Biggest Solar Panels...

[s/v Jedi]

Originally Posted by Seafarer7

S/V Jedi: interesting analysis and food for thought here (re: series being better than parallel). But doesn’t the quoted scenario above ignore the fact that the parallel panels are connected to an MPPT controller that constantly sweeps the voltage range searching for the sweet spot? ie: I would assume immediately after the shading event above the MPPT controller would drop from 45v to somewhere nearer to 30v if the total power output at 30v exceeds that at 45v. So even though the two unshaded panels wouldn’t be operating at their peak MPPT output at 30v, still the total output at the new 30v point would still be much more than 720w?

That is to say: after the shading event above, with a new 30v tracking point output: all three panels would be contributing power, with two unshaded panels operating somewhat below their rated maximum power (below 720w), and the shaded panel outputting 2/3rd of it power(~240w). Sum total of the three should be much better than the total removal of one panel that would occur if the MPPT controller continued to pin its intake voltage at 45v

No that doesn’t work because you simply have a panel that only outputs 2/3 of the voltage of the other panels. With parallel connections, the panels must have the same voltage.

Also, the MPPT controller can not sweep the whole voltage range. When you have panels at 45V and one at 30V then you would need to be somewhere down at 20-25V to get power from the 30V panel but then the other ones are way mismatched and don’t perform anymore.

It’s easy to try in a lab setup… just use two benchtop power supplies and connect them in parallel to the MPPT controller input with a battery on the output. Now you can change voltages and immediately see what happens.

You can also connect the two power supplies in series (remove ground to negative jumper at the terminals) and give each power supply a bypass diode. Now switch one off and see what happens with the other

[s/v Jedi]

Here is a picture where I am doing exactly that test the two devices on the left are the two power supplies.

When you test, you know

Second picture shows the lfp battery I test against, with cell monitoring :-)

[Pete7]

Originally Posted by rslifkin

Based on what you've got now, could you extend forward and make a bimini of sorts out of panels? As long as you can keep them under the boom, it looks like you should have space.

Sadly, I think I only have about 8" before reaching the boom which is at a similar height as the forward edge of the panels. The existing panels are 1.5m in length whilst the Hyundai are 1.7m so could pinch a bit.

The other problem is if you are behind the wheel and it rains, guess were the rain drips off on to Yup me.

Pete

[Pete7]

Originally Posted by Grith

Hi s/v Jedi Thanks for your continued informative posts.

Yes, I would like to add my thanks to Jedi, Noelex and indeed everyone contributing, particularly the argument for parallel or series connections.

Previously having watched lots of YT on the subject (see below) and following the recommendations on CF, we wired the two 295w panels in parallel. However, I am now starting to doubt this and some field testing is needed.

Easy enough to switch the wiring round and do a snap shot in time. However, what really counts is the daily output averaged over a series of days with similar weather conditions, not that easy in England. The shading is going to change whether at sea and changing course or in harbour as the sun moves.

More testing required, meanwhile I can smell the roast port in the Remoska is nearly cooked

Pete

https://www.youtube.com/watch?v=1qD3...newiththeWynns

[rslifkin]

Originally Posted by Pete7

Sadly, I think I only have about 8" before reaching the boom which is at a similar height as the forward edge of the panels. The existing panels are 1.5m in length whilst the Hyundai are 1.7m so could pinch a bit.

The other problem is if you are behind the wheel and it rains, guess were the rain drips off on to Yup me.

Pete

Could you put additional panels forward, but mounted slightly lower so they sit just under the boom? Or is headroom already at a premium there?

[s/v Jedi]

Originally Posted by Pete7

Yes, I would like to add my thanks to Jedi, Noelex and indeed everyone contributing, particularly the argument for parallel or series connections.

Previously having watched lots of YT on the subject (see below) and following the recommendations on CF, we wired the two 295w panels in parallel. However, I am now starting to doubt this and some field testing is needed.

Easy enough to switch the wiring round and do a snap shot in time. However, what really counts is the daily output averaged over a series of days with similar weather conditions, not that easy in England. The shading is going to change whether at sea and changing course or in harbour as the sun moves.

More testing required, meanwhile I can smell the roast port in the Remoska is nearly cooked

Pete

I think this is the video making everyone go for parallel. But something is wrong and they are not knowledgeable enough to realize this and find out what is going on.

I wish I find the time to do an actual test with panels.

[Pete7]

Originally Posted by rslifkin

Could you put additional panels forward, but mounted slightly lower so they sit just under the boom? Or is headroom already at a premium there?

Yes you guessed it, I am just safe during a jybe but still duck, No 1 son at 6'4" no chance.

Were we do have space is out the back so 20cm more in length for 400w panels is neither here nor there. Our club marina doesn't measure boats (yet) and if we visit somewhere else for a short stay then don't bother and accept that if we say its a Moody 31, they bill us on that.

The other question having just fitted 2 x 295w panels is do we need to change again? It's a shed load of work that took 3 people last time. We are away in September for a few weeks which will give us a better idea of what we use in colder weather and generate in Autumn sunshine rather than glorious sun in June. We haven't used the alternator so far this year, so that is the card up the sleeve if we are a bit short due to inclement weather.

