Various solar panel wiring questions.

Nostrodamus

Nostrodamus

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www.cygnus3.com
I am trying to fit some new solar panels and would obviously like to do it right first time.
I am no expert when it comes to electrickery so any help would be greatly appreciated.

My set up is 4 x 95w Kyocera panels which I intend to join in paralell. These will have a run of about 6 to 8m to a Morningstar 45amp MPPT controller. From the controller to the batteries (6 Trojan T105's 6v wired in parallel and series giving 3x 12v) is about 2m.

1) What size wire is best between the solar panels and Mppt and between the Mppt and batteries.

2) Where is the best place on the batteries to connect the wires from the Mppt box. Should it be either end of the whole bank, the positive to a battery and the negative to the main negative shunt of the boat or something else.

3) Should you have a switch between the panels and the Mppt box if for some reason you wanted to isolate the MPPT box to work on it or stop the solar power. If so what sized switch would I need to cope with the amps?

4) Should the MPPT box be grounded and if so where. I have a galvanic isolator on the boat and earthing wires connecting a lot of things together. There is a convenient earthing wire close by the Mppt controller on bolts that go through the hull to the large hull anode. Could I ground it there?

5) When shore power is available in winter should you hook up to it and try and stop the panels from working saving the batteries or just try and run on the panels. When hooked up to shore power is there any point in leaving the panels exposed or should they be covered up?

Sorry for some basic and stupid questions but as you can see I am to electrikery and solar panels what Angela Merkle is to topless modelling.
 
They would probably be better if wired as two pairs in parallel.

The system voltage would be increased from around 20v to 40v, reducing the current in the cables an thus the overall voltage drop from panel to controller. it also allows the MPPT controller to derive optimum power from the panels. Going any higher ( 3 in series say ) gets you into some rather nasty voltage area where a loose wire could arc or shock quite severely.

Basically you need to get the biggest possible wire possible to reduce losses in the wiring runs. In all parallel you will be sinking 30 amps of current from panel to controller, in 2 pairs paralleled only 15 amps.

Lets start with the controller to battery run. Nominal voltage 13.2v ( charging ) cable run 2.5m, For a 1% loss 25 mm², 3% loss 10 mm², for a 5% loss 6 mm²

A 10m run at about 14v ( Panel loaded ) needs 95 mm² to keep a 1% drop in the cable, 25 mm² gives 5% loss

if you double the system voltage by running two pairs in series you can drop down to 10 mm² for the run to the controller - far more manageable and cost effective

2 - You want to arrange your charging so that it is sensed by the main shunt. Your battery monitor can then 'see' what is going in as well as what's coming out.

3 - A switch is another set of contacts to corrode and introduce losses to. rather disconnect the panel run at the panels MC4 connector. ( not easy as they tend to lock up ) Btw when assembling MC4's cover the contacts in vaseline or a proprietary stuff like contralube. They DO corrode and after a year or two will be almost impossible to separate.

4 - A high voltage system will need grounding, refer to the manual on your controller, introducing a stray current at 20 volts or more could dissolve anodes at best or cause hazardous situations at worst.

5 - Use shore power where available for the kettle, toaster heater but keep the batteries connected to the panels. My panels have been on the boat for 5 years now and I'm not seeing any drop off in performance after all that time uncovered in the Greek sun. Couldn't be arsed with covering them up! In another 10 years when performance drops off 20% new panels will cost less, be smaller and develop more power!
 
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Nostrodamus said:
I am trying to fit some new solar panels and would obviously like to do it right first time.
I am no expert when it comes to electrickery so any help would be greatly appreciated.

My set up is 4 x 95w Kyocera panels which I intend to join in paralell. These will have a run of about 6 to 8m to a Morningstar 45amp MPPT controller. From the controller to the batteries (6 Trojan T105's 6v wired in parallel and series giving 3x 12v) is about 2m.

1) What size wire is best between the solar panels and Mppt and between the Mppt and batteries.

2) Where is the best place on the batteries to connect the wires from the Mppt box. Should it be either end of the whole bank, the positive to a battery and the negative to the main negative shunt of the boat or something else.

