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thoughts about this solar panel from Amazon?

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Posted by danny burstein on January 12, 2012, 4:35 pm
 
Just got this offer from Amazon and it sounds like
a decent match for what I'm planning.

We want to set up an outdoor LED fixture (ok, it'll
be a menorah/candelabra) using a total of about 20
watts of LED lighting.

It'll be on a timer, so only be lit for 2 or so hours
after sunset. Hence 40 watt-hours/day.

Assuming they're telling the truth and this panel would
provide 50 watts in direct sun, that would (rule of thumb)
get us about 200 watt-hours on sunny days, and maybe
a quarter of that on a typical foggy/misty one.

Even if they're optimistic and doubling the real number,
we'd still do ok.

So... attached to a 500 watt-hr battery, that would
get us through a week, or even two, of drizzle...

Anyway, the price looks good, at $19.00. Throw in a decent
controller gets us into the $00 range. Batteries would
be extra, of course.

It's a "Ramsond Monocrystalline Photovoltaic Solar Panel",
and the url is at:
(Amazon.com product link shortened)

(or: http://goo.gl/3w1MA )

Thoughts?

Thanks


--
_____________________________________________________
Knowledge may be power, but communications is the key
             dannyb@panix.com
[to foil spammers, my address has been double rot-13 encoded]

Posted by vaughn on January 12, 2012, 5:56 pm
 


In the real-world, expect about half of the advertised panel output.  Why?  That
"50 watts" only happens with a perfectly matched load, in full sunlight, and
with the panel tracking a perfectly full sun.  You won't have a sun tracker
(derate) and at that price-point you won't have an MPPT charge controller
(derate).  Also, your battery only gives back about 80% of what you put into it
(derate).

Still, from my own experience, I think that panel will likely do the job you
describe.

Vaughn



Posted by danny burstein on January 12, 2012, 6:07 pm
 

That

Thanks. As you could see in my earlier description, I figured
that their advertising claims were about as valid as EPA numbers...

But it still looked practical.

- the reasoning behind using solar power / battery for this
  is that running an up-to-code power line outdoors would
  be a Big Pain and Expense. A stanalone unit would be simpler
  and might even be cheaper.

- I was considering doing it all with a 12V circuit, thus
  letting me set up wiring without Code issue. At 20 watts
  the cable size wouldn't be an issue... Might yet do it
  that way with a transformer inside the building.

  But being able to put up a placard saying "solar powered"
  is kind of cool...


--
_____________________________________________________
Knowledge may be power, but communications is the key
             dannyb@panix.com
[to foil spammers, my address has been double rot-13 encoded]

Posted by vaughn on January 12, 2012, 7:43 pm
 

That might be the best & cheapest way.  Look at Malibu cable at your local
big-box building supplies store.  It's the stuff used for landscape lighting.
If you are going to bury the cable, consider putting it in PVC.  Will last
longer and be easier to repair.

FWIW: I do my yard lighting with Malibu cable AND a solar power system.

Vaughn



Posted by Mho on January 13, 2012, 9:44 pm
 My experiences totally disagree with your 80%.

Some caveats
- Now I am using a MPPT circuit but my panels put out 100% of rating in
spring and fall. Less in summer (see below)
- In the summer I have my panels at too steep of an angle temporarily but it
keeps most of the snow off them.
- In the winter my panels put out 125% of their ratings due to higher
efficiencies in the cold, and they are still too steep an angle for the sun
at solar noon.
- Cheaper panel manufacturers may "cheat" at their ratings agreeing with
vaughn's statements.
- These ratings are into a 48 vdc battery bank charging at 56 vdc and ~70
vdc panels at MPP.

Battery losses are agreed and more.

This project may be fun and experimental as a hobby but in view of *easy*
grid power a total waste of money. At this battery development stage date
batteries always cost more than the any energy saved from grid energy costs,
forever.

Note: Grid energy costs may include digging a trench, remote switching and
wiring, inspection and many other costs.
LED costs would be constant. I have many LEDs that have not lasted more than
two-three years in outdoor sunlight and Christmas tree strings. The light
produced is slightly cheaper than equivalent incandescents and they
typically last longer but the costs still outweigh savings over other
technologies.

---------
In the real-world, expect about half of the advertised panel output. Why?
That
"50 watts" only happens with a perfectly matched load, in full sunlight, and
with the panel tracking a perfectly full sun. You won't have a sun tracker
(derate) and at that price-point you won't have an MPPT charge controller
(derate). Also, your battery only gives back about 80% of what you put into
it
(derate).
Still, from my own experience, I think that panel will likely do the job you
describe.
Vaughn
-------------------


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