Solar PV Wiring

[Jambo]

After much faffing with getting racking made that will tilt our panels we will shortly be in a position to go ahead and fit the panels and wire them up (hurrah!).

 

I've been mining this forum and the internet for information about how to do the wiring and have created a diagram and description of my approach. I would be very grateful if anyone with knowledge of solar systems could take the time to have a look and tell me where I'm going wrong or where it could be made better.

 

Below are the wiring diagrams and a description of the setup. At the end are a few questions that I still have about it.

 

I've gone for a comparatively large installation of 1kW of PV because I'm keen to get as far into winter as possible on PV.

 

Thanks!

 

Wiring Diagrams

 

Panel Layout:

 

Four 245W Sharp panels will be arranged along the boat's centreline running from the stern hatch to around the level of the kitchen side hatch. The panels will be mounted on racking which allows approximately 35 degrees of inclination either side. Cables will run down through a cable gland through a hole in the roof under the rearmost panel into the engine room.

 

Panel Wiring:

 

2 pairs of Sharp ND-R245A5 panels connected in series (with each pair connected in parallel).

 

Wiring 4 panels in series would give a Voc at STC (standard test conditions, 25°C) of 149.2V but the FlexMax FM80 has a limit voltage of 150V (which would be exceeded at temperatures below 24°C).

 

Wiring the panels in two pairs gives a Voc of 74.6V at STC and the Vmax of the FM80 will not be exceeded at any temperature. Isc for the Sharp panels is 6.96A so the array’s Isc will be 13.92A. The Outback FM80 can take a maximum current of 64A.

 

The wires connecting the panels to the FM80 will be 4mm2.

 

 

Engine Room Wiring:

 

The FM80 will be mounted to a board which will be glued to the engine room's forward bulkhead. The board will be mounted directly above the boat's leisure batteries.

 

The panel wires will come down from the engine room ceiling to a 16A DC isolation switch mounted on the board and then into the +ve and -ve PV terminals in the FM80.

 

35mm2 wires will run from the FM80's +ve and -ve battery terminals with a 100A inline MEGA fuse on the +ve wire mounted close to the battery.

 

Remaining questions:

 

- If I have an isolation switch between the panels and FM80 do I need one between the FM80 and the batteries? I've seen wiring diagrams for grid-tied PV systems and they all have it but I haven't seen many wiring diagrams for battery systems so not sure if this is needed (or is it just good practice?).

- What is the best way of connecting the 35mm2 wires to the battery terminals given that some fairly chunky wires running to the charger/inverter are already attached? I was thinking of fitting battery terminal extenders.

- My three leisure batteries are connected in parallel, can I simply connect to the +ve and –ve terminals of one of the batteries?

- Is panel earthing necessary? (or even possible in a boat??)

Edited September 13, 2013 by Jambo

[matty40s]

Connect pos and neg to different ends of battery bank, no earthing needed.

[Ex- Member]

I did wonder about fitting in series.

 

Our 2 x 250watt panel array is simply done with pair of pigtails in paralell. Each pigtail takes the 2 neg cables from the panels and the other the 2 poz cables from the panels. The single outlet of each pigtail then direct to Outback poz Neg. With your set up and 4 panels you would just need another pair of pigtails.

 

 

 

You seem to be wiring in series. Is there an advantage in doing this from my point of view having just 2 panels. I will be adding a third 250watt panel shortly, so wondering how best to add this in. I have seen available 3 tail pigtails.

 

I didn't bother with an isolator or fuse between the panels and Outback as you can simply unplug.

[Jambo]

Thanks Matty!

 

Julynian my understanding is that the higher the voltage of the array the better - as long as it's within the limits of your controller.

 

At a wild guess (and my electronics knowledge is very shaky) I would say that if you operate with a lower voltage you'll have a higher current and therefore have higher I²R losses?

 

I couldn't wire all 4 in series as it would be bumping up against the 150V limit voltage of the FM80. I could wire all 4 in parallel but the voltage would be lower so I'd get bigger losses. So I've settled for a compromise of wiring each pair of panels in series and then wiring the two pairs to the FM80 in parallel.

