Installing serial solar panels

[downunder]

Originally Posted by ramblinrod

DOT,

This forum is for boaters with vessels of all sizes.

There are lots of boats less than 100 ft and far fewer more than 100 ft.

I suspect the average boat of people following this thread is around 30-40 ft

I have stated many times in this thread and others, that when configuring a solar charging system for any vessel, one reviews the vessel design, expected energy consumption, and user needs.

My point in the prior post, is that the solar charging system is not sized based on LOA, and especially not alone.

As I stated, a 400W solar charging system may be absolutely suitable for a 100 ft yacht or larger, if all the boater needs, based on this review, is a 400W system, as I clearly stated.

There are lots of large boats with solar charging systems of 400W and less.

Now rather than your attempt to change the subject...

Remembering Kirchoff's First Law, if that system had 4 x 100W panels in parallel, and one panel had 15.0 Vdc across it, what voltage would the other panels have across them?

Yes DOT I believe RR is trying to avoid the fact many vessels even small are looking at much larger designs of solar installation. Picking out only the small installations in the solar panel thread.

Perhaps he is in one of the areas where there are lots of small vessels and little sun. Small system design does not cover the majority of new designs in my area of the world.

RR How would you wire up a 4x360W sunpower mounted on the stern of a catamaran?? The vessel already has 300w.

[Paul Elliott]

This would be much more interesting if you guys would spend less time arguing about who has the bigger solar setup, and more time discussing the pros and cons of the different panel and controller configurations. Many of these issues are fairly independent of array size. Others not so much.

For what it's worth, I have a 44 ft sailboat with three 100W panels that are often shaded. These panels support about half my power consumption when underway, and usually 100% of my at-anchor-in-the-tropics usage.

[ErikElmgren]

I'm impressed this is still going, thank you for the advice on solar panel installations.

If anyone is interested I decided on 4 mini circuit breakers from Siemens (SENTRON 2-pole B characteristic) rated for 60VDC/400VAC and 10kA (my batteries should not be able to deliver more then 3kA with 10mm² conductors in case of a short-circut). With a 8-unit DIN box this part of the installation ends up at a reasonable US$ 86.

[DotDun]

Originally Posted by noelex 77

The new Victron models do, but as you say if you want to run 36 cells in parallel there are perhaps better MPPT controllers. The high start up voltage is quite rare and is more to do with Victron trying to decide a sensible wake up routine rather than any inherent need for this voltage difference.

Solar cells generate reasonable voltage even under poor light where they cannot produce any useful current. If the controller wakes up at an early stage the self consumption from the MPPT circuitry can consume more power than the array is producing, loosing significant power.

The Victron requirement is not as bad as it seems, as it is looking at Voc not Vmp. Voc is typically 3-4v over Vmp for a 36 cell panel. Once the Victron controller has woken up it only needs 1v over battery voltage so the problem only effects the initial startup. On wake up the panel will be cool and close to its specified Voc, which is typically around 21V. There will be no voltage drop in the wiring and the battery voltage is likely to be low so I think it will only rarely be a problem, even with the Victron controller.

Most other MPPT controllers are fine with parallel connection of 36 cell panels. In fact I think this is probably the most efficient system, although I am always interested in alternative theories.

Good to know. Yes, most of my experience is Victron.

[DotDun]

Originally Posted by ramblinrod

DOT,

This forum is for boaters with vessels of all sizes.

There are lots of boats less than 100 ft and far fewer more than 100 ft.

I suspect the average boat of people following this thread is around 30-40 ft

I have stated many times in this thread and others, that when configuring a solar charging system for any vessel, one reviews the vessel design, expected energy consumption, and user needs.

And yet, you failed to mentioned such in the referenced thread.

Originally Posted by ramblinrod

My point in the prior post, is that the solar charging system is not sized based on LOA, and especially not alone.

As I stated, a 400W solar charging system may be absolutely suitable for a 100 ft yacht or larger, if all the boater needs, based on this review, is a 400W system, as I clearly stated.

