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Old 06-07-2019, 21:15   #1
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Newbie solar controller question

Hi

This is a bit of a newbie question but I have not found a straight answer online.

Should I have my solar panels wired in series to one controller or seperate controllers per panel?

Currently the setup which is quite old has 3 x Gensun GV10 (1 per panel) all with its own wiring between controller and panel.

I would like to change to Victron since thats what the rest of the boat is, but should I replace leaving wiring as is with 3 new controllers or wire the panels in series with one controller?

Cheers

Al
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Old 06-07-2019, 22:41   #2
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Re: Newbie solar controller question

If you use a single big controller, you will suffer more losses due to shading whether series or parallel than if you use a small controller for each panel. If you have to use one controller then there is an advantage to either the series or parallel, I can't remember which. Diodes help but there is voltage loss with them.
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Old 06-07-2019, 22:56   #3
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Re: Newbie solar controller question

When we put the solar on our boat the supplier recommended that we use a separate controller for each panel. The cost for 2 smaller Victron controllers was about the same as for 1 large controller. I am happy to have taken the advice as there are times when 1 panel is shaded and putting out as little as 3 amps while the second ipanel s producing 18 plus amps.
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Old 06-07-2019, 23:20   #4
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Re: Newbie solar controller question

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Originally Posted by njoynthewater View Post
When we put the solar on our boat the supplier recommended that we use a separate controller for each panel. The cost for 2 smaller Victron controllers was about the same as for 1 large controller. I am happy to have taken the advice as there are times when 1 panel is shaded and putting out as little as 3 amps while the second ipanel s producing 18 plus amps.
If they were wired in parallel to one appropriately sized controller then surely the result would be the same.?
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Old 07-07-2019, 00:05   #5
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Re: Newbie solar controller question

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If they were wired in parallel to one appropriately sized controller then surely the result would be the same.?
Yes.
There are benefits and drawbacks for each design.

Large controller are usually more sophisticated, have a higher efficiency and are better configurable.

The current is everywhere in the loop the same, solar panels are current sources. The voltage reaches very soon the upper Voc with little radiation, the current goes up almost proportionally to the radiation.

Connecting panels in series brings a higher input voltage, and if the panels are unshaded stationary mounted on a roof of a building, this is the most efficient setup, due to the higher voltage and the simpler wiring. It is cheaper to set up an array and voltage drops along the wiring results in less power losses at the controller. When shading one panel, the current is limited by it, and the whole string drops power until the bypass diodes break through, but in general you have a huge power drop then.

If you have a moving roof with partial shading, like on a boat or RV, connecting the panels in parallel is a better option. With 3 or more strings in parallel it is advisable to take protection measures for reverse currents on partial shading or hardware failures of one panel, it can be string fuses or diodes. The current in a parallel set up is the summ of the currents per string, so each panel contributes to the total output its part according to the radiation on it. The system voltage is lower and the currents are higher to the controller, so you need thicker cabling to mitigate power losses by voltage drops.

The most expensive and inconvenient set up is a separate controller per panel, small controllers usually have not all features, you have more transformation losses and cabling, more maintenance, but also redundancy if one controller has a failure.

Regarding the power output you will end up similar to a parallel setup.

If you plan a new array, first you have to make a decision on the controller technology you want to use MPPT OR PWM.
Both are efficient with the right panels. If you decide for MPPT, your panels must yield at least 3V Vmp more than your cut-off voltage for absorption, the higher the better. AGM batteries this are 14.8V, so you need at lest 18..20V Vmp. There are high voltage panels on the market with 30V or even 60V output, ideal for MPPT controllers. A PWM controller requires a panel voltage near the cut off voltage, higher voltages are not beneficially, so a 18..20V panel is the upper limit for a 12V installation with a PWM controller, also there is only the parallel option available, no panels in series.

