Re: [Paddlewise] Solar Panels

From: <Rstewartretired_at_aol.com>

> I am planning a 4-6 month trip and would love to hear anything you have on
> solar panels. I am trying to work out, how to take my digital camera and
> small laptop as well.
>
> I am also researching using the solar panels to recharge the batteries for
> the VHF, flashlights etc..
>

This is a topic I've been researching in that past month or so - an offshoot
of the electric pump thread.  I've purchased an electric pump and a big(ish)
AGM battery (absorbed glass mat - safest to transport of the lead acid types).
I'm planning on using the battery as a general power source for the pump
and to recharge other, smaller batteries (VHF, cell phone, NiMH AAs etc).
The problem turns to maintaining the big battery - hence solar rechargers.
So far I've limited myself to web searches and reading - last night I
discovered a potential retail source walking distance from my house - if it
wasn't a holiday today, I'd go over and check it out.

The big battery (2.75x3x4 in, 4 lb) is 12 volt - that way I can use
off-the-shelf rechargers and stuff made for auto use.  The big battery
will have a female cigarette lighter socket to plug everything into
(dry use - the pump'll have a dedicated connection that's waterproof).
If you go with 12V everything, you could do the same (big battery not
required, obviously, just plug whatever directly into the 12v solar
panel.)

The things I look for in a photovoltaic (PV) panel include waterproofness,
quality of power absorption and price.  The quality of power absorption
(I can't think of the right term) refers to a unique property of photovoltaic
cells.  If you shade a cell, its power output drops.  If you link several
cells into a grid, and one cell is shaded, its potential drops below that
of the other cells and the power flows from the brightly illuminated cells
into the shaded cell, reducing the effectiveness of the whole grid.  The
better panels have diodes placed between the individual cells to prevent
the reverse currents from forming.  This adds to the price.

Unisolar makes flexible solar panel that looks good in 5, 11 and 32 watt
versions.  Only the 11 and 32 have the diodes installed.  See:
http://www.ovonic.com/unitedsolar/flex.html for an example.  They are
designed for outside use, including marine, and are weather resistant.
How they would perform on the deck of a kayak remains to be seen.
The advantage of the flexible panel is that it can adapt to the shape
of the deck - no extreme bends, though.  The 11 watt version isn't
small - almost 22x17 inches (5W 22x9)!  But it does deliver up to 0.6 amp -
enough for most recharging uses.  Check the current requirements of the
laptop auto recharger - it's the only large battery of the devices you've
mentioned.  If you're not hung up on the shade problem like I am, the
5W unit is definitely an option.

Rigid PV are also out there, as are dedicated PV rechargers.  The latter
tend to be small and trickle charge (think 10-14 hour recharge time).
That means sitting still for that long, since they aren't likely
waterproof enough to put on the kayak deck.  Rigid, higher capacity panels
can provide the power to rapid charge or are weather proof enough for
on-deck operation.  Larger marine suppliers have lots of options, e.g.
http://www.westmarine.com/webapp/commerce/command/CategoryDisplay?cgmenbr=201&cgrfnbr=453&outlet=.

If you're handy are electical stuff, you can make the thing up from
just a PV panel and a few parts.  If you want hands-off reliability
(like automatic protection from overcharging etc) you pay.  YGWYPF.

Mike

PS - web searches get lots of hits on this topic.

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