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Old 07-11-2016, 14:43   #241
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Re: What is your Real Amp Hour per Day Usage

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Originally Posted by a64pilot View Post
OK, so more like four to one, five to one to be conservative.
So if your consumption is 200 AH a day, you will need a Kilowatt of panels.
It's very location dependent. SailorBoy's info says "NorthEast". Assuming that's NE USA, he will be getting a lot less per day than your proposed "Caribbean".

3:1 or 4:1 is quite feasible there.

Take a look at this Insolation map:
Solar Insolation Map | Ameresco Solar - Green. Clean. Sustainable. We distribute solar components, manufacture solar panels, and engineer solar systems

The numbers are kWh/m2/day which roughly translates to the "usable" hours discussed earlier. As you can see the "north east" has a lot less available solar energy than the Caribbean.

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Old 07-11-2016, 15:39   #242
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Re: What is your Real Amp Hour per Day Usage

Map is I guess average over a year? If so then I assume lower numbers in Winter as less sunlight plus more overcast days?
Sounds like I'm going to need 1KW to have a comfortable margin as I will have shading issues and will not be able to track the panels with the sun.
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Old 07-11-2016, 15:57   #243
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Re: What is your Real Amp Hour per Day Usage

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Map is I guess average over a year? If so then I assume lower numbers in Winter as less sunlight plus more overcast days?
Sounds like I'm going to need 1KW to have a comfortable margin as I will have shading issues and will not be able to track the panels with the sun.
Yes, that's annual.

And it's may also be for panels tilted for latitude, that is quite common on such maps. If that is so, since the vast majority of boat mounted panels are horizontal, the comparative efficiency increases considerably with decreasing latitude so the effective difference between "NorthEast" and "Carribean" could be a lot more than that map would indicate.

You can find more specific seasonal or monthly insolation maps if you search the intertubes.

Here's a good start: NREL: Dynamic Maps, GIS Data, and Analysis Tools - Solar Maps
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Old 07-11-2016, 16:24   #244
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Re: What is your Real Amp Hour per Day Usage

I have 750W now but have not hooked them up. I have one more 250W panel gathering dust. My Outback 80 will take 1000W. I think I will now put that other 250 on my Bimini, not the best place of course but it will add some.
I had been looking for some rule of thumb to determine amount of Solar needed, but concede that like bank capacity, you can't have too much.
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Old 07-11-2016, 16:47   #245
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Re: What is your Real Amp Hour per Day Usage

A good conservative rule of thumb is:

You should have approximately the same Wattage of solar panels as you have total Ah in the battery bank and your bank should be sized to 3 times your average daily demand.

So if you are using 100Ah per day on average, you should consider 300Ah of batteries and 300Watts of solar.

If you use 300-350Ah per day, look at 1kW of solar and 1000Ah of batteries.

Most of the time you will not run your batteries down below about 75% SOC and should be able to have them full in the late afternoon. You will also have a reserve for cloudy/rainy days without pulling down below 50% SOC.


(The above figures assume LA batteries)
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Old 07-11-2016, 16:51   #246
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Re: What is your Real Amp Hour per Day Usage

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Originally Posted by a64pilot View Post
Question, on an average day in the "Caribbean" during the Winter months how much Solar is needed to replace 100 AH? I know there are huge variables, and I do know my average consumption, just trying to get a feel as to how much Solar is needed.
One of the numbers that dropped out of our son's Energy Budget calculations is: If you divide the WATTS of solar panels by 3, that's the number of AMP-HOURS you'll get into your batteries on a sunny day in the tropics for horizontally mounted panels with no shading. Another way of saying this would be: to get X Ah into your batteries, install 3X Watts of solar panels. I've yet to find any solar panel folks who will tell you how much you'll actually get into your batteries (& yes, there are lots of variables here as well, but it's a good place to start).
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Old 07-11-2016, 16:52   #247
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Re: What is your Real Amp Hour per Day Usage

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Originally Posted by StuM View Post
A good conservative rule of thumb is:

You should have approximately the same Wattage of solar panels as you have total Ah in the battery bank and your bank should be sized to 3 times your average daily demand.

So if you are using 100Ah per day on average, you should consider 300Ah of batteries and 300Watts of solar.

If you use 300-350Ah per day, look at 1kW of solar and 1000Ah of batteries.

Most of the time you will not run your batteries down below about 75% SOC and should be able to have them full in the late afternoon. You will also have a reserve for cloudy/rainy days without pulling down below 50% SOC.


(The above figures assume LA batteries)
I like this line of thinking and it makes sense to real world data I have seen. I have never met a cruiser that said, "ya know Rich, I put too much solar on my boat". So if you error, let it be on the side of too much solar because well....so what...
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Old 08-11-2016, 17:28   #248
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Re: What is your Real Amp Hour per Day Usage

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I like this line of thinking and it makes sense to real world data I have seen. I have never met a cruiser that said, "ya know Rich, I put too much solar on my boat". So if you error, let it be on the side of too much solar because well....so what...
Not only so what, but in winter, we experience far less solaring. Just sayin'.

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Old 09-11-2016, 07:50   #249
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Re: What is your Real Amp Hour per Day Usage

So far only

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Our actual A / day are within 10% of our measured values, I think.

About 20 A / day anchored.
About 15 A / day sailing.

House bat 100 Ah. Solar 150W. Alt 60A (not required but present).

LEDs, windvane, vegetarians, etc.

Boat 26'. Two onboard.

b.
has provided sufficient information to figure out some of his boat electrical installation.
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Old 09-11-2016, 09:53   #250
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Re: What is your Real Amp Hour per Day Usage

I write this about 02/08/2009

“Be also aware that any rigid Bimini or arch with or without solar panels can affect the steerage of a vessel in a storm.”
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