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Old 17-09-2019, 11:25   #1
DK2
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Solar panel config question

OK all you solar experts I am planning to add 900w of solar to a solar arch over the davits. This will be 3 x 300w 24v mono panels. Iím looking for comments on whether to connect them in series or parallel (or even individually) pros and cons for each. Shading of individual panels shouldnít be an issue back there. My other flex panels are connected in parallel and that works fine. My thought is that if I connected in series, the cables to the MPPT could be lighter (10awg) since they will be carrying around 75v and 10a max, whereas if in parallel I will need some bIgger cables from the point at which they join to the MPPT since they will be around 24v/30a. Am I overthinking it? Any other thoughts? Thanks team!
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Old 17-09-2019, 12:17   #2
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Re: Solar panel config question

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Am I overthinking it? Any other thoughts? Thanks team!
Pretty much.

If the controller is a mppt and the panels Vmp is well above the battery voltage the only difference in the long term real world use is the cable size (IMO because this topic goes on and on and on and on)
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Old 17-09-2019, 12:35   #3
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Re: Solar panel config question

There are always some shading issues with solar panels on a sailboat. You just cannot get rid of the pesky mast and standing rigging. Yachts mounting the solar panels on an arch well to stern, above the level of the boom, and without any aerials or wind generators above them will have fewer shading issues than other boats, but even slight shading has a very significant impact on solar panel output.

In terms of shading performance, the best results are with individual controllers for each panel, followed by parallel connection, with series connection the worst choice. The cost and difficulty of installation is normally the exact reverse order of the above, although there are anomalies. For example several small solar controllers can be a similar price to a single larger controller in some cases. However, the cost and difficulty of installing the thicker (or multiple) wiring for the first two options is often significant and that results in series connection being significantly less expensive and easier.

The important question is how much of an improvement in output is seen with the more expensive and difficult options. Unfortunately, this is hard to quantify. There have been few valid and scientific comparisons. My impression is for most boats given the difficulty and cost of fabricating a solar arch and the cost of the panels themselves etc it is usually worth doing it right and at least using parallel connection, if not individual controllers, despite the extra wiring cost and difficulty over series connection.
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Old 17-09-2019, 12:40   #4
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Re: Solar panel config question

When I first installed my two 100w , 19v panels in parallel I was not happy with the performance. Turned out there was not enough head room to really drive 14v into the batteries on anything but direct sunlight. I then wired them up in series and found the performance much improved in sub optimal lighting conditions.
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Old 17-09-2019, 13:09   #5
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Re: Solar panel config question

If house batts at 12V - wire as you like. (panels are already 24V as you said)



If house batts at 24V - wire panels up, to bump voltage on the panel side. (48, 72, etc.)



MPPT regulators deliver best when the panels are delivering way more volts than the battery side of the circuit.


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Old 17-09-2019, 13:12   #6
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Re: Solar panel config question

And use fat wires anyway as voltage drop is energy lost. So you want as little voltage drop as you can get.


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Old 17-09-2019, 20:59   #7
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Re: Solar panel config question

get 3 mppt controllers. wire each to own

best results
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Old 17-09-2019, 21:53   #8
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Re: Solar panel config question

Look for higher voltage panels (36+). Wire individually to their own controllers. This provides redundancy and should ensure maximum harvest.
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Old 18-09-2019, 01:41   #9
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Re: Solar panel config question

I've xperimented with various configurations.


I now use and will stick with a series parallel arrangement, two panels a side each side wired in series and then both sides in parallel into a MPPT controller. Battery bank is 12v (13.7 ) voltage is usually around 32v at the charger input.



I might add another 2 panels over the davits for the times the mast or sail shadow falls across a bank. I'll just parallel these into the feed from the other 2 banks.



One good MPPT controller has worked well with this setup it also interfaces with a PC, does the intelligent battery charger routine.



I've seen a lot of small cheaper chargers that say they are MPPT but they aren't they are actually PWM.



Most significantly I'm getting a much better result than the older PWM regulator.


My charger tech info says specifically not to parallel other solar chargers as it will go from bulk charge to float too early and will confuse it's intelligent charging based on current sensing, voltage and programmed battery bank size.



But you can parallel PWM to your hearts content
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Old 18-09-2019, 08:37   #10
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Re: Solar panel config question

Based on your situation I'd go serial
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Old 18-09-2019, 08:58   #11
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Re: Solar panel config question

Quote:
Originally Posted by noelex 77 View Post
There are always some shading issues with solar panels on a sailboat. You just cannot get rid of the pesky mast and standing rigging. Yachts mounting the solar panels on an arch well to stern, above the level of the boom, and without any aerials or wind generators above them will have fewer shading issues than other boats, but even slight shading has a very significant impact on solar panel output.

In terms of shading performance, the best results are with individual controllers for each panel, followed by parallel connection, with series connection the worst choice. The cost and difficulty of installation is normally the exact reverse order of the above, although there are anomalies. For example several small solar controllers can be a similar price to a single larger controller in some cases. However, the cost and difficulty of installing the thicker (or multiple) wiring for the first two options is often significant and that results in series connection being significantly less expensive and easier.

The important question is how much of an improvement in output is seen with the more expensive and difficult options. Unfortunately, this is hard to quantify. There have been few valid and scientific comparisons. My impression is for most boats given the difficulty and cost of fabricating a solar arch and the cost of the panels themselves etc it is usually worth doing it right and at least using parallel connection, if not individual controllers, despite the extra wiring cost and difficulty over series connection.