We use a Victron 150/100 smart solar controller with 5 x 330Wp 96 cells panels, panel voltage 60V, Vmp 52V. We get a charge current of up to 100A out of it, and the controller has a built in Bluetooth interface.

We could have set up more than one controller, but then system monitoring gets inconvenient, and also smaller cheap controllers cannot cope with the high input voltage.

We have a spare controller on board just in case.
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Old 07-07-2019, 00:08   #6
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Re: Newbie solar controller question

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Originally Posted by Uncle Bob View Post
If they were wired in parallel to one appropriately sized controller then surely the result would be the same.?


Nope.

If part of one panel has multiple cells fully shaded (shadow or a sail) the voltage from that panel will be decreased. In parallel the panels will be seen by the controller at the lower voltage or maybe slightly above. If the voltage is below what is needed to recharge the batteries you get nothing out of either panel.
In series you probably the the 2 voltages added but amperage is affected.

If you have partial shading of cells (shadow of stays or sheets) you’ll get nominal voltage but amperage will be compromised.
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Old 07-07-2019, 00:18   #7
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Re: Newbie solar controller question

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Nope.

If part of one panel has multiple cells fully shaded (shadow or a sail) the voltage from that panel will be decreased. In parallel the panels will be seen by the controller at the lower voltage or maybe slightly above. If the voltage is below what is needed to recharge the batteries you get nothing out of either panel.
In series you probably the the 2 voltages added but amperage is affected.

If you have partial shading of cells (shadow of stays or sheets) you’ll get nominal voltage but amperage will be compromised.
We are talking about a properly sized system... It is always the current drop, the voltage Voc of a shaded panel does not drop much, at least not at this extent you mentioned. A current drop in a serial loop affects the whole current, a current drop in a parallel installation affects only the according branch, be it with a single controller or a controller per string.
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Old 07-07-2019, 00:45   #8
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Re: Newbie solar controller question

Ideal is one SC per panel, matched to suit.

Only downside is more wiring, but that's already in place.

Victron makes this much more cost effective than most.
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Old 07-07-2019, 00:47   #9
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Re: Newbie solar controller question

The degradation of output is dependent on how the panel is shaded.

Each panel is made up of a 1 or more strings of solar cells. How many cells in each string affects voltage. Each cell produces 0.5v-0.6v. 30 cells at 0.6v gets you 18v. 36 at 0.5 also gets you 18v. The area of a cell affects how many amps it will produce.

Unshaded the voltage of each string is the sum of voltages for each cell and the amperage is the amperage of the weakest cell.

If whole cells are shaded voltage for the string will drop by 0.5-0.6v for each cell shaded.

If cells are partially shaded (ropes or stays) amps will drop but voltage will be maintained.

If you have 2 parallel strings and one has fully shaded cells the voltage on that side will drop and the unshaded side will be trying to push power into the shaded panel as well as the controller.

The land side solar industry is pursuing micro-inverters for each panel or small groups of panels to deal with shading effects.

If you want to know how much energy all your panels are pushing into the batteries, run all the panel outputs thru a single shunt. $20-30 with a readout.
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Old 07-07-2019, 01:19   #10
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Re: Newbie solar controller question

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Nope.

If part of one panel has multiple cells fully shaded (shadow or a sail) the voltage from that panel will be decreased. In parallel the panels will be seen by the controller at the lower voltage or maybe slightly above. If the voltage is below what is needed to recharge the batteries you get nothing out of either panel.
In series you probably the the 2 voltages added but amperage is affected.

If you have partial shading of cells (shadow of stays or sheets) you’ll get nominal voltage but amperage will be compromised.
Interesting! Was on my boat today, two of the four panels were fully shaded, 190 watts in total yet the system was producing 13+ volts at 6+ amps in winter down here on a somewhat overcast day. My experience is that this is not uncommon, perhaps the system doesn't know that it shouldn't be working in these conditions.
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Old 07-07-2019, 01:34   #11
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Re: Newbie solar controller question

Quote:
Originally Posted by BigAl.NZ View Post
Currently the setup which is quite old has 3 x Gensun GV10 (1 per panel) all with its own wiring between controller and panel.