Provide one example, boat name please!

Can't do it, hmm, wonder why?

You don't even understand that 100 ft yachts don't have 12v house banks.

Originally Posted by ramblinrod

There are lots of large boats with solar charging systems of 400W and less.

More blather.

Originally Posted by ramblinrod

Now rather than your attempt to change the subject...

Remembering Kirchoff's First Law, if that system had 4 x 100W panels in parallel, and one panel had 15.0 Vdc across it, what voltage would the other panels have across them?

If I connect a 60 cell panel (34v nominal) in parallel with a 36 cell panel (20v nominal), what law will I break? Somebody coming to arrest me?

With no shading, does the 20v panel suddenly morph into a 34v panel? Does the 36 cell panel suddenly react like a 60 cell panel? No, it's still a 20v panel and reacts in the circuit as a 20v panel, it's doesn't magically morph into a 34v panel.

You keep stating all devices in a parallel circuit must be equal voltage, it's the law! So what happens in this example?

You will observe the same voltage when measured with your DVM at the output of each panel, but that does not make them equal voltage sources.

We can't have an engineering discussion if you continue to confuse the conversation stating that all voltage sources must be equal. We have to be able to understand what devices are in the circuit, and in the above example, which carries over to the shaded panel discussion, it's clear that not all devices are equal.

And I agree with others, your use of 'voltage source' is a very poor moniker for power source in a parallel circuit. But, at this point, that isn't surprising given your demonstrated lack of engineering expertise in application design.

Carry on.....(I'm sure you will!)

[newhaul]

Can we please stop the splitting of hairs and needless argument that is not doing anything except provide me entertainment.

[ramblinrod]

Originally Posted by downunder

Yes DOT I believe RR is trying to avoid the fact many vessels even small are looking at much larger designs of solar installation. Picking out only the small installations in the solar panel thread.

Perhaps he is in one of the areas where there are lots of small vessels and little sun. Small system design does not cover the majority of new designs in my area of the world.

RR How would you wire up a 4x360W sunpower mounted on the stern of a catamaran?? The vessel already has 300w.

Well, perhaps stop banging your head and you'll have enough wits about you to realize what you are stating confirms my position.

Look at your last sentence, "The vessel already has 300W."

Why would the vessel have a 300W system, if at the time the system was selected, the owner didn't want a 300W system? (In my experience, people rarely buy what they DON'T want.)

Few are still in the boat today that they originally purchased, it isn't because the first boat wasn't what they wanted, or was wrong for them, it's just that their needs changed, or developed.

So for someone who has no solar, and isn't sure it is right for them, but wants to get into it, but doesn't want to blow the whole boat budget on it now, a 400W system may be the right choice, regardless of the size of vessel or energy consumption. In this case, the boater drew the line at 300W.

And that brings the fourth point into the decision making equation,

1. Boat Design
2. Energy Consumption
3. User Needs
4. Budget

Budget is sorta tied into user needs, but is such an important factor we'll consider it on it's own.

All that aside, in answer to your question...

I am a professional marine service provider.

I make my living (at least part of it) providing professional consultation for a fee.

PM me if you would like my advice for your personal solar charging system needs.

[ramblinrod]

Originally Posted by DotDun

If I connect a 60 cell panel (34v nominal) in parallel with a 36 cell panel (20v nominal), what law will I break? Somebody coming to arrest me?

DOT, I'll gladly answer your question, but first, you owe me an answer to my question in post # 175 that you referenced.

"Remembering Kirchoff's First Law, if that system had 4 x 100W panels in parallel, and one panel had 15.0 Vdc across it, what voltage would the other panels have across them?"

I, and everyone following this thread, are eagerly awaiting your answer.

I'm trying to help you learn something very important.

Answer the question please.

[noelex 77]

Let's remember we are on the same side.

Solar panels are complex and in many ways counterintuitive. They don't behave like other power sources, such as batteries. Personally I find posts on this subject make me think even if I believe they are incorrect, and ultimately they help my understanding (although I don't claim to understand solar panel behaviour well).

