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Old 19-12-2014, 13:02   #1
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Solar ratio on amp output

I'm thinking of installing solar. If I get a small panel say 60 watt with 12 volt system the max amps per hour is 5. On Lake Superior in the summer do you think I'll actually average 50% of that for 8 hours a day?


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Old 19-12-2014, 14:24   #2
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Re: Solar ratio on amp output

Probably not, just maybe, IMO.

But it depends a lot on how much shading the panel will get and the variations in orientation of the panel
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Old 19-12-2014, 15:00   #3
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Re: Solar ratio on amp output

Maine Sail has a great article on his website about how to install solar panels that includes a section on how to calculate sizing.
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Old 19-12-2014, 15:26   #4
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Re: Solar ratio on amp output

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Originally Posted by Ketchgould View Post
I'm thinking of installing solar. If I get a small panel say 60 watt with 12 volt system the max amps per hour is 5. On Lake Superior in the summer do you think I'll actually average 50% of that for 8 hours a day?


Christian Gould
St. Paul, MN
S/V Sea Dog
Apostle Islands Lake Superior
No, I don't think so.

12v is a misnomer. In order to charge a "12v" battery, you need to be putting out more like 15v. In my case, 15.5v. A 60w panel is putting out less than 4A @15.5v and that would be under perfect conditions - an MPPT controller, a solar tracking mount, absolutely NO shading, etc.

Why such a small panel? I won't even pick up a drill and drill a hole for anything less than a 200w panel, the effort to mount it isn't even worth the small amount of power they put out. Price can't really be the issue, the last panels I bought were 230w for $135. Most people spend $200 or more for a decent MPPT controller, might as well spend a few $$ for the panels and get 400w or more.

Aside from space considerations, there really is no such thing as too much solar power. Did your batteries get fully charged by 11am? Is that a problem? After all, a decent MPPT controller is also a 4 stage battery charger, the good ones give you full control over bulk, float charge voltage, etc.

What if it's partly or totally cloudy for a day or 2? An "oversized" system is still going to be able to crank out some power under partly cloudy conditions, a system that's barely enough on sunny days is going to be nearly worthless when it's cloudy, and even worse if it gets shaded.
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Old 01-03-2015, 22:32   #5
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Re: Solar ratio on amp output

Hi, where did you get 230W panels for $135??? I'd be interested in a few of those!
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Old 01-03-2015, 23:59   #6
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Re: Solar ratio on amp output

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Hi, where did you get 230W panels for $135??? I'd be interested in a few of those!
Me to I just spent $320 usd for two 100 watt panels
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Old 02-03-2015, 00:26   #7
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Re: Solar ratio on amp output

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Hi, where did you get 230W panels for $135??? I'd be interested in a few of those!
The website is SolarBlvd.com. They still have them, 10x Amerisolar 230w panels for $1,357.00.
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Old 02-03-2015, 09:27   #8
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Re: Solar ratio on amp output

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The website is SolarBlvd.com. They still have them, 10x Amerisolar 230w panels for $1,357.00.
OK that's really expensive for a mere 230 watts in your original post you stated it was $135 USD not $1,357 USD but I see that price was for a lot of ten panels so 2300watts in a single purchase that takes a lot of real estate to mount on a sailboat likely the entire deck plus davits off the stern most pl don't even have a fourth of that in panels
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Old 02-03-2015, 09:53   #9
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Re: Solar ratio on amp output

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OK that's really expensive for a mere 230 watts in your original post you stated it was $135 USD not $1,357 USD but I see that price was for a lot of ten panels so 2300watts in a single purchase that takes a lot of real estate to mount on a sailboat likely the entire deck plus davits off the stern most pl don't even have a fourth of that in panels
I think they'll sell singles as well, for a little bit more per panel. There are other places selling panels down in that price range as well.

Here's a link to their solar panel page, they sell the Unisolar 136w flexible panel for only $99, the single Amerisolar 230w is $149.50, or 65 cents/watt. The Hanwha 245w is $145, 59 cents/watt.

https://www.solarblvd.com/index.php?cPath=1_270&&page=1
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Old 02-03-2015, 10:05   #10
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Re: Solar ratio on amp output

OK thanks for the reply also to clarify my 320 was for a 200 watt kit with all mounting hardware, connectors, 40 ft of cable and a pwm controller.
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