I would like to change to Victron since thats what the rest of the boat is, but should I replace leaving wiring as is with 3 new controllers or wire the panels in series with one controller?
Multiple controllers (ideally one per panel) generally harvest the most power from marine solar panels. Given you already have the wiring installed I would not change this system. Multiple small controllers are usually not much more expensive than a larger single controller, but this depends on the available models and pricing, so you need to check.

However, the Genasun GV10 is an excellent controller with good tracking and particularly low self consumption. This is ideal for multiple controller installation. It also does not suffer a couple of the minor irritations of Victron controllers such as the high start up voltage and the tail current cut off feature. The main limitation of the Genasun is the lack of user adjustability, which would frustrate a geek like myself, but is probably only a minor irritation for most users.

Quote:
Originally Posted by Uncle Bob View Post
If they were wired in parallel to one appropriately sized controller then surely the result would be the same.?
The difference in the total harvested output between a solar array wired in parallel and one controller per panel is not high, but in general the one controller per panel will deliver more total output in a marine installation.

The easiest way to explain the difference is to understand that the purpose of an MPPT controller is to select the ideal voltage where the solar panel produces the most power. Thus the controller is continually adjusting its input voltage to find this ideal point where the power produced is optimal.

However, each controller can only have one input voltage. Solar panels that are in different conditions (for example if one panel is in full sun and another is partially shaded, perhaps by the mast) will have significantly different voltages where they producing the maximum power. A single controller must select a compromise voltage. One controller per panel allows each controller to have a different input voltage depending on the needs of panel it is wired too. Thus the total output is higher.

There are drawbacks. Multiple controllers have more self consumption and there can be occasional conflicts between the charge algorithms that are working independently. But in general providing you are prepared for slightly more complicated wiring, a slightly higher total cost (although this varies between a lot more expensive to actually cheaper depending on the particulars), then multiple controllers are superior.

The other advantage of multiple controllers is redundancy. MPPT controllers are not the most reliable bits of electronics, so multiple units are nice to have, especially with high voltage panels, as these cannot be directly connected to the batteries without very reduced output.

There are other options. Rather than one controller per panel, one controller for panels on the port side and one controller for panels on the starboard side (or variations on this theme) are a popular option. The aim is to group panels that are likely to be experiencing similar conditions to one controller, thereby achieving most of the voltage matching advantages of one controller per panel.
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Old 07-07-2019, 01:41   #12
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Re: Newbie solar controller question

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Originally Posted by john61ct View Post
Ideal is one SC per panel, matched to suit.

Only downside is more wiring, but that's already in place.

Victron makes this much more cost effective than most.
How does the Bluetooth monitoring work with multiple controllers?

Do you need to disconnected and reconnect to each different controller to view the stats? (Because if so that would get really annoying!)

Cheers

Al
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Old 07-07-2019, 01:54   #13
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Re: Newbie solar controller question

https://youtu.be/nUBtKNzoKZ4

Parallel them and Color Control GX shows them as one
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Old 07-07-2019, 02:02   #14
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Re: Newbie solar controller question

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Interesting! Was on my boat today, two of the four panels were fully shaded, 190 watts in total yet the system was producing 13+ volts at 6+ amps in winter down here on a somewhat overcast day. My experience is that this is not uncommon, perhaps the system doesn't know that it shouldn't be working in these conditions.
No one said it all just stops.

Optimization might only mean a 15-30% difference, but for those that rely mostly on their solar that van be very significance.

Owner priorities and preference are important, there is no one answer fits all.
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Old 07-07-2019, 02:41   #15
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Re: Newbie solar controller question

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https://youtu.be/nUBtKNzoKZ4

Parallel them and Color Control GX shows them as one
Do I need that Color Control GX? They are quite expensive.....more than the solar controllers.
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