Originally Posted by DotDun

If I connect a 60 cell panel (34v nominal) in parallel with a 36 cell panel (20v nominal), what law will I break? Somebody coming to arrest me?

With no shading, does the 20v panel suddenly morph into a 34v panel? Does the 36 cell panel suddenly react like a 60 cell panel? No, it's still a 20v panel and reacts in the circuit as a 20v panel, it's doesn't magically morph into a 34v panel.

You keep stating all devices in a parallel circuit must be equal voltage, it's the law! So what happens in this example?

Expect a knock on the door from the voltage police .

If there is one MPPT controller and the panels are connected in parallel, the panels must be at the same voltage (ignoring wires losses etc). The controller will seek out the optimum Vmp of the array as a whole, which will be very close to the voltage of the lower voltage panel (if they are both producing reasonably similar amounts of power). So the 20v panel will be working normally and the 34v will be operating with reduced power at the same voltage of 20v (or whatever the Vmp is ).

If they are connected in series both panels can have a different voltage, but the current must be identical. If one panel is carrying 2.5A the other panel must also carry (or allow the bypass diodes to pass) 2.5A.

With two controllers both panels can be at different voltages and currents, but the controllers must output the same voltage (the battery voltage).

[ramblinrod]

[QUOTE=noelex 77;2408295]Let's remember we are on the same side.

I would normally agree, however based on many of his posts, I don't think DOT does.

So I'm trying to teach him something.

Please bear with me, just a little bit longer.

Now DOT, you can end this line of questioning with your next post.

Just answer the simple question from post # 175, that anyone with any knowledge or experience with electrical circuits, should be able to answer, clearly, simply, and without any hesitation whatsoever.

"Remembering Kirchoff's First Law (this is a big hint by the way), if that system had 4 x 100W panels in parallel, and one panel had 15.0 Vdc across it, what voltage would the other panels have across them?"

[ramblinrod]

Originally Posted by DotDun

And I agree with others, your use of 'voltage source' is a very poor moniker for power source in a parallel circuit.

As with every other discussion, you are entitled to your opinion, including the right to be wrong, but you have no right to treat others poorly, while expressing it.

From a search of "Voltage Source" in Wikipedia.

A voltage source is a two terminal device which can maintain a fixed voltage.[1] An ideal voltage source can maintain the fixed voltage independent of the load resistance or the output current. However, a real-world voltage source cannot supply unlimited current. A voltage source is the dual of a current source. Real-world sources of electrical energy, such as batteries, generators, and power systems, can be modeled for analysis purposes as a combination of an ideal voltage source and additional combinations of impedance elements.


This clearly confirms, that my use of the term "voltage source" in reference to solar panels connected in parallel, for the purpose of evaluating the voltage across them in a parallel circuit, is 100% valid, whether you agree in your opinion or not.

Rather than trying to deflect attention away from your prior errors and attempting to argue that a solar panel is substantially different from a battery or generator or other power producing device...

please answer the question from post # 175.

"Remembering Kirchoff's First Law, if that system had 4 x 100W panels in parallel, and one panel had 15.0 Vdc across it, what voltage would the other panels have across them?"

It is taking you a long time to reply with the correct answer, so I'll give you another really big hint, "Your correct answer can only be one value."

[OceanSeaSpray]

The entertaining phase of the argument might have ended long ago...

A solar panel doesn't behave like a voltage source, but a current source. It is not very far off from being an ideal current source at that, which we can see immediately by checking its specs. I was looking at a late generation 36-cell monocrystalline glass alloy-framed Chinese panel no later than yesterday:

P=100W, Voc=22V, Vmp=19V, Imp=5.25A, Isc=5.0A

This means that we get 5.25A at maximum power (at 19 volts) and still 5.0A in short circuit with zero volts and zero power: this is a current source. The current is almost independent of the output voltage. This is significantly different than what happens with a voltage source, like a battery or generator, where the current keeps increasing as the voltage drops.

