Polycrystaline of Amorphous silicon ?

[SandS]

Hi. I require a solar panel of approx 20watt to be fitted to the
roof of my motorhome and have found 2 suitable units of
comparable price but different types. One is Polycrystalline and
the other is High-performance Amorphous silicon. Although I
believe the Polycrystalline is said to be more efficient in
strong sunlight I am wondering which will be better given its
fixed position on the roof and average UK weather conditions such
as light cloud cover (the motorhome will be used in the UK
between April and September).

Any advice appreciated.
Thank you,
Steve

 

[John Beardmore]

In message <[email protected]>,

If both are 20 watts, and you have space, does not really matter much. But I
doubt that a 20 watt panel will do much for you except basic battery upkeep
when you are not using the RV.

How long are the warranty periods ? Old amorphous could be quite short
lived. My instinct would be to go for the poly. I assume it would be
smaller ? Smaller target for vandals, and more space to put up more
handles if needs be.


Cheers, J/.

 

[samc]

Hi. I require a solar panel of approx 20watt to be fitted to the
roof of my motorhome and have found 2 suitable units of
comparable price but different types. One is Polycrystalline and
the other is High-performance Amorphous silicon. Although I
believe the Polycrystalline is said to be more efficient in
strong sunlight I am wondering which will be better given its
fixed position on the roof and average UK weather conditions such
as light cloud cover (the motorhome will be used in the UK
between April and September).

Any advice appreciated.
Thank you,
Steve

your main choice is between poly and mono crystalline both of these
technologys have long output warrantys 20-25 years to 80% . in my
experience with amorphous the output reduces very quickly with age in
direct sunlight . amorphous is ok for small loads like electric fences
e.t.c....

 

[SandS]

Thank you for the info. I figured 20Watts would give about 1.5
amps per hour for 8+ hours per day that would equal 12AH, which
combined with an hour or so driving (charging off the alternator)
each day would be enough to replace the 18 AH power lost from the
leisure battery due to internal lighting and water pump etc per
day. Is this significanly incorrect?
Regards, Steve

 

[SJC]

Thank you for the info. I figured 20Watts would give about 1.5
amps per hour for 8+ hours per day that would equal 12AH, which
combined with an hour or so driving (charging off the alternator)
each day would be enough to replace the 18 AH power lost from the
leisure battery due to internal lighting and water pump etc per
day. Is this significanly incorrect?
Regards, Steve

I personally do not think it is realistic to expect 20 watts per hour
for 8 hours per day from a 20 watt panel. I would estimate 10 watts
for 4 hours a day and hope the sun comes out.

 

[SJC]

Neither wats nor amps come in "watts per hour" or "amps per hour"

Then what is a kHW? It is 1000 watt hours.
Perhaps 20 watts FOR one hour is the way to express it.

 

[SJC]

Bingo.

"per" implies division. Gallons per mile.

Watt hours is multiplication. 1000 watt hours could be 200 watts *for*
5 hours.

Rather than correcting terms, I would rather address the issue as I see it.
A 20 watt panel is unlikely to produce 20 watts for 8 hours per day. Which,
as I read it, was the assertion made by the original poster.

 

[Steve Spence]

Then what is a kHW? It is 1000 watt hours.
Perhaps 20 watts FOR one hour is the way to express it.

Nope, it's 20 Wh.

 

[John Beardmore]

and that new clever mirror arragement that doubles the sun on
the panel and can double the output again. \_/ (2 mirrors next to panel)

New ???


J/.

 

[Ecnerwal]

and that new clever mirror arragement that doubles the sun on
the panel and can double the output again. \_/ (2 mirrors next to panel)

Not new (by at least 30 years, probably longer), voids warranty
(concentrating sun on non-concentrating-rated cells/panels), fails code
inspection (due to previous factor, and currents in excess of rated
design currents).

 

[SandS]

Bingo.

"per" implies division. Gallons per mile.

Watt hours is multiplication. 1000 watt hours could be 200
watts *for*
5 hours.

Rather than correcting terms, I would rather address the issue
as I see it.
A 20 watt panel is unlikely to produce 20 watts for 8 hours per
day. Which,
as I read it, was the assertion made by the original poster.

----------------
Thanks for the info. Clearly a lot of expertise here so apologies
if the terminology is incorrect but I'm sure most will know what
I meant.
I'm rather disappointed with the low power expectations quoted
but it is a great help in deciding how best to meet the leisure
battery load demands. I can't really afford to go to a 40+ panel
so perhaps I'll opt for a Stirling Battery-to-Battery Charger and
the occasional mains hook up instead. About 3 times the price but
a lot less hassle to fit and I can transfer the B2B charger to
another van in future.

Thank you all for the helpful comments.
Regards,
Steve

 

[Steve Spence]

Oh poo. He's in England for heaven's sake. If I could get 30 watts out
of a 15 watt panel with two cheap mylar mirrors, I'd say thank you very
much. Show me any spec or warranty on any panel that says 'dont put too
much sun on this panel or it will put out too much current and void
your warranty'. That excess current idea is bo-o-o-gus. You seem to be
one of the nattering nabobs of negativism I've heard about.

It's not an excess current issue, it's UV degradation of the potting
material. Turns the panels brown and degrades efficiency. I have a old
set of Carizo quadlams that got browned in a focused sun install.

 

[SJC]

The two are not mutually exclusive. This is not to take away from your
point.


I agree with that. He's in the UK with its northern latitudes. During
the summer months, he's got longer days that I do, state-side. But
then, he has to take the UK's overcast skies into account.

At least the issue was finally addressed. It would be good to hear
some real world examples about the amount of electrical energy that
a user could expect from a PV panel.
Sometimes I am left with the impression that some people on here
have "answers" waiting for a question. If they have none, then they
talk about top posting, as if it is a mortal sin.

 

[SJC]

The sat dish is a different problem than a solar tracker. The dish
only has to be aimed and doesn't have to follow a moving target. The
solar tracker has to track. Could it be done? Sure, but at what
complexity and cost? The simplicity of just mounting a panal on the
roof of the RV has a lot going for it. As for cost, I imagine that
buying more panal would be cheaper than the tracker.

I would imagine so too, which is why I was addressing the issue
of how much a 20 watt panel really produces in a day, mounted flat
on a roof. I believe that it produces much less than 20 watt hours
times 8 hours per day. I think that if you estimate that it will produce
160 watt hours per day, you will be disappointed.
A 20 watt panel might cost you $200 and a 40 watt might cost $300.
I would be inclined to go with the 40 watt panel and still be able to
start the vehicle after using some stored energy for other things. But then,
I would not be using the energy from the vehicle battery to run other things
in the first place.

 

[John Beardmore]

In message <[email protected]>,

I supply a 20W panel for
£159, get in touch if you are interested.

But buying a larger one might be a lot more cost effective. I believe
we can supply 85W panels for £250.


Cheers, J/.