Solar panels (again)

I

ip485

Well-Known Member
Joined
13 Feb 2013
Messages
1,614
Visit site
So the collected forum wisdom please.

I am having an arch installed but have to populate this with panels. I have in mind somewhere between 600 and 1000 watts - the house batteries are 800 watts and although there is a 8KW Genset I am hoping that the solar array will produce most of the DC power. The boar system is 12V not 24V, not that I think that matters.

So what would be the collected wisdom as to the best panels to purchase, the best deals and the best controller to deal with the output please?
 
A 100 watt panel will be getting on for 1 square metre so you are talking about the best part of 10 square metres of panels. Are you sure that you can fit that many panels on your arch?
 
Best bet might be 4 x 250w domestic panels - they're about 160 by 80 cm and output at around 34 ish volts

You then need a good quality MPPT charge controller to handle it all and output at the 14.4v needed for the batteries - my personal choice is Morningstar - I've used one for a while now and the quality and performance is excellent. This will for want of a better term split the high voltage from the domestic panel into two lots of the correct voltage to charge so you don't lose the power generated by the panels and because you're getting higher voltage at the panels you don't lose as much in the wiring - it "pushes" through better and you don't have to go so heavy duty on the cable as you will of course have lower amps.
 
Thank you i had heard about using domestic panels previously. Do you have a make in mind and how do they cope in the marine enviroment? Just about to research morningstar.
 
I've had domestic on for 2 years now and they still look like new - I guess if they'll last for 15 years on a Hebridean Island home they'll cope with life at sea too - as for make I don't really think it matters too much if they are CE certified as they all have to meet the same standards and are almost all made in China anyway - I bought from Triple Solar in London who do many makes but were very helpful and knowledgable.
 
Unless Ip485 has a very big boat I think he has the wattage wrong by a factor of 10. As said 1000w is huge. Most larger boats may fit a couple of 80w sid eby side on an arch.
So the end wattage will be dictated by the area available on the arch. Then go for MPPT controller. good luck olewill
 
The user name suggests it is an Island Packet 485. This is a reasonably large boat and 600 to 1000w sounds feasible.

The first rule is to fit the maximum wattage you can. This is very dependent on the exact size that is available, and which panels fit best. It is hard to give useful general recommendations.
Some of the latest panels such as the SunPower E and X series are very efficient and often allow more watts to squeezed in (at a price)
For controllers this sort of large solar array means you will need a high capacity controller. Outback and Midnight are generally regarded as the best.
 
Last edited:
One thing to be careful of is shading. Panel output falls dramatically once any part is shaded. So if the arch holds the boom, mount the panels away from the boom. It might be better to have a bigger number of smaller panels if it means some of them are never shaded.
 
Trident said:
Best bet might be 4 x 250w domestic panels - they're about 160 by 80 cm and output at around 34 ish volts

You then need a good quality MPPT charge controller to handle it all and output at the 14.4v needed for the batteries - my personal choice is Morningstar - I've used one for a while now and the quality and performance is excellent. This will for want of a better term split the high voltage from the domestic panel into two lots of the correct voltage to charge so you don't lose the power generated by the panels and because you're getting higher voltage at the panels you don't lose as much in the wiring - it "pushes" through better and you don't have to go so heavy duty on the cable as you will of course have lower amps.
Click to expand...

I'd second the suggestion about using domestic panels - I bought mine from Kyocera at the time they were claiming an 18% efficiency. The MPPT controller I bought from BZ in the States, 24v in and 1 volt above system volts when charging and going on to float @ 14.4volts. Total 328 watts nominal. Don't economise on the cabling from MPPT to batteries - I've has as much as 18 amps through in May/June in the Ionian.

By the bye, Will H my boat is 9.45m long, though I do agree 1000 watts appears optimistic in the extreme.

The MPPT controllers in the States are a light-year ahead of anything available in Europe - the BZ 500 will handle up to 72 volts @ 500 watts input, and you can set output charge and float as you wish.
 
Last edited:
ytd said:
One thing to be careful of is shading. Panel output falls dramatically once any part is shaded.......
Click to expand...
Because of shading wire the panels in parallel not series. This is a very controversial subject, but series will mean less voltage drop along the cables, but MAY mean much less current from the array if there is any shading. It often depends on the panels you buy and how many BYPASS diodes they have. This subject needs a book to cover it properly, and dealers aren't usually very helpful - land based solar installation don't have shading problems, but any sailboat will ALWAYS have shading problems.

The simple solution is to do your own tests on your system on your boat by wiring the system first in series and then in parallel. You might be very surprised by the difference.