 

I hadn't come across the pigtails but was planning on using MC4 branch connectors (such as this) which will allow me to plug two MC4 connectors into one cable.

[Ex- Member]

Thanks Matty!

 

Julynian my understanding is that the higher the voltage of the array the better - as long as it's within the limits of your controller.

 

At a wild guess (and my electronics knowledge is very shaky) I would say that if you operate with a lower voltage you'll have a higher current and therefore have higher I²R losses?

 

I couldn't wire all 4 in series as it would be bumping up against the 150V limit voltage of the FM80. I could wire all 4 in parallel but the voltage would be lower so I'd get bigger losses. So I've settled for a compromise of wiring each pair of panels in series and then wiring the two pairs to the FM80 in parallel.

 

I hadn't come across the pigtails but was planning on using MC4 branch connectors (such as this) which will allow me to plug two MC4 connectors into one cable.

 

Hi Jambo

 

I see where you're coming from. I think maybe I should swap some connectors tomorrow and try them in series. Panels are around 30v so they will double to 60. I've been so impressed with the results so far, If I get more out of them that will be even better for coming winter.

 

The branch connectors are as good possibly better, you do get an extra 1/2 meter of length out of the pigtails though which was really handy in my case as I would have needed to buy a longer length of cable. I used 6mm cable as well.

 

Im about to order another 250 watt panel £177.00 I think I could get that in series also. We have the Outback 60, but I think it's the same voltage limit as the 80. 3 in series would be 90v

 

The third panel will in fact put us over the max amps level by 2.5 amps, I wouldn't think that would ever happen though getting max out of all 3 panels LOL

[David Mack]

Connect pos and neg to different ends of battery bank, no earthing needed.

All your battery connections should be to the diagonally opposite corners of the bank. So your solar cables will be connected at the same points as the domestic take off.

[Justme]

 

1, Wiring 4 panels in series would give a Voc at STC (standard test conditions, 25°C) of 149.2V but the FlexMax FM80 has a limit voltage of 150V (which would be exceeded at temperatures below 24°C).

 

2, The wires connecting the panels to the FM80 will be 4mm2.

 

 

3, with a 100A inline MEGA fuse on the +ve wire mounted close to the battery.

 

 

4, If I have an isolation switch between the panels and FM80 do I need one between the FM80 and the batteries?

 

 

1, Good call. Staying below about 120v design voltage will enure even when it hits -15c you will be ok.

 

2, 4mm2 seems a little small for the 10m & 14amps

 

3, again that is a little small for a possible max output of 84amps. The standards normally ask for at least 120% of peak value.

 

4, Yes you do. You have a device that can be powered up via either power source (PV or battery) (side point you should always start it up & turn it off on battery power & not PV power).

 

 

The third panel will in fact put us over the max amps level by 2.5 amps, I wouldn't think that would ever happen though getting max out of all 3 panels LOL

 

 

Dont worry about that. I have 1200 watts into an FM80. So I am 20amps over the spec.

 

It just gives you a flat top to the amps charge curve when they are working flat out.

 

We often see it hitting MORE than its rated amount. Obviously the FM80 then throttles it back off.

Edited September 13, 2013 by Justme

[Jambo]

 

The branch connectors are as good possibly better, you do get an extra 1/2 meter of length out of the pigtails though which was really handy in my case as I would have needed to buy a longer length of cable. I used 6mm cable as well.

 

This is a good point. Might come in useful to have a little bit of extra length to play with.

 

All your battery connections should be to the diagonally opposite corners of the bank. So your solar cables will be connected at the same points as the domestic take off.

 

Cheers. Will check when I get back to the boat but that sounds like the way to do it.

 

2, 4mm2 seems a little small for the 10m & 14amps

 

3, again that is a little small for a possible max output of 84amps. The standards normally ask for at least 120% of peak value.

 

4, Yes you do. You have a device that can be powered up via either power source (PV or battery) (side point you should always start it up & turn it off on battery power & not PV power).

