Solar Panels

Things 12V and 24V
Jim
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Joined: Fri May 19, 2006 8:25 am
Location: Cairns

Solar Panels

Post by Jim » Sun Oct 25, 2009 7:52 pm

Hi all, I know as much about solar panels as I do about the Polaris missile, however I have to learn a bit because I have held off buying anything up till now, but the time has come. I found this company on Ebay, so have a look and tell me what you solar literate people think.

http://shop.ebay.com.au/luxuryhomesydne ... ksid=p4340

I was thinking about a couple of the 250w ones, although the one I inquired about is 24v, I don't know if the regulators can knock that back to 12v or not or they may have them in 12v.

Opinions please.

Jim.

44c
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Joined: Tue Aug 08, 2006 5:08 am
Location: Hervey Bay, Qld

Solar Panels

Post by 44c » Sun Oct 25, 2009 10:01 pm

They look like decent value. You'll need a good charge controller for them since you could possibly see over 40 amps at 12 volts.



I suggest something like the Outback Flexmax 60 - it can handle up to 60 amps, and can step down from 150 volts to 12. Xantrex also have a similar model, similarly priced.



Then wire the panels in series - make it a 48 volt array, so there is less current in the wires from the panels to the charge controller.



Then if you position the controller near to the batteries you only need a short run of wire heavy enough for 40+ amps, whereas the longer runs from the panels can be lighter wire.



ie, you'd have 10.4 amps at 48 volts rather than 20.8 amps at 24v. You'll also get better shade or low light performance from them this way.



The Flexmax 60 isn't cheap though, $553 us, from where I got mine: http://www.solarblvd.com/index.php?cat= ... Power.html



The FM80 was only $40 more, so I got that.



With this set up you should have power to burn!

Jim
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Location: Cairns

Solar Panels

Post by Jim » Tue Oct 27, 2009 5:15 am

Thanks for that. I will get a book and work out what you mean exactly with the volts/amps thing. I have made some really complicated and high precision things over the years, but I just don't get electricity.

Jim.

44c
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Location: Hervey Bay, Qld

Solar Panels

Post by 44c » Tue Oct 27, 2009 5:10 pm

Watts = Volts x Amps. so a 250 Watt panel at 24 volts can produce 250/24 amps, or 10.4 amps.



If you connected 2 in parrallel, you'd have 500 Watts at 24 volts, so 20.8 amps.



2 in series would be 500 Watts at 48 volts, so 10.4 amps.



Then the charge controller will change either the 24 or 48 volts down to 12 volts, giving you either 20.8 x 2 = 41.6 amps, or 10.8 x 4 = 41.6 amps.



So you get the same maximum output either way, but going 48 volts has the advantage of not having such high current in the (usually) longer cables from the panels on the roof to the charge controller.



Another advantage of having a higher voltage array is when there is less sunlight or partial shading.



Lets say you had 4 12 volt panels in parallel. As soon as you have enough shadow or cloud cover to reduce the output below 12 volts, the panels will put nothing into the batteries.



ie. 11.9 volts isn't enough "pressure" to push into 12 volts.



But if you had the 4 in series, you'd still have 4 x 11.9 volts = 47.6 volts, so still enough pressure to push current into the batteries. Even with more shade, dropping the output to 6 volts per panel, you might still get some current.



Does that help?

judy
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Location: Darwin
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Solar Panels

Post by judy » Tue Oct 27, 2009 8:47 pm

44c wrote:Watts = Volts x Amps. so a 250 Watt panel at 24 volts can produce 250/24 amps, or 10.4 amps.

If you connected 2 in parrallel, you'd have 500 Watts at 24 volts, so 20.8 amps.

2 in series would be 500 Watts at 48 volts, so 10.4 amps.

Then the charge controller will change either the 24 or 48 volts down to 12 volts, giving you either 20.8 x 2 = 41.6 amps, or 10.8 x 4 = 41.6 amps.

So you get the same maximum output either way, but going 48 volts has the advantage of not having such high current in the (usually) longer cables from the panels on the roof to the charge controller.

Another advantage of having a higher voltage array is when there is less sunlight or partial shading.

Lets say you had 4 12 volt panels in parallel. As soon as you have enough shadow or cloud cover to reduce the output below 12 volts, the panels will put nothing into the batteries.

ie. 11.9 volts isn't enough "pressure" to push into 12 volts.

