Biggest Solar Panels...

[Statistical]

One additional complication on the endless shading series vs parallel debate is that some very large panels these days are actually using twice as many half cut cells in a series & parallel configuration internally.



There are a couple of advantages of this but the largest one for sailing vessels is that hard partial shading may bypass a smaller portion of the panel. Of course shading is a complicated mess because there is no one type of shading. A lot matters on exact where and how much of the panels is shaded and if that shading is hard or diffuse. Another advantage related to shading is that when you have shading you create localized hotspots in the first shaded cell from power flowing into it from the other producing cells in the string. Having more fewer cell strings in half cut cell panels reduces that effect.

One MPPT per panel is certainly an option and becoming a lot more viable with these supersized panels. You still have to consider the shading impact on the panel output itself and half cells may be an option.

Some people might even have half cell panels and not be aware because at a macro level they "work" just like any other panel. They usually can be identified visually by the pretty pronounced busbar running down the center. In a large array they busbar combined with metal frames can make it look like twice as many "square" panels.

[s/v Jedi]

Originally Posted by noelex 77

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.

Yes, that would be bad and can even overheat the shaded cell and cause a fire.

This is why, since 30 years ago, they include bypass diodes which fix everything. As long as they have not been blown up.

[RedneckRedcoat]

We mounted 3 410watt bifacial on our arch and have not looked back. If you can mount 2-3 panels go for as large as you can. You can never have enough solar

[OS2Dude]

Bigger is not necessarily better. You could go with smaller panels in series, one string per side, to an MPPT controller for each string. (Maybe even a center string as well.) Each string will supply higher voltage, meaning you can get away with smaller gauge cables. The output from the MPPT controllers would connect to a common bus that feeds the batteries. The controllers will convert the higher voltage from the panels to what the batteries need.

Output from panels in series is degraded by shading on any member panel, but the higher voltage lets you run smaller gauge cables.

Output from panels in parallel is not as affected by shading, but the higher amps requires larger gauge cables.

[Nicholson58]

550 or greater, two wires, what gage? The standard solar wire plugs are for #6 or #8 wire. To use the same connectors you will want a high open circuit voltage to keep the amps down. That’s OK and would work out well with MPPT controllers. Make sure the panel internal circuitry has diode separation for dropping shaded cells.

Move your radar.

One of our cruising friends glued flex panel to his deck, each with diodes. Big boat, 1 kw on deck. Lots of shading under way but good exposure at anchor. We are generally anchored about 95% of the time

I too am concerned about the possible flexing of a panel that large. Think of twist. A series of smaller panels will naturally stress relieve at their boundaries. Huge panels are no doubt more desirable in a fixed installation like open field or roof top.

[Statistical]

Originally Posted by OS2Dude

Bigger is not necessarily better. You could go with smaller panels in series, one string per side, to an MPPT controller for each string. (Maybe even a center string as well.) Each string will supply higher voltage, meaning you can get away with smaller gauge cables. The output from the MPPT controllers would connect to a common bus that feeds the batteries. The controllers will convert the higher voltage from the panels to what the batteries need.

Output from panels in series is degraded by shading on any member panel, but the higher voltage lets you run smaller gauge cables.

Output from panels in parallel is not as affected by shading, but the higher amps requires larger gauge cables.

The one circuit for each side of the boat is a good practice regardless. Shading always has an impact at least some impact but there is a good chance that if shading occurs it only happens on half the boat. By having seperate strings on each side of the boat you can at least up the odds that one half will be at max power.

Of course the alternative is one MPPT per panel which is one reason to potentially consider larger panels. However even there maybe not the largest. If you can fit four 400W panels but only three 500W panels then 400W panels may be the way to go. On the other hand if you can only fit three panels regardless of 400W or 500W then 500W would probably be better. Sure you could also have six panels each either their own MPPT but there is a point where larger panels make more sense.