 

2. Hmm yes I think you're right. I'm not actually on the boat at the moment as it's in dock having work done to it so I haven't been able to do the final measurements. I've been thinking about it this evening and it might be closer to 8m. But either way I think it makes sense to go for 6mm2 to reduce the losses.

 

3. I see they do a 125A fuse so I'll go with that.

 

4. This is what I was wondering. Will fit something.

 

 

Cheers all!

 

Happy to hear further comments if anyone wants to pitch in.

 

I'll also post the list of odds and sods I buy to make this installation happen for future reference for others who want to do this.

[Ex- Member]

 

This is a good point. Might come in useful to have a little bit of extra length to play with.

 

 

Cheers. Will check when I get back to the boat but that sounds like the way to do it.

 

 

2. Hmm yes I think you're right. I'm not actually on the boat at the moment as it's in dock having work done to it so I haven't been able to do the final measurements. I've been thinking about it this evening and it might be closer to 8m. But either way I think it makes sense to go for 6mm2 to reduce the losses.

 

3. I see they do a 125A fuse so I'll go with that.

 

4. This is what I was wondering. Will fit something.

 

 

Cheers all!

 

Happy to hear further comments if anyone wants to pitch in.

 

I'll also post the list of odds and sods I buy to make this installation happen for future reference for others who want to do this.

 

Me too LOL

 

I've previously bought fixed lengths of solar cable with MC4 connectors already connected. I've just realised how simple they are to fit yourself thanks to some you tube tutorials. I really shouldn't be so lazy LOL

 

I've also decided this 3rd panel will also swivel on a ball like the first larger array we're now using. Much easier job this time around being half the size and weight. I'll post how I make it soon.

[smileypete]

4mm should be fine.

 

4mm at 14A will lose 0.83W/metre.

 

6mm at 14A will lose 0.56W/metre.

 

What's the cost difference between 4mm and 6mm?

 

cheers, Pete.

~smpt~

[Ex- Member]

4mm should be fine.

 

4mm at 14A will lose 0.83W/metre.

 

6mm at 14A will lose 0.56W/metre.

 

What's the cost difference between 4mm and 6mm?

 

cheers, Pete.

~smpt~

 

If you shop around pete you can pick up 6mm as cheap as 4mm.

 

This seller even throws in 2 MC4 connectors.

 

When you only want shorter fixed lengths say 5-10 metres it's just quick & easy to order of e-bay. I suspect 100m reels will work out far cheaper per meter though.

 

 

http://www.ebay.co.uk/itm/Solar-PV-Cable-6mm-DC-rated-55A-1-Pair-Free-MC4-CONNECTOR-Free-P-P-/251154408993?pt=UK_Gadgets&var=&hash=item80194ccd83

[Rich]

 

 

4, Yes you do. You have a device that can be powered up via either power source (PV or battery) (side point you should always start it up & turn it off on battery power & not PV power).

 

Do you mean that the controller should be disconnected from the panels before disconnecting from the battery bank?

 

Sorry if it's a dumb question but I'm not sure of your meaning.

[Justme]

Do you mean that the controller should be disconnected from the panels before disconnecting from the battery bank?

 

Sorry if it's a dumb question but I'm not sure of your meaning.

 

 

Yes you should shut down the array before disconnecting the battery bank.

 

The other way round (IE first turn on after installing it) is even more important as the unit needs the battery bank connected so that it can set the battery system voltage correctly.

[Rich]

 

 

Yes you should shut down the array before disconnecting the battery bank.

 

The other way round (IE first turn on after installing it) is even more important as the unit needs the battery bank connected so that it can set the battery system voltage correctly.

 

Thanks

[WotEver]

- My three leisure batteries are connected in parallel, can I simply connect to the +ve and –ve terminals of one of the batteries?

 

See here: http://www.smartgauge.co.uk/batt_con.html

 

Tony

[Laurie St Lyon]

This is a great link. Thanks Tony. They have helped me settle this which was actually puzzling me.

 

See here: http://www.smartgauge.co.uk/batt_con.html

 

Tony

[Jambo]

Getting close now but I'm a bit confused by the isolator switches and so have a possibly stupid question...

