operate independently have any benefit over series?

Correct.

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4 minutes ago, IanD said:

Switching between series and parallel will mean a more expensive MPPT controller, since it has to be rated to cope with 2x voltage (series) and 2x current (parallel). Also there doesn't seem much point, the panel voltage for maximum power output doesn't change much with light level, it's mainly the current that alters... 😉

My controller can handle the voltage of the two panels in series or parallel. The point is though, with my Tracer controller(s) is that they are much slower tracking in series.

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4 minutes ago, rusty69 said:

My controller can handle the voltage of the two panels in series or parallel. The point is though, with my Tracer controller(s) is that they are much slower tracking in series.

There's no technical reason for slower tracking in series, that could be a "feature" of your controller... 😉

 

Parallel is better with partial shading than series.

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12 minutes ago, IanD said:

There's no technical reason for slower tracking in series, that could be a "feature" of your controller... 😉

 

Parallel is better with partial shading than series.

I agree. Tracer (and outback branded tracer) controllers appear to be notoriously bad for tracking though, so parallel connected panels may work better with them . 

 

Or perhaps I just got a duff couple. 

Edited by rusty69
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I've seen YouTube reviews which say the same thing, but I've got a Epever Tracer controller 150v/60a AN model and it seems to react instantly to differing light conditions - at least according to the MT50 remote unit connected to the controller and also my shunt type BEP battery monitor. 

 

Perhaps it's partly down to the type of panels too? Mine are mono perc HiKU (whatever that means?) I think they're half cell although I can't see that anywhere on the spec sheet. 

 

Edited by blackrose
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38 minutes ago, blackrose said:

I've seen YouTube reviews which say the same thing, but I've got a Epever Tracer controller 60a and it seems to react instantly to differing light conditions - at least according to the MT50 remote unit connected to the controller and also my shunt type BEP battery monitor. 

 

Perhaps it's partly down to the type of panels too? Mine are mono perc HiKU (whatever that means?) I think they're half cell although I can't see that anywhere on the spec sheet. 

 

Perhaps it is, and how they are mounted and what type of batteries they are connected to. 

 

Ours are flat mounted charging Lithium batteries. 

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1 hour ago, IanD said:

Switching between series and parallel will mean a more expensive MPPT controller, since it has to be rated to cope with 2x voltage (series) and 2x current (parallel). Also there doesn't seem much point, the panel voltage for maximum power output doesn't change much with light level, it's mainly the current that alters... 😉

 Hi Ian I don't think I have ever seen max input current listed as a specification on an Mppt unit. Most are rated for output current which would be the same if wired series or parallel.Out of interest which units are you referring too ? Obviously input voltage does need to be considered.

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The problem with Epever Tracers is that they do no tracking at all until the panel current is over 1A (or 1.5A? I forget), so for high panel voltages it takes a lot of power to start tracking.

 

They leave the panels at just above battery voltage until tracking kicks in, which for high-voltage panels/strings is way below Vmp making it worse.

 

Putting two panels in parallel rather than series halves the power threshold for tracking to start, which makes a huge difference on cloudy days.

 

Series for low-light output is a red herring in any case with modern panels and 12V batteries. With 30-50V panels, open-circuit voltage will be well over 15V before there's any power that's not a rounding error.

Edited by Francis Herne
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34 minutes ago, nottheone said:

 Hi Ian I don't think I have ever seen max input current listed as a specification on an Mppt unit. Most are rated for output current which would be the same if wired series or parallel.Out of interest which units are you referring too ? Obviously input voltage does need to be considered.

Depends on the controller, but you're right that in many case (simple buck converter) it's the output current that matters. Doubling Vin does often increase the price though, depending on exact model range.

Edited by IanD
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3 hours ago, Francis Herne said:

The problem with Epever Tracers is that they do no tracking at all until the panel current is over 1A (or 1.5A? I forget), so for high panel voltages it takes a lot of power to start tracking.

 

They leave the panels at just above battery voltage until tracking kicks in, which for high-voltage panels/strings is way below Vmp making it worse.

 

That isn't the case with mine. It's dusk now and even with about 43v and only 0.3A at the panel I'm still getting about 1A going into the batteries.

 

Anyway  all I can say is I'm really happy with mine. My batteries never fell below about 90% SoC in April according to my Smartgauge. I use the toaster, microwave, washing machine and sit there watching too much TV until late at night. By 10 or 11am the batteries are generally back to fully charged. I can't really see the point of a more expensive over-specified controller if what I have does what it needs to do.

 

https://www.eossolarsolutions.co.uk/product/tracer6415an/

 

 

Edited by blackrose
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3 minutes ago, blackrose said:

 

Well, all I can say is I'm really happy with mine. My batteries never fell below about 90% SoC in April according to my Smartgauge. I use the toaster, microwave, washing machine and sit there watching too much TV until late at night. By 10 or 11am the batteries are generally back to fully charged. I can't really see the point of a more expensive over-specified controller if what I have does what it needs to do.

 

https://www.eossolarsolutions.co.uk/product/tracer6415an/

 

 

That's certainly cheaper than the equivalent from Victron, which is probably only worth it if you want to integrate with other Victron gear like a Multiplus/Quattro and lithium batteries.

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17 minutes ago, blackrose said:

My batteries never fell below about 90% SoC in April according to my Smartgauge.

Don't forget a Smartgauge is useless unless it's dark outside😱

When charging* it is only within about 10% or so  of the actual value.

 

*Reading any voltage that is not the actual battery voltage. 

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8 minutes ago, Loddon said:

Don't forget a Smartgauge is useless unless it's dark outside😱

When charging* it is only within about 10% or so  of the actual value.

 

*Reading any voltage that is not the actual battery voltage. 

I didn't know that. It has to be dark to give an accurate reading?🤥

 

Oh, you meant its not accurate whilst charging.

Edited by rusty69
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3 minutes ago, rusty69 said:

I didn't know that. It has to me dark to give an accurate reading?🤥

Yes if you have solar.

If using a battery charger it needs to be turned off to get an accurate reading.

It is within 10% when charging so when reading 85% it could be 75 or 95 you just don't know.

 

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Just now, Loddon said:

Yes if you have solar.

If using a battery charger it needs to be turned off to get an accurate reading.

It is within 10% when charging so when reading 85% it could be 75 or 95 you just don't know.

 

Oh, right. I knew that.

 

I suppose that might be an issue if they are LA batteries and you are only ever getting them charged to 90%, or 75%, but OP says they get a full charge every day, so not a problem.

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1 minute ago, rusty69 said:

Oh, right. I knew that.

 

I suppose that might be an issue if they are LA batteries and you are only ever getting them charged to 90%, or 75%, but OP says they get a full charge every day, so not a problem.

Even when it reads 100% it might only be 90%. However if it reaches 100 at midday then there's a good chance it will be fully charged by the time the sun goes in.

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