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Solar panels work by means of crystals which, when struck by the sun's rays emit electrons. A single solar cell creates a potential of around .45 volts so it takes about three dozen cells, connected in series, to produce the
(approximately) 16 volts required to charge up a 12 volt battery.
The larger each cell, the more current it produces in relation to its area, so that, whilst a 4" cell will produce just over 3 amps, a 6" cell produces just over 7 amps.
If you calculate your requirements on the basis that each solar panel will provide between 30 and 50% of its rated wattage in daily amp hours, you won't go far wrong. In other words, a panel rated at 80 watts will produce between 25 and 40 amp hours each day that the panel is facing the sun.
There are different kinds of solar panel generally available.
The Monocrystalline type (like the ones made by Siemens, for example) have dark gray cells, are rigid, glass-covered and give the highest output for the given area. They usually cost the most too.
Polycrystalline panels (like the Solarex), the ones that look like cracked ice, are also rigid and covered with glass and are only a little less efficient than the Monocrystalline panels but usually cost quite a lot less to buy. Because the cells are square, Polycrystalline panels tend to be smaller than their Monocrystalline counterparts, too, which is another plus.
The Amorphous type, (Uni-Solar, for example) is fabricated by attaching active silicon to a stainless steel plate, or to a flexible backing, this sort being generally referred to as 'Thin Film' panels. It is difficult to say much about these without sounding rude - they are supposed to be unbreakable and less affected by shadows but each cell is only about half as efficient as those of the Polycrystalline type so you'd
have to have quite an acreage to get the power you needed!
'Self-regulating' solar panels are to be avoided for much the same reason - they produce less voltage so you need more of them. Much better to get a regulator, which won't cost you all that much anyway. Whatever you do, don't be tempted to try and skimp on getting a regulator though. It's easy to think that you'll remember to check regularly and cover up the panel(s) when the batteries are in danger of overcharging. The day you forget to and the batteries get damaged will be a far more expensive day than the one on which you have the sense to buy a regulator and let it look after your batteries for you.
Why go over to solar panels?
Solar panels make no sound. In a peaceful bay, you can be generating power without ruining your own and other people's enjoyment of the surroundings.
Solar panels do not rely on any fuel other than naturally obtainable sunlight
so solar power gives you freedom without loss of convenience.
You can stay out at sea for longer since your power source is naturally renewable wherever your boat is, charging the batteries that power your pumps, lights, refrigerator, radio etc. Whilst others need the shore-power at marinas, you can be
independent and, while you are off the boat, the solar panel continues to maintain your battery power in a state of readiness.
Seems to me, all of those are pretty compelling reasons to consider it
sooner rather than later. What do you think?
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