Worth considering the efficiency of the panels as well. For rooftop solar there is no need in many cases because the roof max output is often larger than any planned installation. For boats space is limited and valuable so higher efficiency panels will get more power from the same area. Most quality panels these days are in the same 18% to 21% range so it isn't a huge difference but every bit helps.

[RedneckRedcoat]

I would put a separate mppt controller on each panel and not string them in series. If one of the panels is shadowed you will also loose output from the other.

You really need the maximum amount of amps hitting your batteries and I found Parrellel with separate mppt controllers has worked best for us.

[Senojev]

Originally Posted by HarrisonM

Hello:

I am in the process of upgrading my electrical system to Lithium batteries and Victron. I have a pretty big arch and want to install the largest panels I can. Renogy makes a 550 watt panel. Does anyone know if a larger one exists?

They keep getting bigger and bigger...

Link
https://www.renogy.com/550-watt-mono...xoCYKIQAvD_BwE

The problem with getting any panels is the shipping costs which can run into hundreds of dollars. Home Depot has the 550W Renogy for $960 for two with free delivery to the store. I have two Renogy slightly smaller and have been very pleased with results.

[hzcruiser]

Originally Posted by michaeld

Here is what works for us: three 175W panels in parallel. We get about 20A on a clear day.Attachment 277278

3 * 175 W = 525 W
525 W / 12 V = 43.75 A

Or do you have a 24V bus? In that case, you're golden.

[hzcruiser]

Originally Posted by OS2Dude

[...]

Output from panels in parallel is not as affected by shading, but the higher amps requires larger gauge cables.

I'm afraid not many people would subscribe to that statement.

[Pete7]

Originally Posted by s/v Jedi

The parallel connection is the worst option. You stack current so multiply resistance losses, you don’t get more voltage so no extended period of production and when a panel gets partially shaded you loose output of that complete panel instead of just part of it.

So in a parallel array of two panels, one shaded string in one panel means no output from that panel. That would be a big hit with two panels

Just thinking about the sorts of shading we have seen over the years. Surprisingly we don't often sail south for any length of time, so sails probably aren't a big factor. However, our mast or someone else's mast if we are rafted up is. This is a big variable, but tends to be one or at worst two of the 6 strings suggesting parallel may not be the ideal I thought it was. 10m of cable losses drop from 3.77% to 0.8% too.

Hmm, food for thought, or just buy a second MPPT and not worry.

Pete

[hzcruiser]

Originally Posted by GreenWave

Beau and Brandy is a great channel. Don't drink the kool aid though that they are hurting and on a limited budget. Youtube is definitely paying their bills and then some.

They ave 50k subscribers and 20-50k views on average, very few over 100k.

YT pays $18 per 1k views, that's $360-$900 per video. Not bad if you put out one every week.

Given that with the Amazon kickback from their big list of stuff should keep them afloat, yes.

However, to get those subs you need pretty expensive camera equipment plus at least a drone and then lots of time for editing.

[hzcruiser]

Originally Posted by Pete7

[...]

Hmm, food for thought, or just buy a second MPPT and not worry.

Pete

That would require a second run of wires down below, which sometimes is not feasible or fairly expensive. Pushing another set of wires just through the arch tubing can be difficult enough.

But yes, every solution has its merits.

[s/v Jedi]

Originally Posted by Pete7

So in a parallel array of two panels, one shaded string in one panel means no output from that panel. That would be a big hit with two panels

Just thinking about the sorts of shading we have seen over the years. Surprisingly we don't often sail south for any length of time, so sails probably aren't a big factor. However, our mast or someone else's mast if we are rafted up is. This is a big variable, but tends to be one or at worst two of the 6 strings suggesting parallel may not be the ideal I thought it was. 10m of cable losses drop from 3.77% to 0.8% too.

Hmm, food for thought, or just buy a second MPPT and not worry.

Pete

Yes, you can fix this by giving each panel it’s own controller. They must be MPPT controllers. With partial shading, this gives you partial output, just like series connection (so why not series….)