Agree with all. And don't forget shading from bird poop! You don't want to have to climb around cleaning your panels because a single spot of bird poop is degrading the entire series array. Go parallel. Wire isn't that expensive, and you can have thinner gauge wires from each panel to the parallel common connection point. It's true that each panel having its own MPPT controller is best, but good controllers aren't cheap, and multiple controllers add significant complexity (more stuff to go wrong). If your budget can support four controllers and four panels, or one controller and eight panels -- it's better to have eight panels. If your budget is unlimited, it's better to have a nuclear reactor ;-)

I always install a schottky steering diode in series with each panel output to both block back-current into shaded panels and to prevent a failed-shorted panel from drawing current from the entire parallel array - which could become a safety issue.

This diode, or similar, should do the job provided the OCV voltage of each panel is below 40 volts and the short circuit current of each panel is below 8 amps: https://www.mouser.com/ProductDetail...AHy7cKIywGc%3D

Yes, there's some loss from the diodes, but if you use schottky diodes, they have a forward voltage drop of only 0.6 volts at full rated current. The loss in watts is very small (at 5 amps, the loss is 3 watts). The diodes cost less that a buck, and it's worth the assurance that a shorted panel won't force you to climb around troubleshooting at sea, or need to empty your fire extinguisher.
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Old 18-09-2019, 12:44   #12
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Re: Solar panel config question

Three 100/30 Victrons cost less than $700 total for the Bluetooth models.
A single Victron 150/85 is $700.

Plus you have failure modes. There is no complexity. The wiring is more simple. If one fails you still have power. No need to carry an expensive spare. If you want a spare, you carry a $225 item vs $700 item.

Add on you will likely get more total harvest per day.
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Old 18-09-2019, 13:42   #13
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Re: Solar panel config question

Five million solar posts and THIS ONE is by far the most succinct and useful reply, ever.


Thanks for your clarity.


Not that the OP couldn't have found this answer with a little reading, right here on CF.


Well done!


And I don't even have solar (other than a small maintenance panel connected to a pwm cheap controller to allow me to unplug the boat between cruises).


I keep asking myself "Why is budget an issue when it comes to wiring when the panels and their supports cost so much to begin with? Why not get the very most one can from the concept?"


Sure, it all adds up, but why do it wrong to start off?



Quote:
Originally Posted by noelex 77 View Post
There are always some shading issues with solar panels on a sailboat. You just cannot get rid of the pesky mast and standing rigging. Yachts mounting the solar panels on an arch well to stern, above the level of the boom, and without any aerials or wind generators above them will have fewer shading issues than other boats, but even slight shading has a very significant impact on solar panel output.

In terms of shading performance, the best results are with individual controllers for each panel, followed by parallel connection, with series connection the worst choice. The cost and difficulty of installation is normally the exact reverse order of the above, although there are anomalies. For example several small solar controllers can be a similar price to a single larger controller in some cases. However, the cost and difficulty of installing the thicker (or multiple) wiring for the first two options is often significant and that results in series connection being significantly less expensive and easier.

The important question is how much of an improvement in output is seen with the more expensive and difficult options. Unfortunately, this is hard to quantify. There have been few valid and scientific comparisons. My impression is for most boats given the difficulty and cost of fabricating a solar arch and the cost of the panels themselves etc it is usually worth doing it right and at least using parallel connection, if not individual controllers, despite the extra wiring cost and difficulty over series connection.
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Old 18-09-2019, 15:45   #14
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Re: Solar panel config question

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.............
I always install a schottky steering diode in series with each panel output to both block back-current into shaded panels..............



My panels came with blocking diodes installed, it's inside the connection box. I was told that was standard now ?
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Old 18-09-2019, 17:00   #15
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Re: Solar panel config question

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My panels came with blocking diodes installed, it's inside the connection box. I was told that was standard now ?

It would be very odd to see a factory installed steering diode because steering diodes are only compatible with a parallel array and will disable panels connected in series. You can verify that with an ohmmeter. With the panel isolated and no light on the panel (put something opaque over the panel like a towel), connect the probes in reverse polarity. You should read infinite or very high resistance. If you read only a few ohms, the diode is connected in parallel, and instead of being a steering diode, it's a bypass diode intended to pass current around a shaded panel when connected in a series array. If that's the case - you can leave the factory diode in place but you still need a steering diode for a parallel array configuration.


If you can see the diode, you can also visually verify its function. If it is connected in parallel with the panel output, and the end with the stripe marking (the cathode) is connected to the positive panel output, then it's a bypass diode, not a steering diode -- and it will do no harm but also do no good in a parallel panel configuration.


The conventional configuration is to connect each steering diode in series with the positive output lead of each panel, with the anode (the end farthest from the stripe marking) connected to the panel positive lead.


I should have mentioned in my post above that another advantage of a parallel array is the flexibility of connecting several panels of differing outputs on the same array - as long as their Vmp voltages are the same or very closely the same. My strategy is to harvest power over the full arc of the sun. I have nine 12.5 watt panels, two 50 watt panels, and two 70 watt panels. They all are within 0.5 volts of the same Vmp, but would not function well at all in a series array -- nor could I possibly have space and budget to install 13 MPPT charge controllers: one for each panel. But they work quite well in a parallel array.
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