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Old 09-01-2010, 16:03   #1
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Solar Output in Higher Latitudes

Hi everyone,

Right now I'm living around 48 deg north latitude (Washington state). I'd love to have a solar system, but I understand that the angle to the sun greatly effects the output. Yeah, yeah, I know its always cloudy up here too....

I really can't imagine continually adjusting a panel array so that it is at an optimum angle, especially while swinging around at anchor, so I would mount them flat. I think that would mean about 48 degrees from optimum in spring/fall? My second issue is it is very cloudy 6 months of the year here, at the time the sun is at its lowest angle (winter). But, we do get a lot of sun in the summer, which is when we spend most of our time on the hook.

So my questions are 1) Does anyone have any real-world experience with solar in higher latitudes? Or even the Pacnorwest?? What kind of set-up do you have?

2) Does anyone know any calculations on how the angle of the sun effects solar output?

We will probably be moving to either 36 or 30 deg latitude here in a year or two, so I have a lot to consider there as well!



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Old 09-01-2010, 17:40   #2

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I sent you a PM.

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Old 10-01-2010, 06:47   #3
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Solar panel output is basically the cosine of the sun angle. Table of Cos(a)

For example, at 45 degree sun angle on the panel, the cosine is .707, so you would get 70.7% of full output.
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Old 10-01-2010, 09:07   #4
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We spent two months last summer at 56-58N and relied on our solar panels for much of our daily use. With long hours of daylight you might get less concentrated output, but more low level output accumulated per day, if you're prepared to put a little effort into getting it.

We have two 45W panels on a gantry aft that can be orientated fore and aft, and two deck mounted semi-flexibles (45W each) on deck, and the difference in average output between the two arrays is huge - far more from the aft panels. We check the angle of the aft panels regularly and can monitor their output and it's hardly a chore. We also have an 85W flat panel with lashings on it to enable us to mount it to best effect when we're at anchor - again we move it every hour or so to get the best output. Between the three arrays we gain most of our daily output, to run pumps, lights, laptops etc.

You don't mention whether you already have a wind generator - in our latitudes where we have plenty of wind a powerful turbine (we have a Superwind) is well worth having, and on the days that it's wet and windy the Superwind takes up the slack from the solar. We still reckon that solar gives us more bang per buck, but as has so often be said, a combination probably makes most sense.

During the whole period living aboard we never once ran our engine to charge the batteries. As it was a windy season we motored far less than usual, so we were really pleased with the set-up we have.
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Old 10-01-2010, 19:21   #5
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In the summer, if they are flat, they will still deliver reasonable amt of juice (the sun will be N of Eq too, so your angle won't be that bad.

But overcast is a problem. So if you have bright sunny summers and if you want solpanels just for the summer time then I would go for it.

We used our panels as far as 60N (Oslo and beyond) and got good Amps on sunny days.

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Old 10-01-2010, 21:01   #6

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For every 15 degrees that you are off, you lose about 10% power. There's no elegant way to regain that when you are forced to use flat panels.

One pricey option is, which mounts them on adjustable arms on a pole. Gets them off the deck, outboard of the boat, and allows you to adjust the angle and direction every hour or two if you ARE on the boat. Emphasis on PRICEY and really scaled to fit boats 36' and up in size, but a big difference in efficiency. Probably cheaper to add one more flat panel on the deck and ignore the angle if budget is any kind of consideration, and you have the space to do it.

There are also published tables on the web, from university and government standards, that will tell you how the panel output degrades with lattitude. All you can do, is all you can do.
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Old 10-01-2010, 21:42   #7
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Thanks everyone- I think we're sold on solar (translation: the admiral bought off on it! ). Time for a good ol fashioned boat project!

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pacific northwest, solar

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