solar panel usage data

Things 12V and 24V
sea_bee
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Location: Pillar Valley NSW

Re: solar panel usage data

Post by sea_bee » Wed Feb 01, 2012 9:52 pm

mahnamahna wrote:Am I better off joining them up there and sending all that load down one big cable or sending each panels wiring down individually and then joining them just before the regulator.
I took the advice of the local solar retailer when I hooked up my last bank of panels on my (remote area standalone) house. That advice was to run a separate cable from each panel to a bank of breakers, and from there to the regulator.

As each panel runs through a separate breaker, that makes it easy to check the output from each panel by flicking through the switches.

Smooth Cruiser
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Re: solar panel usage data

Post by Smooth Cruiser » Wed Feb 01, 2012 10:08 pm

Being able to switch each panel in and out of the array will certainly be useful at times.

Either 1 wire pair carrying 60A or 6 wire pairs carrying 10A will have around the same total copper cross sectional area if they are sized correctly - and hence from an electrical point of view both serve your purposes equally well. However 1 pair of wires will be easier, tidier and have an overall lower diameter to route than tying 6 pairs of wires together. 10A wires will be around 2mm in diameter, 60A wires will be around 5.3mm diameter - do the maths and you will see that in each case the total wire cross sectional area is the same, around 0.00002m2.

What will help is wiring the panels into pairs and running them as 3 24V panels instead of 6 12V panels. With a 24V system the total current will be around 30A rather than 60A and hence the wire diameter used can be reduced by a factor of 0.7. So three pairs at 1.4mm or one pair at 3.7mm diameter.

Of course in either case if you go up a few mm in wire size then the efficiency will be better and losses reduced - or choose the same diamter wire for 12V or 24V systems and enjoy the benefits of better efficiency.

Note - I am not an electrician and someone qualified or who you trust should do the final sizings of your wires!

Jim
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Re: solar panel usage data

Post by Jim » Thu Feb 02, 2012 7:46 am

When I made my davits I installed wire (not removable) for future solar panels, then when I was ordering my panels I checked the wire size and realised I had stuffed up for 12 volts, a bit undersize, so I went with 24 volt which is OK for that gauge wire. I will do some checking over the next couple of days and report back.
Jim.

44c
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Re: solar panel usage data

Post by 44c » Thu Feb 02, 2012 8:52 am

mahnamahna wrote:Smooth, Please excuse my ignorance, like others here Electricity is a dark art. If the solar panels I am looking to import work out (being tested at the moment) they are so cheap, and I have so much roof real estate, that I am going to put 6 x 180 watt panels up there. Am I better off joining them up there and sending all that load down one big cable or sending each panels wiring down individually and then joining them just before the regulator. Sending over 1000 watts @ 18v down one wire, isnt that about 60 amps and is that wire going to be as thick as say and power extension cord? Or will it be thicker than that? The wires that come out of the panels now are about that thickness so sending 6 of them down will need either multiple routes or a really big conduit.

Or is 1kw just going to be way over powered? The way my uneducated mind thinks, is that if I can put them up there then I am not likely to ever exceed their feed, in usage. Does it work that way. Am thinking on having 400amp hour lifepo4 battery bank, maybe 600AH (but cant afford the extra 200AH yet). Will have outboards so they only charge at 15amps. Will probably have one of those Honda 2000 petrol gennies for emergencies or for when we want to use the convection microwave to roast. I have a 200 litre Isotherm fridge/freezer not sure what it draws yet, it depends on ambient temp I think but it has a danfoss 50 compressor which I believe are pretty good, I will have the usual array of electronics including radar, plotter, sounder and ais, 19in lcd tv with dvd player, laptops (cant imagine life without internet!), led lighting throughout, and will be buying a watermaker, probably an 80e Katydyn, makes about 12 litres an hour and uses about 8amps an hour. Will probably want to run that every second day.
For that size array, you should get an MPPT charge controller. I have an Outback Flexmax 80. You can then wire your solar panels in series - ie positive to negative - so then you increase the voltage, but the current "upstream" of the charge controller will stay the same as if you only had one panel.