[Statistical]

Originally Posted by Pete7

So in a parallel array of two panels, one shaded string in one panel means no output from that panel. That would be a big hit with two panels

Well no not unless the panel is completely shaded.

All panels have internal bypass diodes. That brakes the series wired cells inside the panel into three sub strings which can each be bypassed.

So what gets super complicated about shading is there is no one simple all situation answer. If you have 20% shading how much power output do you lose from a panel?

Trick question it depends on exactly how that shadow lies. If the shadow lies completely across one of the three substrings you would still have 66% output. ~2/3rds volts and full amps. If it lies across two of the substrings then you would have 1/3rd volts and full amps. If it lies across three of the substrings you would have zero volts output.


As an example consider two panels. At full sun they are 30V and 10A = 300W. The numbers are just illustrative.

One panel is completely unshaded and one panel has shading on two or more cells within the same substring.

Output:
Shaded panel = 20V 10A = 200W
Unshaded panel 30V 10A = 300W

The key thing is only volts are reduced because cells inside the panel are in series. Losing one cell means losing 1/3rd substring. Technically you lose a bit more voltage because the bypass diode has a voltage drop as well but that doesn't materially change the conclusions. Note: in a half cell panel you could lose even less due to having six not three substrings.

Series Output:
Putting them in series is super simple. Voltages simply stack. You end up with 10A @ 50V = 500W. The losses in one panel do not impact the other panel. The only issue would be if voltage pushes you below the MPPT turn on voltage (which depends on pack voltage) but really only a concern if string voltage is very close to pack voltage. Proper panel selection can avoid that.

Parallel Output:
This gets complicated. We now have two different voltages wired into parallel We have 20V and 30V in parallel @ 10A each. Without an MMPT this would be very terrible at worst you could get as little as 20V*2 = 40V @ 10A = 400W.

To understand MPPT it is important to recognize panels don't have fixed voltage. Most examples just use the voltage at vMPP. The MPPT controller can force the voltage of the circuit to a different value. So it could bring the string voltage down to near 20V. Now at 20V instead of 30V the unshaded panel will produce more amps. Not 50% more amps but maybe something like 13A instead of 10A. So you have 20V & 23A (13A + 10A) = 460W.

So series is always better? In this example it was however this involved hard shading (like bright sunny day with no clouds) creating a distinct shadow sufficient to cause the voltage drop in one or more cells to exceed the bypass diode leading to the substring cleanly but punitively cutting out the entire substring. Shading can also be diffuse on cloudy days resulting in bypass diode not being used but altering the amperage of the panels and they can be different. One panel might be 9.2A and the other 8.7A. Now you have the reverse bad situation for series arrays. The good panel will be forced down to 8.7A. So series ends up worse. Now the losses from diffuse shading tend to be a lot smaller so the impact isn't as big on output.

One area that series should never be used is when you have panels or groups of panels with different angle to the sun. Like 3 panels on a solar arch which are parallel and then two more panels on a bimini with a slight cant. The angle to sun will impact power intensity but amperage varies more significantly than voltage so the two groups should not be in series with each other. The best option would be two put groups of panels with different mounting characteristics on their own controller but if you absolutely had to use one controller parallel would be less bad than series. This is because the panels will have different voltage and amperage outputs but the amperage will differ more significantly.

TLDR: It is complicated. There is no one perfect answer. It depends on exact how much shading, what type of shading, where exactly the shading lies across the panel. However the use of bypass diodes makes the impact on series strings less bad than most older "textbook" examples indicate. Likewise the effectiveness of modern MPPT controllers makes parallel less bad than it might otherwise seem on paper. The combination of the two has made panels a lot less vulnerable to light partial shading. The introduction of half cut cell panels improves that even further. MPPT are also cheap enough these days that simply bypassing the entire issue and going with one MPPT per panel is also a very viable option.