But if you had the 4 in series, you'd still have 4 x 11.9 volts = 47.6 volts, so still enough pressure to push current into the batteries. Even with more shade, dropping the output to 6 volts per panel, you might still get some current.

Does that help?


I helped me, thanks. Later in our project, when I can clear enough space in my head to start thinking about boat electrics, I think I should use you as my tutor!

KosmicKreeper

Solar Panels

Post by KosmicKreeper » Wed Mar 24, 2010 7:49 pm

Hi all,



KosmicKreeper is the name of the boat we are yet to start building, so we are very new to this caper. Hence our joining this site.

So why respond to this thread. Presently we live near Ballarat in a fully solar powered house on 40 acres where we will be building the Kreeper, so I have 25 years experience living with solar power. I also have a Cert IV in Renewable Energy Technologies.

Our house system comprises 6x100W and 2x175W panels, both mono and poly feeding a 600Ah lead acid battery via a Plasmatronics PL40 controller. We run everything DC at 24V as the best compromise between efficiency and cost.

My contribution to this thread is: Why drop voltage down to 12V when every change results in loss, plus a current increase which needs larger wire size?

Our intention is to wire the boat for 240Vac and use a Selectronics pure sinewave inverter, as we do in our house. Then we can run all sorts of stuff that is commonly available.

We are building a Mike Waller 1100 Mk II.

Cheers for now. The Kreeper.

kjay
Posts: 149
Joined: Thu Oct 26, 2006 2:03 am
Location: brisbane

Solar Panels

Post by kjay » Thu Mar 25, 2010 3:57 am

Kreeper, Welcome to the forum and best wishes for your build. Just a few questions regarding your post and please remember you have forgotten more than I will ever know about solar power and general electricity. Do you require a qualified electrician to install 240v and won't all you appliances need testing and tagging yearly? also My fear with 240 is the shock situation with salt ingress. I am aware of earth leakage but it still frightens me. A guy I went to school with many years ago died while trying to fix a washing machine and he was an electrician. I always say don't muck around with something you can't see that can kill you and you may be a long way from help in the hopefully unlikley event of a serious shock. Any way this is just my baseless thoughts good luck with the waller. BTW saw the one in gosford just before launch nice boat and huge for its size.

Thanks

John (Sarah 16)

KosmicKreeper

Solar Panels

Post by KosmicKreeper » Thu Mar 25, 2010 7:35 pm

Hello John,

Yes, you are right. There is a problem with electric shock, but hopefully no more than in any domestic situation. Also, I will have to get a sparky to check the installation and sign off on it.

25 years ago this wasn't the case. If you were not connecting to the grid, the authorities didn't want to know and didn't care. Now is a bit different.

Our boat will actually be a mixture of DC and AC with the AC being used for the larger appliances. Washing machine etc, as we will be living aboard for long periods. Lighting, nav, TV? refrigeration will be DC. There are some excellent LED lights available that draw litle current and give off good light.

We are experimenting with some LED lights at home as they don't attract moths and other bugs.

I expect corrosion to be a problem with domestic type appliances.

I can turn your comment around a little, you will have forgotten more about building than I know, which is why I joined this forum.

Bye for now,

Peter & Steph.

The KosmicKreepers.

Chrisg
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Joined: Wed Feb 17, 2010 6:55 am
Location: Country Victoria

Solar Panels

Post by Chrisg » Thu Mar 25, 2010 11:43 pm

The KosmicKreepers.

And we thought we were the only ones down south build a cat.

Your comments re electrical are all welcome.



Chris and Michelle

(Easy Sarah 22)
Chris & Michelle

Outback Dreamer - Sarah 23
http://www.outbackdreamer.com

Smooth Cruiser
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Joined: Thu May 11, 2006 1:51 am
Location: Brisbane

Solar Panels

Post by Smooth Cruiser » Thu Mar 25, 2010 11:53 pm

Welcome to the forum KosmicKreeper, good to have you aboard.



I think most people just stick to 12V because it is what is known, it is only fairly recently that boats really even started having 240V appliances aboard.



Nothing wrong with running 24V for efficiency reasons - you may find you still need a 12V circuit for instruments, radios and possibly for nav lights, mast head lights, bilge pumps etc which are mostly available in12V . 24V gear is available for all of this but is typically only for commercial vessels and hence doesn't have as wide a range, is more expensive and is usually bulkier and "uglier".



Good luck with your build!

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