The charge controller will step that down to the battery voltage and the current will multiply. So you only need heavy gauge wire between the charge controller and the batteries.

This also has the bonus effect of improving yeild in poor conditions. ie, if you had low light and each panel could only manage about 11 volts - in parralel you'd get no charge - 11 volts won't charge 12 volt batteries. But in series there would be 66 volts, which the charge controller can reduce to battery voltage, and produce a little current.

IMO you can't have too much solar. In good sunlight your batteries might be fully charged well before lunchtime, but when it's crappy (like it is in Sydney now) you want every Watt you can get.

mahnamahna
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Location: Gosford NSW

Re: solar panel usage data

Post by mahnamahna » Thu Feb 02, 2012 8:13 pm

Thanks 44c, yes the outback 80 is exactly the unit I have been looking at. I mistakenly thought they were an Australian product and was super annoyed when I discovered that they are half the price in the US that you can get them for here. I have not purchased yet as I need to make sure that it is compatible with Lifepo4 batteries. Whimsical thinks it is due to its variable adjust-ability, but its literature does not mention them. But I also understand them to be a very good battery management system.

As I say, I sadly dont yet understand enough about batteries and electricity but I intend to read up a bit more about it. (I have Marine Electrical Bible by John Payne). I have started but I tell ya, if you suffer insomnia, read some of the electrical books, I guarantee you a great nights sleep about half an hour after you pick it up. Either that or a headache! Actually thats not quite true, I have actually enjoyed some aspects of reading it.

44c
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Re: solar panel usage data

Post by 44c » Sun Feb 05, 2012 8:18 am

Electrics (not electronics) is pretty simple really. You just need to remember Watts = volts x amps, and consult a wiring guage guide to give you an idea about wiring sizes required.

I'd be surprised if the flexmax 80 wouldn't be suitable for lithiums, as pretty much all it's charging parameters are user adjustable.

S-berg
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Re: solar panel usage data

Post by S-berg » Wed May 16, 2012 12:55 am

This question may fit this thread as it relates to solar panel output. Its a bit theoretical, sorry.
I have been told from a solar panel installer that partial shading of a panel (say from the boom over the cabin roof) can severely effect the panels output and reduce it to a voltage that will not go into the battery bank.
If i were to have two 190w (total of 380w)panels on the cabin roof and one got partially shaded, the output could theoretically drop by half (slightly less if in series?)
If I were to have eight 50w (total of 400w) panels in a similar location on the cabin roof, I think it would be less likely to have four of them partially shaded to a point where their voltage is too low for the battery. perhaps two would be shaded by the same situation and therefore output would only drop by a quarter, not half?
This is a bit of a silly question and it hasn't quite come out right :oops: but, is it better to have more small panels or fewer large panels or does it not make any difference at all in regard to shading. (you bi-riggers with less shading over the cabin roof best not answer "get rid of the central boom" :lol: )

Jim
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Re: solar panel usage data

Post by Jim » Thu May 17, 2012 6:57 am

I believe that one type of panels output is cut completely with partial shade and the other type is partially reduced with partial shade. One of the electrickery guns can step in here and confirm or otherwise.
Jim.

44c
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Re: solar panel usage data

Post by 44c » Thu May 17, 2012 8:01 am

Generalisations: Monocrystalline panels are more space efficient - more watts per m2, but multicrystalline ones work better in part shade.

Smooth Cruiser
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Location: Brisbane

Re: solar panel usage data

Post by Smooth Cruiser » Thu May 17, 2012 12:01 pm

Theoretical answer to your question - Yes more smaller panels will be less affected by shade. However each panel also has it's own diodes and wiring and hence having more of these boxes also very slightly increases your losses. In a side by side comparison I would expect more smaller panels to provide more power over a day than the equivalent wattage in larger panels in a partially shaded situation.

Practical answer to your question - The total impact will probably be not worth the additional cost, hassles of installation and wiring involved in setting up the additional panels. Most people choose to go with fewer large panels.

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