If we connect two panels of different open-circuit voltage in parallel, the higher Voc panel will initially set the output voltage.
When we start loading this configuration, the output voltage starts dropping. Until this common output voltage reaches the lower Voc of the second panel, only the higher Voc panel will supply current. Then the lower Voc panel starts to contribute as well and the output current reaches a maximum somewhere, but with very poor efficiency as the higher Voc panel is way below its Vmp by then.

This is why we don't connect in parallel panels that don't have about the same output voltage: it fundamentally can't work properly and there is nothing a MPPT controller can do about that.

The common output voltage of a set of panels in parallel ends up wherever the load forces it to be. Connected directly to a battery, the solar voltage simply gets dragged down to battery voltage.
Incidentally, when Vmp is around 17V with the panels being cold, it drops down towards 15V in hot sunny conditions. If the charging voltage is a little over 14V, there is almost nothing left to improve upon with a MPPT in those conditions. This is why a set of 36-cell panels in parallel in the tropics tends to do extremely well with just a switching regulator.

[downunder]

Originally Posted by ramblinrod

Well, perhaps stop banging your head and you'll have enough wits about you to realize what you are stating confirms my position.

Look at your last sentence, "The vessel already has 300W."

Why would the vessel have a 300W system, if at the time the system was selected, the owner didn't want a 300W system? (In my experience, people rarely buy what they DON'T want.)

Few are still in the boat today that they originally purchased, it isn't because the first boat wasn't what they wanted, or was wrong for them, it's just that their needs changed, or developed.

So for someone who has no solar, and isn't sure it is right for them, but wants to get into it, but doesn't want to blow the whole boat budget on it now, a 400W system may be the right choice, regardless of the size of vessel or energy consumption. In this case, the boater drew the line at 300W.

And that brings the fourth point into the decision making equation,

1. Boat Design
2. Energy Consumption
3. User Needs
4. Budget

Budget is sorta tied into user needs, but is such an important factor we'll consider it on it's own.

All that aside, in answer to your question...

I am a professional marine service provider.

I make my living (at least part of it) providing professional consultation for a fee.

PM me if you would like my advice for your personal solar charging system needs.

We are talking about a purchase of a 2nd hand vessel here which was fitted with 300W around 15 years ago. It is my choice to add additional solar.

Solar has developed a bit (including cost) in the intervening years and I cannot question the former owner’s decisions 15 years ago... There has been a lot of development particularly with catamaran owners. Even catamaran manufacturers seem to be stepping up to the mark to a degree. One Australian manufacturer that used to have 200W standard to cover their refrigeration system initially are now fitting 800W as standard.

It is simply my decision to add 4 additional Sunpower panels because I can.

However the general consensus amongst many owners and referenced in that mentioned thread is to fit over 1kw and 1500W is not uncommon. In the case of the vessel I am referencing there is currently no panels on the stern of the vessel and I have the opportunity to fit an extra 4 or 5 Sunpower 360W panels. For our climate owners find that these panels in this position also help provide shade in an ideal spot in our climate.

So boat design, energy consumption, user needs and budget is covered and I will seek experienced design engineers at the time. Thank you for your offer of personal advice RR.

On this forum I am simply looking for suggestions from experienced and knowledgeable posters for the principles of a common installation in terms of size it seems everywhere. After all the title of the thread covers all commonly used installations I would think.

Paul Elliot “This would be much more interesting if you guys would spend less time arguing about who has the bigger solar setup, and more time discussing the pros and cons of the different panel and controller configurations. Many of these issues are fairly independent of array size.”

Don't see where anyone is arguing about who has the biggest solar setup.
Simply many have over 800W these days.

Cheers

[aXis]

Originally Posted by DotDun

If I connect a 60 cell panel (34v nominal) in parallel with a 36 cell panel (20v nominal), what law will I break? Somebody coming to arrest me?

It's a physics law. I.e. a physical phenomenon that has been proven to be absolutely true over repeated scientific observations and experiments. You will be unable to produce with a scenario that breaks it.

