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Old 13-06-2012, 18:18   #1
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solar panels

Is it better to go with one big panel or two smaller ones.
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Old 13-06-2012, 18:52   #2
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Quote:
Originally Posted by ralphmacey
Is it better to go with one big panel or two smaller ones.
At the same total wattage and panel quality it should not matter from a practical sense.

However, if space is a consideration a single panel may be better. Each panel has an unusable margin arund the edge so it could be one big panel is better.

If mounting locations are different, two panel could be the go so that if one panel gets partially shaded the other may still be unshaded.

Installation requirements would drive my decision more than power output considerations.

Hard to tell without more info from you and currently, it depends.
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Old 13-06-2012, 19:17   #3
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Quote:
Originally Posted by Ex-Calif

At the same total wattage and panel quality it should not matter from a practical sense.

However, if space is a consideration a single panel may be better. Each panel has an unusable margin arund the edge so it could be one big panel is better.

If mounting locations are different, two panel could be the go so that if one panel gets partially shaded the other may still be unshaded.

Installation requirements would drive my decision more than power output considerations.

Hard to tell without more info from you and currently, it depends.
I notice that larger panels may have higher voltages, is that an issue.
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Old 13-06-2012, 19:22   #4
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Re: solar panels

One big panel.
Less wiring
Less mounting.
Simple install
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Old 13-06-2012, 19:38   #5
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Re: solar panels

I agree that one big one will be a simpler install and less things to go wrong with corrosion in the connections. It will be easier to trouble shoot the connections.

We have four 70 watt panels on Exit Only, and they are still working after 15 years. So far I have not had any problems with them. I don't remember the brand of solar panel.
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Old 14-06-2012, 00:30   #6
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Re: solar panels

Quote:
Originally Posted by ralphmacey View Post
Is it better to go with one big panel

Not if you drop a winch handle on it!
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Old 14-06-2012, 00:42   #7
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Re: solar panels

For the same wattage 2 smaller panels will give slightly more output than 1 larger panel when there is any risk of shading.
Usually 2 smaller panel will be phisically larger for the same wattage however. (because there is more framing for the same watts)
All these differences are small so the best advise is to fit the largest number of watts that you can cram in.
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Old 14-06-2012, 00:43   #8
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Originally Posted by Celestialsailor

Not if you drop a winch handle on it!
Are u speakiing from experience???
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Old 14-06-2012, 02:55   #9
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Quote:
Originally Posted by ralphmacey

I notice that larger panels may have higher voltages, is that an issue.
It still depends. Like everything on a boat you can go from extremely simple to vastly complex.

I run 40 watts of top up solar with no controller. Alternately You can have a system with MPPT controller that offer extensive power management for larger arrays.

Maybe if you give us a hint what you are trying to do? The basic info is pretty simple.

Power consumption - take everything you plan to use on the boat and determine how many watts each item draws. If the item only shows amps the formula is volts X amps = watts. Then multiply each item by how long you plan to use it each day. Example - 40 watt light X 5 hours = 200 watts or 200 / 12 volts = 16 amps. For reference an average cruising boat consumes between 80-100 amps a day. 100 X 12 volts = 1,200 watts. There are lots of ways to reduce consumption these days.

Storage (batteries) - the second step is to determine how long between charging you expect to go. You can get rain for a few days, for example. The second consideration is that a basic rule of thumb is you do not want to discharge your batteries below 50% of their rating. So 210 a/h of battery would last one day with no charging. 650 a/h would go three days.

Charging - most people use the engine alternator as the primary charging unit. It is very inefficient but relatively quick. In our case you would run the engine every day for a couple of hours - assuming a 60a alternator.

Solar - the amount of usable sun per day varies with lattitude. I reckon here we get about 6-7 hours usable but I have seen 5 hours as a rule of thumb also. To generate 1,200 watts in 5 hours you need 1,200 / 5 hours to be free from the engine or 240 watts of panels. However, this covers one day consumption and requires 5 hours of sun every day. Two 175 watt panels would have the potential to deliver 145 amps in 5 hours and would seem a decent margin for our hypothetical 100 amp boat.
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