We are at home on mains at the moment and this tonights tea, but also what we cook on board with sunshine.

Pete

[Pete7]

Originally Posted by s/v Jedi

I think this is the video making everyone go for parallel. But something is wrong and they are not knowledgeable enough to realize this and find out what is going on.

I wish I find the time to do an actual test with panels.

The Sailing with the Winns video was filmed 6 years ago and we don't know the age of the panels, so could be that they have used panels without diodes. It would need careful watching to see what happens to the parallel tests.

off grid garage

Andy did a much newer and easier to understand tests recently with 440w shingled panels. However, it depends on how the shingles (like roof slates that overlap so no cell bus bars) work.

What happens to bifacial panels if one is shaded, oh lordy more conundrums.

[noelex 77]

Originally Posted by s/v Jedi

Here is what really happens:

Let’s say we have three panels of 45V, 8A in series. This means the array becomes 135V 8A = 1,080W. Each panel has three strings, three diodes. So each string is 45 / 3 = 15V

Now let’s say shading hits one string of one panel. The bypass diode of that string in that panel starts conducting. We lose the 15V voltage of that string, plus we have a 0,6V voltage drop over the diode that is a loss. The array becomes 119.4V (135 - 15 - 0.6) and 8A so we have 955.2W left.

Yes, the whole array is affected because voltage is lowered by 15V and the current from the unshaded part is affected by the bypass diode, which is wasting 8 x 0.6V = 4.8W of power as heat.

But is that bad? Let’s compare with the same panels connected in parallel. Let’s also assume there are no wiring losses and no reduced daily period. So we now have an array that is 45V 24A equals 1,080W. We get the shaded string so one panel reduces it’s output voltage to only 30V and can’t output current to the 45V input terminals at the controller. We are simply left with a 45V 16A array which equals 720W.

So shading in parallel doesn’t alter the array voltage but it does alter the amperage. In series you loose only the shaded string(s) which may not be the whole panel. You do get the additional loss of the diode but this is less than 5W.

In real life you don’t have this shading all the time. But no matter how you spin it, the series connection still outperforms even before considering other losses like in wiring or reduced period of production.

The mathematical modelling of series versus parallel connection of solar panels is incredibly complex. Not only are there multiple possibilities of how the shadows can fall, in some cases affecting one string, in other cases multiple strings, in practice very few shadows are so absolute the cell output drops to zero. In most cases the shading is more diffuse and reduces the output of the cell, but does not cut it completely. There is also the problem of calculating the new Vmp for each shaded condition.

It is possible to give examples where either series or parallel connection is superior, but this does not answer the more important question that is, on average, which will perform better.

The only way to assess which is the better configuration on average is to do a practical test. Personally, I have never had the patience or opportunity to do a well controlled experiment, but I know several cruisers that have gone to this trouble and parallel connection always seems to win. The only caveat I would place on this is that for optimum performance with series connection an additional whole panel bypass diode is helpful (although the improvement is small) and few people go to the trouble to incorporate this into the experimental design.

It should be noted that the differences between series and parallel connection is not great. Also that series connection is much easier and cheaper because the wiring can be smaller. So series connection can be a sensible choice even if the total energy output is lower, especially if it is not practical to fit thicker gauge wiring.

Finally, the best choice in terms of total output (with rare exceptions) is always one controller per panel so if optimum performance is your goal, this is the best solution. It is often not much more expensive (or in rare cases it may be cheaper), as multiple small controllers are generally little more expensive than one larger controller, and in addition you gain valuable redundancy.

[Nor]

Originally Posted by s/v Jedi

No, that is a myth from 30 years ago when solar panels for boats were new. It is persistent, even though they have been putting in bypass diodes for decades.

When you have two large panels in parallel and one of them gets partial shading, triggering a bypass diode… then this partially shaded panel has a lower voltage and the other panel tries to dump charge into it. Even when that is blocked, the array will never perform because it has lost 50% output.

The same panels in series only lower output voltage for that single string, which may only be 1/3 of that panel and the rest just keeps on going.

Thanks for the useful info and experience!

I'm considering putting 3 or 4 550W panels in series, using a Victron Multi RS 48 6000 inverter/charger/solar controller.

https://www.victronenergy.com/upload...S-Solar-EN.pdf
panels
https://www.enfsolar.com/pv/panel-da...stalline/48941

These panels are 2279mmx1134mm so, totally 3,4meter wide on my 6.1M wide catamaran.
I could put another panel on the bimini, however it could be more shaded by the mast, so I'm not sure if this will help or hurt the whole array when connected in series to the Multi RS. The Multi RS needs 120V to startup, so I'm a bit worried that it won't start with only 3 panels if partially shaded, however it can track down to 80V once started.

Seems not much info on the Multi RS on the forum, I assume not many running 48V banks. I'm planning to add a separate 48V bank for the inverter, and then just charge the 12V bank from 230V when needed.

