Solar Panels

[Christianonthecut]

Hi all,

 

I am in the process of deciding which Solar kit to fit to my boat and have a few questions which hopefully you can help with.

 

I have been specifically looking at the big 250w panels and am intending to fit a 500w array towards the bow. I will be single handling locks and don't want the roof space compromised towards the stern. The problem I see with my chosen location for the panels is the length of wire run required from the panels to the charge controller and batteries.

 

I am expecting to need a 10m run from panels to controller and am concerned about the voltage drop over this distance. I had originally intended to use 12v panels but quickly realised that the 10m run of cable would have to be extremely heavy duty to get round the inevitable voltage drop and I am intending to drop the wires through a mushroom vent in the roof so want them as thin as possible but little voltage drop.

 

I have therefore turned my attention to the higher voltage 250w panels and have noticed a difference in specs on these also. I am looking at some panels that are rated at 51 volts and 4.9 amps and thought that these would allow for the use of much thinner wire for the 10m run as voltage drop is not such an issue at the rated higher voltages.

 

Most of these 250w panels seem to be rated around the 36volts mark with a current rating of 7 amps. The same 250watts output then, but requiring thicker cables to achieve the same efficiencies in voltage drop.

 

Does anybody know what the pros and cons of these different panels are?

 

Thanks in advance

Edited September 8, 2012 by Christianonthecut

[Justme]

You seem to have answered your own question.

 

The lower the amps the thinner the cable can be for the same losses.

 

You can also wire them in series so the voltage doubles but the amps stay the same IF the charge controller has a suitable input voltage range.

 

You do loose one or two % on the controllers efficiency by using the higher voltages but in most cases that is clawed back by the savings in cable losses & the increased charge times due to the higher voltages.

 

The controllers with the higher input voltage ranges tend to cost more than the lower range ones.

[Arthur Brown]

Higher voltage panels give good power into your batteries with thinner cable because the volts drop is less. However this assumes the use of a MPPT controller with short thick wires to the battery. Be careful not to exceed the MPPT's input voltage range, or they die.

[NB Lola]

Try two ropes from mid point to stern, one either side. This might increase your options?

[Biggles]

I have exactly this arrangement 2x 245w 37v panels wired in parallel. I used 40amp cable to the charge controller which is about 3.5 meters from the last Panel, the same from the first panel.

 

See here how I did it, and you can see the size of cable used as well.

 

The best charge rate I've seen is 35.7amps, my display doesn't log , it only shows real time data.

[Ark Right]

Try two ropes from mid point to stern, one either side. This might increase your options?

 

Not really understanding the concept " single handing " are we ?

[Biggles]

Not really understanding the concept " single handing " are we ?

 

I think he means a center rope each side instead of one in the middle that would have to cross over the solar panels. Again I have on each side.

[NB Lola]

I think he means a center rope each side instead of one in the middle that would have to cross over the solar panels. Again I have on each side.

Correct

[Grace and Favour]

I've an array of the Sanyo / Panasonic HIT 240w panels, use the 6mm2 Solar cable to an Outback MPPT controller, (and 50mm cables x 1.5m to the batteries.)

 

I can thoroughly recommend the panels, controller and cable

[smileypete]

I am expecting to need a 10m run from panels to controller and am concerned about the voltage drop over this distance. I had originally intended to use 12v panels but quickly realised that the 10m run of cable would have to be extremely heavy duty to get round the inevitable voltage drop and I am intending to drop the wires through a mushroom vent in the roof so want them as thin as possible but little voltage drop.

 

No problem, if you lose a few watts between panels and controller that's fine.

 

Put it this way if solar costs £1/watt, there's no point spending £20 extra on thicker cable to save just a few watts. I think domestic installs use 4mm or 6mm, but even 2mm on a boat may be OK.

 

The cable between contoller and batts is a different matter, as any volt drop makes a fair difference to batt charging, and ideally you want to get them full as poss before the sun goes down.

 

cheers, Pete.

~smpt~

Edited September 8, 2012 by smileypete

[Christianonthecut]

Excellent, thank you all. I found a couple of manufacturers who use the very slightly higher voltage for the panels and it just kind of confused me as to why they deviated from the norm.

 

Know next to nothing about any of these things but have had a week digging deep to get the set up right from the word go.

 

I was planning on wiring them in parallel and hadn't even though about the possibility of wiring them in series...What is the best option with that? I was planning on using the morningstar MPPT, as it seems to be keenly priced and able to do everything. Only question is, do I go for the 45 or 60 amp version at this stage, the 45 amp will cover my 500 watts, but leaves nothing for another panel upgrade later on if needed...But then I'd probably need a bigger boat to starp the thing to, so another controller at that point will be small fry!!

 

SO many decisions to make.

[Biggles]

Input voltage is also something to be considered. Make sure your MPPT can take the voltage of them wired in series if you go that way. I think if I emember rightly parallel is better if part of the array becomes shaded.

[Kitsto]

Apologies if this is off-point (I'm a newbie): does anyone use solar panels just to charge laptops, mobiles and other devices? What I have in mind is using a portable / briefcase style solar panel rather than having one permanently on the roof (my boat doesn't have heavy-duty equipment such as TV or washing machine so its electricity needs and means are modest).

[John V]

Apologies if this is off-point (I'm a newbie): does anyone use solar panels just to charge laptops, mobiles and other devices? What I have in mind is using a portable / briefcase style solar panel rather than having one permanently on the roof (my boat doesn't have heavy-duty equipment such as TV or washing machine so its electricity needs and means are modest).

 

This reply is poss. off point as well, I have a small open cockpit Shetland used for sea fishing and generally getting away from "her indoors". For the last couple of years I have had 2 x 10watt panels wired in parallel mounted on the cabin top, these happily keep the battery topped up (in spite of the considerable drain by the bilge pump this summer).

[Lesd]

I have exactly this arrangement 2x 245w 37v panels wired in parallel. I used 40amp cable to the charge controller which is about 3.5 meters from the last Panel, the same from the first panel.

 

See here how I did it, and you can see the size of cable used as well.

 

The best charge rate I've seen is 35.7amps, my display doesn't log , it only shows real time data.

 

Hi Biggles

Can you let me know what type of panel and what supplier you used please ? Im looking for a large 36V panel to parallel up with my existing 2 x 18v panels. Most of the better value units Ive found have been 30V

Thanks

Les

[Theo]

I think he means a center rope each side instead of one in the middle that would have to cross over the solar panels. Again I have on each side.

 

Noticing the emoticon I took it as a joke. Two ropes. One in each hand like riding a horse.

 

N