Originally Posted by DotDun

With no shading, does the 20v panel suddenly morph into a 34v panel? Does the 36 cell panel suddenly react like a 60 cell panel? No, it's still a 20v panel and reacts in the circuit as a 20v panel, it's doesn't magically morph into a 34v panel.

You keep stating all devices in a parallel circuit must be equal voltage, it's the law! So what happens in this example?

As state multiple times, if you connect two items with different voltages together, they will equalise to a common voltage. The exact nature of how they achieve this depends on the the characteristics of the devices, but it will happen.

For your example, connecting a 34V/60 cell panel and a 20V/36 cell panel together (with blocking diodes) *will* result in a common no-load voltage of 34V. Internally there will be 20V across the string of cells in the 36 cell panel, and the remaining 14V will appear across the blocking diode. The polarity of the voltage across the blocking diode will cause it to be reverse biased and so no current can flow. The 36 cell panel will be completely useless, effectively isolated and unable to contribute.

If you then apply a load to the system, the common voltage will reduce from 34 volts and the voltage across the 36 cell panel's blocking voltage will also reduce equally. Initially all of the current will be supplied from the 60 cell panel only. If you keep loading it so heavily that the voltage drops to 19.7V or so, the blocking diode will become forward biased and the 36 cell panel can start to contribute weakly.

If you load it further such that the voltage drops down to 13V or so, the 36 cell panel will be contributing it's full rated amps, and the 60 cell panel will be delivering something between rated amps and short circuit amps. This 60 cell panel will be running very inefficiently though.

In practice, if you were to connect this to an MPPT controller you would have variable results. Ones that use a genuine hill climbing algorithm may settle on an intermediate voltage between 13V and 19.7V and allow both panels to contribute, but ones that use the open circuit method would probably settle on about 26V and only the 60 cell panel would contribute.

[ramblinrod]

Originally Posted by OceanSeaSpray

The entertaining phase of the argument might have ended long ago...

A solar panel doesn't behave like a voltage source, but a current source. It is not very far off from being an ideal current source at that, which we can see immediately by checking its specs. I was looking at a late generation 36-cell monocrystalline glass alloy-framed Chinese panel no later than yesterday:

P=100W, Voc=22V, Vmp=19V, Imp=5.25A, Isc=5.0A

This means that we get 5.25A at maximum power (at 19 volts) and still 5.0A in short circuit with zero volts and zero power: this is a current source. The current is almost independent of the output voltage. This is significantly different than what happens with a voltage source, like a battery or generator, where the current keeps increasing as the voltage drops.

If we connect two panels of different open-circuit voltage in parallel, the higher Voc panel will initially set the output voltage.
When we start loading this configuration, the output voltage starts dropping. Until this common output voltage reaches the lower Voc of the second panel, only the higher Voc panel will supply current. Then the lower Voc panel starts to contribute as well and the output current reaches a maximum somewhere, but with very poor efficiency as the higher Voc panel is way below its Vmp by then.

This is why we don't connect in parallel panels that don't have about the same output voltage: it fundamentally can't work properly and there is nothing a MPPT controller can do about that.

The common output voltage of a set of panels in parallel ends up wherever the load forces it to be. Connected directly to a battery, the solar voltage simply gets dragged down to battery voltage.
Incidentally, when Vmp is around 17V with the panels being cold, it drops down towards 15V in hot sunny conditions. If the charging voltage is a little over 14V, there is almost nothing left to improve upon with a MPPT in those conditions. This is why a set of 36-cell panels in parallel in the tropics tends to do extremely well with just a switching regulator.

I seem to be doin' a lot of schoolin' these days.

Thank you for sharing your opinion, however any device that produces electrical power, can be referred to as either a voltage source or current source.

So, in case you didn't read my previous post, because the discussion was about the voltage across the panels, I chose to refer to the panels as voltage sources. For that discussion, we weren't concerned about the current.

Referring to a solar panel as a voltage source is 100% correct, especially in this case.