 

I've found a reasonably priced 300A 12V battery isolator switch which will hopefully do for between the Outback and the batteries but I'm looking at 16A isolator switches for between the panels and the Outback and they all see to be rated at different voltages. Does it not matter as long as the rated voltage of the switch is greater than the Voc of my panels (about 75V)?

[Ex- Member]

Getting close now but I'm a bit confused by the isolator switches and so have a possibly stupid question...

 

I've found a reasonably priced 300A 12V battery isolator switch which will hopefully do for between the Outback and the batteries but I'm looking at 16A isolator switches for between the panels and the Outback and they all see to be rated at different voltages. Does it not matter as long as the rated voltage of the switch is greater than the Voc of my panels (about 75V)?

 

Why waste money on an isolator when you can simply unplug the panels in seconds.

 

Durite do a nice small battery iso switch, I actually have one on our main battery bank.

 

http://www.batterymegastore.co.uk/product/0-605-11/?ref=bmuk&gclid=CLz9tpfE87kCFRPItAod3VMAEQ

 

A 100 amp fuse would be a lot cheaper though, and you simply undo a nut to isolate.

 

http://www.ebay.co.uk/itm/2-X-MEGA-FUSE-HOLDER-WITH-100AMP-500AMP-FUSE-SCREW-DOWN-CLEAR-TOP-COVER-/290971371322?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item43bf3ec73a

[Jambo]

I'm getting something similar to that switch for the Outback-battery connection. Fair point on unplugging the cables though! I guess it's more useful if you're in a house and you can't necessarily access the cables very easily.

[Phil Ambrose]

Thanks chaps, a very informative and interesting post. I have just started on fiting PV array to my boat. I had 5 X 100w panels on my previous boat which I fitted 10 years ago and the tech has changed enormously and panels are now less than half of which I originally paid.

Phil

[Ex- Member]

We're about to add an additional 240v solar panel to our existing 500 watt array currently consisting of 2 x 250 watt panels.

 

The 2 x 250w panels are wired in series, so how should I wire in the 3rd panel as it's not a pair, do I simply leave the 500w array as it is and use a pigtails to feed the 3rd panel in where the Poz and Neg come from the existing panels. Or should I revert to wiring all 3 in parallel?

 

Could have had this fitted today buy a crucial item didn't arrive, so annoying when the sun is shining LOL

[Justme]

A usual more info is needed.

 

First off you cant have the two existing panels in series & then parallel the new one across them as its very unlikely that the combined voltage of the existing ones will be close enough to the new one for it to be viable.

 

So now you need to know the max voltage that the controller can take plus its amp rating.

 

Then you need to know the OCV of the existing panels & the new panel. Also the peak amps & MPP voltage of both old & new panels.

 

Then you can work out the best wiring method.

[Ex- Member]

A usual more info is needed.

 

First off you cant have the two existing panels in series & then parallel the new one across them as its very unlikely that the combined voltage of the existing ones will be close enough to the new one for it to be viable.

 

So now you need to know the max voltage that the controller can take plus its amp rating.

 

Then you need to know the OCV of the existing panels & the new panel. Also the peak amps & MPP voltage of both old & new panels.

 

Then you can work out the best wiring method.

 

Hi justme

 

Yeah I have an Outback 60 controller, max volts 150, I thought these could handle a mix match of panels. Each panel is ball park 30v Peak amps 61 from panels.

 

I could do them in series but I think they work better in paralell.

 

I'm thinking I just leave the 500w as they are and just add the 3rd panel.

[Justme]

Dont even think about leaving the existing two as they are & adding the third one in parallel. You will have two strings but one will be at 60v & one at 30v. You cant do that with a single MPPT input controller.

 

They would be better in series (if there are no shading issues) but the peak amps of all 3 need to be about the same or you will get 3 x the lowest one).

 

If you cant do all 3 in series then all 3 would need to be in parallel.

[smileypete]

What's the Imp (current at max power, not mischievous faerie ) of both the old panels and new one?

 

It it's the same they can go in series, subject to controller max input voltage.

 

cheers, Pete.

~smpt~

Edited October 9, 2013 by smileypete