[CaptainRivet]

Originally Posted by s/v Jedi

No that doesn’t work because you simply have a panel that only outputs 2/3 of the voltage of the other panels. With parallel connections, the panels must have the same voltage.

Also, the MPPT controller can not sweep the whole voltage range. When you have panels at 45V and one at 30V then you would need to be somewhere down at 20-25V to get power from the 30V panel but then the other ones are way mismatched and don’t perform anymore.

It’s easy to try in a lab setup… just use two benchtop power supplies and connect them in parallel to the MPPT controller input with a battery on the output. Now you can change voltages and immediately see what happens.

You can also connect the two power supplies in series (remove ground to negative jumper at the terminals) and give each power supply a bypass diode. Now switch one off and see what happens with the other

But does the voltage of the panel drop if you partly shade it. Per row the wavers are in series creating one string with bypass diode, then their strings are wired in parallel. So if the panel gets partly shaded voltage stays nearly the same (due to some losses) but amps decrease.
The voltage will only drop if most or all strings are partly shaded. At least thats how my Longli Bifacials work.
So paralleling them is prefered to connect in series then, only series if you don't get shading.
Don't care as each is on his own MPPT as the backside is also there acting differnetly then top. They create 10-15% more per day on its own MPPT then in series or parallel.

[CaptainRivet]

Originally Posted by Nor

Thanks for the useful info and experience!

I'm considering putting 3 or 4 550W panels in series, using a Victron Multi RS 48 6000 inverter/charger/solar controller.

https://www.victronenergy.com/upload...S-Solar-EN.pdf
panels
https://www.enfsolar.com/pv/panel-da...stalline/48941

These panels are 2279mmx1134mm so, totally 3,4meter wide on my 6.1M wide catamaran.
I could put another panel on the bimini, however it could be more shaded by the mast, so I'm not sure if this will help or hurt the whole array when connected in series to the Multi RS. The Multi RS needs 120V to startup, so I'm a bit worried that it won't start with only 3 panels if partially shaded, however it can track down to 80V once started.

Seems not much info on the Multi RS on the forum, I assume not many running 48V banks. I'm planning to add a separate 48V bank for the inverter, and then just charge the 12V bank from 230V when needed.

Due to redudancy i would stay away from it and get Multi plus seperate MPPTs.
The MPPT in the RS must start much earlier then 120V, for 48V MPPT its normally in the area 53-60V.
2nd get Bifacial panels from a top tier manufacturer they are perfect on davits and back creates +20% plus they work with diffusion light means less affected by shading. On pasaage i get now 70% instead 30% of my production compared to on anchor. Same location just Longli bifacials instead of good LGs.
I would wire 2 panels in series to get the needed voltage for the MPPT in 48V but put only 2 on one controller. Add also Bimini the backside won't produce much but top will do and put them on seperate MPPT too.
Fit As much solar as you can as this is cheapest, quiet maintenence free power and you can never have enough of it.
Yes more cabling effort but you need redudancy on a boat unless its a costal cruiser.

[noelex 77]

Originally Posted by CaptainRivet

So if the panel gets partly shaded voltage stays nearly the same (due to some losses) but amps decrease.
The voltage will only drop if most or all strings are partly shaded. At least thats how my Longli Bifacials work.
So paralleling them is prefered to connect in series then, only series if you don't get shading.

This is how solar panels fundamentally behave with diffuse shadow. Shadows on boats are very common, but are not generally absolute, the solar cell still receives some indirect illumination.

When exposed to lower levels of illumination such as in a shadow area, solar cells will produce much less current, but a similar voltage. This creates problems for panels connected in series.

This can be seen in the graph below. Notice how as the illumination drops the voltage drops only slightly, but the current decreases dramatically.

[s/v Jedi]

Originally Posted by CaptainRivet

But does the voltage of the panel drop if you partly shade it. Per row the wavers are in series creating one string with bypass diode, then their strings are wired in parallel. So if the panel gets partly shaded voltage stays nearly the same (due to some losses) but amps decrease.
The voltage will only drop if most or all strings are partly shaded. At least thats how my Longli Bifacials work.
So paralleling them is prefered to connect in series then, only series if you don't get shading.
Don't care as each is on his own MPPT as the backside is also there acting differnetly then top. They create 10-15% more per day on its own MPPT then in series or parallel.

No, that is not how it works and this is exactly how misinformation gets spread. Why do you write that? How can you have strings with bypass diodes in parallel? This is impossible!

A modern solar panel has three strings.

Each string consists of cells in series and it has a bypass diode anti-parallel to the string of cells.

The three strings of the solar panel are connected in SERIES. Again, in SERIES. So when one string gets shaded, voltage becomes 1/3rd lower plus you lose 0.6V extra because of the bypass diode loss.

This is why it’s actually funny when people say panels must be connected in parallel. Because their panels are actually three panels connected in series in one frame.

To summarize: when a string of cells gets shaded, it’s bypass diode passes the current if the whole array around the shaded string, which means that the current stays the same and the voltage is reduced.

[rslifkin]

Noelex has a good point. Diffuse shadows may lose less power in parallel, while shadows severe enough to drop a section of a panel down to near-zero will do better in series.