Do make sure the cable sizing is more than adequate to cope with the current. This is often the hardest part, and sometimes the biggest compromise. Don't follow the manufacturers simple cable size recommendations - they don't know the length of your cable run or the array size.
 
sailinglegend420 said:
Because of shading wire the panels in parallel not series. This is a very controversial subject, but series will mean less voltage drop along the cables, but MAY mean much less current from the array if there is any shading. It often depends on the panels you buy and how many BYPASS diodes they have. This subject needs a book to cover it properly, and dealers aren't usually very helpful - land based solar installation don't have shading problems, but any sailboat will ALWAYS have shading problems.

The simple solution is to do your own tests on your system on your boat by wiring the system first in series and then in parallel. You might be very surprised by the difference.

Do make sure the cable sizing is more than adequate to cope with the current. This is often the hardest part, and sometimes the biggest compromise. Don't follow the manufacturers simple cable size recommendations - they don't know the length of your cable run or the array size.
Click to expand...
Who says landbased systems don't have shading problems? My chimneys and trees made domestic solar uneconomic due to shading - particularly in winter.
On a boat you just have to compromise and accept that you're not going to get the theoretical maximum because of orientation and shading, but you'll still get useful output from them. I'm not convinced that the MPPT contollers are worth the extra dosh.
 
Thank you for your thoughts. Yes the yacht is 50 foot so a reasonable sized stern for the array. There should not be much shading with a stern arch, although I guess at times the main could throw some shadow. I am inclined to use domestic panels as suggested. I need to discuss with the engineer how many panels can be safely accommodated but also take into account what will look reasonable. I hope between 600 w and 1,000 w is possible. There is a large Genset and Balmer but inevitably the Genset is noisy and I prefer not to use the engine if it is possible to sail. The Genset will take care of the water maker and other 240V needs as and when, but it is surprising how long the Genset needs to run to bring the house batteries up to charge whilst putting a very low load on the Genset which is not ideal.

Which Morningstar MPPT would you suggest? I take your point about the cable. I am guessing it would be a reasonable cable run to the MPPT - or looking at it another way about 7 to 8 metres between the solar array and the house batteries. Does it make any difference whether the MPPT is located nearer the array or nearer the house batteries and what is the collected wisdom on the ideal size of cable between the panels and the MPPT and the MPPT and house batteries?

You will have guessed the arch is outside of my skill set but I am inclined to do the wiring, the panels and controller with your help - thank you!
 
Its best to have the controller as near to the batteries as possible with the shortest cable run possible - the size of cable and controller will depend on what panel sizes you end up with - just work out the maximum possible load when you've decided on the panels and then get a wire to cope with that (go one size up) - even on a 1000w of domestic panels you may only have a maximum 30 amp load so size 10 cable should be plenty - but do the maths when you have the hard figures from the panel outputs.
 
Actually wire size for solar panels is not nearly so critical as people suggest. A solar panel has significant internal resistance. 40volt 5 amp panel has an internal ressitance of about 4 ohms. So that a .04 ohm wire resistance total -ve and +ve would have a 1% loss in wiring. Almost negligable but .04 ohms is quite high for wire resistance. Any volt drop in the cabling will be covered by the MPPT or other controller.
So the concern is not liike say a nav light on mast top where resistance in the wire causes volt drop which then reduces the current as well as voltage of the incandescent lamp.
Of course you need decent cabling for the panels to the controller if only for robustness against corrosion and mechanical damage but don't imagine fatter wires will give any or much more charge. As said domestic 40v panles are far cheaper per watt around here than 20v panels all from China of course. good luck olewill
 
It is interesting that some say wire size is important, others that it isn't so important, then there is the debate about wiring in parallel and series.

I guess at least with wire size there is probably not a lot to be lost slightly over specifying (as the cost is not significantly different and the gain / loss cant readily be tested) whereas with the parallel series debate at least both can be tried and the gain assessed.

Any recommendations for a good source of panels from a UK supplier?

Any recommendations on the MPPT controller than would suite me best from Morningstar?
 
Try Triple Solar in London for panels - then when you have the panels you can decide on the controller - the models vary according to the likely maximum current which will be determined by how many and what size of panel you end up with but one of the sizes of Tristar MPPT from Morningstar would be my choice
 
Well thank you to everyone for your help.

I have opted for two panels which will provide 640W and an Outback Controller. I have the option to fit one extra panel over the bimini which would lift the output to 960W and have chosen the Outback Controller that can cope with three panels.

Hopefully it will all go together over the next couple of weeks and will be interesting to see how it performs.

Interestingly the panel supplier recommended each panel be wired directly to the controller rather than using one wire to supply the output.

I am hoping these panels will provide sufficient power with only limited resort to the other sources - we shall see. I suspect the third panel will prove necessary.
 
You must log in or register to reply here.

Share this page

Top