Hi John,
Voltage changes on the supply line only because the potential to feed the batteries is very low. Many PV panels have an open voltage of 20 or more volts. This voltage will not change in sunlight or other light sources that are compatible with the cells being used. Wattage will change with how you face the panel to the source. It should be noted that reflection off the surface is the reason for most of the energy loss from the sun. Surface area and panel tech determine how much you can get from the sun.
The type of window may effect the output of the panels more than you are thinking. One reason is transmittance of light waves. Some glass will let more of a wave length spectrum through the glass or plastic than one composed of other material. It is good to know what part of the spectrum a panel works best in to determine if your windows will effect the output to much to make the plan worth while.
You can build your own panel using cells from ebay. If you do this you can use plexi-glass as the protecting surface of the panel making location less of an issue. Although it is said anyone with a soldering iron can do this job, I would suggest you avoid the idea if you are not competent with soldering low temp connections.
If I were making a aux sailboat from scratch I would invest in rigging that sent all the sheets aft to the cockpit and plan never to need to go on deck. The deck would be mostly solar cells. This in it self is problematic as a panel needs to be in the sun without a shaded cell or two, as output is severely effected when a cell is shaded.
Some poly panels are produced using silkscreen techniques. I am wondering if one could use a roller furling and silkscreen the sail to help charge the bank. Such an Idea would be short lived as far as life expectancy, but the idea would be a neat one just the same.
Kevin Pemberton
On 05/29/2011 08:05 PM, John Green wrote:
Hi, Kevin, thanks for the interesting mine of info on this.
Seems that it is not as easy as I thought.
Am I correct that you are saying that you have a wind generator that
produces
100 volts, and you feed this direct to the battery with no controller,
and the
'shorting' effect of the battery cushions it at roughly 12 volts?
Hmmm, if that's the case, might be better not leaving that running
unattended!
I have, in the few days since my last post, checked out my little
'battery top-
up' solar panel a bit more. It is about a single watt, as far as I can
remember.
You would think it would be written on it, but nothing, not even in
Mandarin.
Seems from my experiments that the volts do not go much lower when it is
faced even 45 degrees away from
direct sun.
I am not sure if panels get the power from the sun increasing the amps,
or just
the volts, but if it is solely the volts, I was getting 20 when facing
the sun,
and still as high as 17 or 18 when it was no longer direct. And I was
still
getting well over 14 volts even with no sun, just light, medium bright
day, but cloudy.
If this is the case, I could fit solar panels on the insides of the
cockpit
footwell when away from the boat. There is also a little room under
where the
hatch slides to when open. Again, my understanding is that provided I
get over
about 13.7 volts, I am good to go, just feed it into a charge
controller, and
bingo. I realise that a controller probably converts the extra volts
into more amps, so the higher the output the better.
I have to admit to have given up on the idea of a small trickle charging
windmill. Maybe something to experiment with later. I suspect solar
might be
better suited. Your experiences seem to back that up.
I am going to soon be wiring up for the bilge pump, and once the boat is
in the
water, will get a pair of batteries, one I can put on the car as a
second
battery to charge when doing the 30 mile or so drive to the boat, then
swap them
out each visit or as required. Or I might find that I have no need to.
My first electric drive experiment will hopefully be using a 24 volt 500
watt motor, on a
15 foot dinghy as a test bed. I will know more about that later this
week, I am
trying to gather parts locally to avoid massive shipping charges.
I probably will not pull out the Atomic 4 gas engine from the sailboat
this
season, but neither will I bother getting it running.
So, from what you are saying, windmills on boats are problematic.
I just might be able to get enough power from solar panels, bearing in
mind that
I will have only two batteries, not a big bank of them.
My understanding is that I can just add panels wired in parallel, and if
so, I can
build up a piece by piece system. And I can mix in wind power later as
well, I
assume, provided I have diodes so the power goes only one way. I know
that adding small panels is expensive, but it also gives greater
redundancy if a panel gets broken, and they can be hidden more,
especially on a small boat, where larger panels would look overpowering.
(no pun intended, but it was a good one!)
Another place for solar when away from the boat would be directly in the
windows, kind of against the
glass.
That would give me about 5 watts from a single square panel in front of
the
hatch, and another 4 watts total from the main windows, and I could
probably fit
another couple of 1 watt ones beside the mast. About 10 watts, but at
low
efficiency. Maybe another 5 watter vertically over the hatch door while
away.
Low efficiency, but quiet. And that is with only discreet mounting
places used.
Overall, I think after looking at what you have experienced, I ought to
be
getting a few solar panels first, then look into wind as a secondary
thing.
Even using 24 volts, I can charge 12 v singly, and have a changeover
system like
RV use, in their case charging the starting battery first, house battery
second.
Interesting that your experiences match my own reservations, with having
stuff whizzing around!
Of course, at the low levels of solar I am speaking of, maybe a mini
windmill or two makes a bit more sense.
My battery drain might not even be measurable most of the time. Just a
few minutes use for approaching and leaving a mooring. But, human nature
being what it is, the appliances get added later, or, laziness
encroaches, and the sails don't go up as often as they should.
It will be interesting to see what comparative results you get with a
'designed' prop.
Thanks again,
John
-- AspireOne Netbook running Ubuntu 11.04 Safe, Secure, Easy to use, Free Open Source Linux OS. Leaving Virus worries to the Windows Users!
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