3) Should you have a switch between the panels and the Mppt box if for some reason you wanted to isolate the MPPT box to work on it or stop the solar power. If so what sized switch would I need to cope with the amps?

4) Should the MPPT box be grounded and if so where. I have a galvanic isolator on the boat and earthing wires connecting a lot of things together. There is a convenient earthing wire close by the Mppt controller on bolts that go through the hull to the large hull anode. Could I ground it there?

5) When shore power is available in winter should you hook up to it and try and stop the panels from working saving the batteries or just try and run on the panels. When hooked up to shore power is there any point in leaving the panels exposed or should they be covered up?

Sorry for some basic and stupid questions but as you can see I am to electrikery and solar panels what Angela Merkle is to topless modelling.
Click to expand...

I can only tell you what I have done and found effective:-

1. If the Morningstar will accept a higher voltage than the nominal 12v, then wire them in two pairs outputting a nominal 24v each. Having tried both with my BZ I've found that I get a consistently higher charging current than in parallel - my BZ will accept up to 72v, so I could have had the whole lot in series but 2 of the 3 pairs are likely to be shaded.
2. I've used a 16mm2 cable from PV panels - each pair fused and wired direct to the MPPT controller and then a 25mm2 from controller to the system bus bar. Not scientifically calculated, just the cable I had available.
3. Yes definitely have a switch - essential for working om electrics - mine is on the 12v feed so cuts off all PV arrays. If I want to cut out any pair, I use the fuseholder.
4. The instructions on the board will tell you. The BZ people told me not to bother, unless I was neurotic about galvanic corrosion.
5. I leave my PV panels on, keeping the charge up in one or another of my batteries. If you turn off the PV panels, they're still producing power, but on open circuit - higher volts so, IMHO, more likelihood of damage.

The cheap/cheerful amorphous panels from Marlec are producing about 45% of quoted output, the KC Kyocera about 75% and the KDs about 85% (all taken @ noon in May 2013 @ 40-41N.
 
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The morning star will take up to 72v and convert it to 12v.
What is scaring me is the size of the wires I may need. They sent me 4mm wire with the panels although i was going to put 6mm on which now seems dangerous.
Are you saying the switch should be between the MPPT and batteries or between the panels and batteries.
As usual there are two answers.. one to ground and one not to ground.
 
Tony Cross said:
Try an online wire size calculator. There is one at http://www.solar-wind.co.uk/cable-sizing-DC-cables.html and another at http://www.freesunpower.com/wire_calc.php. That's how I sized mine.
Click to expand...
The problem with these online calculators is they don't make it clear if you take the single length or the length there and back to take into account the losses in both the positive and negatives cables. All table calculators tell you to double the lengths, these online calculators take that into account, but don't tell you.

Try this one from BlueSeas that does tell you to double the length and offers more options. They also do a much better version as an App.

http://circuitwizard.bluesea.com/

You might like to check for yourself to see if you agree with nimbusgb's calculations of 10mm2 for 2 in series/pairs connections!!!!! I think he has halved the current and double the voltage - and then added sum!!!!

If they supplied you with 4mm diameter wire that would be ok for each panel down to the controller for a 3% loss.

There's are many other threads on series or parallel because of the large losses you can get from shading on panels connected in series. One totally shaded panel in series with another unshaded will allow zero current to pass through from the unshaded series panel.

In general the consensus has been that parallel connections are better - if you can fit large enough cables to cut the voltage drop.

It's also worth noting that even with parallel configuration a 10% shadow can cut the output by 90%. This is a highly complex and controversial subject and worth searching the archives for more information.
 
I agree leg end.
It initially seems strait forward but if I joined the panels together at the panels to make less wiring running through the boat I would need a pretty big wire that may be a pain to get through some parts. Joining two panels in parallel and the other two in parallel and then putting them into series would reduce the thickness of the wire required.
I have looked around a good few of the boats here and according to the calculators their wiring is far too small. Most seem to have their wiring from the panels in parallel.
 
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